Dynomotion Forum

I have two different brand and different spec brushless motors driven by SnapAmps. I found that after setting them up using AutoPhaseFind the current amplitudes were measurably different depending on the direction of motion. I was able to equalize them by adjusting the Commutation Offset value 10 counts at a time initially them 5 counts at a time to optimize the balance CW and CCW. I have a 2048 line encoder on both motors. You can see this difference comparing the current plots for (CGI_2_current_plot) Vs (CGI_2_current_plotA).

The second thing I saw was that the phase currents were not equal during running at about 80% max velocity.
Attached are the data plots. Use Axis(CGI_0_current plot) for this discussion. The pattern was consistent where running CW phase U was lowest, Then V, Then W. And running CCW the pattern was reversed. I also noticed that the motor was not running smoothly at speed and I attributed that to the variation in currents. P gain was reduced and increased to no real effect. Is there a way to customize the current command for each phase as a percentage of lets say Phase A? Where Phase B would be 95% of Phase A and Phase C would be 90 % of Phase A or something to that effect?

The third thing I noticed was on (CGI_2_current_plotA), one of the phases (Phase B) was always running at a higher offset from the other two phases. in contrast to Axis 0 that showed all three phases crossing the same Zero line.

I tried swapping the motor to output from the other Snap Amp with the same results. Do you think this indicates a bad motor?

AZ

Some additional information:
Attached is another current plot with the Axis 0 running at about 90% max speed (300000 with 8192 counts per rev).
The peaks of the sine wave forms all show a Peaky flat where at lower speeds (200000) the wave forms were rounded at the peaks. At this speed (300000) the motor is running with a hum where at 200000 it sounds smooth.
Any idea what this indicates?

AZ

Hi AZ,

I don’t see any of your attachments.

Corrected information:
The motor Axis (0) is actually rated for 4000 rpm at a 75 V bus and the speed we are running in the test is 2197 rpm. So we are actually running at about 55% of max speed at a bus voltage of 80 v so there is more than enough voltage headroom for operation.

AZ

PS I saw that you couldn't see the files. I attached all of them again to this post.

I see them in the Attachments folder below...

Still not attached. When you do a Preview of the Post do you see them?

Test

I tried attaching in the Config forum and no luck there either. I'll try Previewing in this one. I noticed in the Config forum there was an additional folder called " Polling" next to the Attachments if that means anything to this issue.

I tried Preview after doing the Attachments and there was nothing there. I did see the progress bar cross as the file download happened on all the files I attempted to attach. I'm going to try loading from my Desktop instead of directly from my flash drive.

Nope I stlll don't see them in the preview ??

AZ

Hi AZ,

Strange. What type of file are you trying to attach? How big is it? After attaching is there a green success checkmark after it in attachments?

Try only one image. Try saving and re-attaching the cat.png file I posted.

The files are txt files from the Step function tuning page. There were 4. Each was 1.3 Mb
I'll try the cat attachment and another one that I had done previously. There is no GreenCheck, it's a yellow triangle but no explanation.


The cat pic worked, Green check and all.

I'm going to re do those plots so they're smaller files.
AZ

Those worked. I tried a 1.9MB .txt file and it worked for me.

If you click the yellow triangle it should give an explanation.

Here they are smaller. The attachments worked once I got them below 1 Mb.

AZ