Autorotation main gear wobble.

Hooray! I'm done with school and I can finally work on my ECO again!

I should first say that I know that there was another post about the wobble of the main gear, and that this is not the same issue. I have drilled out the holes on the autorotation hub to match the hole size on the main gear, and used bolts/locknuts to fasten the two together.

The second thing I should mention is that I am using the hardened main rotor shaft, and I'm pretty sure that it is true.

Ok, so here's the problem:

When the main rotor is freewheeling, (the main gear is stationary) the main gear wobbles up and down as the main rotor shaft rotates, similar to the problems people have had when the main gear is misaligned and spinning. I have found that the one way bearing in the autorotation hub has a little bit of play with the main shaft, so that you can tilt it off the axis of rotation very slightly. In fact, if you tilt it too much, it will be out of alignment with the bearing and will have a lot of friction.

I think the cause of this wobble is the plastic retainer and pin that holds the main gear hub on the shaft. The pin that holds the retainer can slide back and forth in the retainer, and because of this, the retainer is allowed to tilt very slightly. This tilt is then transferred to the main gear. I have noticed that the gear wobbles a different amount when the pin is in the middle, or at either end of the slot.

So, even if you've taken every precaution and made sure that your main gear is perfectly mounted, this tilt would still cause a wobble.

My initial thoughts were to make my own pin, with a diameter to just fit the hole of the main rotor shaft, and a length to match the slot of the retainer. That would prevent any tilt due to the pin moving around in the hole of the main shaft, but then if the retainer inside diameter isn't the exact diameter of the main shaft, it would still be able to tilt in the direction perpendicular to the direction of the long axis of the pin. There's also the possibility of the retainer being uneven.

I'll probably order another one of those collets that attach onto the main shaft just above the top mainshaft bearing. That would be a tight fit, and would be perfectly flat, so no wobble.

I figured I would mention this, since I overlooked the possiblity myself and just happened to stumble across it. I also have a few questions:

Has anybody noticed this?

What do you think of the collet idea? I'm just a little worried about it falling off. Aside from having a part machined to match the stock piece (with tighter tolerances), I guess I could make a flat on the mainshaft and just locktite it thoroughly.

Has anybody come up with a better solution?


[This message has been edited by Ryan (edited 06-12-2000).]

Ryan
Another possible fix is to place shrink tubing on both sied of the cotter pin after in place on the shaft. The tubing friction fits nicely into the grove where the play exist.
giheli