Thanks for this informative video. I had just installed a used treadmill motor on my Harbor Freight lathe and was immensely disappointed to discover the remarkable lack of torque. I, of course , bought it based on the HP rating. A little research led me to your video and cleared things up. Now that I understand, I ordered another motor that is 3hp @ 4300 RPM which should provide more than double the previous amount of torque. Thanks for the clear explanation.
Glad it helped, also remember gearing is your friend. As an example If the original motor was 1500 RPMS and the new motor is 6000 you want to gear it down to 1500 which will give you 4 X the torque. This video should also help ua-cam.com/video/uA4__ltMMcY/v-deo.htmlsi=4kffKcOgR3pwv16t
One slight practical consideration with DC treadmill motors is that there is a minimum usable RPM. If you risk extracting max torque at too slow a speed there’s a chance of cooking the DC controller or overheating the armature. I agree that torque is fairly flat but sometimes other factors may be in play 😜
I appreciate the cautionary warning it is good advice for people. It is however beyond the scope of this video. My intent was to illustrate that HP numbers can be misleading. As a further example I removed a 3/4 HP 1700 RPM AC motor from my lathe and replaced it with a larger 3 HP 4000 RPM DC motor BUT had I used a smaller 2.5 HP 6700 RPM treadmill motor it would have actually been less powerful than the 3/4 HP AC motor because of RPM range and the math bares this out. With regard to your statements I did want to mention you ARE talking about two different potential side effects of low RPM. A motor that burns out at low RPMs is a function of heat. At slower speeds the cooling fan has less cooling ability and that can fry a motor. Burning up a power supply at lower RPMs is a function of the relationship between amps and volts. As volts drop on most power supplies so do amps. This is only a concern at the bottom 8th or so of the speed range as most power supplies come up to full amps fairly quickly BUT if you are at that lower 8th (ish) where the resistance of the coil can not be overcome by the volts than yes you have reduced amps and it can be hard on the power supply at those lower ranges.
@@dazecars Okay, Think of ' volts ' as pressure, in a water /air piping system. Ohms' Law, shows this relationship, between current ( amperes) and voltage. Which is why, ' high tension '' powerline wires, are very very high, in voltage, but very low in current. Increase one/ decreases the other. Step up/step down transformers, do the ' ends ' of the high- voltage lines, from generation, to customer delivery.
Great video. Wished you went further so that we could relate this to our project requirement. e.g. amount of torque for lathe,cnc, diy self-propelled rc lawnmower, as well as brushless versus brushed in terms of performance
Got mine working 👍 Now I need to find a suitable coupler to connect it to a sander backing plate. Can’t work out my torque unfortunately as no rpm is listed on the motor.
If you contact me through my website you can email me a pic of the motor and I will probably be able to give you a rough RPM range. I have parted out a lot of these and there are not that many different motors.
You are comparing 4.1F# motor @3200rpm vs 1.176F# motor @ 6700rpm while downplaying the rpm effects. To compare them more fairly, lets say you needed an output rpm of 3200rpm, the first motor will provide 4.1F# @3200rpm while the 1.176F# @6700rpm motor will become equivalent to 2.46F# @ 3200rpm with some sort of gearing. A lot of scenarios are going to use some sort of gearing/belts already (ie drill press), so in these scenarios its not a big deal to factor in. If it's direct drive or you don't want to deal with gearing, then you can ignore the effects of rpm I mentioned.
you are completely correct gearing is a huge part of using a motor and depending on the application could make the smaller motor a good option if geared properly, but that is beyond the scope of this video. The original footage I shot went over gearing but I realized the torque calculation is the foundation for determining what motor to use. how you set it up is what you add to that foundation and will be felt with in a future video.
I am not "completely downplaying RPM effect" In most cases a person runs a treadmill motor to have variable speed. In other words they will seldom if ever be running the motor at max RPM. Being that horse power is a calculated number based on Torque AND RPM, you loose horse power as you slow the motor down. The purpose of this video was to show that for variable speed applications torque is the important number, horsepower is a misleading number and to pick the best motor for your application some math is required.
Here’s one for you… I have a DC treadmill motor rated 3 hp, 4000 rpm with a 24-amp 90-volt rating. I switched out an old 1/3hp (no torque) a/c motor on my very old Sears table saw. The plan was to use this setup exclusively for dado cuts and box joinery. I recently bought a low-priced speed controller to complete the build. The problem is, while the controller worked fine with the rpm part, it didn’t do squat for torque. In fact, it bogged down quicker than the old 1/3 hp a/c motor. And after several attempts at sawing, the controller died. Now I know the DC motor is fine because I tested it afterwards. I’m guessing that the little cheap box controller just didn’t have the electronics to handle the demands. In the meantime, I’ll just wait for any input I can get here… jack of all trades, master of none…
Ok Daze... The rpm is 1750... I tried to attach the picture of the spec plate on the a/c motor. Anyway, it's a 6.4 amp , 1/3 hp Montgomery Ward 1950's model... Hope this helps to brake the case.
I did the calculations and the "new" motor should have a lot more torque than the original motor. The limitation you experienced is probably the power supply. I have put together 3 different videos on treadmill motor power supplies and a quality unit would probably fix the issue. Also if you do not need the max RPMs of the treadmill motor I would recommend using a pulley ratio ill give it more torque. If you go 2:1 you will cut the torque in half but also double the torque. Last thing to consider, at lower RPMs a lack of kinetic energy can create bogging issues. If you are not running a flywheel one might be a good idea. Let me know if I can be of further help.
Thanks for the video. I've been looking at videos for a speed controller for my DC treadmill motor but I'm still not sure which one to get that would get the most out of the motor.
Glad I could help. This video should help you decide: ua-cam.com/video/AdGypyO_UuM/v-deo.html and then if you are looking for component links for all the parts, there is this video: ua-cam.com/video/NUOCo01qARE/v-deo.html
Based on that formula and all available torque vs rpm graphs, the torque of a DC motor decreases as you increase the rpm. So the motor will produce it's max torque at next to zero rpm (within reason since there is a minimum run speed).
No that’s not correct. A fixed magnet DC motor produces a flat torque curve. Constant torque through the entire RPM range except reduced torque at the lowest speeds. The formula does not indicate a reduction in torque as HP is a function of torque. I think you are assuming HP is constant but HP decreases as RPM decreases. The HP spec is at the max RPM spec. Stepper motors and other similar motors do have a decreasing torque curve but not a treadmill motor or other motors like a treadmill motor.
@dazecars good points. Thanks for the explanation. I'm currently building a 16" bandsaw from Matthias Wandel's plans and will be using a large 4hp treadmill motor with a max 4k rpm. My plan is to set it up so that I'll use a max of 3200 rpm. I'm currently running my small wood lathe on a 2hp treadmill motor using an Arduino as the pwm input on the 2100 board. It has been on service for about 4 years now. I built a shroud out of PVC pipe to fit over the fan on the rear end and ran dryer vent hose outside the shop so that it sucks in cool clean air to prevent sawdust buildup inside the motor. I feel that keeping the motor clean, especially the brushes and contact points is key to longevity.
