I think you are definitely on to something with a potential short through the lift motor. I would guess that the motor became damaged during one of the matches. The largest difference between practice and matches is that in practice, we almost never over extended our lift. There is a hard stop at the very top. When we over extend there is a horrible grinding noise. I’m pretty sure it’s the chain slipping, but the chain is pretty tight, so it must put lots of strain on the motor. In matches we regularly over extended. In autons that activate the lift, it sets a PID setpoint. It would lose connection immediately once the lift activates in auton, and the setpoint would be the same. Because the setpoint is still set to go up, once comms comes back, the lift activates, shorts, and loses comms again. Now, all of this is assuming that there is actually a short in the motor, but this seems like a pretty good lead.
Another note: In our last elimination match, where we had no communication for all but about ten seconds of the match, our driver noticed that he only lost communication when he tried to use the lift, which also points to the issue being with the lift motor. It went out at the start of auton, when the lift should have raised. When we got communication back they tried the lift right away and lost communication almost immediately, and the next time we got communication back (with <10 seconds left of the match) he didn’t try it and we were able to keep communication for the rest of the match.
How can we test for a short through a motor?
As pointed out earlier, the disconnects are a combination of whole robot and RIO only.
The other thing to notice is that the total current usage of the robot is quite low. Like about half what I would expect. About the only motor pulling any current is hooked to PDP 2. This isn’t PWM 2, but PDP 2.
I would look for loose connections at the battery, the PDP, and the main breaker.
Determine what PDP 2 is and see if it makes sense that it is using high current for extended periods. For Qual 68:1, it is pulling 100A for seconds at a time and likely popping breakers. During auto, it was pulling 60A for 6.5 seconds. Either the motor is bad or it is being poorly geared or a mechanism is binding.
Greg McKaskle
PDP 2 is the lift motor, which further confirms a potential issue. The lift motor has to run constantly throughout the entire match to keep it in position; we don’t have a physical stop to keep the lift in place, so we have to constantly run power through the lift motor.
After some sleuthing, I think I confused your team with your pit neighbor. Sorry for the confusion
You should open up the case of your rio and check for metal shavings.
We had a similar issue last year, which plagued us throughout Ontario District Champs. We replaced pretty much every electrical component on the robot except for the rio when troubleshooting, and nothing worked. When we finally swapped our rio for a loaned one, we took off the case of our rio and discovered there were a ton of tiny metal shavings in it, that would move and cause shorts at seemingly random times on the field. We cleaned out the rio and swapped back after the competiton, and it worked completely fine for the duration of Worlds.
Not sure if this is your issue, but best of luck figuring something out!
How would the metal get into the roborio? Is that a factory defect thing? I’ve heard of metal shavings getting into the ports, but our roborio is both vertical and almost completely isolated from moving parts. We pulled the rio out befire we bagged the robot, so I’ll get it checked out.
Did you do a root cause analysis and implement training, process, and quality control changes to prevent future occurrences?
Shavings almost always get into RoboRIO through the ports. It never hurts to open the RIO if you suspect shavings made their way in (and that does NOT void the warranty). If you’re not sure, take a look at the RoboRIO power lights (Here’s a handy reference). If the POWER LED is red, you most likely a short.
Adding to this growing list of information, I found alonther thing that seems pretty weird. I’m don’t consider myself very familiar with all of the ins and out of the underlying functions and processes, but I’m pretty sure that when the robot is disabled, no current should be going through the PDP, or at least none in substantial amount.
I’m looking at the log data I shared, 2018_03_03 12_44_06, and discovered that although the robot has browned out and lost communication, there are about 5 amps running through PDP 2, which is our lift motor. This continues until we reconnect and re-enable. Only PDP 2 is active. Would this explain why our lift motor is warm/hot after a match?
Somehow I wasn’t paying enough attention the first time I read these logs and missed the pdp2 current consumption.
It’s a little inconsistent but in several matches the current draw is very substantial.
Would you be willing to share mechanical details of your lift or pictures?
With the amount of current passing through the motor in the earlier matches it’s very plausible the motor overheated and it’s windings are shorted.
You could also check the resistance between the motor leads with it disconnected.
Can you post a screenshot of a completed JVN spreadsheet for the lift and for the the arm?
And the drivetrain too.
We had a communications issue at Finger Lakes last year that ended up being a bad ethernet port on our driver station laptop. We fixed it temporarily by taping the ethernet cord into place to make sure it couldn’t come out. Not sure if this is your issue, but hopefully this helps!
Something to check would be the power to the rio. We had a similar problem where during matches we would start out connected then during the match loose connection, and regain connection right before the end. We found the problem to be the screws holding the power wires that go into rio had come loose thus making the power to the rio flicker during the match. This would drop power to the radio and force our radio to have to reboot during the match which would take around 30s sec. We fixed this by tightening the connection on the rio and adding a power by ethernet to our radio. This way if the power drops to the rio, the radio will still have power and not have to reboot. Not sure if this the problem you guys are having but might be good to check.
…wat? The radio power has absolutely nothing to do with the RIO power…
Last year we ran into a strange issue where we could lose control of our Drive Train for about 30 seconds at a time, but it only happened at competition. We had problems at every competition, and it seemed to get worse as time went on. We tried everything. We changed code to be more efficient, we reset every board on the robot, we had 3 different CSAs look at the problem. Eventually, as a last guess, a CSA at Gitchi Gummi Off-Season mentioned something about overloaded current draw from one of the motors on the Drive Train, so just as a last-ditch effort, we swapped out the gearboxes on the Drive Train between off-season events.
Here’s the crazy part:
The problem never returned. Our gearing was too intense for the motors and it would result in the breakers popping, causing us to lose controls. May not be your issue, but it’s something to consider.
Maxcr1, I’ve also been thinking it could be a strain problem. We have one motor (775-pro, 70:1 gear) that operates the lift. I checked with my mentor about putting a stronger gear ratio on it, but he said something about it wouldn’t be good with all the forces being applied.
Another question- what actually records brownouts? Is it the PDP that tells the rio that it has browned out, or does the PDP send the voltage reading to the rio for the rio to interpret?
The RIO reads the voltage rating, when it drops below 7V the rio goes in to brownout protection mode and commands all attached motor controllers to cut all power, this is done to prevent the rio from losing power and rebooting.
The rio also sends the brownout indication in its bundle of other data from the PDP to the driver station.
In a brownout, is the radio supposed to lose power?