Feb 062012
 
 February 6, 2012  Posted by  Components, Motors, Propellers  Add comments
Choosing a Quadcopter Motor and Prop

Choosing a Quadcopter Motor and Prop

When building a quadcopter, deciding which motors and propellers to buy is tricky, but a very important decision. There is a lot of math and science that goes into understanding how the motors and propellers effect how a quadcopter flies or if it flies.

As a novice, it is very easy to be overwhelmed by all of it. The correct motor/prop combination needs to be chosen by considering the size and weight of the quadcopter, the length of flying time and the power and agility that are desired. Also, the battery and ECSs must be chosen to effectively drive the motor/prop combination. Continue reading to find out how to decide the combination that is best for you…

How to Decide?

The way I see it, there are two different ways to go about making this important decision.

  1. Research what other experienced pilots use and buy the same or similar equipment. Personally, I prefer this approach because it doesn’t require an understanding of the physics involved and I know the solution is proven.
  2. Understand all the science and purchase the motors, props, battery and ESCs based on that knowledge. This approach will take more time, money and could be frustrating if the parts don’t work according to spec.

Now here’s more on each approach..

Who are some great pilots and what are they using?

I am interested in First Person Video flying (FPV) and two of the best FPV pilots are juz who flies quadcopters and David Windestål who mostly flies trciopters. For over all amazing flying skills, Warthox is unmatched. These guys publish the equipment they are using either with their videos, on their websites or on various forums. Hey, if it works for them, it is plenty good for a novice like me.

Check out this amazing video by Warthox:

Configuration

Towards the end of the video he shows that he is using:

Motors – Turnigy Aerodrive SK3 – 2822-1090kv Brushless Outrunner Motor

Props – 8″x4.5 Carbon reinforced AP Propeller Set black 2 CW and 2 CCW

ESCs – HobbyWing 10 Amp

Battery – 3S1500 20C

Frame – Flyduino frame

This is just one example, but I encourage you to watch these great pilot’s videos, go to their websites or various forums they post in to find out what equipment they use. FPV rigs carrying cameras will likely require bigger motors and props. For FPV, a great place to find tricopter building information is David’s site at rcexplorer.se or see what juz is doing over at the openpilot forum. All of these guys share their configurations openly and I sure do appreciate being able to learn from them.

Also, I have started a list of pilots and some of the configurations they fly. You can also submit your own proven configurations to be added to the list.

Motors & Props Tip Motors & Props Tip
A quadcopter uses two clockwise(CW or pusher props) and two counter-clockwise(CCW) propellers. It is possible to use all CCW props, which are more readily available, if two of the motors are angled a bit, but I have never tried it and it is not very common.

The APC brand propellers are good quality and used on many quadcopters. EPP (expanded polypropylene) props are not as durable but are less expensive. Usually the props used on quadcopter are listed as “slow fly” props. Some folks use three bladed props, but they are not as common as two bladed.

Propellers are listed by length and pitch with lengths typically ranging from 8 inches for higher Kv motors to as long as 12 inches or more for lower Kv motors. 10×4.7 is a common size for motors in the middle Kv range. The section below covers the calculations that need to be made to choose the correct prop size for a given motor and frame.

I started out using APC propellers. For 8 inch props they are about $16 a set. They are great props, but I was crashing a lot when I started out, so I switched to Gemfans that can be had for less than $5 a set. Now, I am not crashing much, but I still like the Gemfans. I found the props I currently use for $4.00 per set at DIYQuadCopters.com. They are Gemfans and Dan who runs the site is very helpful and ships from the USA. A set of four includes 2 CW (labeled R on the prop) and 2 CCW props.

On the other hand, if you want to build a quadcopter from the ground up and decide on a configuration of components from scratch, here are a few places to start…

Understanding the Science

If you prefer to understand the science, I can suggest a few resources that may help. Realize that you may spend a lot of money on various part combinations to test your theories.

