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From: Paul Ratajczak <pratajczak3017-at-charter.net>
Subject: Re: motors [TANKS]
Date: Sun, 21 Jan 2007 0:14:37 -0500
Reply-To: tanks-at-rctankcombat.com

On Saturday, 20 January 2006, Derek Engelhaupt wrote:

> BTW, tank T048 made by Paul Ratajczak is using this same type of chain

The conveyor chain tabletops (TTs) on my tank are slightly different than what you 
guys are using.  Mine came without the small 'wings' which you had so much fun 
removing Derek, and are size #60 (3/4" pitch).

Be mindful of the TTs, which are made of acetal.  This material appears to be 
leading to two relatively easily surmountable problems.  First, acetal, a.k.a. 
Delrin by DuPont, is pretty slippery stuff.  I haven’t had any trouble driving 
around my fairly level driveway and front yard, but I suspect that when I get into 
hillier and slipperier terrain I‘ll have a traction problem.  Second, the 
side-by-side road wheel pairs on a T34 leave the track unsupported in between them.  
I happened to run over a quarter-sized stone and the TT snapped in half right in the 
middle where its unsupported.  I’ve cooked up a couple of solutions to these 
problems.  One solution that I considered involved putting another wheel in between 
each road wheel pair just for supporting the chain.  This only addresses the TT 
breakage problem.  The other method would be adding some sort of 
traction/reinforcing pads to the tabletop faces.  This could solve both problems at 
once.  I’ll be experimenting with both oak and rubber pads about ¼” thick.  It 
will come down to how can I attach these to the acetal.

Otherwise the TT chain works nicely.  Its biggest downsides are that it is expensive 
new (but not on ebay), and that it is one of the heaviest systems on the tank; 
easily 30 lbf for the two ~7 foot long lengths.   The upsides are that it is ready 
to use out of the box, sprockets are readily available from Tractor Supply and 
McMaster-Carr, it can easily be adjusted for length, different length table tops are 
available for different track widths, and because it is so heavy, its natural sag 
keeps it tight on the drive sprockets.  Oh, and it makes all of the proper T34 
noises that the Wehrmacht came to know and love.

My drive system, from the prime movers out to the tracks is as follows:
Prime movers:  Kollmorgen 300W brushless DC scooter motors with integral speed 
control & regenerative braking
Speed reduction:  #25 roller chain (i.e., scooter chain) and sprockets; 2-stage 
speed reduction (11/26 primary & 15/40 secondary) for a total speed reduction of 
Final drive:  14 tooth x #60 (¾”) pitch sprockets

Hope this helps.

Paul (I can't wait for spring cuz' the cold and grey skies are driving me INSANE)