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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: William Crolley w.crolley at mchsi.com
Date: Wed May 31 11:08:04 CDT 2006

The main reason for using torque clamps is that they can do a phase
adjustment, which is impossible to do with a plain keyed shaft.  By phase
adjustment I mean that the angle that something is attached to the shaft
can be changed.  Not really needed for mounting wheels on a shaft.  An
example of where phase adjustment would be needed is on a conveyor line
where the bottom conveyor has fixtures holding bottles that must be lined
up with a top conveyor having fixtures holding the caps that go on the
bottles.

William Crolley

----- Original Message -----
From: Glenn Pipe
To: Chris Jang ; Jonathan
Cc: dprglist at dprg.org
Sent: Wednesday, May 31, 2006 7:28 AM
Subject: Re: [DPRG] Re: DC Motor Shaft Adapters - Obstacle #1 of Many.


Actually trantorques work really well, and hold up well to high loads and
shock. The
battlebot people would use them alot for that reason. Last time I looked
though there was
minimum size that was available and it was around 3/16"

And like the previous post says - they're VERY pricey.

A number of people in the club have lathes including myself and might be
willing
to make an adaptor for you.

Glenn


----- Original Message ----
From: Chris Jang <cjang at ix.netcom.com>
To: Jonathan <szarzynski at earthlink.net>
Cc: dprglist at dprg.org
Sent: Wednesday, May 31, 2006 2:44:19 AM
Subject: Re: [DPRG] Re: DC Motor Shaft Adapters - Obstacle #1 of Many.


> 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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