Simon Chaddock Posted June 4, 2011 Share Posted June 4, 2011 In a typical RC brushless motor the magnets spin round and the winding stays still.However the winding itself is notionally in perfect balance so it too could rotate in the opposite direction.The advantage of such a layout is it would to all intents and purposes be torque free on the airframe regardless of power setting. It would also in effect halve the motors kV rating. Apart from the mechanical issues of arranging suitable shafts and bearings the real problem would be whether the commutation 'sensing' required by the ESC would be effected by the necessary slip rings. I did use such an arrangement on a small brushed motor and it worked well although balancing the can was not easy. Of course in a brushed set up any small electrical interference from the slip rings was not really significant. Has anyone actually tried this on a brushless motor? Quote Link to comment Share on other sites More sharing options...
PatMc Posted June 4, 2011 Share Posted June 4, 2011 I think it would be simpler just to have two motors concentrically mounted, the front one with a hollow shaft & bearings to take an extended shaft from the rear motor. Both sets of windings fixed of course.IIRC it's already been done. Quote Link to comment Share on other sites More sharing options...
Solid Snake Posted June 4, 2011 Share Posted June 4, 2011 Seems like a good idea, but where would you mount the motor if every part is spinning? Also I have seen Contra Rotating Brushless Motors but they seem to be 2 motors joined end on end rather than a single motor with the separate parts spinning separate propellers. Wonder if this could be done with ducted fans to create a turbofan of sorts Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted June 6, 2011 Share Posted June 6, 2011 Interesting thought Simon, after all the brushless stator isn’t aware that it isn’t rotating and it shouldn’t bother the ESC either. It won’t be a brushless motor after modification though. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 6, 2011 Author Share Posted June 6, 2011 BriianWell I suppose it depends on your definition of brushless! The motor would have to have 2 ball bearings attaching it to the airframe. Now if these bearings were insulated from each other and the shaft then each bearing could be a conductor with just one simple 'brush' on the shaft for the third wire. I am not sure how good a conductor a ball race is. If I ever do get a vertical take off from my Bachem Natter a torque-less motor would be highly desirable seeing how small the Natters elevons are. Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted June 7, 2011 Share Posted June 7, 2011 Simon, Just checked a couple of sealed bearings with a meter, more an insulator than a conductor. You could always graft insulated slip rings to the bearing casings and then add a third axial slip ring (insulated) to the ‘stator’ shaft. Quote Link to comment Share on other sites More sharing options...
Plummet Posted June 7, 2011 Share Posted June 7, 2011 As soon as you start having to conduct your leccie between moving parts you run the risk of sparking, which could lead to interference. Yes, you can suppress the sparking with capacitors, but this might modify the electrical characteristics of the motor, so that the ESC is seeing something unusual as it tries to control the motor. This would be a "Bad Thing!" Plummet Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 7, 2011 Author Share Posted June 7, 2011 BrianThat's rather what I feared. Hardened steel in point contact is not a particularly good conductor. In fact ball bearings are only really required between the rotor and 'stator' to maintain a close tolerance under load. The motor to fuselage bearings could be plain as a small amount of play would not effect the motor performance. Steel on bronze would be a much better conductor.This was what I did on my brushed contra rotating motor but the current was only a couple of amps. As Plummet points out the effect of any momentary EMF interruption to the ESC could be the killer. I will have to cobble something up to see if it works. Quote Link to comment Share on other sites More sharing options...
Adam Lomax Posted June 7, 2011 Share Posted June 7, 2011 Is this what your thinking of Simon? Quote Link to comment Share on other sites More sharing options...
Pat (rActive) Harbord Posted June 7, 2011 Share Posted June 7, 2011 That looks to be exactly what Simon is describing. Sounds great Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted June 8, 2011 Share Posted June 8, 2011 Somebody got there first. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted June 8, 2011 Share Posted June 8, 2011 Could this be easier or this, may even cost less. Certainly they match my skill level. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 8, 2011 Author Share Posted June 8, 2011 AdamYes that's exactly it! I knew somebody had to have done it but his slips rings seem to have quite a bit of friction. But it does mean I can think seriously of a vertical ramp take off with my Bachem Natter! Quote Link to comment Share on other sites More sharing options...
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