Motor moves!

In our last post we mentioned a couple of problems that we had with trying to get our stepper motors working. In order to clear things up a bit we spent a few hours in Waterloo's Mechatronics Lab (also known as the Church Lab) in order to try and diagnose the problem.


Here we are trying to hook up the output of one of the stepper motors to the oscilloscope. You can see the abnormally noisy output on the oscilloscope that David is pointing at. We weren't too sure what the problem was with this noise (as the voltage on the logic inputs from the microcontroller were fairly clear and steady). In our fumblings we managed to burn out one of the stepper motor drivers (how we did that exactly, we don't know). We also found that I made a very novice mistake when wiring the protoboard together in that I left the sleep and enable pins floating and not pulled up to High >.< Even after fixing these problems we still had problems with the stepper motor output, with it rotating smoothly for 1 second before suddenly seizing and vibrating between two states irregularly. Additional poking around with the multimeter and schematic scouring made us realize that the issue likely had to do with not setting the onboard potentiometer on the stepper motor driver board.

A second visit to the lab had us repairing the omissions/mistakes we found in the first session, and trying to deal with the tiny potentiometer. At that point we found something weird, in that the onboard resistor leading to the potentiometer was listed in the schematic was 20kohms, but we measured it to be more in line with 10kohms. This of course would affect what resistance level we would have to set our potentiometer to (our aim was to get 0.8V across the potentiometer, as that was what was calculated when referring to the current-limiting section of pololu's website). Even more odd was the fact that we couldn't get the desired 0.8V through the calculation way (ie. using voltage divider law to calculate what resistance we needed to make our potentiometer, given our desired voltage of 0.8V and a second resistor of value 10kohm). In the end we got the correct voltage through powering on the electronics and adjusting the potentiometer until the multimeter read 0.8V. The result? smooth motor motion and no more issues. See below for a quick video of the motor operating.


Now that we know how to wire the motor up to at least make it move, our next step will be trying to implement the whole cartesian system (and replace the broken stepper driver board) so that we end up with a fully functioning xyz stage.

'Til next time,

Eric