View Full Version : Direct Drive

10-03-2007, 01:07 AM
This is more out of interest than actually do it, but could a out-runner motor be built to- directly drive the main blades on a Micro/Mid size Helli ie Walkera 36 say? Thanks to All Rog.:)

Bill G
10-03-2007, 05:55 AM
Doable, with the correct motor. Some speed controls are better than others, with this type of startup. You would need to apply throttle slowly though, to not overload the motor. May not be able to throw that much pitch at it either, depending on motor again.

Of all applications, however, a heli really lends itself to gearing. Perfect situation for a high kv motor with deep gearing. Low end torque and high top rpm.

10-03-2007, 06:42 AM
All good points Bill.

The other factor that enters into it - and the other reason why helis are so deeply geared - is because the main blades are only designed to be turning in the 2000-2500 rpm range.

If your running a small heli on say a 3S pack thats holding around 10.5 volts under load, that means your motor would have to have a Kv of only 238 or less.

No small - or even mid to large - outrunners have a Kv that low. You have to get into the giant scale outrunners to see that low a Kv.

Even if you managed to wind a small one with that low a Kv, it couldnt handle enough power to fly the bird.

You would be forced to run rediculously small main blades (prop down as it were) or try to run the motor on a 1S10P pack. The extreemly low voltage would force you to pull hi amps to get enough power and low voltage at very hi amps is very inefficient and hard on the equipment. Heat losses go up as the square of the current.

Not a dumb question at all tho :)


10-03-2007, 05:34 PM
Yea thanks. I can understand what you're both saying. And why change something that works perfectly as is. But a little lateral thinking never goes a stray. I was thinking of something along the lines of the motor used on a certain washing machine, the one with all the magnets around the plastic can, they use it for wind generators, I have been asked to machine the center rotors for that use. These motors certainly produce plenty of torque as they have to agitate and spin up also. If something had say thirty magnets would that do it? (might get a bit heavy though) I thought it could take the place of the main gear near enough. And I suppose it would need a sp. ESC but that's not out of possibilities. Thanks again. :silly:

10-03-2007, 05:45 PM
I've actually seen this done. A guy here in town builds his own electric motors (mills the case and all) and build a direct drive motor for a heli about the size of a blade CP. The motor was about 4 inches in diameter and 1/4-1/2 inch high. I had just started flying then and never got the chance to talk to him about it, but it did fly.

Actually, the motor looked A lot like the kind you would get out of an old 1.4mb floppy drive. very wide and flat.

10-03-2007, 10:50 PM
T-Rex big enough ?



Yes. its possible
Lower noise and increased reliability are the main advantages

disadvantage is a heavier Heli. with less acro performance
and slightly reduced flight times

10-04-2007, 06:41 PM
Several direct drive motors & videos:

Vriendelijke groeten ;) Ron

10-04-2007, 08:22 PM
I like being wrong when its somethng as cool looking as those motors that I didnt know about :)

Any problems esc wise with those 60 pole motors Ron?


10-04-2007, 08:37 PM
I haven't seen any reports by Pontus Claesson yet Larry. Probably in the building phase. He had a lot of laminations made specially for that project.

10-04-2007, 08:45 PM
For the 'German impaired', a direct link to direct drive helicopters on www.powercroco.de (http://www.powercroco.de)

Very clever manufacturing method

Picture and drawing/sketch:


10-05-2007, 09:45 PM
I have not had time to follow all the video links yet, but hey that's brilliant. It's excactly what was in my mind! it's "been done" talk about
trying to reinvent the wheel! I think I could build one of those, on the other hand I think I will leave well enough alone. Thanks Ron and others.