In the last 3 days our robot’s brain has had about 15 ports die. We have had ports die in the past but never this many and never this quickly. Additionally, the same motor, our left intake motor, is the one that has had all the ports die. We have switched out both the motor and the intake wire. Does anyone know what causes this and if there is any way to prevent this from happening in the future? (Our brain is mounted using the mounting holes in the bottom and the cable is a vex stock cable 1200mm long)
Maybe your intake motor is electrically isolated from the rest of the robot through the plastic bearings, causing it to build up charge when intaking until it discharges into the brain port through the cable, frying the port
Coaches FB page has reported that metal shavings falling into motor ports when cutting metal on the robot with brain attached can cause to rapid multiple port deaths. To prevent this failure, remove brain before cutting, or tape over unused ports. Also make sure bins carrying robots do not have metal debris.
Air dust for metal shavings, Blow out all ports, Put electrical tape on steel parts( I don’t know if that an actual thing but it worked for us), Reduce ABS and Poly Carb(Teams in my club had success after they reduced ABS), when not using the robot take it off the field and unplug brain ports
Best Advice I have
My best guess is that the cube plastic contacting with the intake is generating a large amount of static electricity, causing the port failures. I have heard a lot of arguments claiming that metal shavings are shorting the brain, but our investigation into the failures didn’t lead to this conclusion. Our teams investigation and repair can be read at this post. In summary, the RS-485 tranciever chip is weak to static electricity. Friction between components builds static in the motor which travels down the wire to this chip in the brain, breaking it.
I would suggest doing what @marinmersenne suggested. If the intake is floating on plastic bearings or other joints, try to find a way to connect it to the metal contacting the brain.
Unfortunately, unless Vex decides to reinforce the smart ports with static protection, we may have to live with this. I have detailed a repair process for the brain ports for those out of warranty. It technically makes it unusable for competition due to modification restrictions, however the repair does not affect performance and is using the exact chip the original brain uses.
With all due respect, I don’t see where you did an investigation. Seems like you did the same as the most of us, guessed or used anecdotal evidence. Because of that, I’d be very careful in stating the static electricity is the only cause of blown ports.
Looking back, I should of documented our process. We suspected the RS-485 chips were the cause of issue. To test, we desoldered a known “dead” port’s RS-485 and a known good port’s RS-485, and reattached them in swapped positions. After the change, the previously good port was now dead and the dead port was good. We didn’t suspect a short circuit as the RS-485 used is rated to ±70 volts fault protection, more than double the voltage present in the V5 system. A short circuit should not affect this component. This lead us pursue the static electricity theory as the chip is only rated to 16kV discharge and is not rated for static current.
Looking at the circuit, there are very few points of failure on these brains. The RS485 can fail or the current limiting fuse IC can possibly fail, though after repairing 13 ports on one brain, we have yet to see this problem occur. If any damage were to go further, I would expect more of a total brain failure as the traces lead to a microprocessor, which I speculate manages the ports and commands from the user processor.
Our club has just attached wires with a screw, and the end of the wire has a standoff on it so it drags and releases any static. Since we added them, we have had no problems with ports or motors dying.
This is excellent work, by the way.
Would you mind sending me a picture of this. I am a little confused about what this would look like.
I agree with @marinmersenne, I had the same problem with intake ports rapidly burning out because the arms and rollers were electrically isolated from the rest of the robot. So for each arm I stripped a 3-wire cable and attached one end to the arm and one end to the chassis. After that the problem was much better. I also tried grounding wires from the chassis to the ground, but they didn’t seem to do much for me
I will send it tomorrow. I am in class at the moment