Choosing the right prop diameter for a drone of a certain weight: What prop for sub 250g?
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- Опубліковано 9 лип 2024
- In this video I use an analysis of optimal blade tip speed to provide some recommendations for what prop size to run for drones of different take off weights.
I consider how best to manage the heavier GoPro Hero cameras and what is the best prop diameter for drones in that sub 250g range.
Prop deep dive: • How to choose the righ...
Motor deep dive: • How to pick the best m...
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Slides: drive.google.com/drive/folder...
This is what we need in our hobby, just basic science facts instead of overhyped marketing quotes, thanks for your insight !
You sir, are one of a handful of people who are shaping the development of this wonderful hobby.. Thank you for your contribution.
Thank you sir, for your kind and positive comment!
if JB is a racing drone engineer, you are all drone professor. thank you
All I heard was, "250g five inch sucks JB was right the whole time."
Hopefully knowing the reason behind it proves useful in your future conversations on the subject 👍
I think both JB and Rosser have science on their side. However, I still comfortably prefer a 5" quad, even at 250g. Keeping that weight equal, a 5" quad will never feel the same as a 3". I can tell the difference in split-s and power loop moves. I think the throttle and yaw feel of the 5" quad is noticeably different. Just my two cents.
~300g 5" is 👌. It just needs at the very least a 2203 or 2204 to be good.
@@Kabab Agreed. the 2203 is a big step up from 2004.
We have been so focused on 5 inch feel, and directly correlating prop size, I walked away with the weight and prop combination is maybe a focus worth exploring.
Finally, the part that was missing all the time on FPV, Science! 👨🎓👩🎓
I have several 2.5" quads that are just at 100gr. I think they are some of my best flyers. I am right on that green line. I am using 32gr 2S batteries too.
A lot of "accepted truths" are being challenged lately.. And that's a good thing.
Loved this analysis. Finally someone who put the time in to debunk this arbitrary sub-250g 5" goal, which to me doesn't make sense if the weight is no longer 600g.
I would love to see a video on aero drag vs AUW to try to optimize the "floatiness" of a quad. In other words, put quads on a spectrum between beach ball and golf ball.
Parachute effect is linked to disc loading so a quad with a lower disc loading will feel more floaty with less fling.
Many Thanks Chris, great work, really enjoy your presentations. Very nice, brief and effective analysis.
Another great video Chris! Will definitely be taking into consideration all this data designing future quads. Keep up the great work.
Awesome, thank you!
Chris, thanks for sharing your knowledge!
My pleasure!
Excellent video series
This is GREAT information
THANK YOU
I do enjoy your engineering deep dives great job thank you
This is one of the useful instructional videos I have seen. Very good.
Would have been skeptical of the smaller prop size a few months back, but ever since I received a set of T-Motor 4943 props I don't run anything else. The spool-up speed and responsiveness on them is fantastic. Which, if I've been paying enough attention to Chris, has to do with their moment of inertia.
Oh you are so right!
I love how you made this so easy to understand. Well done! I just sub'd.
Thanks and welcome. I hope you enjoy my other videos 😁
Great video like always full of information good inf. that we need i think i have to watch it again to get it right and dont get me wrong most of the time when the video is interesting and with good inf i watch it a couple of time thank u.
Here comes the 3.25-3.3" props!!
Absolutely loving the Babyhawk 2HD and you just told me why!!
Huge respect and appreciation for what you are doing!!!
I like your science based instruction/presentation. This I can get behind. This was very useful, even for my hexacopter.
I love engineering discussions, subscribed.
Thank you for your support!
Really enjoy your physics approach to finally answering our debates.
Thanks for your support! Facts make everything better :)
Very interesting.
Good stuff!
Glad you enjoyed it
Thank you so much for this
BRILLIANT!!! thank you so much.... your channel is superb.....
You're superb! Thank you for your support.
Great information! It would also be nice to see an analysis of the best prop diameter and motor rpm for maximum endurance for long range quads.
Just changed frame to be able to mount 5.2 props and a bit steeper angled props to carry my gopro. I hit right that green sweet spot and that thing now flies smooth as butter without gopro - haven't tested it with a gopro yet, but already it feels a lot better to fly it based on your scientific insights :) thanks a lot!
