Preventing Roll Trim Cord Slippage
I have heard repeatedly about the cord slipping on the capstan of our aileron trim motor. The cord slips because the surface of the capstan is very smooth. To avoid this, I sanded the capstan surface, wiped it clean with acetone and sprayed two light coats of PlastiDip Multi-Purpose Rubber Spray Coating, 40 minutes apart. This is a flexible coating that allegedly provides non-slip control and resists abrasion. It is the same compound sold to plastisize or rubberize tool handles but in a spray can. Once dry, I used 4 turns of the cord over the capstan and had to put some effort in adjusting the length of the springs because the cord would not slip over the capstan. I am sure there will be no slippage.
The parts from McMaster are shown below. I just picked the longest belt they had, since the price didn't go up much per length and I was going to cut it, anyway, I thought I'd get one long enough so that I might have a second chance if I cut it too short.
There's quite a range of springs in that size, so I suspect you would find one that is effective but not too stiff. Its possible that it would have worked with the original springs - I went right to stiffer springs as I found that even pulling the original springs with my hand, it was not enough to move the ailerons appreciably (and mine move very freely). But, on the other hand, I moved the spring attach point further out the bell crank arm, so maybe in that new position the original springs would have worked ok (didn't try the original springs in that position).
|Parts to order from McMaster-Carr Online|
|1||1375K39||Mxl And Xl Series Timing-belt Pulley, 1/4" Belt Width, .685" Od, 20 Teeth||1 Each||$ 10.45|
|2||1679K683||Trapezoidal Tooth Urethane Timing Belt, .080"pitch,trade Sz 482mxl,38.5"outer Circle,1/4"w||1 Each||$ 6.14|