We are having problems with our power expander, we have all four of our robot’s arm motors wired to the power expander we have a 7:1 gear ratio and the motors are geared internally for torque. we can lift our arm fine with no extra weight on it and it works perfect, but when we try to lift a cube we can only lift it once. if we try to lift it again the light on the power expander turns red and the motors shut off and the light will blink from orange to red until we turn the robot off and back on. Does anyone know what’s going on?
You are tripping the PTC inside the power expander. That is, the motors are using too much current.
Yes, as Mr. Pearman pointed out, your motors are probably drawing too much current. Are you using elastics/rubber bands to assist the arm in lifting? Elastics often improve lifting capabilities by a lot.
Ok thanks, but how would i fix this?
Should i switch out two of the motors with the base motors so two motors from the base and two motors from the tower are on the power expander?
Reducing torque means less current draw which means less trips of the PTC.
Add lifting assistance to the arm so it does not need to use so much torque to lift the arm.
Adding rubber bands is the typical method of reducing lift force/torque.
Reducing weight farthest out on the arm is the next step as torque is force times the distance. Reducing weight close in does not have the same effect.
Changing the lift strategy is probably the next item if all else fails.
Team 80 is correct, rubberband assistants is the first thing we would do to help lift your robots arm.
Hayden, you are on the right track here, but you need to take it a step further. Remember ultimately there are 2 PTCs in the Cortex. Circuits 1-5 flow thru 1 PTC and circuits 6-10 flow thru another. So make sure you put 2 circuits thru EACH on your lift and your drive.
ok so I rewired it so 3 base motors and two arm motors are 1 to 5 and the other 3 base motors and 2 arm motors are 6 to 10, and I added more rubber bands. when we rewired it to of are base motors were fighting which caused smoke to come from the brain. this is the second time we have smoked a brain. 
It’s pretty hard to let the smoke out.
Can you post some pictures?
How tough is it to move this mechanism with the shafts out of the motors?
The Microcontroller is designed to cut-off current before it overheats. If you burned one of your motor ports most likely you have a direct short in your wiring. Please inspect your wiring and look for any cables with damaged insulation.
If your Microcontoller is still covered by the warranty, please contact [email protected] for further assistance.
Regards.
-Eli
Please correct me if I’m wrong but as to the motors running through the power expander this should not matter and they can be ran through either side of the cortex as they are controlled by the separate PTC in the expander. But this is pertinent to the extent that if Hayden took two lift motors off the power expander and ran them direct to the cortex he would want to split them between the cortex’s two PTC one on the 1-5 bank and one on the 6-10 bank.
Ouch! I hate the smell of smoke when I give a cortex the sniff test! So the one thing I am almost OCD about is turning off the cortex whenever we are wiring, rewiring even switching out a single plug. On a per hour basis, it takes a lot of on/off switchings to make up for the cost of a single $250 cortex replacement and at child labor rates it takes ever so much more. It is not always possible on the digital/analog ports but I always like to work with a full motor port bank as with the keyed plugs it almost impossible to then have one plug in two ports. An ounce of prevention is worth a 1/2 lb cortex.