Great vid
It’s funny to see all The Who’s and who’s in the hobby gathering in your channel, proficiency in science will do that no more guessing 😊
I'm very grateful that these very experienced pilots think the content is interesting and useful!
Really helpful the work u do thank alot
Happy to help 👍
Excellent, subscribed!
Welcome aboard!
Thank you for well thought-out and presented data. I have always loved 3.5" props for micros and 5.5" for my GoPro rigs ( I also fly at 5000ft altitude). Hopefully we will see more 3.5" (thank you baby hawk hd) and 5.5" (gf 5551 only ones around these days) props come out. I usually have to cut down 6" props to 5.5" and it's a pain. It's hard to get a 5" freestyle rig with gopro in the 600 gram range. At 670 to 720g range 5.1" quad blades do help. Thanks again...you rock and keep up the great work.
Outstanding!
Thank you kindly!
Thanks Chris
No problem 👍
Ha! Loooove this! I’ve always said “3” is the best size”. I’ve had 0 interest in sub250 5” and def think 3” is the future. Thanks for all of this great info Chris!
Thanks for video!
Now i know the science why my 300g 4” build feels good to fly 😀🤓
Very good person you are,thank you.good day.
I’ve been saying that 4” is the way to go for the last 18 Months, hasn’t stopped me trying a few Sub250g 5” builds along the way 😉😁👍
Right on, no reason not to experiment!
Awesome!
I also figured out a while ago that 450-500g is the actual best performing weight for a 5 inch (at least in my opinion).
I think that 4 inch is veery interessting for the sub250 class. I will definitly use your research as a base for future testing!
Thanks a lot!
I hope your future testing goes well. Good luck! 👍
Chris I am really excited by the type of knowledge you have shared with regards to motors and propellers . It is ofcourse a little difficult to sum up the effects of motor stator volume to its torque and thereby the continuation of the same math with props . Would be actually helpful if you could show us a total guide based on these vids , how one of us could use these understandings to combine them up as a calculation and not make a mess out of them in our minds and make the best selection.
Also how do motors draw power based on different props at particular voltages has always made me think if there happens to be some other fool way to determine exactly the power draw of a motor without doing a physical prop test but by simply using the size numbers.
If you start with your target weight, that'll give you the right prop diameter using the graph in this video (green line). Then go to the motor video and the graph there will give you the motor volume you need. Pick your motor KV so that 0.7*KV*2*pi*Diameter ~ 450mph. Battery should be 1/3 of takeoff weight and that should get you in the ballpark :D
Than you Chris for applying the physics to debunk the hype. I love the way you are tactfully telling those who are driving trends that they are wrong.
I wonder how many rtf models are designed using real data?
I'm glad you enjoyed the video! Not trying to tell anyone they are wrong just trying to show how if you want a quad to behave a certain way there are concrete steps to get there 😁
new visitor subscribing after this great video
The most exciting video from motor volume / prop / disc loading series so far. Interestingly I was kinda intuitively leaning to that green line. Because I thought 5" 700g AUW having flight time 3.5min and landing with battery hot wasn't right. And according to the graph you need 6". And that's the size I stopped on. I had a 7" frame and I started to cruise around at about 60kph logging speed vs power. I replaced 7" with 6" and repeated. As a result I've got 2 elliptic clouds of dots (normal distribution) which were coinciding. Which meant 7" wasn't more efficient then 6". So why carry more?
Now I'm building 250g free style / long range quad with 4" props and 1207 motors. And it also hits that sweet spot :)
That's great to hear. I love it when theory aligns with people's real world experiences. Thanks for sharing!
I knew there was something special about my Babyhawk HD II's flying characteristics...Oh it's just science.
You my friend, are killing it. Allowing us to make Data driven decisions on our purchases. So tired of following the hype. This is good stuff. Working on a 4 inch build now, using this advice along the way. Keel it up.
I like to think of my channel as a hype free zone. I'm glad you value this approach and thank you for your support!
Interesting. It's funny I've been flying a 4 inch apex a lot lately and I think it's my favorite flying quad. Wonder if I should give some 3.5 in props a try
Ha, I'm building one now. Can't wait to get done
I love physics, and quads. Cheers!
