Well thanks for your interest David. It goes something like this.
I'm trying to sort out a safety issue, a point of failure. I'm creating a rocket motor test stand that others may use.
The point of failure is on purpose for safety reasons. It's hard to explain. This is the first prototype:

The bottom of that blue vertical V structure (rocket motor holder) is a weak point - in case the rocket motor blows up on the test stand, the load cell and the rest, will not be destroyed - but nevertheless, it should be strong enough for "normal usage".
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So, what I'm wanting to achieve is to make a simple device that tests the strength of that (on purpose) weak point. Attach a small motor on the V-mount, spinning with an off-centre device like a really big vibration. Until the point that it fails.
It's a process of testing until it fails.
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I can do the physical part. With the Arduino, I can direct the motor to spin up and put force on the structure (sideways) - like a real rocket motor out of control - until it fails.
It's important for me to know this.
how do you use an electric motor to test a rocket motor?
This is how.
I guess you wished you never asked. 
Edited by stix, 30 August 2021 - 08:50 AM.