Broken Cortex


#1

Hi all!

2381X recently competed (saturday, the 8th). During this competition, we slowly killed a cortex (must’ve been painful for that lil grey box); and I’m trying to figure out why so we don’t kill another expensive box. Here are our robot specs, and then I’ll go through what kinda happened during the competition:

8 drive, turbo 1:1 4" wheels. (2/3/4 7/8/9)
2 fly, turbo 15:1 through power expander (5/6)
1 intake, high speed. (1)
1 descore, 1:5 high speed. (10)
here’s our reveal in case it helps: https://www.youtube.com/watch?v=qGNFWMYMqIk

So, we played around 5 matches before our cortex completely went out. The first match we played was against some heavy v5 bots, and there was a lot of pushing and jostling. We stalled our drive, but then recovered and continued normal match play. After this game, we spent about 30 minutes tuning autonomous before our second game, which had no defense, and we encountered very little issues with the robot. The third game followed soon after, and we noticed the right side drive slowly stalling out. We waited 5 seconds and then continued, no issue. We went back, and continued testing auton. We noticed that during auton, the right side drive was again exhibiting stall characteristics, so we decided to give the robot a half hour break before our next match. This should allow the motors to cool down - we took the batteries out and hit it with some cold air. During the match however, both sides of the drive started exhibiting stall characteristics - the right side first, then the left - but not totally. The drive would jerk back and forth to move, and we would have to slowly inch forward. The drive itself was also very slow, and seemed to have no torque. This match was ended when our partner tipped us over. We thought still that maybe motors had broken, or motor controllers had broken. We swapped all of these out in between matches - nothing changed. We entered the match and sat there basically unable to move.

Once back in the pits, we realized that maybe the cortex was having issues - our flywheel (on power expander) worked fine, these ports (5/6) were ok, with or without power expander. The left drive worked half the time, sometimes you would run it forward and it would run, sometimes one motor would run backwards and cause issues. At this point, the intake, descore, and right drive all stopped working. We started testing with code that would drive a single port at the same time (we took all the shafts out). Running ports 2/3/4 didn’t run the wheels, but instead ran 5/6. When we pulled the cortex off the robot, planning to swap it in, we started doing individual port tests - again, same thing. Only 5/6 worked - 2/3/4 sent to 5/6, and not to themselves. port 1 still worked, but was very (VERY!) weak - everything else was dead.

Unfortunately, that was the end of our competition - but that’s ok, we have another one coming up. Before that competition though, it would be cool if somebody could explain how this had happened (so I don’t do it again).

Thanks!


#2

Turbo mode likes to draw out a lot of power, especially if the robot is heavy. The weight puts a lot of stress on the motors, which slows them down, requiring more power.


#3

You could possibly have a shorted motor on your robot? If you want to check for any hidden shorts try unscrewing the green backing to a 393 motor and pulling down the little black rubber that’s meant to protect the motor’s wires from bending too sharply. Sometimes this rubber padding breaks or is moved out of place causing the motor’s wire insulation to tear and short the motor. The reason I suggest this is because I have had a similar problem in the past and this was the fix (we had 3 shorted motors.)

It could also be a shorted sensor such as a quadratic encoder.
Damaged wire.PNG


#4

Thanks to everybody who helped out! We managed to borrow a cortex and get a dub!