I think what would be an interesting further development of this is to look more closely at the scaling of all the components and then look at the ideal prop size for the payload, rather than the AUW since that is impacted itself by size.
i like my 168g auw 4"
7min flights with a 750mAh 3s
i wonder if a 3s 18650 pack would push it more into the optimal disk load area
i'd like to see the tubular los quads in that graph
btw amazing channel
the vibration analysis results videos should be on every frames product page
no wonder of all the micro quads i have, the diatone 349 gives me the most smoothness of moves under 250 for freestyle. but I am eyeing for babyhawk HDII efficiency though.
So when i saw the graph at 9.40 the Babyhawk 2 HD is a good BNF sub 250gr. Rig realy close to the sweetspot.
Thank´s Chris Rosser for your amazing work due to the FPV Community.
Thank you for your kind comment! And spot on with your interpretation of the data.
Thanks!
Very generous! Thank you 🙏
9:30 graph is really help me a lot.
No more guessing and arguing lol.
People build as light as possible 3 inch quad, for me it is too flooty.
It turns out my 3 inch quad just at the point for flying outside, especially on windy days.
My 3 and 7inch is on point with all of TPU protection and gopro 😅 but need 5.5inch prop for my 5inch quad 😅
Thank you sir.
perfectly in line with my own tests, but much better explained. The only thing I want to add is, the graph gets a bit distorted on the very low prop sizes side because it's only an approximation that the fixed electronic weight cancels out other scaling factors and that approximation fails on the very low weight side. That's why on the very light side if you only consider prop load I find the chart suggests a little bit too small props, but only a tiny bit (maybe 0.5")
Absolutely right. Such a simplification can only be so good but it provides a starting point. Definitely small quads can benefit from slightly larger props. 👍
@@ChrisRosser do you know how the disc surface impacts wind resistance? I cant figure out if it only depends on the disc surface or also on the blade number because I feel like wind resistance per weight is the second most important part of the "feel" or "throw" in the air
@@JulianBauknecht I think the disc loading will be the primary factor with blade count as a secondary consideration. The idle RPM of the prop also plays a part with a higher idle RPM providing more drag in reverse flow conditions.
@@ChrisRosser ah ok tyvm, that would explain why I can't get definitive results wheater or not blade count matters if it's in between in real life. That would partly explain why on 5" 250g kwads 2blades fly much nicer (besides the fact, that a super lightweight 2blade is stiffer than a similar heavy 3 blade)
13:30 - "engineering effort". Make sure to quote that stuff. ;-)
I knew I would find you here, sooner or later and here you are.
Ooooh that's a nice burn... 😁
My A0S-5 with, Caddx Vista, DJI action 2, 1300mah battery and 5226 Gemfans came in at 665g. 654g if I drop to a 1200mah. Easiest quad to fly I've had yet.
Great video, although I think you skipped one important aspect: static thrust. Which is higher using a larger propeller (at fixed motor power).
This is due to the lower exhaust speed, which increases specific thrust. It is more efficient to accelerate at lot of air by a little bit, than to accelerate a small amount of air by a lot. (That is why human powered helicopters are huge.) The flip side is a lower top speed. You don't get any thrust if the exhaust speed equals the speed of inflowing air.
So by changing disk loading you can trade off top speed vs. acceleration (up to a point).
For 250g:
2" too inefficient
3" low acceleration, crazy top speed
4" good balance imho
5" crazy acceleration, lower top speed
6+" unresponsive (small motors for props with large moment of inertia), frame flexing, low durability
I don't think I neglected static thrust because static thrust is wrapped up in disc loading. I think the that static thrust/mass is among the most important criteria!
If I understand you correctly your analysis of speed and acceleration vs prop size may neglect some limiting factors such as prop pitch, tip speed, and motor/battery mass.
In real word testing 5 inch quads have a higher top speed than 3 inch quads because they are typically able to achieve higher prop tip speeds.
@@ChrisRosser Static thrust is dependent on disk loading, but you did not explicitly talk about it. And the propulsive efficiency you used @2:40 is zero by definition when hovering (no work done at zero velocity). Given the importance of static thrust for drones I think it is quite important to cover it (and may be a topic for another video).
Your anaylsis and presentation is great nonetheless and matches my experience when comparing my 3" and 4" 250g racers to my nazgul 5.