To learn the the basics of watts, amps, volts, motors, props, etc. I suggest reading through an excellent series of articles called “Understanding Electric Power Systems” by Jim Bourke. There are five articles in the series:

Understanding Electric Power Systems – Part 1

Understanding Electric Power Systems – Part 2

Understanding Electric Power Systems – Part 3

Understanding Electric Power Systems – Part 4

Understanding Electric Power Systems – Part 5

Quadcopter Motor and Prop Calculators

After getting a good understanding  of electrical power systems, there are some great calculators on the web that allow you to model combinations of components to see if they will work together and how they will perform. Two good calculators are the “Estimate Electric Motor & Prop Combo” calculator found at rchomepage.com and xcopterCalc that is designed specifically for multicopters.

Conclusion

So, good luck on choosing the correct combination of motors and propellers. Do it the easy way or the hard way. I think it is easier and better to go with a proven combination that other pilots are using.


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  35 Responses to “Choosing Quadcopter Motors and Props”

  1. Is there any one who knows the calculation of coefficient of lift and drag for elliptical propeller?

  2. [...] Choosing Quadcopter Motors and Props » Odd Copter [...]

  3. It would be really helpful if people posted the total weight of their copters along with their motor setups.

  4. what do you mean by Add. payload in the eCalc.? do this mean that i can still add a load or this is the excess load I add in the system?

  5. Hi, can somebody help me to understand what is the meaning of cont.Current and the MaxCurrent of this calculator for quad? http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en, is it the esc current found in its specs?

    thanks for the help guys.

  6. It is so true that this tutorial is best on the internet. It helped me a lot and guided me how to start my FYP.
    Brother I need another help from you if u can, I need to lift 2-3kg of weight with my copter, in this case how to select motor and what should be the min RPM and props diameter and pitch is required to lift my copter.

    • That is starting to get pretty heavy. I have never built a quad big enough to carry that kind of load and probably never will. What will you be lifting? I have noticed that when people start carrying heavy and valuable loads they tend to build hexacopters or octocopters which increases the lifting power and they can still stay airborne if a motor fails, which is important if you have valuable cargo. I wish I could be of more help, but I have never done it. I would use xcopterCalc to try out different scenarios. Here is the link:

      http://www.ecalc.ch/xcoptercalc_e.htm

      It will show you the expected flight times for various weight, motor, prop combinations. Also, you should probably do a google search on hexacopters and octocopters. I may try to build one at some point, but currently it is beyond my budget.

  7. Hi,

    My senior engineering design class was given the following project:
    Design a quadcopter that can reconfigure mid-flight into a conventional fixed wing aircraft.

    I was wondering if you had any recomendations for motor/prop combinations that would perform well in both configurations.

    Also, depending on motor placement we are considering using two or more ducted fans (EDFs). How do EDFs compare to open props in terms of power consumption, thrust, weight, etc.?

    Thanks!

    - Seth

    • Wow, that sounds tricky, I have no idea. I have never even flown a conventional fixed wing aricraft. You should try the question on the RCGroups multicopter thread

      http://www.rcgroups.com/multirotor-talk-659/

    • Hi, I do not recommend EDF. EDF are most powerful when the it is moving fast enough for air to be rammed into the intake.When moving at slow speeds or stationary the EDF has to pull air into the intake which is another setback. However when your craft is in “plane mode” EDF would work about the same as a prop. Prop is much more efficient in a quad. Check You’Tube for some folks that have made a switchable aircraft.

  8. Having a huge interest in electronics and quad-copters I’ve googled my butt off lately.
    Your information / tutorials is the only thing that make sense. Thanks a lot mate, this is the only one I found worth bookmarking so far. (And as web developer, an awesome implementation of WP!)

    I’m in the “fortunate” position of being able to get nearly any part very cheap (even much cheaper than HobbyKing) but still totally overwhelmed by all the parts that is available.

