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
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