Static thrust is propotional to the momentum change of air, whereas the power is proportional to the kinetic energy change of air. So you get T ~ m_dot * v_exhaust and P ~ m_dot * v²_exhaust **. Lower disk loading implies lower exhaust velocity (during hovering), which leads to more efficient hovering. The wikipedia article on disk loading has a nice graph of the relationship.
As for top speed, at 250g and ~900W power (static thrust), a 5" is slower than a 3". The lower pitched 5" props just unload too much at higher speeds. If you want to play around with some numbers i can recommend the calculator on ecalc.ch. Of course when using the same power at top speed, a 5" should be faster. But then the 5" setup would not be able to handle full throttle punchouts. At lower power this changes as well. The extreme example would be a very low powered 3" setup that can just about hover. The increased efficiency of the 5" propellers means there is excess thrust, and forward flight is possible.
** The conrol volume needs to be chosen so that the exhaust is fully expanded, ie. at ambient pressure. See en.wikipedia.org/wiki/Momentum_theory
These are great questions you are raising so I'll do my best to answer. The principle behind the video is a scaling analysis. The key is finding the things that stay the same as you change the size of the props.
As you correctly point out static thrust changes with prop size so its not useful on its own for the scaling analysis. You run into a similar problem with power, a larger quad is more powerful than a smaller one so on its own power isn't useful for the scaling analysis.
Disc loading and a constant tip speed capture the same variables but critically can stay constant as you change size. Power and thrust scale naturally as a result of disc loading and tip speed. I hope that explains why they don't appear separately in the video.
@@ChrisRosser You are right and I was not clear. Comparing absolute numbers is not that useful if you have scaling laws. So maybe my comments were just a long winded way of pointing out that the hover efficiency is also directly dependent on the disk loading. :)
But creating a concise video is important, so I think you could have included that not you that you should have necessarily.
@@LS-xb2fh I really enjoyed this conversation. Thank you for your suggestions and feedback. I hope we can have more chats like this about future videos! 😁
Kinda shows why the Emax Babyhawk 2 HD is so good! 😎🤘
Thank you, the level of clarity you bring is fantastic.
Im building model F35s derived from Nicholas Rehms design. His plane has 3 motors in a tri copter configuration. His plane weighs about 850gr uses 2205 motors and 5045 props on 4s batteries. They fly just fine. My design is scaled 50% larger, weighs 1090gr and uses 2306 1900kv emax motors with 5545 props on 5s battery. The motor overheats within 1min. of Hover time. Based on your data tip speed is to high so reduce prop dia to 5045 or change motor to 1400kv. Sound about right?
11:07 literally where my session 5 carrying freestyle quad sits with 5.1" p3 props lmao, you wizard.
Engineer: Someone who does precision guesswork based on unreliable data from questionable sources, see also Wizard, Magician 😋
@@ChrisRosser maybe I missed it. At what rpm do common prop sizes hit 450mph at the tips? What is the equation for that?
Ie:
31mm whoop
2"
3"
4"
5"
5.1"
6"
What I am after is approximate optimal kv for a quad size. I know kv numbers on quads are not super accurate, but it would be nice to know. IE if 15000 RPM on a 3" gets you 480mph (pulled out of my butt) than anything over ~5000ish KV on 3s would basically be additional amp draw for no gain and less throttle resolution.
I know it's not all about KV, and you need to the volume to manage the prop, but that would be useful to know.
@@mouseFPV I did the 4" and its 3222 on 4s...
need to find a tip speed calculator to find RPM.
I'm sure there is a better one than what I used...
but
Thanks
No problem 👍
Always great info, are you setting up a discord for discussion?
Sir, do you have any good, scientifically sound info on motor stator height and effects on tip speed on props? You mentioned volume of stator being related to its torque and power.... can you elaborate?
Thanks very informative as always! What about the effect of the arms length? Could it be that running longer arms provides increased stability? Or should the arm length always be proportional to the prop size?
Run the shortest arms you can. Long arms can cause a lot of problems especially for larger quads.
I feel like we should just set up a conversation channel in a discord you frequent to discuss some of this... although practically this is still a great venue (algorithm/engagement and all).
