large diameter outrunner?

[thrmaln]

Hello All,

I have seen a lot of the go brushless outrunners installed in micro helicopters but I was wondering if a specialized outrunner could be made to eliminate the geartrain. What I am thinking about would be an outrunner motor about the same diameter of the main spur gear that is on most micro helis. The large diameter motor could possibly have enough torque to spin the heli blades direct drive. by doing this, the heli would be able to autorotate (until the magnets overpowered the rotor) without the need for a one way bearing. Anybody try something like this? Unfortunately I have not built a gobrushless kit, but plan to soon to get my feet wet and persue this idea?

The main problem I see would be the availability of large diameter stators and also calculating the amount of winds to acheive good results. I can make my own stators and the winds would most likely be trial and error. I am a design engineer and could draw up the parts quickly and have them made, but would need help in stator size.

Best regards,

Marc Webster

[Q]

Your idea has been done before. The guy posts on the Yahoo LRK forum IIRC. He used the stator from a 3.5" floppy disk drive. There's not much advantage in the system, except from it's symplicity. The system weighed almost as much as the geared version and the efficiency of the big, flat motor was not as high as the small CDrom geared types.
AFAIK you should use a high gearing and fast motor speed with brushless motors. That gives the best efficiency.

[ron_van_sommeren]

Niels Polfliet from Belgium :) did it:
http://www.rcgroups.com/forums/showthread.php?t=197862&highlight=direct+direkt

[thrmaln]

Hello Ron,

That is exactly what I had in mind. However, his motor looked quite complicated in relation to a go brushless kit. In your opinion, could a simpler version with less poles be made to work? I would imagine this application lends itself better to the LRK type of format.

Please forgive me, but I am just beginning to get my feet wet with the outrunner type motors so I may ask some dumb questions.

If it can be done, I am a design engineer and have access to a full machine shop to have my parts made. I just need to understand just how the motors work and I can draw something up in solidworks. The only hurdle I see would be the stators. I would need to have them stamped or edm cut? Could a stator be made of one piece rather then layers? If so, do I want the material to be ferous or non ferous? Would a one piece 6AL-4V titanium stator work?

Best regards,

Marc Webster

[ron_van_sommeren]

You need the diameter to get the torque. Read Christian Lucas's contributions in that thread, he did not use the lrk winding in his direct drive motor, even though he developed the lrk principle for RC flight. Better continue the discussion there since GB is not into that size/type of motor.