I tried to test F1D motors by stretching but the knot, frequently failed. The same type of knot works perfectly well if the motor is tested by winding and measuring torque so I revered to winding to test.
Bob
On Mar 1 2011, Tapio Linkosalo wrote:
On 28.2.2011 21:11, Carl Bakay wrote:
> I have done a lot of rubber testing thanks to Goldstein's prodding
> during my INAV days, testing mostLy 7 inch loops of 1/8 strip, and
> without exception, those that broke did so at the knot. These knots were
> un lubricated, due to the difficulty of tying a lubed knot. The stye of
> the knot did not matter ... It seemed that that was where all of the
> stress was located.
I test all my F1B motors by stretching, and have also found the knot to
be the weak link, very hard to tie so that it would take similar load as
the rubber strand when stretched. It seems, that a lubed knot tends to
slip open, while knots tied to unlubed strip cut into the rubber itself
and then fail from the cuts. With many, many failed motors I have ended
up with my current practice of using the "norsk strikk-knute" tied to a
lubed motor to make the knot, but the knot needs to be lubed with a
thinner silicone (500 to 1000 CTS) than I use to lube bu motors (for
this I use silicone of 14,000 CTS). The "norsk strikk-knute" (which I
learned from Bror Eimar) is a double overhead, with extra loops to hold
the ends.
-Tapio-
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