Quote:
Originally Posted by Al Skierkiewicz
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As a reminder, the power wiring does contain some resistance that you should add to your calculations.
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Yes you are right, the voltage on the motor will not be as simple to calculate as it might be (e.g. battery voltage X PWM duty cycle) because there is some wiring resistance to factor in. But even with this, given the current, it is still pretty straight forward as compared to the pain and suffering associated with getting a sensor out on the end of an arm or some other inconvenient spot.
As to the particulars, it is a pretty simple thing to calibrate: command a known duty cycle, read the current from the Jaguar, read the battery voltage, read the motor terminal voltage, calc a wiring voltage drop, use V=IR to estimate the resistance of the wiring.
For extra credit, repeat this at several duty cycles & loads while approximating (or measuring if you can) the actual speed of the motor. A simple curve fit later and you can know motor speed for that motor in real time without having any other sensor than the Jaguar. Pretty nifty.
For double bonus you can even try to model motor temperature...
...but I don't suppose it's worth it. After all, I am just trying to keep my ball possessor rollers going at a constant speed. Let's not get crazy here... ;-)
Cheers,
Joe J.