How do brushed motors turn?? (Episode 2)
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- Опубліковано 9 жов 2024
- Episode 2 of understanding permanent magnet, DC motors. In this episode we cover brushed commutation and how it allows us to turn continuously. Additionally, we show the origin of the torque constant and its multiple meanings.Like, comment, and subscribe, if thats your thing.
Outstanding Job
1:20 On which plane does the force vector lead the current vector by 90 degrees? Confused at which point along the wire and what theta actually is with relation to A and B. Are A and B (d) and (ilB) or (F) respectively? Thanks, great videos!
Hey great question! Sorry the way i showed/said that is unclear. If i were to re-record this, i would word that differently. The long short of the answer to the question is that A is (d) and B is (F). A little more clarification in case you or someone else needs it: The force F is iLxB, which if the current vector and magnetic field vector are perpendicular, is equal in *magnitude* to iLB (note that the current in question here is the into and out of the page current, shown at the left and right edges of the loop). So the magnitude of F is equal to that, but, iLB as multiplication doesn't produce an output with a defined direction (because at that point you are just multiplying their magnitudes, and not keeping up with the orientation of the input vectors).But, cross products require vectors, so we need to know the orientation of the force being represented by that iLB. Because a cross product generates an output perpendicular to its inputs, the force vector will be orthogonal to both current and magnetic field. I think now that it would have been better to say that the force vector will be 90 degrees from the magnetic field vector. The theta in question will actually be the angle between d and B.
Thank you for your question and for watching, hopefully it helps!
fantastic set of video's. What package do you use to create the animations as it makes the concept being explored easy to understand
Thanks so much! So I use a MacBook Pro as my primary personal computer, so I use apple motion/final cut for the animation and video, Logic Pro for audio, and I do all my initial drawings in affinity designer. As a small aside, affinity makes alternatives to several adobe softwares (designer is like illustrator, photo is like photoshop) that are well worth the cost in my opinion.
Thanks for making these videos, they are quite informative 👍
One Question:
Torque is produced by the force generated by the interaction of Magnet's Magnetic feild & current flowing through the Copper wires (I.B.L.Sin(theta), Amperes Law). Back EMF is produced due to rate of change in Flux from PM of Rotor. how does the energy associated with I.BEMF equals the energy produced ?
In an idealized motor (ignoring losses, and idealizing commutation) back EMF times current flow will equal the torque produced times the velocity
Great video series !!!
Would you explain the differences between high voltage vs high current motors in the upcoming videos?
Thanks !!!
Hi, first off thanks so much! As far as your question goes, I hadn't been planning to really get into motor design type stuff too much in this series, but I can give you what knowledge I have here!
Basically, what it comes down to is the motor's winding pattern and its purpose. The maximum speed at which a motor can provide torque is related to the voltage applied. So, higher voltages supplied can mean more speed. A motor's failure modes (With respect to supplied voltage and current) typically comes from overheating. Heat generation in motor windings is dominated by joule (resistive) heating. There is also some heat generation due to bearing friction, but its minimal. So, in order for a motor to stay at a safe temp, it has to be able to get as much (or more) heat out via convection and conduction as it is generating by resistive heating. As I talk about in episode 4, joule heating is equal to I^2R, so its really a function of current, not voltage. Sure, if you supply more voltage, you can produce more current. However, the current is what causes failure. So, the primary limit of a motor is the amount of current running through it. If you are using a motor turning continuously (as in a non-servo operation), this does mean that applying too much voltage can and will burn your motor out. however, if you are using your motor as a servo and/or you are using an H-bridge, you can certainly use a much higher voltage than they list as nominal, so long as your RMS current doesnt go above the rated current.
I am not 100% confident in what follows, but it is my understanding that the primary difference between "low voltage" and "high voltage" motors is the way they are wound. The wires used in the winding have some inherent resistance, which is proportional to their length, and also goes up as they get thinner. so the wires chosen, and the number of turns in the windings will effect the resistance of a motor. The change in resistance does change the amount of joule heating, but for a given voltage it also changes the current that would be flowing. So, it is my understanding that higher voltage motors have a larger resistance, thus meaning that they need a higher voltage to reach the same current levels. Whereas a low voltage motor has a lower resistance, and thus will produce more current for a given voltage. As far as "high current" motors go, I am honestly not super sure without doing some research on my own, but my intuition would be that A) they may do a better job of getting heat out, so they can run more current, and B) they will have lower resistance, which means that for a given amount of current they will have less resistive heating.
