[TowerTalk] TIC plastic gears

[Leeson]

This looks like a very good call. I was browsing various other catalogs 
for Delrin 64 pitch hub spur gears, and eventually came up with the same 
page Jim had already identified. I should first have read his posting in 
more detail, I would have saved some time. There appear to be other 
gears of this same type that are used on different TIC Ring versions, 
including the 72-tooth gear on the same page.

Part Number   Teeth  PD     OD   Hub Dia. Set screw
A1P2-Y64 055C  55   .859   .891   33/64    6-32
A1P2-Y64 072C  72  1.125  1.156    5/8     6-32

As background, pitch characterizes a family of gears that can mesh, 
since the tooth size and spacing is the same for all members. Pitch is 
defined as the number of teeth that a gear with 1.00" pitch diameter 
would have. Pitch diameter can be calculated from OD:
(Pitch Dia) = OD * (number of teeth)/(number of teeth +2).

A remaining uncertainty is the possibility that the TIC Ring gears 
aren't 20° pressure angle, but that value seems most common.

For some general info on plastic gears, see 
https://www.mcmaster.com/plastic-gears/component~gear/ Click on Gear 
Pitch, then click on the info symbol, "i" in a circle. For another 
summary of the formulas used to characterize gears, see 
http://www.omnicomponentscorp.com/64-pitch-delrinreg-spur-gears.html

Because I want a bullet-proof setup, my own long-term plan is to use a 
boom-mounted electronic compass with DC output to replace the current 
pot setup, which loses direction all too often and finally led to a coax 
parting. I'm leaning toward using a compass chip in a waterproof plastic 
box, mounted to the boom. Most chips for this purpose nowadays seem to 
use I2C, and to get 0-5V I've found an inexpensive compass and I2C DAC 
on Adafruit. See https://www.adafruit.com/product/5579 and 
https://www.adafruit.com/product/935#technical-details These are really 
inexpensive, and I'm hoping someone will grab hold of the idea and 
integrate such a device.

But even if I can get more reliability, I don't want to rely on 
direction indication alone as the critical element of a limit system. So 
I also plan to set up some physical limit switches, as for example KZ1W 
has done with his TIC Rings. I plan to do this also on my prop-pitch 
rotators.

Dave, W6NL/HC8L