speed issues

[couvillion]

We have varying speed our shooter motors, the speed varies from ~100 to ~500 un-calibrated encoder units with a period of maybe 4 or five second. This happens more on one wheel of the shooter than the other, but it happens on both. I started attacking the issue as a programming problem removing all feedback from the Labview program. After that failed I swapped out the talon, after that didn't fix the problem We reverted the shooter from CAN to PWM. The problem go better but it still exists, whole ever I haven't measured it yet after dropping CAN. I've not had any reason to believe that this is happening with the drive system

Any ideas?

[cjl2625]

Earlier in the season, we built a really rough prototype shooter, and it was going on and off when we tried running it at full speed. I checked the current readings on the CIM, and they were upwards of 50 amps when running at constant speed. The assembly was put together rather poorly, and it put a lot of strain on the motor, leading to these crazy high currents. I think the cycling problem was something on the roborio periodically cutting power to the motor to prevent the high current.

Maybe you're facing a different issue, but perhaps you could try checking the current readings from the PDP, or remove the motor from the shooter and see if the speed still fluctuates.

[Joe Johnson]

Originally Posted by cjl2625

Earlier in the season, we built a really rough prototype shooter, and it was going on and off when we tried running it at full speed. I checked the current readings on the CIM, and they were upwards of 50 amps when running at constant speed. The assembly was put together rather poorly, and it put a lot of strain on the motor, leading to these crazy high currents. I think the cylcling problem was something on the roborio periodically cutting power to the motor to prevent the high current.

Maybe you're facing a different issue, but perhaps you could try checking the current readings from the PDP, or remove the motor from the shooter and see if the speed still fluctuates.

Good points. Also you should consider if your shooter wheels are spoked wheels then they may be acting as a fan and that moving air is adding to your loading and possibly triggering current limiting events.

Dr. Joe J.

[couvillion]

Do current limiting events show up on the driving station? I was looking for signs of voltage drops. Or do I need to code up some current monitoring code?

[Mark McLeod]

A robot voltage plot can be seen in the Driver station log files for every robot run.
Brownout events are marked as well.
The gear icon on the right side of the Driver Station is a menu. Choose View Log File.

[couvillion]

Looking though yesterdays logs I do not see any brown outs and although I am somewhat guessing as to what the robot was doing at various points. It appears to me that even when the mini-CIM that power the shooter were probably stalled the current draw did not spike, all the spikes that I saw were at motor start up.

How much additional current does a stalled motor appear to draw on this graph?
I am beginning to think it is a mechanical problem with our strength shooter arms.

[couvillion]

Since the answers to these problems so rarely get put at the end of a thread.

I would like to report that you can not solve he problem of unkeyed shooter wheels with programming or electrical troubleshooting.
I think that will get a very controllable shooter shortly after we get to the competition. Right now we are just so thankful for a robot that behaves in a proper fashion we bagged the robot knowing that the future has explicable
behavior, and not this random stuff we've been seeing.