That is a really good treadmill motor!! It will likely work well as is with a max RPM of 3200 BUT I would still recommend gearing it at 1.25:1 if you can rather than limiting the top speed. The more torque you can get to the blade the happier you will be. People don't realize that the large wheels of the bandsaw actually reduces torque. It's kind of like gearing it up. I ran into that same issue with my own bandsaw conversion and even though it worked with lower RPMS and a limiter at the top RPM I was way happier with it when I changed the gearing. I wanted to follow up on the torque and horse power question. Most people don't realize you cannot measure horse power. Everyone thinks you can measure it because thats the number that everyone knows but its not measured it's calculated. What we can measure is torque and RPM and these two things are what go into the calculation resulting in the HP number. When you see a stepper motor graph that shows the torque decreasing as RPM goes up all these data points are being measured on a dyno and the horse power graph is calculated. Same is true of a gas motor or any other motor. I created this video because we can work backwards to find one data point. The HP number on the motor is the rating at the specific RPM so we can use the calculations to determine torque at the one point. Thankfully the torque is consistent across the entire RPM range or the motor would need to be tested on a dyno to know the torque at other RPM points. I hope your project goes well let me know if I can answer any other questions or be of any further assistance.
@@dazecars Thanks for the reply. I'm planning to use the stock pulley which is about 1.4" on the motor and a 7" pulley on the wheel. That will give me a blade speed of around 2500 fpm, which will be suitable for resawing. The alternative is to use a 3.5 " pulley that I have in place of the 7, but then I'd be running the motor at about 1500 rpm to achieve my desired blade speed. I'm still trying to decide if I want to remove the flywheel from the motor pulley. On my lathe I did so using a hole saw that just fit over the pulley. It made a nice clean and even cut using the drill press. I'll likely try it with the flywheel and if shutdown takes too long I'll look at removal and/or adding in a resistor for the brake effect.
I would not gear it so that you need to run the motor at half speed. Just leaves to much on the table and reduces torque to much. Because of the "high gear ratio" nature of a band saw blade it would be better to run the flywheel if you can. I wish that would have been an option on my bandsaw conversion but it wasn't due to the machine being so small.
You mentioned AC motors torque changes at lower RPM. Can you provide a link that gives a better understanding of that. Otherwise. Nicely done. Dead on with the calculations and the importance of Torque.
The statement is a generalization. If you look at torque curves for AC motors peak torque is always at designed operating RPMs and any other RPM result in lower torque. That is not considering a VFD. When you change the frequency to change speed the torque curve changes. The biggest thing with AC motors is in most cases they are optimized to run at one speed.
I have been searching UA-cam for hours trying to find this information. Great content and very well explained. I have the same 2.5hp X 3200rpm treadmill motor and the 16" bandsaw I'm fabricating requires that the motor run between 195 to 2376 RPM. Will the 195 RPM introduce an increase in heat being a bit on the slow side? Thank you
because these motors are designed to run treadmills they are built too cool very efficiently so they can be run at slow speeds. A lot of people only walk on them. With that said if your motor has blue wires I would hook them up as that will add an extra protection against overheating.
This video DOES SHOW how to how to calculate torque based on motor specs - BUT - how about a video on how to calculate TORQUE NEEDED based on vehicle type, rider weight, top speed requirements, battery pack constraints, and so on....?? THIS is what I came here searching for, and I believe it’s a much needed video that YOU can handle.
That is beyond the scope of what I do. My car videos are related to gas burning classic Fords. My treadmill motor videos are related to putting them on shop tools like mills and lathes and then building a power supply to plug them into the wall. I am not doing anything with electric vehicles.
That is the purpose of the entire video. As a minimum you want to maintain the same torque as the original motor. So if the original motor has 1 foot pound and a gear ratio of 3:1 you want to have a minimum of 3 foot pounds after the gearing. But even better is more torque. Due to the high RPM ability of a treadmill motor if you gear it at 4:1-6:1 (depending on desired RPMS) you could get a lot more torque and you will be better off. You use a treadmill motor for variable speed and often slower speeds, but because horse power is a function of RPM and torque you want to maximize torque to still have good power at low RPMS, and you always want to gear it in such a way that max treadmill motor RPMs = Max desired RPMS after gearing. In other words if the max RPMS of the motor is 6000 and you only need 1000 max than you want to gear it at 6:1 to have 6 times the torque. Does that make sense or did I make it about as clear as mud.
Have you seen had the chance to measure the M-295727 from golds gym? It’s 2.0 continuous, but I can’t find any information online about rpm. Do you know the rpm rating for that one?
I am not familiar with that specific motor BUT based on what you have said it kind of sounds like a smaller one. 3-4” diameter is the smaller size and 5-6” is the bigger size. The smaller ones typically run at the 6000-1000 range and the bigger ones 2500-4500
Excellent point about size and torque when it comes to DC motors. Thank you! Maybe I'm wrong, but I've always understood that DC motors (at least the permanent magnet types like those found in treadmills) only produce their full torque at max RPM, with torque falling off exponentially as voltage & RPMs decrease, until you can easily stop it with just your fingertips at their minimum speed. (Don't try this with the shunt-wound DC starter motor from a car or truck though!!! They can produce hundreds - or even thousands - of ft-#'s of torque at 0 RPM @ 12 volts and ~500 amps.) Beyond that (admittedly excessive & probably ridiculous) example, sometimes the claimed "horsepower" ratings of motors on consumer products are just outright lies. Ex: wet/dry vacuums from every manufacturer I know of. My Rigid claims 4.5HP running off of 110 volts AC, and comes with an 18 gauge power cord about 20' long. 1 HP = 746 watts, and watts = volts × amps. So 746 watts × 4.5 HP = 3357 watts. 3357 watts ÷ 110 volts = 30.518 amps. ...through an 18 ga. cord. ...plugged into a standard residential circut that will supply a maximum of 15 amps. There's JUST NO WAY. If it was really 4.5 HP, the breaker would instantly trip. If I made up a custom 110v circuit that would supply unlimited current and tried to run a 30+ amp load through 20' of 18 ga. cord, the plastic insulation on the cord would melt in seconds, followed by the copper inside exploding when the two conductors shorted out! ...Okay, end of my 😠 rant about stupid marketing claims that have run far afield from the topic of your video. Thank you again for a good and informative video.
You are not exactly correct but you are not exactly wrong depending on the situation. First of all there is no one size fits all rule. There are all kinds of different AC motors and there are all different kinds of DC motors and depending on how each motor is configured can significantly change the torque curve. With that said there are some generalizations that apply to the vast majority of each specific motors. The rule I said in my video, in general, applies to the type of DC motors found in treadmills. Your statement "DC motors only produce their full torque at max RPM, with torque falling off exponentially as voltage & RPMs decrease" is how it works with most AC motors but not at all how it works on DC motors. On a DC motor, voltage controlls speed and amps alone controls torque, so assuming the motor has full amps available to it the torque curve will be flat like I show in the video. This is perfect world scenario and your observation of lower torque at lower RPMs is most often the result of a power supply that the amp output drops as voltage drops which is the case with all but high end power supplies. To put it another way if you take a 4000 RPM 90V 15 amp DC motor and power it with 7 car batteries in series (84 volts) you will get 93% of max RPM 3700 and full torque because the batteries have more amps than the motor will draw. If you power that same motor off of one car battery you will get 13% of max RPM 520 BUT the exact same torque as the 7 batteries because one car battery can put out more amps than the motor will draw. Now in the real world we have the problem because we are not running these motors off of batteries but with a power supply. With most power supplys the amps increase fairly quickly so the torque will increase quickly and then once we reach the max amp draw of the motor the torque will level off and stay constant as long as the amp output of the power supply is as high or higher than the motor amp requirements. On my lathe running a treadmill motor I can take a deep cut at 100 RPMs (when threading) and the motor will slow a little as the tool loads but it will not stop. At higher speeds the same things happens but to a far lessor degree due to the kinetic energy stored in the moving parts. The long and the short of it, in most caseses, is that DC motors have a flat torque curve.
