Problems with the Rockbot.

I’ve been having some intermittent skipping issues on the Y-axis on my Rockbot and I wanted to go over some of my settings on my polulos..  My table is very smooth running, although in hind site it’s inertial mass is probably a little more than it should be.

Going back through my notes, I have this motor

and this driver

If memory serves me, I sorted calibrated by feel and sound..  It probably should be dialed in a little better.

Anyway, I found this guide.

So According to this it looks like my limiter is the A4988 Driver..  It looks like they only want  me to drive 1 amp with air cooling only…  My motors can handle up to 1.5 amps.

The magic formula’s are here

Another way to set the current limit is to measure the voltage on the “ref” pin and to calculate the resulting current limit (the current sense resistors are 0.05Ω). The ref pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board. The current limit relates to the reference voltage as follows:

Current Limit = VREF × 2.5

So, for example, if the reference voltage is 0.3 V, the current limit is 0.75 A. As mentioned above, in full step mode, the current through the coils is limited to 70% of the current limit, so to get a full-step coil current of 1 A, the current limit should be 1 A/0.7=1.4 A, which corresponds to a VREF of 1.4 A/2.5=0.56 V. See the A4988 datasheet for more information.

So  I measured a reference voltage of  .156 Volts X 2.5   = 0.39 amps…
Yikes.  It looks like I’m stalling out the motor versus triggering the thermal shut off for the motors.

So seems like I want to crank this up to 1/2.5 = .4 Volts.  Something for tomorrow.





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