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[DPRG] Re: DC Motor Shaft Adapters - Obstacle #1 of Many.

Subject: [DPRG] Re: DC Motor Shaft Adapters - Obstacle #1 of Many.
From: Chris Jang cjang at ix.netcom.com
Date: Wed May 31 02:44:19 CDT 2006

> The motor came with a machined part attached to the shaft by
> a pin.  I call this part the shaft adapter.  The problem with this
> part is that it has a smooth outside diameter for a roller-clutch. 
> ...
>
> I found one answer to my question - keyless bushings:
>
> http://www.smallparts.com/products/descriptions/ttq-mttq.cfm
> http://www.fennerdrives.com/catalogs/trantorque_gt.pdf
>
> A little pricey, but it's a start.

That's pretty neat, some kind of compression fitting that seizes the inner 
shaft. I'm not sure if this will hold under the torque for a heavy robot. 
Forces are enormous. The keyless bushing seems to me as ideal for a timing 
chain but not for a drivetrain. In my experience, anything based on 
friction never holds up in a drivetrain. It comes loose.

What does work are pins and keys. A good deal of your problem is already 
solved for you. The shaft adapter only needs to have a centered hole 
drilled to accept a roller pin. This is the kind of solution I am using. I 
expected it to break as the pin is tiny. But it's quite strong and has 
held up. David showed me jBot's shaft to wheel mating system. This uses 
conventional RC parts. It is based on a roller pin that fits into a mating 
cup. Seeing this convinced me to use roller pins. I really think that a 
conventional pinned or keyed approach is the way to go. And don't even 
think about adhesives. They will not hold! Here are some photos that show 
what I mean.

http://golem5.org/robot1/images/img2790.jpg
   - note the tiny pin through the driveshaft after the CV joint, this
     mates with a polycarbonate (guessing here) cup that fits in the wheel
     hub

http://golem5.org/robot1/images/img2796.jpg
   - those are 5/64 inch roller pins and the threaded rod is 1/4 inch
     stainless steel, the wheel is 12 inches in diameter

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