Okay, that makes sense. Thanks for taking the time to exain it thoroughly. (It's been a decade or three since my last class that touched on electrical theory.) Now that you mention power supply current limitations, most of the toy DC motors I played with as a kid probably had their "variable" speed controlled by little more than a simple varistor. ...assuming I put my Radio Shack kit together right anyway; it was all black magic to me back then. 😊
So I am trying to figure out what kind of treadmill I should be looking for. I am 220 lbs and have found even walking on cheap treadmills, my walking overpowers the motor when I step forward, causing the belt to slow down or move forward slightly. It is very jarring. Since manufactures only advertise HP and speed, should I actually be aiming for a treadmill that has a lower max advertised speed at a given HP, as that would suggest it has a higher torque? Not sure if I am making thigs up here.
yes and no. Calculating the torque (HP * 5252)/ RPM will get you in the ball park. small treadmill motors are typically 1-2 foot pounds medium are 2-3 and the best ones are around 4 and above. Problem is treadmills all use gearing on their belt drive, that gearing is not the same and that gearing can impact the torque as well. In other words a treadmill with quiet a bit of motor torque is likely good but if there is not much gearing it might not be as good as a treadmill with a slightly smaller motor and more gearing. It's hard to know for sure one way or another. It's a whole bunch easier with what i'm doing because I am creating the system the motor is going into. Please let me know if I can be of any further assistance.
Great video, I was looking for something like this to figure out motor swaps on my vintage tools I collect. I do have a question for you. Right now I need a new motor for my Old Craftsman Table saw. Its an 8amp 3/4 horse with 3480 RPM. I need to Upgrade it and cant afford to rewire my garage for 220 nor have the money needed for a 3hp ac motor. I do have a few treadmill motors laying around including a 90Volt continuous 2.0 hp, 20 amps at 3800 rpm. Do you think I can get away with it for a while till I can afford the money to redo what I need? I am at a loss and cant find any documentation of it being done or tried. Any help would help!
"get away with it"? it's an upgrade. It has about three times the torque. My only concern is you are at near max RPMs. is there a continuous RPM rating on the label?
@@michaelevans2989 Are there two horse power numbers or just 1? if just one continuous and max are the same. If there are two horse power numbers I can calculate the continuous RPM amount.
Hello, I recently acquired another treadmill motor, It is physically much larger and heavier than my previous motor (good sign). However, this motor does not state max rpm. It tells me that it is 2.25 HP continuous duty @ 130VDC/2200 watts, and thats it. is there a way to calculate max rpm (without hooking it up to power and using a tach)? The motor part number is M-237595. I have searched alternate part numbers to no avail. I have reached out to the company on the sticker to ask if they would have the max rpm rating somewhere, but im not holding my breath on that one. Do you have any thoughts? thanks in advance.
You are trampling all over a video that will be dropping in a week or two 😂 Because the size of the magnet has a direct relation to the amount of torque the bigger the motor the more torque. Cheap low torque motors are usually 3"-3.5" in diameter where as the better motors are 4"-5".
I have an L-405564 motor that came out of a Nordic track. It does not show its rpm and I can't find it. The controller is bad so 8 plan to build an scr controller. It did not have a motor choke so I will have to build one of those too. I have a microwave for that. Can you tell me what rpm this motor is rated for?
I don’t know the specific RPM of that motor. What you need to do is apply the amount of voltage listed on the tag and then measure the RPM with an RPM meter. If you’re not able to do that if you tell me what the diameter of the motor is I can at least give you a ballpark as to what the RPM range likely is. Smaller motors tend to have a higher RPM where bigger motors tend to be slower.
The 5252 was the result of a calculation. The original definition of horse power was created and then applied to steam engines. This established what 1 horse power was. From there torque and rpm were measured and and used to calculate the 5252 number.
I have a question. I'm trying to install/buy a treadmill DC motor on my lathe ..it says on the label 29 amp .. can I still use this on my lathe ??.. has 3.5 hp and 4,000 RPM .. 90 Volt.. just worried about the amperage and the voltage since my house is wired for 15 amp .... and 110 Volts .. thanks..
How do you estimate the torque at half or quarter rpm? Can you assume it’s linear? The standard rpm of a treadmill motor is way too fast for my WWII era milling machine, but way slower may be too low of power.
If you look at this video at time 2:37 you will see that (in theory) the torque curve is flat and does not change through out the entire RPM range. I say "in theory" because at lower RPMs the voltage drops below the amperage threshold due to the resistance in the coil.... okay how about in english now, the coils inside the motor are what create the magnetic field and the number of amps going through the coil determines torque. At higher voltage (=higher speeds) you are at max amps limited by either the power supply or the draw of the motor. But at lower voltage (lower speeds) the normal resistance found in the coil limits the amps because there is not adequate voltage to overcome that resistance. Lower amps means lower torque but I have observed it to only be an issue at the bottom 1/8 to 1/10 of the RPM range. Above those speeds the voltage is enough to overcome the resistance of the coil and you are at "max amps" meaning max torque from there to max RPM. The most important thing for your situation is to gear it correctly. Both my mill and lathe are powered by a treadmill motor and I took max RPMs of the motor and divided that by max RPMs of my machines. On both machines that was about 3.5:1. With that number I correctly geared my lathe and mill. This way I am maximizing torque and never running the risk of running my tools faster than they should go. Make sense? The result is lots of torque at low RPMs. I have never had my mill bog down or slow when making a pass, and on the lathe I single point thread grade 8 bolts 3/8 16 all the time without a compound (meaning high tool pressure) at about 100 RPMS and there is enough torque that the spindle only slows slightly as I make a pass.
@@dazecars great. To me, assuming normal operating range (25% power to 100% power?), I’ll assume constant torque, and therefore that 50% rpm would mean 50% torque? Or do I assume full torque at 50% rpm? Meaning no more likely to bog than at full speed (not withstanding inertia)? I can “gear” (jackstaff pulleys) the lathe down, but the milling machine will be a lot more complicated. Thanks for your replies. And keep the videos coming! I’ve been all-in since I found them.
@@davidkask510 I would say worst case scenario you are at max torque by 25%. And more likely already at max torque around 10-15%. Being that you like my videos you may have already seen this but if not check out my “adjustable column mill build phase 1”. I had to use a 3 pulley setup to properly gear my mill. Not sure what you are working with, if you contact me through my website and email me pix of your mill maybe I can come up with a gearing option.
think of it like this with 2:1 gearing. If 1 foot pound is created per revolution at max RPM and at 2:1 you are now getting 2 revolutions from the motor at 1 revolution at the final pout put you have doubled the torque. This is how gearing works in everything. You can convert torque into RPM or the other way around by gearing.
Someone else might find this useful, I just noticed my 125 CC gas push mower has 4.5 foot pounds of torque. What's funny is, it doesn't say what the horsepower is. But from using one for so long, I'd say it's about 3.25, maybe. I've used a 3, and also a 3.5, and this one seems like it's in the middle. I'm guessing it's a 3hp with overhead valves.
Good information but keep in mind gas engines have a torque curve and torque changes as RPMs change and this will have the same effect on HP. If you know at what RPM that gas motor is producing the listed torque you can calculate HP at that RPM by inverting the equation. (TRQ * RPM)/ 5252
So, if torque = HP x 5252/RPM, how can torque be constant? Unless you’re talking about maximum RPM and assuming the motor is always running at top speed. I guess I’m still unclear on what you are saying Day. Suppose I have a TM motor rated at 2.5 HP and maximum RPM of 3600. I want to hook this up to a lathe that can spin from 30 RPM to 3600 RPM. Does this mean I must have have a pulley system that’s 30/3600 ratio , or about 100:1?
