whats the matter!

[Tom]

I've wondered about this too. We buy motors based on charts and curves, but the manufacturers don't declare anything of the test method.
How tricky would it be to build a simple test rig? Budget ~£100?

Stepper -> direct coupling -> load
The load could be something like a motor with variable resistance across it.

I'm thinking: set a stepper, drive, and power supply combo running at a known RPM from mach or EMC2. Measure the voltage and current through the load, gradually increasing the load (by removing resistors in small steps), until the stepper stalls. Plot the data point, then increase the RPM and repeat.

Obviously the results would only be valid for the stepper/driver/power supply combination tested. And the results between different test rigs (if more than one were built) would not necessarily be directly comparable because of efficiency differences of the load motors. It would allow you to check the effect of a power supply voltage increase, or a new motor type, or a new driver, or moving to microstepping, or etc etc etc...

How much work is there to get to the point where the results might be comparable between rigs? Would defining a "standard" dc motor type be good enough (eg choose an appropriate RC motor P/N from a popular manufacturer)?

Just thinking out loud...

[John S]

Tom,
Good idea but still relies on "Is the motor in the box the same one the spec sheet is for ? "

And to be honest working with the Chinese I'm very sceptical.
Out of a box of 40 rotary tables that all had the exact same run out error according to the spec sheet? every one ?