Legality of running a capacitor inline with roboRIO power

[cmwilson13]

Originally Posted by ImOn3618

When we set the robot up on blocks (minimal load), only the motors go into brownout protection mode.

That should not be happening. I'm surprised no one else caught this unless i missed a post. you have a problem somewhere if the drive is going into brown out protection when the bot is on blocks. mechanical issues with drivetrain components, or wiring.

[Kevin Sevcik]

Originally Posted by cmwilson13

That should not be happening. I'm surprised no one else caught this unless i missed a post. you have a problem somewhere if the drive is going into brown out protection when the bot is on blocks. mechanical issues with drivetrain components, or wiring.

I was suspicious of this as well, thus the top speed question. Also don't forget software. Only driving one CIM out of 2 could cause fun problems like this.

[cmwilson13]

Originally Posted by Kevin Sevcik

I was suspicious of this as well, thus the top speed question. Also don't forget software. Only driving one CIM out of 2 could cause fun problems like this.

we had to drag a cim few years ago on a practice bot and we drove it for a while without major issues. but code is definitely a possibility

[DonRotolo]

Originally Posted by ImOn3618

When we set the robot up on blocks (minimal load), only the motors go into brownout protection mode.

As cmwilson13 notes, this is your problem.

It could be mechanical, but I suspect one of your CIMs is turning against the other. Unplug all breakers except one, run the drivetrain and note the direction. Repeat for all other CIMs. Let us know what you find.

As for mechanical: If you cannot easily turn the wheels by hand (robot off), disconnect things until you can. Whatever you just disconnected has a mechanical problem, for example a gear in backwards and rubbing the housing. Happens all the time.

[GeeTwo]

Originally Posted by ImOn3618

As far as the brownouts go, all components go into brownout protection mode when actually driving. The roboRIO also loses connection.

When we set the robot up on blocks (minimal load), only the motors go into brownout protection mode.

Given the second sentence, I agree that a mechanical problem (chain alignment, grinding gears, etc.) is the most likely culprit. However, we had an issue very much like your first problem stated yesterday. That is, when we would hit an obstruction that largely stopped the wheels (moat was worst) or quickly reversed direction, the robot would lose connection. We spent a good bit of time brainstorming ways to prevent brownout (including the same capacitor you were considering) and strategies for the order we would attack the defenses. The thing is that if the issue seemed to be that the RoboRIO did NOT brown out, but go straight to blackout with no current spike in the logs. We finally tracked it down to a loose connection at the PDP inputs. The collision/sudden acceleration were giving us a voltage drop deep enough to reset the radio rather than just the motors. I don't recall if the RIO was resetting or just the radio. We changed to the correct bolts (long story there) and the problem did not recur over the next half hour or so of similar driving. OBTW, we found the issue just by wiggling and pulling on wires. A few queries revealed that the main power wires were secured by someone who did not know what LCKR (pronounced "locker") stands for. Loose Connections Kill Robots.

[cbale2000]

Regardless of the specific cause of this particular issue, control system brownouts are, in my opinion, a strong reason for FIRST to re-adopt the backup battery.

Back when we used backup batteries on our robots (pre 2009), the controllers on the robots, even without a backup battery, would restart and reconnect to the control system in about 5 seconds after a power loss, and even this was deemed so unacceptable that the backup battery was required.

These days you can wait upwards of a minute or more for a complete restart and reconnect of a robot between the Rio and the radio, meaning if you loose power at any point, your robot is basically dead for the rest of the match.
Why FIRST ever thought dropping the backup battery requirement was a good idea is unfathomable to me.

[cmwilson13]

Originally Posted by cbale2000

Regardless of the specific cause of this particular issue, control system brownouts are, in my opinion, a strong reason for FIRST to re-adopt the backup battery.

Back when we used backup batteries on our robots (pre 2009), the controllers on the robots, even without a backup battery, would restart and reconnect to the control system in about 5 seconds after a power loss, and even this was deemed so unacceptable that the backup battery was required.

These days you can wait upwards of a minute or more for a complete restart and reconnect of a robot between the Rio and the radio, meaning if you loose power at any point, your robot is basically dead for the rest of the match.
Why FIRST ever thought dropping the backup battery requirement was a good idea is unfathomable to me.

it was for safety. battery dips caused weird behavior on that control system.
but yea i don't know why they got rid of it

[Alan Anderson]

Originally Posted by ImOn3618

We wouldn't have passed inspection if it was powered from the wrong place. We've got it running off the same rail as the VRM and PCM(which we don't have) on the PDP.

That is not the correct place to connect the roboRIO power. The VRM and PCM outputs have a green label and share a 20A fuse. The roboRIO power is a specific output from the PDP with a blue label and a 10A fuse.

[Robo Hamsters]

Originally Posted by DonRotolo

I suspect one of your CIMs is turning against the other. Unplug all breakers except one, run the drivetrain and note the direction. Repeat for all other CIMs. Let us know what you find.