Neither. HP is calculated at max motor RPM, torque is "mostly" constant, and your ratios are way off. Let's say your motor is 4500 max RPMs and you want a max top speed of 1500 RPMs. You gear it at 3:1. This will give you full RPM range up to 1500. The variable speed gives you the lower RPMs you are looking for. That is why for this application HP numbers are worthless because at lower RPMs you have lower HP but lots of torque. Torque and proper gearing are the important things.
Ok. When you say 3:1 ratio, does that mean that the pulley wheel on the motor is 1/3 the diameter of that on the spindle? Your motor would turn faster than the spindle, right? P
@@dazecars Yes, so that’s small pulley on motor. Large on spindle. As a physicist, I shouldn’t have the problems I’m having understanding everything. I can’t even seem to write a paper anymore, and I have a big one due this week for a conference. Getting old sucks.
Torque is constant, BECAUSE IT IS 😁 The HP number is a moving target and the HP rating on the label is based on the RPM rating on the label. as far as ratios your numbers are way off AND you can't gear it to have a minimum of 30 and a max of 3600. Max of 3600 would require a 1:1 ratio and assuming your cold start RPM is 300 If you wanted a minimum of 30 RPMs you would need a 10:1 ratio. More reasonable and useful would be to do a 3:1 ratio your range will be 100RPMs to 1200 RPMs. There is almost never a reason to spin a metal lathe up past 1500 RPMS so why would you want to go to 3600? Also I would not spin your lathe up faster than it was designed to go from the factory as the spindle bearings are going to have a max RPM range. Chucks also have a max RPM range. On my machine I have it geared at 5:1 because I wanted the low end torque. That puts my max around 1200 RPMs which is short of the 1500RPM max the machine started with but again 99% of the work I am doing is in the 500-1000 RPM range.
Horsepower and torque are completely different physical variables whether you’re talking ICE engines or DC motors Many heavy vehicles have only 200 hp or so but 550 ft lb My Subaru has 146 hp (not too much less than 200) but only like 125 ft lb That’s because top speed isn’t important for large vehicles but moving heavy loads is So the ratios between hp and torque can differ wildly I know you’re talking DC motors so, totally different mechanical regime, but the concept is the same which is that the purpose of the design is important
The important thing is HP is a function of RPM and torque. It is the ability to do work. If a motor puts outs 1 foot pound that footv poundc is per revolution. So at 500 RPM you have 500 1 pound applications of force. But if it's producing that same 1 foot pound at 1000 RPM you have 1000 applications ofv1 foot pound. Basically doubled the work the motor is able to do. The reason it is so important with electric motors is HP is based on a specific RPM typically max and the moment you reduce that RPM you reduce the HP. Anyone wanting to use a treadmill motor is usually doing so to have variable speed. That is what this video is about HP means nothing in a variable speed application. The trap that most fall into is thinking HP is THE number but torque is the only thing that really matters. Your vehicle example is over simplified because it does not take into account gear ratios. Low ratios take high RPM and turn it into torque but lower ratios turn torque into higher RPM and because HP IS a function of RPM and torque it has a dramatic effect on how the motor works.
That number is derived by people smarter than I. In the early days of steam engines the term "horse power" was uses as a way to equate the work an engine could do to something people understood "the work a horse could do". One horse power was later quantified numerically as 33,000 foot-pounds of work per minute. When you take that information and begin calculating how "work per minute" relates to rotations per minute and torque (more complicated math than I am wanting to deal with) a simple equation is eventually derived (torque * RPM)/5252
@@dazecars thanks for your valuable explanation. I want to run a 1hp ac 230v 2700rpm single phase irrigation pump with threadmill motor of 180vdc 4500rpm 1.75hp . I have selected 1.75hp motor after applying your formula,which gives nearly 2.0 foot pounds of torque. But two things are causing problem in this design 1. My supply voltage will be 150vdc 2. Making the pulleys for both pump and motor.
@@netrocker9990 150V DC is probably a good thing. You will slow down the DC motor slightly but it should be close enough to get your job done but have the advantage of running cooler. I'm guessing about 3700 RPMs that means your pulley setup will need to be about 1.25:1 I say about because pulleys slip a little and you will loose a few RPMS.
I have to disagree with this video. Power is "work done" and a function of torque and RPM. This being so, the more powerful motor can ALWAYS be geared to have more torque than the least powerful motor
Some of what you have said is correct but unfortunately you have totally missed the point of the video. Yes by using gearing (assuming there is enough RPM available) you can gear any motor to have more torque; however this video does not go into gearing because that’s not what the video is about. It is about comparing two motors directly both with the same horse power rating even though one is superior to the other. By calculating the torque you see that the larger motor is superior by almost double and you get the other half of the equation, a direct apples to apples comparison. Your statement of “the most powerful motor can ALWAYS be geared to have more torque than the least powerful motor” Does not even consider the torque half of the equation and how it effects motor life. Based on your statement the two motors I show, both having equal horse power, would function exactly the same with the correct gearing, but how can that be if the bigger motor is the better motor?. For the same power the smaller motor must run at 6700 RPMs but the larger motor gets that power at 3200 RPMs (Illustrating this point is why I used two motors that were rated at the same power) Based on what you have said they are completely identical and there would NEVER be a reason to ever run the bigger motor because the smaller motor does the same work and fits in a smaller package. It does not consider that the higher the RPMs the hotter a motor is going to run and the quicker it is going to where out. You may disagree with what was said in my video but there is nothing incorrect with my statements, they are the actual math and science.
The other problem with your statement is the entire reason a person uses a treadmill motor is to have varriable speed. In other words the motor is seldom if ever run at max RPM at which point HP means nothing regardless of gearing. But torque remains constant (assuming the power supply is accurate) and at low ROPMS torque is what is important not HP.
Wow, I’m 77 and still learning things. Where were you when I was in math class?haha great video with loads of info I can use.
Happy to help!
Thanks for this informative video. I had just installed a used treadmill motor on my Harbor Freight lathe and was immensely disappointed to discover the remarkable lack of torque. I, of course , bought it based on the HP rating. A little research led me to your video and cleared things up. Now that I understand, I ordered another motor that is 3hp @ 4300 RPM which should provide more than double the previous amount of torque. Thanks for the clear explanation.
Glad it helped, also remember gearing is your friend. As an example If the original motor was 1500 RPMS and the new motor is 6000 you want to gear it down to 1500 which will give you 4 X the torque. This video should also help ua-cam.com/video/uA4__ltMMcY/v-deo.htmlsi=4kffKcOgR3pwv16t
Thanks for the info. Now I can take my motors and see which one's work the best for different applications based on torque.
Glad to help
Please keep going with your channel.
I've been learning so much from you and Jeremy Fielding. You two should do a collab or something
Thank you 👍❤️
I would love to colaborate with him but he is a much bigger creater than I and there would be nothing in it for him.
Very helpful information, thank you. I knew the hp thing had to be BS but I just couldn't understand the why and how it was so. Now I know.
Glad it was helpful!