I think the outright disc loading starts to grow wider error bars at the higher area/weight ranges, but that goes a fair way to explaining why 7" quads are pretty indifferent about all-up weight in my experience, and can broadly handle like race quads with a session on top if kept below 750g.
Omg! You are JB squared on tech info 😎
I try, I like to think that I emulate UAVTech but for hardware components rather than filters and PIDs. 😁
Emax Babyhawk 2 HD - sub-250g, 3.5 inch props - now I know why all reviewers praise it so much....
Absolutely, they've hit on an great size. 😁
@@ChrisRosser also it seems like the frame design is interesting from the resonance mitigation pov... I've just ordered one, even though I have no DJI goggles yet 🙃
If you have a 4" drone, does it make sense to run 3.5" 3 blade props in 250g acro config and 4" 2 blades in 300g long range config?
I think it definitely makes sense if you want a bit more snappiness and performance for acro flying but still want a great LR cruiser. Great thinking! 👍
Chris - the physics of unloading please. You have touched on it in previous videos- AOA adjustment & Inflow Velocity.
Can this be converted into rules of thumb to help when testing static thrust and knowing what will happen once the aircraft is in the air? Will it be different for fixed wing and multirotor?
It will be very different for fixed wing and multirotor. It's very hard to give a rule of thumb for a quad as they fly over a huge range of speeds from negative inflow to fast forward flight. If you know how fast you want to go you can use an efficiency vs advance ratio plot to find the right prop for you.
Hi Chris- any chance of an analysis of props vs noise - I high pitch long chord 3 blades seem to be quietest on my 2.5 inch toothpick- Gemfan D63s cinewhoop props - weird???
Super informative! But I am having difficulties in following your reasoning about motors sizing. Why do they "need" to be bound by the prop diameter, up to the point they are not able to reach the maximum desirable speed anymore? If a motor is not able to bring the tip of the blades up to 450mph, couldn't you just use a bigger motor, by leaving all the other parameters the same? It's unclear to me why a sub-250g 5'' drone with oversized motors should still fly bad due to its uncapability to make props reach certain speeds. Maybe it will burn the battery sooner, due to the higher consumption with respect to its battery discharge rate, but according to your reasoning it SHOULD fly better, isn't it?
I am sorry if I sound pedantic, but I just want to be sure I got everything right! I'd love to understand physics behind drones, and these videos are pure gold! Please keep up with the great work!
If your motor cannot reach 450 mph tip speed then you need a bigger motor. You also need a bigger battery as well because a batteries ability to supply current depends on its size. Then you find you have a much heavier drone. That's the key takeaway from the chart.
Do you think we will se a better selection of different pitched 3.5 " props than what we have now ? i think 2 and 2.8 is the only option right now!
Another question is how many blades on the prop? Which amount gives the best results? Max/min props or prop? Should the prop get smaller towards the tip or wider?
Hi Chris,
thank you so much for the info!
Does the optimal tip speed of 450mph relate somehow to airfoil chord length of the prop?
I found high chord length props likes to run at lower speed, for example the 2.5-inch Emax Avan Rush.
It has a lot of thrust with low rpm but increasing the tip speed I noticed that the efficiency decreases a lot.
I don't think so. Its to do with Mach number so more related to the air properties than anything about the prop.
down to aspect ratio.. look at glider wings long and skinny, jet short and wide... the long skinny can handle higher aoa giving better low speed performance as lift is greatest just before the stall
My quad is over 800g on 4S and I'm trying to find the right pitch prop for efficiency,5146 does better then smaller pitch,but 5236 feels nice too.but idk bout which was more efficient because my flights time varies sometimes ,one minute I can get 5 minutes and then another flight only get four and a half minutes while doing same style flight.if that makes sense.
please how can I calculate the blade tip speed ?? i I found this formula (3,14 *D*rpm) with D: prop diameter but I'm not sure if it's the right formula or not?
JFYI: 0.59 mach is roughly 200 m/s or 730 km/h, which is 30,400 rpm on a 5" prop or 50,700 rpm on 3". This feels a little high to me, maybe the 0.59 mach value does not fit 100% for tiny props (compared to man-carrying aircraft) but I could be wrong.