    Could you perhaps give me a shove in the right direction as to what is “top of the range” (I know that sounds lame, not mean it that way)

    • Hmm, I was thinking my WP design be improved, but thanks, ha. If you ever want to get involved, let me know. Not sure I understand your question. What does “top of the range” mean? What is the best equipment? What is the most expensive equipment? Which components are you wondering about?

      • Are you in China? Low cost sourcing of parts might really help me when I release “The Oddcopter”.

        • Been a while since I’ve been working with WP, but drop me a line if there’s anything I can help with.
          Not in China, but wife is Chinese, buy me stuff on taobao.com (chinese ebay) and mother-in-law deliver. Long route, but I’m getting some stuff really cheap (though I noticed multi-rotor parts are rather expensive. Might be low demand due to laws not allowing you to put in air whatever you like)

          Top of Range (still lame, I apologize) I mean specifically things like motors and esc’s.
          I’d like to put together the flight controllers myself (learning and *that’ts* the part I’m most interested in). Put a set of motors/esc’s on a good frame and leave it at that.
          Rather get ones that are much more than I need so I don’t keep waiting 3,4 months for stuff delivered from China.
          So from what I gathered you want to go with motors less than 1000kv, and weight less than 160gr each?
          But totally lost. SO MANY MANY choices! Figured go for something everyone want because really good, even it’s a bit over priced. (Yeah, I’m stupid….keep spending more than I should on tech stuff…lol)

          Make sense?

  9. oh ok, that’s nice to hear.
    Nice to have such a good blog, bc I could be busy for weeks to get all these information that I get in a few minutes here!

  10. Hi,

    I saw the motors and props and searched for it.
    I see that the props have a hole of 5mm, and I think the motor is 7mm.
    I am pretty sure that they can’t fit on each other, but I am probably wrong.

    Could anyone help me with this question?
    Thanks,
    Isaac

    • Usually there is an adapter that comes with the motor or may be purchased separately that is bigger than the diameter of the shaft. It fits over the shaft and is used to tighten the prop down. Also, the Gemfan props I typically use have a large hole and come with a set of adapters that are inserted in the props to match the size of the adapter on the motor. However, they don’t always match perfectly and I have often had to drill the prop holes or adapters to be bigger to match the motor adapter. I hope this helps.

  11. Thanks for the quick reply. One more question. Ive read about thrust to weight ratios and trying to know what makes a motor powerful when looking on HK. I see different kv ratings but if I understand right you can get the same trust with different prop and motor combos. There is someone on rcg (bobepine) has how to videos for quads and he has a very nice one using a kk2 board that you mentioned. Its right around the size I want, ~350 size frame. He uses an rcx kv2600 motor with 8in props. It seems very different from the warthox’s video above using a kv1090 motor with an 8in prop and it looks like almost the same size. I could be way off. Just trying to understand why the specs are so different but the size is similar and in the videos the performance looks similar too. I believe both are using a 3s battery. Thanks for helping out a novice!!

    • That is my understanding too on the thrust, but I am no expert on the physics part. However, it is my understanding that a particular kv motor will only work with a certain range of props sizes and the efficiency will vary greatly depending on which size you choose. Lower kv = bigger props, higher = smaller. I mostly have looked at what others have used and tried to duplicate it. I have built most my quads as 450 size. There are so many variables that it can be overwhelming. Things like the quality of the fc, motors, escs and props play a big part too in how well it all works. A lot of configurations on 450 size quads seem use motors from 800kv-1200kv. And prop sizes usually range from 8-10 inch or bigger. The e-calc program is great to plug in different configurations to see how they should perform:

      http://www.ecalc.ch/xcoptercalc_e.htm

      Some quads and tricopters I see use very low kv, high pole count motors. I have never tried them. One reason is that those motors tend to be pretty pricey, but also, I have been pretty lucky with higher kv motors and smaller props. It seems I usually end up with 1000-1100kv motors using 8 or 9 inch props, but things can vary greatly depending on the motor and its size. Again, use e-calc to see the differences! They have a ton of motors loaded into that program.

