[TowerTalk] Rotor Selection

Patrick Greenlee patrick_g at windstream.net
Sat Apr 5 15:06:27 EDT 2014

  I am definitely not a worm drive expert and was just relaying some 
info I had read but not necessarily recalled accurately.   When I was 
presented here with information above my level of experience but in 
conflict, at least a little bit, with my recollections of a previous 
source I thought it better to consult the oracle/guru friend who has MS 
in Mech Eng from UCLA and 35+ years of hands on experience.  Here are 
his comments.

Patrick - The standard ratio for non-freewheeling is 15:1, but depending 
on the pwr source, electric mtr, arm and crank, etc, the direction of 
load, the direction of drive, and lubrication/friction in the gears; 
that may need to increase.  If the load is loading the gear in the same 
direction that the worm is driving the gear then a motor shut off may 
not stop the gear from continuing to turn.  If the worm is turning 
opposite the gear load direction then the worm would stop the gear when 
the motor is shut off.  An electric brake on the motor windings normally 
will stop the first condition and is normally not necessary for the 
second condition. The first condition may need 20+:1 to stop the worm 
turning when the motor is shut down without the electric brake.  In the 
static condition of worm to gear, 15:1 should work.

I did not go into detail with him regarding the cheap and dirty 
approximation type gears so his comments are most likely aimed more 
toward the "real" worm drive situation.

Patrick NJ5G

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