Wireless Bridge Disconnects when driving?

Our team has been having an issue with the cRIO disconnecting while attempting to drive. Not sure if there is a problem with the wireless bridge or not, but basically everything works okay(able to download code and run it) when we connect the classmate directly to the cRIO. However, when we connect the cRIO to the wireless bridge, the wireless bridge to the router, and our classmate to the router, our code runs until we attempt to drive and then summarily disconnects after 2-3 seconds. It then does not reconnect until we completely restart the robot. One interesting thing is that it ONLY disconnects when attempting to drive. If the code does not send any pwm outputs, there are no problems.

Any idea what could be causing this?

Thanks in advance!

Is the wireless bridge connected to the dedicated 12V port at the end of the Power Distribution board and not to a regular breaker?

Yeah, last year before we connected the bridge to dedicated power we noticed that every once in a while the bridge would reset. We were confused until we realized that it was correlated with low battery voltage.

What was happening was that large current draws (like drive motors) were causing voltage to drop down below 6V, which was essentially a brownout for the bridge.

We were getting this with dead batteries. If we drove very slow and never accelerated hard, then we could move, but as soon as we did anything that would cause a voltage spike, the robot would disconnect (we’d loss comms on the classmate) and the jaguars would show a slow red blink, which is a jaguar fault code.

Are your jaguars giving you a slow red blink when the robot disconnects? If so, that’s more evidence that your voltages get too low when driving.

When the bridge is connected to the PD normal outputs and not the dedicated outputs, the battery voltage drops when ever a motor starts or reverses. That is why the dedicated output is required. The PD has an internal boost buck regulator designed specifically for this purpose. The wireless has another problem though. It was not designed to be attached to a moving object and as such has a vibration sensitive power connector and a delicate ethernet connector. Teams should be careful to use wire ties to take the strain and vibration of the these cables so that the vibration doesn’t cause noise in the connectors. If you move the power connector and it seems loose, the second contact in the connector is likely out of alignment or you have replaced the power connector with the wrong size part. The power connector should have a firm feel and should provide some resistance to pullout. If it does not, check that the connector is the right size. It that appears correct, the connector on the bridge may be damaged.

Exceptional explanation Al.
Thank you for share the information about the internal Boost Buck regulator on PD!!

Is it possible that the regulator doesn’t react fast enough and the bridge reboots? My team is having the same problem I will try and secure the connections in the mean time.

Another note that might support the vibration/shock idea, when we drove up the ram and fell down the robot disconnected. (Fell from half way to the top of the ramp)

I have not seen the regulators fail to keep up with voltage variations. I would suspect that this is a very well designed circuit and should be able to keep up with almost anything. It has a 4.5 volt dropout but the Crio will disable outputs if the battery voltage falls below 5.5 volts. Of course, the Crio is using the 12 volt jumper on the analog module to sense the battery voltage. The fall in all likely hood damaged the internal connector on the bridge.

You say that you have problems when trying to drive. Have you tried putting the robot on blocks and driving under little to no load? If this fixes the problem, it could be an electrical issue. If it doesn’t, maybe you have some sort of code instantiation problem? Have you tried looking at the diagnostic messages being sent out by the cRio using the NetConsole?

  • Bryce