Spring Coupling

[ARMCORTEX]

http://www.colourbox.com/image/set-of-two-car-springs-and-rubber-spacers-image-4735803

[ARMCORTEX]

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[MarkE]

A motor or generator will not necessarily have a flat efficiency curve.  So, if you are moving up and down the efficiency you will need a calibration curve that you can use to correct the measured values.  The easiest way around this problem is to find a load that is very flat at least in the region where you want to make measurements.

[MarkE]

I have been  stepping by 0.1V from 0.5V up to 3.5V,, this is how I noticed my issue,, when I was done after a few hours of running it and went back to spot check my previous numbers the were off by a fair amount.

After I posted the question here I was thinking that since I have replaced the meters, wires, input motor twice and the load resistors that my problem might be mechanical in the built in gearbox for the output motor,, what if the grease they are using "softens" after so much shear,, but I am not sure if that would give the change I am getting,, any way, I have diluted that lube down with some thin stuff and by itself it spins easier,, but the noise is pretty bad and it is late,, so I will run it back up tomorrow and hope that the issue is solved.

and here I thought that it would be a simple case of set it up and just run it, record it and then I could compare,,, nothing is that simple some days

A gear box adds a lot of variables.  In the ideal case you would have a good torque transducer and then control the load electronically to get your measurement set-points.  You might be a lot better off with something like a prony brake than a gear motor.

[ARMCORTEX]

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