One slight practical consideration with DC treadmill motors is that there is a minimum usable RPM. If you risk extracting max torque at too slow a speed there’s a chance of cooking the DC controller or overheating the armature. I agree that torque is fairly flat but sometimes other factors may be in play 😜
I appreciate the cautionary warning it is good advice for people. It is however beyond the scope of this video. My intent was to illustrate that HP numbers can be misleading. As a further example I removed a 3/4 HP 1700 RPM AC motor from my lathe and replaced it with a larger 3 HP 4000 RPM DC motor BUT had I used a smaller 2.5 HP 6700 RPM treadmill motor it would have actually been less powerful than the 3/4 HP AC motor because of RPM range and the math bares this out. With regard to your statements I did want to mention you ARE talking about two different potential side effects of low RPM. A motor that burns out at low RPMs is a function of heat. At slower speeds the cooling fan has less cooling ability and that can fry a motor. Burning up a power supply at lower RPMs is a function of the relationship between amps and volts. As volts drop on most power supplies so do amps. This is only a concern at the bottom 8th or so of the speed range as most power supplies come up to full amps fairly quickly BUT if you are at that lower 8th (ish) where the resistance of the coil can not be overcome by the volts than yes you have reduced amps and it can be hard on the power supply at those lower ranges.
@@dazecars Okay, Think of ' volts ' as pressure, in a water /air piping system. Ohms' Law, shows this relationship, between current ( amperes) and voltage. Which is why, ' high tension '' powerline wires, are very very high, in voltage, but very low in current. Increase one/ decreases the other. Step up/step down transformers, do the ' ends ' of the high- voltage lines, from generation, to customer delivery.
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Thanks a bunch. The video is quite informative and the information I have received will help me a lot in my project (an electric car).
Glad it was helpful!
Great video. Wished you went further so that we could relate this to our project requirement. e.g. amount of torque for lathe,cnc, diy self-propelled rc lawnmower, as well as brushless versus brushed in terms of performance
Thanks, each application has different requirements so kind of hard to be specific. I have not yet played with brushless motors much.
Got mine working 👍
Now I need to find a suitable coupler to connect it to a sander backing plate.
Can’t work out my torque unfortunately as no rpm is listed on the motor.
If you contact me through my website you can email me a pic of the motor and I will probably be able to give you a rough RPM range. I have parted out a lot of these and there are not that many different motors.
You are comparing 4.1F# motor @3200rpm vs 1.176F# motor @ 6700rpm while downplaying the rpm effects.
To compare them more fairly, lets say you needed an output rpm of 3200rpm, the first motor will provide 4.1F# @3200rpm while the 1.176F# @6700rpm motor will become equivalent to 2.46F# @ 3200rpm with some sort of gearing. A lot of scenarios are going to use some sort of gearing/belts already (ie drill press), so in these scenarios its not a big deal to factor in.
If it's direct drive or you don't want to deal with gearing, then you can ignore the effects of rpm I mentioned.
you are completely correct gearing is a huge part of using a motor and depending on the application could make the smaller motor a good option if geared properly, but that is beyond the scope of this video. The original footage I shot went over gearing but I realized the torque calculation is the foundation for determining what motor to use. how you set it up is what you add to that foundation and will be felt with in a future video.
I am not "completely downplaying RPM effect" In most cases a person runs a treadmill motor to have variable speed. In other words they will seldom if ever be running the motor at max RPM. Being that horse power is a calculated number based on Torque AND RPM, you loose horse power as you slow the motor down. The purpose of this video was to show that for variable speed applications torque is the important number, horsepower is a misleading number and to pick the best motor for your application some math is required.
This is very helpful, thanks so much.
You're very welcome!
Here’s one for you… I have a DC treadmill motor rated 3 hp, 4000 rpm with a 24-amp 90-volt rating. I switched out an old 1/3hp (no torque) a/c motor on my very old Sears table saw. The plan was to use this setup exclusively for dado cuts and box joinery. I recently bought a low-priced speed controller to complete the build. The problem is, while the controller worked fine with the rpm part, it didn’t do squat for torque. In fact, it bogged down quicker than the old 1/3 hp a/c motor. And after several attempts at sawing, the controller died. Now I know the DC motor is fine because I tested it afterwards. I’m guessing that the little cheap box controller just didn’t have the electronics to handle the demands. In the meantime, I’ll just wait for any input I can get here… jack of all trades, master of none…
what was the RPM of your AC motor? with that information we can do some calculations and compare apples to apples.
@@dazecars ... thanks for the quick response... I will get that to you...
Ok Daze... The rpm is 1750... I tried to attach the picture of the spec plate on the a/c motor. Anyway, it's a 6.4 amp , 1/3 hp Montgomery Ward 1950's model... Hope this helps to brake the case.
I did the calculations and the "new" motor should have a lot more torque than the original motor. The limitation you experienced is probably the power supply. I have put together 3 different videos on treadmill motor power supplies and a quality unit would probably fix the issue. Also if you do not need the max RPMs of the treadmill motor I would recommend using a pulley ratio ill give it more torque. If you go 2:1 you will cut the torque in half but also double the torque. Last thing to consider, at lower RPMs a lack of kinetic energy can create bogging issues. If you are not running a flywheel one might be a good idea. Let me know if I can be of further help.
@@dazecars Thanks Daze. Your help and knowledge merits a "subscribe"... count me in... 😎👍
Thanks man this was very helpful.
Glad it helped
Thank you for explaining this so well, I have subscribed and keen to learn more, your explanations makes sense and easy to follow.
Glad it was helpful, and welcome aboard!!
Thanks for the video. I've been looking at videos for a speed controller for my DC treadmill motor but I'm still not sure which one to get that would get the most out of the motor.
Glad I could help. This video should help you decide: ua-cam.com/video/AdGypyO_UuM/v-deo.html and then if you are looking for component links for all the parts, there is this video: ua-cam.com/video/NUOCo01qARE/v-deo.html
Very informatif and educatif explanation friend...thank you very much..
You are welcome
Very well done... Nice to see the Texas sized motor there on the left...😎
Sure is!
Based on that formula and all available torque vs rpm graphs, the torque of a DC motor decreases as you increase the rpm. So the motor will produce it's max torque at next to zero rpm (within reason since there is a minimum run speed).
No that’s not correct. A fixed magnet DC motor produces a flat torque curve. Constant torque through the entire RPM range except reduced torque at the lowest speeds. The formula does not indicate a reduction in torque as HP is a function of torque. I think you are assuming HP is constant but HP decreases as RPM decreases. The HP spec is at the max RPM spec. Stepper motors and other similar motors do have a decreasing torque curve but not a treadmill motor or other motors like a treadmill motor.
@dazecars good points. Thanks for the explanation. I'm currently building a 16" bandsaw from Matthias Wandel's plans and will be using a large 4hp treadmill motor with a max 4k rpm. My plan is to set it up so that I'll use a max of 3200 rpm.
I'm currently running my small wood lathe on a 2hp treadmill motor using an Arduino as the pwm input on the 2100 board. It has been on service for about 4 years now. I built a shroud out of PVC pipe to fit over the fan on the rear end and ran dryer vent hose outside the shop so that it sucks in cool clean air to prevent sawdust buildup inside the motor. I feel that keeping the motor clean, especially the brushes and contact points is key to longevity.
That is a really good treadmill motor!! It will likely work well as is with a max RPM of 3200 BUT I would still recommend gearing it at 1.25:1 if you can rather than limiting the top speed. The more torque you can get to the blade the happier you will be. People don't realize that the large wheels of the bandsaw actually reduces torque. It's kind of like gearing it up. I ran into that same issue with my own bandsaw conversion and even though it worked with lower RPMS and a limiter at the top RPM I was way happier with it when I changed the gearing.