      One thing I have noticed is the prop quality can be a big variable, especially when you get into larger props. You see a lot of people using APC props and the real studs use Graupners. I use cheaper Gemfans and like their 8 and 9 inch props. The 10 inch ones don’t seem to be as sturdy. Obviously, weight is a factor too and the bigger the quad, the better the prop needs to be to support the weight. By the way, the HobbyKing props listed in the inventory link at the top of my blog are Gemfans. At least the ones they shipped me were, ha.

    • This post on rcgroups is good reading on this prop/motor discussion:

      http://www.rcgroups.com/forums/showthread.php?t=1759533

      I am in agreement with neobot.

  12. Im really liking the quad in the video you posted above. It seems very quick, is this typical quad performance? It obvious the pilots skill is way over my head but Id like to build a quad similar to that build. I noticed you put all the components below except the flight controller. Im just learning about all this so its hard to know what kind of controller will give me that performance. Any suggestions would be great. Also Im not sure what size frame it is. If I were to go a little smaller would it throw everything off I were to still use the same motors? I know I need to read more into the power systems that you provided but for now Im just getting my feet wet. Thanks again for all this information youve provided. This hobby can be very overwhelming for someone new to it.

  13. great website, very useful information.
    I’m learning alot of stuff from you..and will try to build a quadcopter in the coming weeks.
    Thanks for sharing!

  14. dear britt ,
    loads of use full information provided here.
    love the organization of ur website.
    some of the cleanest I have seen.
    spexially for novice users.

  15. Hi Brother.

    Indeed your post was very useful for beginners like me. May I know whats the total weight of your custome made Quadcopter and the Lift?

  16. Thanks for the reading resources, just what i needed to get started

  17. can i find a propellor for like size 5 !! ???

  18. Any suggestions for flight control board and gyro to use with the Warthox config above?

    • That is a tough choice and I think it depends how experienced of a pilot you are and how much time you want to spend doing calibration stuff. The cheapest option is the KKMulticopter board, but it only has gyros. I like the boards that have both gyros and accelerometers. You can get MultiWii boards pretty cheap these days, but I like the FH-X46 board more because of its simplicity. It is more expensive though. The CopterControl board is my favorite, but they never available. There are a lot I haven’t tried too.

  19. Very helpful info. Going to build my first quadcopter. Impressed with pilot in video. If I can get halfway that efficient I will be happy.

    • Hey, Richard, thanks! I have been getting about 150 vistors a day, but not too many leave comments, so it is nice to get some feedback. Don’t know if you have been flying other rc stuff, but, I am pretty much new to it. I have learned a lot in a short time. Quadcopters are a lot fo fun to fly, but I must admit it is a bit more expensive than I thought they would be.

      • My feedback is that this little introductive tutorial is the best I could find on the internet, both because is well written and because pointed me to the right resources.

        So thank you and happy flights ;)

      • Hi Britt, very interesting web page you set up here, surely a big, if not the biggest hand I have found so far. Straight to the point and sincere. Thank you very much and congratulations. As I am not yet in the RC business, I have nothing to comment really but that I also invested in HK merchandise to built my first Quad and, after having read for days what the HK forum offers, picked nearly the same configuration as you did. I had to split the order in two, as neither the ESC plush 30 nor the 9XR and its case were available. The first order with frame and everything else should arrive in a few days, I will make a little clip on opening the box and maybe post that, if somebody is interested. The second order I reduced by the case for the 9XR yesterday because this case seems not to be available before march and I am #40 on the back order list. Here a short info which might be helpful for someone interested in cutting back on an order: Even HK announces on its page not being able to pay back shipping costs, they did credit part of those yesterday to me when I requested, using online chat, to cancel the case. And folks, the case cost about 11 $, the whole order was decreased by about 30 $. So if you want to cancel something, do what I did, get on contact in the live chat and talk. I was attended by Ivy. :)

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