It's not too bad when you consider that 1800KV on 6S will hit those numbers on a 5inch. 2800KV on 6S gets you right in the ballpark for 3inch as well. Smaller quads do struggle a little more because the electronics doesn't get much lighter so there is less weight for battery and motor.
This is very useful. I switched to 3" from 5" sometime ago because I don't do use action cameras so I don't see the point... Anyway, the weight of my 3" racers is approximately 184 grams on 4S which is pretty good considering I'm using the Vista with original DJI camera. The bad news is that I need to loose approximately 15 grams to reach the green line. Deceasing the Vista and the Nebula Pro camera should get me there however.
Yes I think decasing the vista is the clear next step 😁
Wish the tp3 was on here! Disc loading king
It's so light. Makes less power than a lot of 3" so I feel it gets away with it. And kabab tried 4" arms couldn't handle it. He def tries everything to try and get the best
If you have a triple toroidal with a built on cinewhoop with a rounded outside edge drones some of these graphs would change again. But good in depth work.
Hey Chris, thanks for this confirmation - which is max. AUW between 600-700g for 5 inchers. One question I have is: how does (if it does) size of individual prop blade surface (for example in mm2) affect prop performance, it probably also affects ideal tip speed and everything else? For example if you look at Dalprop Cyclone 5 inch prop and compare it with for example Ethix S3 or S4, there is obvious difference in blade surface size. Or maybe this is too complex question. But at least recommendation from you like this example of blade shape and surface size is good/efficient and will work well with usual motor sizes and kVs and this is a bad example. Thanks and I appreciate your work. 👍
Have you watched my video on choosing props? I think the answers you are searching for are in there.
What about voltage and voltage sag? If you punch the throttle and drop to 3.5 volts wouldn’t your dip speed drop a lot? So would you want to shoot for a higher tip speed knowing it will drop to 450mph due to voltage sag? Love the content!!
Absolutely, I like to think that 450mph is a target. If you don't quite get there its not the end of the world. But you don't want to be too far away because then you are giving up performance.
If I want to build a 250g 3" build, what motors should I use?
Hi Chris, thanks again for such an interesting information. What about choosing higher kV motor and then limiting motor output to match 450mph prop tip speed according motor rpm log?
You can, but be careful because having more KV than needed and limiting down increases risk of smoked motors and ESCs and also reduces efficiency.
@@ChrisRosserthanks. Just watched this video ua-cam.com/video/QQJ3yGproOg/v-deo.html and as I understood, Max says otherwise about burning ESC’s.
@@Edga_Po My concern is the stall current. If the ESC is trying to spin a stalled motor the current will be higher for a higher KV motor due to V = IR and R is lower for higher KV. If the current is too high the FETs in the ESC will overheat. Perhaps Max doesn't stall his motors that often or his ESCs are very durable. If the motor isn't stalled an output limit might help protect against situations where the motor is commanded to full throttle and then burns out. If you are using an output limit you are losing any benefit of the extra KV but still taking the efficiency hit. Only worth it if you need to run 4S and 6S on the same quad.
@@ChrisRosser Thank you for explanation! So the only solution for best performance and efficiency is proper mechanics, not cheating. 😃
@@Edga_Po I wish it were otherwise! Happy flying!
So what's gonna happen when I hang enough 18650's from my X-Knight 5" to bring it up to 475g for intersecting the green 6g/sqin curve? Peak efficiency 😃, or fried silicon 😭?
I want the babyhawk ii hd with crossfire.. sold out before it came out 😳
Me too 😢
hello Einstein, it's like theory of relativity, which most people still do not understand well, can you give PID's values for 3, 5, 7, 8, 9, 10, 12, 15 inch props on Arducopter with 3-4S lipo ?
How does a 5" 3 blade compare to a 6" 2 blade?
Actually my own design and setup machtes perfect with your theory. 1950KV on 5s with 500g AUW with a Session style HD Camera. Perfect prop tip speed and perfect match between prop size and wight. And it just feels absolutly amazing to fly and is very easy to tune.
I feel a little bit proud now lol :D
Nice work! I love it when theory matches up with experience, seems we're on to something here. 😁
@@ChrisRosser I would say so! I also ordered some pretty high and narrow motors to take a look at your motor volume theory.
Your theory's really made me think again.
