[Behind the Lines] Ep. 3 with Ken Stafford on Motors and Gearboxes!

[Ether]

Originally Posted by Joe Johnson

My criticisms should have been more temperate.

Hi Joe,

Just getting back to this thread.

Just to be clear, I wasn't criticizing your criticisms. Like Richard, I viewed them as to-the-point and thought-provoking.

One interesting follow-up:

I had a private dialog with Ken a few days ago about the method he uses in the spreadsheet to adjust the motor curves for off-spec voltages. He assumes that the free speed of the motor is a linear function of applied voltage, with a y-intercept of zero.

I used the same approach in the motor calculator I posted to CD several years ago, but I've never been entirely happy with it.

I suspect it's probably a good enough model for FRC work (especially considering the wide manufacturing tolerances), but from a theoretical or educational point of view it seems that this model is too simple. I would think the free speed vs applied voltage is not linear and does not have a zero y-intercept. The problem is, the model is likely different for the different types of motors (e.g. fan vs no fan), so a motor calculator would need more than just the 4 classic specs (free speed, free current, stall torque, stall current) to model it.

I plan to run a few tests once I get my hands on a couple of motors. Ken said he was interested in running some tests too.

I will of course post any data as it becomes available :-)