So today my team started testing our shooter(spoiler alert: our team is using a shooter this year), and we are witnessing strange behavior from the motor.
Our current set up is this, a 775 hooked up to a versa planetary 3:1, to chain, to a shooter axle. The axle is a hex shaft simply supported at two places with hex bearings. It has a lot of mass away from its center due to the wheels. Lets say this thing weights 5 lbs and a lot of that mass is 2-4 inches away from the center.
What we have experienced is that when the motor is given full power from the RoboRio, it will go on for spurts of about 1-2 seconds and then off for 3 or 4 seconds. The button is held down the entire time, The motor also gets very hot in a very short period of time when doing this. When we reduce the voltage given to .7 of the full voltage, the motor runs with no problems, it gets hot, but not too hot. The motor also runs fine when given an external 12 volts(not through the spark). The circuit breaker on the PDB does not go off, the spark motor controller just will turn to neutral(blinking blue) after being solid green for a few seconds. Our drive train and other motors run at full speed all the time with no problem.
Does anyone know what could cause this problem? I considered it could be a code problem, but it seems unlikely as every other motor runs fine at full speed.
I am curious if the Spark motor controller would turn its self off if the motor draws too much current to save its self. I cannot find anything in the documentation that would say that. Our current solution will be to add an extra motor and beef up the gear ratio to a 5:1 since all our other motors work at full speed, and those are stressed less. Hopefully that makes it just go away.
What does you battery voltage look like when you’re running the motor? Just to be clear, the Spark LED stays lit, it just changes to neutral? It sounds like the roboRio might be doing brownout protection.
It goes from 12.6 to 10.4 ish. The coder said there was a peak of yellow on that battery and said that might be packet loss, but he wasn’t very sure of that.
I am mostly mechanical so I don’t know much about how to diagnose those problems. Seems hard to believe one motor that doesn’t trip the PDB 40A fuse would cause a brownout though.
Edit: apparently we did save some coms data and the RoboRio did not brownout.
Without diving in too deeply, it sounds like you are popping your 40 amp break powering the shooter. Increasing your drive ratio, checking for binding in your shooter, and adding another motor are all solutions to this problem.
If you measure the current being drawn when you run at .7 (70%), what is it?
The SPARK does not have any internal over current protection. It sounds like your current setup is either popping your breakers or your Rio is browning out. Changing the gear ratio should fix the problem, but before you do that you should open your driver station log files and see if a brownout occurs, in that log file you can also see the motor current.
I agree with Tom on this. It sounds like you are popping the breaker. I’m also surprised it is popping it that quickly. That indicates you are pulling a huge amount of current.
Are you using a 40 Amp breaker?
The very first thing I would do is check for binding in your shooter system. Even with the motor mounted, it should be fairly easy to spin. If you find it feels stiff, try to figure out why, and where, the binding is coming from.
Vacuum your robot up. Particularly around the sparks connection terminals and around the pwm slots. Sometimes metal shavings can get in there and cause issues.
If anyone has an Arduino around or another source of 1-2ms pulses (1ms = full rev, 2ms = full fwd), try providing the PWM signal with that rather than the RoboRIO.
Alternatively, get a scope on the PWM signal.
This will let you figure out if the PWM pulses are the problem or if it is something inside the Spark Motor controller.
Another option to try is to find an old Victor you have hanging around or borrow from a nearby team. See if the problem persists with the old Victor.
I should have said solid blue. The spark is still getting pwm signal from robo rio, just not a signal to make the motor spin.
After looking into it we have found that the problem was most likely the initial current draw being too high. Previously when controlling the motor we had it on a button that went from 0 to 12 volts in 0 seconds flat. When we were able to put the motor on a trigger to slowly ramp up the voltage, it worked as expected. We may still need to change the gear ratio etc. for better performance, but the issue at hand seems to be solved. I think the 40A breaker must have been tripping for a short period of time even though the red light on the PDB wasn’t turning on.
I have no financial connection whatever to any FIRST supplier yet alone Cross the Road Electronics, but this is one of the reasons I really like the Talon SRX.
Setting the slew rate of the output is really nice sometimes. Yes, you can do it in software on the RoboRIO but it is so much cleaner to set it and forget it using this SRX feature (which probably goes by some other name and I am not going to look it up right now… suit me
Yes, that is confusing me as well. The LED never goes black. I am not sure what exactly was the problem but I think it had something to do with either browning out or too much current draw. Hard to tell exactly what was the problem if it wasn’t the 40A breaker.
The fix to our problem was basically to allow the current to build up slowly instead of spiking fast. Everything points to a breaker being popped except the blue LED.