@@jtlee1108 Thanks for your response! Looking forward to your next videos! It's the perfect place to learn about the electric motors and their control systems
Many thanks !!!
while talking about this, it would be great that you explain like issues that may arise due to wear. Like i wont build a motor from scratch, but i will need to know enough to hire someone to fix one for me.
hi! so episode 4 talks about how a brushed motor will wear over time. I personally only work in practice with brushless motors, and the only way I have ever had one break was due to me burning out the hall sensors (soldering errors on my PCB). So I dont know if I am qualified to explain everything about what to expect when fixing, but episode 4 does go into how they typically break (again, my experience is limited to classroom lectures on motors and work with brushless motors, so I can't say with 100% certainty that what I talk about is the only way a brushed motor will break.) but thanks for the feedback, I super appreciate it!
Is the colour coding at 3:00 correct? I think B en C should be swapped
Shoot I totally made a mistake there. The plot is correct, the colors I used for the letters B and C are wrong. B is supposed to be green (as it is when I show the wye and delta) and c is supposed to be blue
@@jtlee1108 Thanks for responding, that's what I thought. I still have a lot of questions about the armature windings of DC motors. The principle is clear when simple schematics are shown with single loops but I don't know how these schematics translate to practical machines. So what do these squiggles represent in the why and delta configuration in a real machine?
Michiel Mestdagh absolutely, I appreciate you watching and your clarifications and questions. So what the differences between wye and delta come down to is how you solder the wires of the winding together. I have personally never wound a delta configuration, but basically what it comes down to is that that is exactly what your soldering looks like at the middle joint of the motor, then you wind the windings of the motor in loops. If it’s a salient pole motor you have some steel poles to wind it around, and if it’s a non salient pole motor, it’s done in a sheet then wrapped around the rotor (like this www.maxongroup.com/medias/sys_master/root/8815461597214/DC-Technology-short-and-to-the-point-14-EN-30-31.pdf?attachment=true but this may be for brushed). I’ll look up some more resources some other time and send them your way, but modeling it as a resistance is basically a way of acknowledging that the wire has resistance, later in the series I shift to modeling inductance to better indicate the generation of a magnetic field
i don't make sense of force vector leading our current vector by 90°, at this point given the conversion sin(90+θ)=cos(θ), i can guess these come to ildbcos(θ) ， please give some explaination here.
1:22 why does the force vector leads current vector?
magnetic field produced by flowing current follows the right hand rule. This is ultimately what causes it.
Can you please explain what is negative torque?
lol first off sorry for how quick this reply is, I just happened to be on right when you posted it, I promise I dont just creep around my own comment sections.
So, like force, torque is directional, you can think of it as a vector. However, torque as a vector is defined via the cross product, where Torque = r x F. Typically, in a planar representation (as in only showing 2 dimensions), torque which drives a body to rotate counterclockwise is considered "positive", and one which drives rotation clockwise is condisdered "negative". Ultimately, me calling it "negative" is just a result of how I define my frame. I may not have clearly stated this, but I define the "X" direction to the right, and the "Y" direction as up. Thus, since the "Z" direction is, within a standard cartesian definition, equal to the cross product of X and Y. So, the "Z" direction is out of the screen. So, when I say a "positive" torque, what I mean (but am not clearly stating) is "a torque vector which points in the positive Z direction", and when I say a "negative" torque, I mean "a torque vector which points in the negative Z direction."
I hope that helps, and if it doesnt im more than happy to try to explain it further.
@@jtlee1108 Thank u for the reply. Now it is clear for me.
Hey bro. Ty by all.
I don´t speak inglish and can´t traduction this video because the lenguaje is in rusian.
If you coul change the lenguaje, please.
You should change the video from Russian to English
To my knowledge, the video is in English. can you clarify what you mean by this? do I have something set wrong in the way it displays?
The captions are in Russian