Re: Re: Comparing Rubber Batches

From: Tapio Linkosalo <tapio.linkosalo_at_helsinki.fi>
Date: Thu, 3 May 2007 09:33:22 +0300 (EEST)

On Fri, 27 Apr 2007, Fred Tellier wrote:

> The numbers are only useful in comparison as anyone using the spread
> sheets will get different values. I have not done any serious testing
> since the 302 batch. Any SS I have tested was so bad I did not bother
> creating a series of tests. With winding type testing the turns effect
> the results much more than actual torque readings and they are
> equivalent to the stretch of the rubber. Accuracy of the torque meter
> used, lube and stretch and speed of winding are also factors in the
> final result.

It is true that winding, lube, temperature etc. all affect the outcome of
the test, but another and maybe more important factor to consider is the
target turns/torque that you wind to. In my stretch test I have a
combination of stretch force / stretch length that I target to, and this
is determined by a percentile of the estimated/guessed braking load of the
rubber. Guessed, of course, as if you stretch to the break, then your
motor is gone, and even if you tested each batch for the breaking (which I
don't - it is too nerv-cracking to break 30 gram motors!), you still need
to allow for some marginal due to variation in the rubber, weak spots etc.
Besides, I typically wind my (wakefield) motors to the same max torque
anyway, thus I conlude that it is reasonable to test them at same load
values. In other words I prefer to test the energy return of my motors as
I use them, rather than the absolute properties of the rubber.



-tapio-
Received on Wed May 02 2007 - 23:33:24 CEST