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Five Fatal Mistakes

Why your robot is dead on the field

Evan Forbes, Control System Advisor

December 16, 2017

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Disconnections are common

  • On average, there are 3 disconnections per 4 matches
  • Tens of thousands of registration dollars wasted due to disconnects

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  • All common disconnections are preventable

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Why are these mistakes so common?

  • Flaky
  • Hard to reproduce in the pit
  • Cause problems only when moving around the field or running into things
  • Get more likely over time with normal usage and vibration
  • Drive teams & pit crews don’t know what to look for

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What actually causes a robot to disconnect?

  1. Radio loses power
  2. RoboRIO loses power
  3. Ethernet disconnects between radio and RoboRIO

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  • Rebooting takes 35-50 seconds

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A minimal robot

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Radio

Battery

Main breaker

Power

Distribution

Panel

RoboRIO

Voltage

Regulator

Module

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1. Loose 6 AWG terminals

If the terminal is loose enough to wiggle around it must be tightened

  • All batteries (2 terminals each)
  • Main breaker (2)
  • PDP (2)

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2. Loose radio barrel jack

  • Secure the jack with a zip tie if possible
  • Add redundancy with power over ethernet

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3. Weidmuller wires stripped too short

  • They can look in even when they aren’t
  • Tug on all critical Weidmuller connections to ensure the wire is fully seated and does not come out

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3b. Weidmuller terminals stripped too long

  • The positive and negative wires on Weidmuller terminals are very close together
  • Even a momentary short on a critical path will cause a reboot

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8mm

5/16”

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4. Bad battery & blackouts

  • Double check every battery’s voltage before putting it in the robot
  • Design with current limits in mind
  • Enforce software limits

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pdp = new PowerDistributionPanel();

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pdp.getCurrent(channel);

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5. Poorly secured electronics

  • All electronics must be securely mounted
  • Batteries fall out frequently

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  • Protect your main breaker from

rogue game pieces

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*Artist’s dramatization

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Troubleshooting

  • Check the driver station logs

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  • Tap components while the robot

is on to see if anything causes a reboot

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Summary

  • Add single points of failure to your pre-match checklist including:

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  1. Verify all 6 AWG terminals are tight (battery, main breaker, PDP)
  2. Ensure the radio barrel jack is secure
  3. Check all Weidmuller terminals to ensure they don’t come out when tugged and there is no exposed wire
  4. Double check battery voltage & health
  5. Make sure all electronics are secured (battery, radio)

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