What about the number of blades? Wouldn't going from 2 blades to 3 blades on, say, Flywoo Explorer also mean using a smaller diameter?
Yes, you're quite right. I have another video on props which covers the effect of number of blades and several other factors. You might find it interesting.
How would one go about creating a quiet or silent quad (as one can get)?
Probably a 3 inch toothpick with a throttle limit is the way to go for super silent.
Got a quad with 1806 motors 3 inch 249 gams with a 850 bat lucky for me what prop do i put on that to get a longer flying thx.
Have you watched my video on props? I think the information you need is in there. Link in the description.
ur very knowledgeableborderline genius lol. funny how all the new 3.5/3.6 inch/4.2 inch bind and flies are coming out
How about for, say, bicopters? Do I just match the overall prop area to get the same disk loading?
If so, I assume for a 200-250 gram bicopter I use 4-5 inch prop. (planning on a tailsitter delta wing :D)
That sounds like a good approach to me.
Finally someone explained it. Thank you.
But one question appeared. If goal is, for example, long range - is it beneficial to use lower KV motors and smaller props, to achieve more prop speed while cruising? Opposite situation - if you have crazy overpowered 8-12s build, isn't it better to use bigger props with same weight, just because motors can build more power/prop speed?
Also, if we take into account power required to spin propeller will efficiency stay the same? Propeller speed to air movement speed is great relation, but propeller is easier to turn on lover RPM, so even with worse RPM to air speed efficiency, it could result in better battery consumption efficiency.
After some research I'm now sure that I was right. 450mph(actually, it's 475) is best performance per rotation. So it's best thrust for the size. But if you can go bigger without adding much weight, you'll always get better efficiency.
So, if you can get same weight with same motor size etc. in 10" it will be much more efficient than 3". Props, same as wings, are more efficient slower you go, and lower is motor kv, better is efficiency.
If you do race drone of some size, you should stick to 475mph. But it's not a surprise that huge and light long range drones have efficiency even with low tip speed.
Hey Chris, thanks for the amazing info! My question is, if you want to design a Freestyle Quad that can also carry a GoPro whilst maintaining efficiency under 250g, my assumption is that you would have to trade off efficiency to thrust in order to carry the GoPro? Or is that fully compensated by the weight reduction?
And by this I am talking about battery life. Considering a smaller Quad, that would only carry a smaller battery, with a GoPro, I would think that the smaller props will give much worse flight times with less efficient thrust?
I guess you could also just increase the battery capacity with the weight saved by dropping a prop size in order to increase flight time? At some point you run out of frame space, but I guess you could always just bottom-mount a larger battery? Does this track?
You have a huge sacrifice in efficiency as you try to carry the same weight with smaller props. Your disc loading increases. You need more power to lift the same wieght with smaller props.
@@ChrisRosser Thanks, so in that case, would something like a 4 inch prop build for a sub 250g drone carrying a GoPro be the better tradeoff for going sub-250g (thinking freestyle/cineflying) whilst still tapping into the Disc Loading optimisation and maintaining some of the payload capacity of a 5 inch? Or better off staying at 5 inch and taking the efficiency hit on "performance" if the goal is efficient payload carry?
To go sub 250g your best bet is 3" with naked go pro or SMO 4k. No standard go pro is going to work.
I am building a hover bike. Can you help me with my motor and rotor size. I will only need to hover
Any motor size data as far up to 12 inch props? I'm building a quad for my daughter inlaw, it will be in auto level mode so it doesn't need to go very fast. Somewhere between 9 and 12 inch props. I need more data to decide. Thanks in advance.
Torque and therefore motor volume scales with diameter^3 so you need 8x the volume of a 6inch motor for a 12inch prop for example.
I said it long ago, best sub 250g 5in freestyle is 3in. You cannot bend physics to match your desires, but you can create new market for people that do not realize that :/ Sub 250g 5in freestyles are a moneygrab.
im pretty confused with the tip speed calculation.
i calculated in metric systhem, so 450mhp are 720kmh and as a formular i used: Pi * (7inch * 2,54 * 0,01)*(22,8V*3350kv/60) = 711km/h
i mean why is it in this video, when even in this unrealistic configuration the tip speed is lower than the max droppoint of the efficiency?
or did i something wrong?