Legality of running a capacitor inline with roboRIO power

[ImOn3618]

Hi, we've been having frequent brownouts through our whole robot, with the roboRIO being the first device to lose power. This happens primarily when we change directions rapidly, or get into a pushing match. In an effort to minimize input current spikes, we're considering adding a capacitor inline between the PDP out and the roboRIO power in.

Is this legal?

Will it help with the input spikes?

[cgmv123]

Originally Posted by ImOn3618

Is this legal?

A capacitor would be considered a CUSTOM CIRCUIT. CUSTOM CIRCUITS aren't allowed to alter the power pathways of key control system components like the RoboRIO.

[Tom Line]

Sounds to me like you are not.powering the roborio from the correct the location. It's sounds like you may have it running through one of the non regulated pdp ports.

[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.

[ATannahill]

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.

Do you live in a perfect world? If so, how do I get in?

Inspection should catch that, but it is not unheard of for robots to go through inspection with a problem like that unnoticed. I know an inspector that will ask if everything is powered correctly and if the electrical system is a rat's nest, he will take the team at their word instead of trying to trace the wires.

You could double check you wires to make sure they are securely inserted on both ends. The wires could be bounced around when you change directions quickly or forcibly slam into a robot or the field meaning the roboRIO is reset.

[Joe Johnson]

Originally Posted by rtfgnow

Do you live in a perfect world? If so, how do I get in?

<snip>

I'm throwing the Unnecessary Sarcasm Flag here. Come on. We're better than that on CD.

Please. I'm begging you. It's easy to run down hill until we are all tumbling head over heals into the mud that so many other discussion forums online live in. Elevate if you can.

Dr. Joe J.

[Michael Hill]

Putting one inline? Besides the fact it being illegal, it wouldn't work. A capacitor in-line (as in in series) with the power line would, in fact, block power from getting through (capacitors are commonly used to AC-couple, which blocks out DC power. What you would want, in this hypothetical situation, is a capacitor from power to ground. This would allow a capacitor to supplement the power rail when the supply decreases.

[ImOn3618]

I can say with 100% certainty that our wiring is not the problem. The wiring is pristine, and correct. My question is what can be done to minimize input current spikes as much as possible, assuming all wiring is correct, and a non-issue.

We've considered adding code to soften drive input, as we tend to brown out when changing directions rapidly.

Changing the Talons to coast mode rather than break would also likely help to soften input, right?Correct me if I'm wrong, this would also make changing directions more taxing if still rolling.

[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.

[Ether]

Some random thoughts:

I was wondering if you or anyone on your team calculated how much capacitance would be needed to actually make a difference.

You should focus on understanding why the brownouts are occurring, and address the root cause rather than treating the symptoms.

If you were to provide sufficient detail about your design, I think there are people here on CD who could make some very constructive suggestions for simple changes you could make that would possibly eliminate the brownouts entirely.

Follow Mike's advice about your wiring, even though you think it is "100% correct and pristine".

[EricH]

Originally Posted by Ether

Follow Mike's advice about your wiring, even though you think it is "100% correct and pristine".

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.

[ImOn3618]

Originally Posted by EricH

Get someone who isn't familiar with your wiring to examine it if you can.

Guess it's worth a shot

[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.

[Fletch1373]

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.

I second the rubber-duck debugging technique.

TIL Software == Electrical

[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.