Recommendations needed with motors stalling

With state coming up next Friday/Saturday, we are urgently trying to work on fixing a recent stall problem which I will describe below. Sadly, we cannot work until Thursday night and Friday morning, and another school in the county is offering us brand new parts Friday morning which we could put to use before skills night Friday.

At our most recent competition, we noticed our motors on the lift would stall after about 2 dumps of loads about 3-5 stars each. This past Saturday, we started doing some testing to see what might be the problem. At first, we rebuilt our entire lift gearing and made sure friction was very minimal, which it is. So, we have ruled this out. We then tried various elastic setups, and some of which include just basic rubber bands from the arm to the tower, attaching them from the gears and running them down the back, and making a flip up attachment to increase our mount above the pivot point to increase leverage. None of this has helped.

Upon examining our sister team, we saw them struggle with lifting a cube + 2 stars, and the effect was that the motors made a straining sound, but they never stall. If we do the same, the arm goes up quickly, never stalls, and then on the next score attempt the motors just fail to bring the arm down.
The same worked with hanging. Their bot is about 12 pounds, ours is 13.7, but we cannot get up for the hang a majority of the time, WITH NO ELASTICS. They have the same lift ratio as us (check bottom of post) and same arm set up all together. The only difference is they have new motor controllers and we do not.

Further testing left us to make sure all motors were working by unplugging them all and running them on their separate motor controllers. We found that they all do run and that all shafts are in the motors.

As of right now we are thinking we need to switch out either the cortex or motor controllers, but I do not know how these products act when they go bad and start to cause motors to trip when they don’t need to.

I cannot post a picture of the build as I do not have access to any, and posting one Thursday will nearly be pointless as I am trying to figure up some ways to fix this before Thursday or Friday. Any help is appreciated.

Below are the specs of the bot just in case it may matter:

Port 2: Front Left Base
Port 3: Front Right Base
Port 4: Back Left Base
Port 5: Back Right Base
Port 6: LiftOne : Power expander, y-split
Port 7: LiftTwo: Power expander, y-split
Port 8: LiftThree: Power expander, y-split
Port 9: Claw: y-split

Lift gearing: 5:1 with 6 torque motors (high strength).

I will be checking this post frequently everyday. I can provide anymore information that may be needed to help troubleshoot our problem (besides pictures), but please do not recommend checking for friction/build quality concerns as we have already done this part in the troubleshooting stage. Thanks!

The problem is that you have all six of your lift motors connected to your power expander, which is tripping the power expander’s internal breaker. The cortex has two built-in 4 amp breakers, split 1-5 and 6-10, with the power expander having it’s own. Having all of your lift motors on the power expander pulls too much current from it simultaneously, tripping the breaker. Try rewiring your robot so that not all of your lift motors are on the power expander.

I would recommend moving around your wiring to spread the load evenly on the cortex PTCs. Do you happen to know the wiring setup of your sister team?

Port 2: Right base, y-split, 1 motor in power expander
Port 3: Claw 1
Port 4: Lift3 1
Port 5: Lift1, y-split, 1 motor in power expander
Port 6: Lift2, ysplit, 1 motor in power expander
Port 7: Lift3 2
Port 8: Claw 2
Port 9: Left base, y-split, 1 motor in power expander

EDIT: Missed the power expander.

Would it be better to only put one of the lift motors on the expander and the other two on 1-5 and 6-10, and maybe two of the base motors on the power expander instead? Or would this cause the same problem.

I will pass on this information. It seems to compliment @Henry 's post and hopefully will be what saves us this weekend.

Thanks for rewriting the ports out to make it easier on us!


Thanks for the help!

No problem! Glad I could help.