Measuring the current on with PWM driven motors has it’s unique challenge. A starting and end point for me was https://www.baldengineer.com/measure-pwm-current.html
To me it looks like I would need a second arduino using algorithms to calculate the current. That’s where I opt out.
However, do we need to run the left motor at full power for calibrating?
I think we don’t. It was an ambitious attempt to try to let the Maslow measure the motor distance, but the goal to measure better then by hand is not achieved.
We could totally skip that step until it can give better results, perhaps with a 1/4 power pull and added chain sag calculation to get a measurement that is at least close to the human error of +/- 1mm.
A full chain (~11ft) pulled hand tight (~1kg) stretches ~2mm with a 15 kg dumbbell. Even a wall mounted frame, sandwiched ->4x4, multiplex, 4x4<- has a flex of ~2mm on the full power ~30kg ‘pull tight’.
My abused chains show no length difference, but others have reported noticeable differences, so the chain stretch is to variable to adjust in the code. The differences in the flex of different frames is another variable that is to wide to account for, to get a usable measurement.
This left motor full power pull could be responsible for failing original shields, power supply and gears.
For the original shield the limits where chosen very narrow to keep the cost down. Small manufacturing differences could be the explanation why some shields run (perhaps a lighter sled) and others fail.
A big issue with the original shield is that it can reach a stage like ‘a liitle fried’ and pretend to be OK but giving unpredictable results. (In my case 1 out of 3). 2 I fried and 1 pretends to be OK but clearly fails on predictable results.
While the TLE will deal with the pull tight, it’s still unnecessary to put shield/motor/chains though the full power task. With the second heaviest sled ~15kg is the max power that would be needed to pull my sled up if it was directly under a motor. That’s 1/2 of what is applied during the distance measurement. If this would be continued to be developed, that’s the max I would target and with the Ridged router it could be even less.