I wanted to follow up on the torque and horse power question. Most people don't realize you cannot measure horse power. Everyone thinks you can measure it because thats the number that everyone knows but its not measured it's calculated. What we can measure is torque and RPM and these two things are what go into the calculation resulting in the HP number. When you see a stepper motor graph that shows the torque decreasing as RPM goes up all these data points are being measured on a dyno and the horse power graph is calculated. Same is true of a gas motor or any other motor. I created this video because we can work backwards to find one data point. The HP number on the motor is the rating at the specific RPM so we can use the calculations to determine torque at the one point. Thankfully the torque is consistent across the entire RPM range or the motor would need to be tested on a dyno to know the torque at other RPM points. I hope your project goes well let me know if I can answer any other questions or be of any further assistance.
@@dazecars Thanks for the reply. I'm planning to use the stock pulley which is about 1.4" on the motor and a 7" pulley on the wheel. That will give me a blade speed of around 2500 fpm, which will be suitable for resawing. The alternative is to use a 3.5 " pulley that I have in place of the 7, but then I'd be running the motor at about 1500 rpm to achieve my desired blade speed.
I'm still trying to decide if I want to remove the flywheel from the motor pulley. On my lathe I did so using a hole saw that just fit over the pulley. It made a nice clean and even cut using the drill press. I'll likely try it with the flywheel and if shutdown takes too long I'll look at removal and/or adding in a resistor for the brake effect.
I would not gear it so that you need to run the motor at half speed. Just leaves to much on the table and reduces torque to much. Because of the "high gear ratio" nature of a band saw blade it would be better to run the flywheel if you can. I wish that would have been an option on my bandsaw conversion but it wasn't due to the machine being so small.
Excellent. Thanks for the equation.
You are welcome!
You're truly Genius 🍀
Thanks but I wouldn't go that far 😂
Great info! So would you say that a “continuous duty” 2.75HP treadmill motor would be better than the typical 3HP motor?
If there is only one HP number it is usually continuous. As to you question it depends on how the torque numbers come out.
You mentioned AC motors torque changes at lower RPM. Can you provide a link that gives a better understanding of that. Otherwise. Nicely done. Dead on with the calculations and the importance of Torque.
The statement is a generalization. If you look at torque curves for AC motors peak torque is always at designed operating RPMs and any other RPM result in lower torque. That is not considering a VFD. When you change the frequency to change speed the torque curve changes. The biggest thing with AC motors is in most cases they are optimized to run at one speed.
I have been searching UA-cam for hours trying to find this information. Great content and very well explained. I have the same 2.5hp X 3200rpm treadmill motor and the 16" bandsaw I'm fabricating requires that the motor run between 195 to 2376 RPM. Will the 195 RPM introduce an increase in heat being a bit on the slow side? Thank you
because these motors are designed to run treadmills they are built too cool very efficiently so they can be run at slow speeds. A lot of people only walk on them. With that said if your motor has blue wires I would hook them up as that will add an extra protection against overheating.
@@dazecars Thank you for your prompt reply. Really appreciated
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This video DOES SHOW how to how to calculate torque based on motor specs - BUT - how about a video on how to calculate TORQUE NEEDED based on vehicle type, rider weight, top speed requirements, battery pack constraints, and so on....??
THIS is what I came here searching for, and I believe it’s a much needed video that YOU can handle.
That is beyond the scope of what I do. My car videos are related to gas burning classic Fords. My treadmill motor videos are related to putting them on shop tools like mills and lathes and then building a power supply to plug them into the wall. I am not doing anything with electric vehicles.
@@dazecars ahh yeah I did see that after leaving the comment, however, I think you may be selling yourself a little bit short...
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I guess the thing is knowing what torque you need per application, say a 2x72 Linisher.
Any ideas?
Brilliant stuff!
That is the purpose of the entire video. As a minimum you want to maintain the same torque as the original motor. So if the original motor has 1 foot pound and a gear ratio of 3:1 you want to have a minimum of 3 foot pounds after the gearing. But even better is more torque. Due to the high RPM ability of a treadmill motor if you gear it at 4:1-6:1 (depending on desired RPMS) you could get a lot more torque and you will be better off. You use a treadmill motor for variable speed and often slower speeds, but because horse power is a function of RPM and torque you want to maximize torque to still have good power at low RPMS, and you always want to gear it in such a way that max treadmill motor RPMs = Max desired RPMS after gearing. In other words if the max RPMS of the motor is 6000 and you only need 1000 max than you want to gear it at 6:1 to have 6 times the torque. Does that make sense or did I make it about as clear as mud.
Have you seen had the chance to measure the M-295727 from golds gym? It’s 2.0 continuous, but I can’t find any information online about rpm. Do you know the rpm rating for that one?
I am not familiar with that specific motor BUT based on what you have said it kind of sounds like a smaller one. 3-4” diameter is the smaller size and 5-6” is the bigger size. The smaller ones typically run at the 6000-1000 range and the bigger ones 2500-4500
Very nice👍👍👍👍👍 video thank you
my pleasure
Excellent point about size and torque when it comes to DC motors. Thank you!
Maybe I'm wrong, but I've always understood that DC motors (at least the permanent magnet types like those found in treadmills) only produce their full torque at max RPM, with torque falling off exponentially as voltage & RPMs decrease, until you can easily stop it with just your fingertips at their minimum speed. (Don't try this with the shunt-wound DC starter motor from a car or truck though!!! They can produce hundreds - or even thousands - of ft-#'s of torque at 0 RPM @ 12 volts and ~500 amps.)
Beyond that (admittedly excessive & probably ridiculous) example, sometimes the claimed "horsepower" ratings of motors on consumer products are just outright lies. Ex: wet/dry vacuums from every manufacturer I know of. My Rigid claims 4.5HP running off of 110 volts AC, and comes with an 18 gauge power cord about 20' long.
1 HP = 746 watts, and watts = volts × amps.
So 746 watts × 4.5 HP = 3357 watts.
3357 watts ÷ 110 volts = 30.518 amps.
...through an 18 ga. cord.
...plugged into a standard residential circut that will supply a maximum of 15 amps.
There's JUST NO WAY.
If it was really 4.5 HP, the breaker would instantly trip.
If I made up a custom 110v circuit that would supply unlimited current and tried to run a 30+ amp load through 20' of 18 ga. cord, the plastic insulation on the cord would melt in seconds, followed by the copper inside exploding when the two conductors shorted out!
...Okay, end of my 😠 rant about stupid marketing claims that have run far afield from the topic of your video.
Thank you again for a good and informative video.
You are not exactly correct but you are not exactly wrong depending on the situation. First of all there is no one size fits all rule. There are all kinds of different AC motors and there are all different kinds of DC motors and depending on how each motor is configured can significantly change the torque curve. With that said there are some generalizations that apply to the vast majority of each specific motors. The rule I said in my video, in general, applies to the type of DC motors found in treadmills. Your statement "DC motors only produce their full torque at max RPM, with torque falling off exponentially as voltage & RPMs decrease" is how it works with most AC motors but not at all how it works on DC motors. On a DC motor, voltage controlls speed and amps alone controls torque, so assuming the motor has full amps available to it the torque curve will be flat like I show in the video. This is perfect world scenario and your observation of lower torque at lower RPMs is most often the result of a power supply that the amp output drops as voltage drops which is the case with all but high end power supplies. To put it another way if you take a 4000 RPM 90V 15 amp DC motor and power it with 7 car batteries in series (84 volts) you will get 93% of max RPM 3700 and full torque because the batteries have more amps than the motor will draw. If you power that same motor off of one car battery you will get 13% of max RPM 520 BUT the exact same torque as the 7 batteries because one car battery can put out more amps than the motor will draw. Now in the real world we have the problem because we are not running these motors off of batteries but with a power supply. With most power supplys the amps increase fairly quickly so the torque will increase quickly and then once we reach the max amp draw of the motor the torque will level off and stay constant as long as the amp output of the power supply is as high or higher than the motor amp requirements. On my lathe running a treadmill motor I can take a deep cut at 100 RPMs (when threading) and the motor will slow a little as the tool loads but it will not stop. At higher speeds the same things happens but to a far lessor degree due to the kinetic energy stored in the moving parts. The long and the short of it, in most caseses, is that DC motors have a flat torque curve.