Definitely check this. We have a 6 cim drive train and we were experiencing brownouts under heavy pushing. We found out one motor out of three on one side was wired backwards compared to the other two. Once we fixed that connection the brownouts stopped. Luckily that happened during testing and not at competition.

[ImOn3618]

Originally Posted by Alan Anderson

That is not the correct place to connect the roboRIO power. The VRM and PCM outputs have a green label and share a 20A fuse. The roboRIO power is a specific output from the PDP with a blue label and a 10A fuse.

We're wired the same way as https://wpilib.screenstepslive.com/s...m#!prettyPhoto
this. Which is correct.

[Alan Anderson]

Originally Posted by ImOn3618

We're wired the same way as https://wpilib.screenstepslive.com/s...m#!prettyPhoto
this. Which is correct.

There is no disagreement. That picture matches the way I described it.

However, it doesn't match the way you described it. You said you had your roboRIO wired to "the same rail as the VRM and PCM(which we don't have)". While both the VRM/PCM power and the roboRIO power connections are ultimately connected to the battery+ connection of the PDP, they are separately fused. Robot rule <R42> requires that the roboRIO power is connected to the terminals specifically labeled for it, and <R44> separately prohibits it from being connected to the VRM/PCM power terminals.

[Al Skierkiewicz]

OK, I have to weigh in here...
If I had a nickel...
If you are browning out there are definite reasons for doing so. I can tell you most teams do not get everything in their primary wiring right the first time. I had more than twenty teams over the weekend with some kind of primary wiring issue. There were improper crimps, loose hardware, loose connection on the main breaker, etc. If you grab any #6 wire and wiggle it. If it moves of the connection moves, you have only found one problem. Keep going. Wire should not move around in a crimped terminal, or a screwed terminal. Hardware should never move, on the main breaker, PDP or battery. Loose means bad which leads to brownout. Sometimes your electrical problem could be a mechanical problem. Just ask if anyone has had issues with transmissions dragging, locking up or skipping.

[Mr. Lim]

Originally Posted by DonRotolo

As cmwilson13 notes, this is your problem.

It could be mechanical, but I suspect one of your CIMs is turning against the other. Unplug all breakers except one, run the drivetrain and note the direction. Repeat for all other CIMs. Let us know what you find.

As for mechanical: If you cannot easily turn the wheels by hand (robot off), disconnect things until you can. Whatever you just disconnected has a mechanical problem, for example a gear in backwards and rubbing the housing. Happens all the time.

Please do exactly what is stated above. Do not take any shortcuts.

Remove all your breakers from your drivetrain.

Put one in, check that the motor for that breaker is both:
a) running - a dead motor work will against you, and can cause potential brownouts
b) is running in the CORRECT DIRECTION - this is very likely the problem as you are browning out even when you are up on blocks. My best bet is that you have a gearbox with multiple motors going into to, and one of them is running in the wrong direction.

Remove that breaker, and install it on the next drivetrain motor. Do not install more than 1 breaker at a time when doing this check.

There are a lot of posts in this thread with a lot of "noise" but please ensure you do this 100% before moving on.

[philso]

Originally Posted by Mr. Lim

Please do exactly what is stated above. Do not take any shortcuts.

Remove all your breakers from your drivetrain.

Put one in, check that the motor for that breaker is both:
a) running - a dead motor work will against you, and can cause potential brownouts
b) is running in the CORRECT DIRECTION - this is very likely the problem as you are browning out even when you are up on blocks. My best bet is that you have a gearbox with multiple motors going into to, and one of them is running in the wrong direction.

Remove that breaker, and install it on the next drivetrain motor. Do not install more than 1 breaker at a time when doing this check.

There are a lot of posts in this thread with a lot of "noise" but please ensure you do this 100% before moving on.

These are the most concise instructions that will likely locate the source of your problem.

The one other thing I would suggest would be to do a "pull test" on every wire connection to make sure every crimp is done correctly. I know you have stated "I can say with 100% certainty that our wiring is not the problem. The wiring is pristine, and correct." but you have not indicated how you have verified that your opinion is correct. I cannot count how many times I have been asked to look at "pristine" and "correct" looking crimps that, later, failed the pull test.

[evanperryg]

Originally Posted by EricH

At the risk of getting another "Unnecessary Sarcasm Flag" thrown, I agree with this. This is CS101 Syndrome: "It's perfect, I did it!" Guess it applies to electrical as well... Get someone who isn't familiar with your wiring to examine it if you can. They'll be more able to find the problem easily than you are, because they don't think "Oh, that's normal" on something that might not be right.

If I could, I would print this out on wallpaper and cover the entire shop with it. OP, don't just check your wiring, check the wires themselves. You could have brownouts due to frayed wires or sketchy splicing. Check that you don't have motors fighting each other, and try replacing the motors, one at a time. My rule of thumb is that, if you can't put all of your weight into the connections on your robot, they're not good enough. I guarantee you that it is possible to make an entire electrical system that meets these standards; we do it every year.