Hi Bob, enjoy reading about your E-flight experiences in carrier. This post about the collet slippage. Isn't it possible to grind a flat on the shaft for the set screw to tighten down on? I would think it would not upset the balance of the shaft that much. I do it on wheel collars to keep them on. I even had some that were loose, but, stayed with the axle until I cinched them down again. My thought for collet slippage. Have fun, DOC Holliday
Doc -
The issue is that there is no set screw - The collet is a tapered OD collet with a tapered ID ring around it.
If you remember the prop drivers on old Supertigre .35's, some Foxes, etc., you'll have the picture.
The only way to get the tapered collet to hang on tighter, is to tighten the prop down more. But since the prop shaft is aluminum, you risk stripping the threads before you actually get it tight enough. Or, as happened to Bob, you simply twist off the whole shaft.
Allen's observation that the ability to go from zero RPM to max RPM in a short amount of time is interesting, and one that I hadn't thought of. The simple fix for THAT one issue is to use the ESC's "soft start" feature. It is there for the purpose of saving gears in gear driven helicopters.
My own observation is that there are probably several possibilities and they all need to be addressed. I have had the prop fly off while the motor was on a test stand. In fact, I've ONLY had it happen while on a test stand. So my conclusion is that part of the problem is the large step up in force that occurs when the motor is physically unable to move forward. The nature of our usage here, kind of precludes using a slower acceleration to address the problem.
The most important issues, I feel, are related to the actual quality of the prop driver - I have bitched to one of the manufacturers that the supplied prop driver was too short (you can barely fit an APC sport prop on and have ANY threads for the nut to grab). Their answer was to send me another prop driver which, of course, was no better than the one I got originally. If there were more threads out the front, one could try to find a nut with more length - like the union nut that comes with some spinners. This would spread the tightening forces over more threads and lessen the chances of stripping them.
Also, there is no way to check the parallelism in the prop-shaft hole itself. I think most can envision that if the hole is not a uniform diameter, the contact surface us reduced. A related issue would be the actual taper cut onto the outside of the collet and the inside of the ring. If the taper is mismatched, you don't get uniform tightening, you get a point contact and that can lead to a prop that stays on one time and flies off the next time you mount it.
Finally, this scheme of mounting depends on the width of two (or sometimes four) slits that are cut into the collet after it is machined. If the slit is not wide enough, you risk running out of "tightening power" before you've actually captured the motor shaft.
Then there is the issue of which aluminum alloy is used, the actual thread used, etc. (I'm not sure machinig them from steel would be the answer, if any of the above issues are unsolved. A thread with more surface area might be helpful, though). Since all of the above are actually quality issues when the part is machined, I think the BEST course for we who use them is to share information on which brands of adapters have (and have NOT) been problematic and where the "good ones" are available.
Also, be very aware of this issue every time you change the prop, and keep the area clear, just like you would with a gas engine.
Oh, one final comment. Most motors have a prop driver that attaches to the rotating bell, and requires that you turn the motor around and mount it using the T-shaped adapter. I can tell you from experience that this mounting has a whole different set of issues, which may or may not make that a better alternative. In the case of the Scorpion brand, which is what I've been trying to get going, it's not an issue, because there is no way to incorporate that mount in the motors, as they come from the factory.
Mike A