Okay, that makes sense. Thanks for taking the time to exain it thoroughly. (It's been a decade or three since my last class that touched on electrical theory.) Now that you mention power supply current limitations, most of the toy DC motors I played with as a kid probably had their "variable" speed controlled by little more than a simple varistor. ...assuming I put my Radio Shack kit together right anyway; it was all black magic to me back then. 😊
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thank you so much dear
You are so welcome!
So I am trying to figure out what kind of treadmill I should be looking for. I am 220 lbs and have found even walking on cheap treadmills, my walking overpowers the motor when I step forward, causing the belt to slow down or move forward slightly. It is very jarring.
Since manufactures only advertise HP and speed, should I actually be aiming for a treadmill that has a lower max advertised speed at a given HP, as that would suggest it has a higher torque? Not sure if I am making thigs up here.
yes and no. Calculating the torque (HP * 5252)/ RPM will get you in the ball park. small treadmill motors are typically 1-2 foot pounds medium are 2-3 and the best ones are around 4 and above. Problem is treadmills all use gearing on their belt drive, that gearing is not the same and that gearing can impact the torque as well. In other words a treadmill with quiet a bit of motor torque is likely good but if there is not much gearing it might not be as good as a treadmill with a slightly smaller motor and more gearing. It's hard to know for sure one way or another. It's a whole bunch easier with what i'm doing because I am creating the system the motor is going into. Please let me know if I can be of any further assistance.
I guess the units of torgue in the equetion are foot_pound force or what? I can just yext an equivalent formular in SI
yes it is foot pounds
Great video, I was looking for something like this to figure out motor swaps on my vintage tools I collect. I do have a question for you. Right now I need a new motor for my Old Craftsman Table saw. Its an 8amp 3/4 horse with 3480 RPM. I need to Upgrade it and cant afford to rewire my garage for 220 nor have the money needed for a 3hp ac motor. I do have a few treadmill motors laying around including a 90Volt continuous 2.0 hp, 20 amps at 3800 rpm. Do you think I can get away with it for a while till I can afford the money to redo what I need? I am at a loss and cant find any documentation of it being done or tried. Any help would help!
"get away with it"? it's an upgrade. It has about three times the torque. My only concern is you are at near max RPMs. is there a continuous RPM rating on the label?
@@dazecars nothing for the rpm but the motor is a Cambridge 2.0 continuous duty JM01-001. That's all i got to work with.
@@michaelevans2989 Are there two horse power numbers or just 1? if just one continuous and max are the same. If there are two horse power numbers I can calculate the continuous RPM amount.
Hello, I recently acquired another treadmill motor, It is physically much larger and heavier than my previous motor (good sign). However, this motor does not state max rpm. It tells me that it is 2.25 HP continuous duty @ 130VDC/2200 watts, and thats it. is there a way to calculate max rpm (without hooking it up to power and using a tach)? The motor part number is M-237595. I have searched alternate part numbers to no avail. I have reached out to the company on the sticker to ask if they would have the max rpm rating somewhere, but im not holding my breath on that one. Do you have any thoughts? thanks in advance.
You are trampling all over a video that will be dropping in a week or two 😂 Because the size of the magnet has a direct relation to the amount of torque the bigger the motor the more torque. Cheap low torque motors are usually 3"-3.5" in diameter where as the better motors are 4"-5".
Awesome. Thank You .
You are welcome!
I have an L-405564 motor that came out of a Nordic track. It does not show its rpm and I can't find it. The controller is bad so 8 plan to build an scr controller. It did not have a motor choke so I will have to build one of those too. I have a microwave for that. Can you tell me what rpm this motor is rated for?
I don’t know the specific RPM of that motor. What you need to do is apply the amount of voltage listed on the tag and then measure the RPM with an RPM meter. If you’re not able to do that if you tell me what the diameter of the motor is I can at least give you a ballpark as to what the RPM range likely is. Smaller motors tend to have a higher RPM where bigger motors tend to be slower.
Thanks
No problem
Where does the 5252 come from? I can’t find any mention of it in Google…
The 5252 was the result of a calculation. The original definition of horse power was created and then applied to steam engines. This established what 1 horse power was. From there torque and rpm were measured and and used to calculate the 5252 number.
1 hp = 746 W
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Phew. Thankfully I live in England where math(s) isn't a four letter word. 😂
😂😂😂 I never knew math had an s in England
Thank you sir !
Most welcome!
I have a question. I'm trying to install/buy a treadmill DC motor on my lathe ..it says on the label 29 amp .. can I still use this on my lathe ??.. has 3.5 hp and 4,000 RPM .. 90 Volt.. just worried about the amperage and the voltage since my house is wired for 15 amp .... and 110 Volts .. thanks..
I can not say for sure but it will likely pop the circuit breaker.
@@dazecars thanks ..
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How do you estimate the torque at half or quarter rpm? Can you assume it’s linear? The standard rpm of a treadmill motor is way too fast for my WWII era milling machine, but way slower may be too low of power.
If you look at this video at time 2:37 you will see that (in theory) the torque curve is flat and does not change through out the entire RPM range. I say "in theory" because at lower RPMs the voltage drops below the amperage threshold due to the resistance in the coil.... okay how about in english now, the coils inside the motor are what create the magnetic field and the number of amps going through the coil determines torque. At higher voltage (=higher speeds) you are at max amps limited by either the power supply or the draw of the motor. But at lower voltage (lower speeds) the normal resistance found in the coil limits the amps because there is not adequate voltage to overcome that resistance. Lower amps means lower torque but I have observed it to only be an issue at the bottom 1/8 to 1/10 of the RPM range. Above those speeds the voltage is enough to overcome the resistance of the coil and you are at "max amps" meaning max torque from there to max RPM. The most important thing for your situation is to gear it correctly. Both my mill and lathe are powered by a treadmill motor and I took max RPMs of the motor and divided that by max RPMs of my machines. On both machines that was about 3.5:1. With that number I correctly geared my lathe and mill. This way I am maximizing torque and never running the risk of running my tools faster than they should go. Make sense? The result is lots of torque at low RPMs. I have never had my mill bog down or slow when making a pass, and on the lathe I single point thread grade 8 bolts 3/8 16 all the time without a compound (meaning high tool pressure) at about 100 RPMS and there is enough torque that the spindle only slows slightly as I make a pass.
@@dazecars great. To me, assuming normal operating range (25% power to 100% power?), I’ll assume constant torque, and therefore that 50% rpm would mean 50% torque?
Or do I assume full torque at 50% rpm? Meaning no more likely to bog than at full speed (not withstanding inertia)?
I can “gear” (jackstaff pulleys) the lathe down, but the milling machine will be a lot more complicated.
Thanks for your replies. And keep the videos coming! I’ve been all-in since I found them.
@@davidkask510 I would say worst case scenario you are at max torque by 25%. And more likely already at max torque around 10-15%. Being that you like my videos you may have already seen this but if not check out my “adjustable column mill build phase 1”. I had to use a 3 pulley setup to properly gear my mill. Not sure what you are working with, if you contact me through my website and email me pix of your mill maybe I can come up with a gearing option.
