View Full Version : High Efficiency motor -Sailplane

07-14-2010, 05:47 AM
My friends and I are interested in designing and building a solar powered UAV and require a motor-prop setup with the best efficency when running at approximately 10-30W (for our cruise speed of about 10ms^-1).

Base on previous designs, other requirements/values are:
Motor mass < 100g (also want to minimise this)
Max power input = 150-200W (for take off)
Plane mass = 2.5kg

Im quite new to electronics and was hoping someone could propose a motor or information useful for having one custom made. If i have left out any info let me know.

Any help is much appreciated.

Sky Sharkster
07-14-2010, 12:11 PM
Hello Eclipse, Welcome to Wattflyer!
One of the highest-efficiency motors made is the Hacker brand from Germany. Although they now make outrunners, for your application I would suggest you look at the B20 "L" series of inrunners with the Maxxon 4:1 planetary gearbox. This motor/gearbox weighs 68 grams, can turn a large prop (depending upon the "Wind", the number after the B20. Like "18L").
I have a B20-15L with 4:1 gearing, in tests using a 3 cell (3S) LiPo and a 9" x 6" APC prop the numbers at full throttle are;
Amps 19.96
Watts 217
RPM 19,510
Volts 11.56
But a motor this size would struggle with the 2.5 Kg aircraft weight, you may need a different wind and larger prop.
Here's a free online motor calc, you can try different wind/prop combinations to achieve better thrust or lower amp draw.
Good Luck!

07-14-2010, 06:48 PM
This is certainly over my head but that doesn't stop people from posting.:D

In general you probably want a very large slow turning prop for best efficiency. Look at the props on personal powered craft-they are huge. To that end a very low geared system of some sort may suit you best. Which one I can't say as I personally use mostly cheaper outrunners. But yours ain't gonna be cheap.

There are folks that take on this task (or attempt to) on a regular basis so some searching may turn up some leads. Good luck, I think you'll need it.

07-19-2010, 04:23 AM
Thanks for both replies.

I came across these hacker motors, but disregarded them as i would likely need to do some large gearing compromising the efficiency.

I am probably looking at turning props in the 24x8, 24x10 range. For max efficiency and would likely trade off some extra weight to obtain it.

I have also come across lrk-torquemax motors and was wondering if anyone has some results in turning larger props with them.

We are not to fussed about cost at the moment, and would be happy to have something custom made along with a propeller.

Thanks again.

07-19-2010, 07:39 AM
Hmm, not to discourage you, but a motor that weighs less than 100g and turns a 24x10 prop will be very difficult to find I think. Even with gearing...

Please let us know if you find one!

07-20-2010, 08:26 AM
^ Truth.

I'm just thinking here...but putting 200W into a 24" propeller is going to make for a very slow spinning propeller. Is it going to have anywhere near the required airspeed to get the plane to takeoff? THe plane is 2.5kg after all. 200W doesn't sound like enough for takeoff of a 2.5kg plane. You guys can't use a catapult for launch? Because then you wouldn't have to worry about a motor-prop combo for takeoff at all and could design around cruise efficiency only with no compromise.

UAVs optimized for cruise efficiency (like yours) have a catapult take off because they are optimized soley for cruise efficiency (small high pitch propellers) so their propellers aren't large enough to provide the required thrust to take off under their own power. Doing that lets you improve cruise efficiency because you don't have to make any compromises for takeoff/climb. You get to use a cruise-optimal propeller with a lighter, lower power motor with less gearing.