But if you gear down the small motor, it’s still running at 6,700 RPM. So how can the torque change?
think of it like this with 2:1 gearing. If 1 foot pound is created per revolution at max RPM and at 2:1 you are now getting 2 revolutions from the motor at 1 revolution at the final pout put you have doubled the torque. This is how gearing works in everything. You can convert torque into RPM or the other way around by gearing.
Someone else might find this useful, I just noticed my 125 CC gas push mower has 4.5 foot pounds of torque. What's funny is, it doesn't say what the horsepower is. But from using one for so long, I'd say it's about 3.25, maybe. I've used a 3, and also a 3.5, and this one seems like it's in the middle. I'm guessing it's a 3hp with overhead valves.
Good information but keep in mind gas engines have a torque curve and torque changes as RPMs change and this will have the same effect on HP. If you know at what RPM that gas motor is producing the listed torque you can calculate HP at that RPM by inverting the equation. (TRQ * RPM)/ 5252
Damn, that answers a lot. Thanks, great explanation!
Glad I could help!!
So, if torque = HP x 5252/RPM, how can torque be constant?
Unless you’re talking about maximum RPM and assuming the motor is always running at top speed.
I guess I’m still unclear on what you are saying Day.
Suppose I have a TM motor rated at 2.5 HP and maximum RPM of 3600.
I want to hook this up to a lathe that can spin from 30 RPM to 3600 RPM. Does this mean I must have have a pulley system that’s 30/3600 ratio , or about 100:1?
Neither. HP is calculated at max motor RPM, torque is "mostly" constant, and your ratios are way off. Let's say your motor is 4500 max RPMs and you want a max top speed of 1500 RPMs. You gear it at 3:1. This will give you full RPM range up to 1500. The variable speed gives you the lower RPMs you are looking for. That is why for this application HP numbers are worthless because at lower RPMs you have lower HP but lots of torque. Torque and proper gearing are the important things.
Ok. When you say 3:1 ratio, does that mean that the pulley wheel on the motor is 1/3 the diameter of that on the spindle? Your motor would turn faster than the spindle, right?
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@@paulmanhart4481 3 turns of the motor for every one turn of the spindle
@@dazecars Yes, so that’s small pulley on motor. Large on spindle.
As a physicist, I shouldn’t have the problems I’m having understanding everything. I can’t even seem to write a paper anymore, and I have a big one due this week for a conference.
Getting old sucks.
Torque is constant, BECAUSE IT IS 😁 The HP number is a moving target and the HP rating on the label is based on the RPM rating on the label. as far as ratios your numbers are way off AND you can't gear it to have a minimum of 30 and a max of 3600. Max of 3600 would require a 1:1 ratio and assuming your cold start RPM is 300 If you wanted a minimum of 30 RPMs you would need a 10:1 ratio. More reasonable and useful would be to do a 3:1 ratio your range will be 100RPMs to 1200 RPMs. There is almost never a reason to spin a metal lathe up past 1500 RPMS so why would you want to go to 3600? Also I would not spin your lathe up faster than it was designed to go from the factory as the spindle bearings are going to have a max RPM range. Chucks also have a max RPM range. On my machine I have it geared at 5:1 because I wanted the low end torque. That puts my max around 1200 RPMs which is short of the 1500RPM max the machine started with but again 99% of the work I am doing is in the 500-1000 RPM range.
Horsepower and torque are completely different physical variables whether you’re talking ICE engines or DC motors
Many heavy vehicles have only 200 hp or so but 550 ft lb
My Subaru has 146 hp (not too much less than 200) but only like 125 ft lb
That’s because top speed isn’t important for large vehicles but moving heavy loads is
So the ratios between hp and torque can differ wildly
I know you’re talking DC motors so, totally different mechanical regime, but the concept is the same which is that the purpose of the design is important
The important thing is HP is a function of RPM and torque. It is the ability to do work. If a motor puts outs 1 foot pound that footv poundc is per revolution. So at 500 RPM you have 500 1 pound applications of force. But if it's producing that same 1 foot pound at 1000 RPM you have 1000 applications ofv1 foot pound. Basically doubled the work the motor is able to do. The reason it is so important with electric motors is HP is based on a specific RPM typically max and the moment you reduce that RPM you reduce the HP. Anyone wanting to use a treadmill motor is usually doing so to have variable speed. That is what this video is about HP means nothing in a variable speed application. The trap that most fall into is thinking HP is THE number but torque is the only thing that really matters. Your vehicle example is over simplified because it does not take into account gear ratios. Low ratios take high RPM and turn it into torque but lower ratios turn torque into higher RPM and because HP IS a function of RPM and torque it has a dramatic effect on how the motor works.
What is the motor torque 2.5hp
max RPMS are required to calculate torque from HP as I explained in the video.
What is 5252?
That number is derived by people smarter than I. In the early days of steam engines the term "horse power" was uses as a way to equate the work an engine could do to something people understood "the work a horse could do". One horse power was later quantified numerically as 33,000 foot-pounds of work per minute. When you take that information and begin calculating how "work per minute" relates to rotations per minute and torque (more complicated math than I am wanting to deal with) a simple equation is eventually derived (torque * RPM)/5252
@@dazecars thanks for your valuable explanation. I want to run a 1hp ac 230v 2700rpm single phase irrigation pump with threadmill motor of 180vdc 4500rpm 1.75hp . I have selected 1.75hp motor after applying your formula,which gives nearly 2.0 foot pounds of torque. But two things are causing problem in this design
1. My supply voltage will be 150vdc
2. Making the pulleys for both pump and motor.
@@netrocker9990 150V DC is probably a good thing. You will slow down the DC motor slightly but it should be close enough to get your job done but have the advantage of running cooler. I'm guessing about 3700 RPMs that means your pulley setup will need to be about 1.25:1 I say about because pulleys slip a little and you will loose a few RPMS.
I have to disagree with this video. Power is "work done" and a function of torque and RPM. This being so, the more powerful motor can ALWAYS be geared to have more torque than the least powerful motor
Some of what you have said is correct but unfortunately you have totally missed the point of the video. Yes by using gearing (assuming there is enough RPM available) you can gear any motor to have more torque; however this video does not go into gearing because that’s not what the video is about. It is about comparing two motors directly both with the same horse power rating even though one is superior to the other. By calculating the torque you see that the larger motor is superior by almost double and you get the other half of the equation, a direct apples to apples comparison. Your statement of “the most powerful motor can ALWAYS be geared to have more torque than the least powerful motor” Does not even consider the torque half of the equation and how it effects motor life. Based on your statement the two motors I show, both having equal horse power, would function exactly the same with the correct gearing, but how can that be if the bigger motor is the better motor?. For the same power the smaller motor must run at 6700 RPMs but the larger motor gets that power at 3200 RPMs (Illustrating this point is why I used two motors that were rated at the same power) Based on what you have said they are completely identical and there would NEVER be a reason to ever run the bigger motor because the smaller motor does the same work and fits in a smaller package. It does not consider that the higher the RPMs the hotter a motor is going to run and the quicker it is going to where out. You may disagree with what was said in my video but there is nothing incorrect with my statements, they are the actual math and science.
The other problem with your statement is the entire reason a person uses a treadmill motor is to have varriable speed. In other words the motor is seldom if ever run at max RPM at which point HP means nothing regardless of gearing. But torque remains constant (assuming the power supply is accurate) and at low ROPMS torque is what is important not HP.
Awesome
thanks
Old saying goes is horsepower is for braggin’ and torque is for draggin’
Agreed!! it is funny to me that HP even comes up on an electric motor as torque is EVERYTHING in most electric applications.