I build static life size robots and usually use external power supplies instead of the vex batteries. My current project drove me about crazy trying to get the external power supply to work.
I’ve used external power supplies and vex on a full scale Robby the robot and on several other robots in the past with no problems. But on this project when I turned on the controller, the controller goes bezerk and then shuts down. I finally figured out the reason is because I’m using servos. My other projects only used vex motors but this project uses several servos.
I don’t understand why there’s a difference between regular motors and servos but that’s definitely the problem. And … if I hook up only one servo it works. And … if I turn the controller on with one servo and then plug in the second servo it also works. But if you turn the controller on with two servos and powered with an external 7.2v power supply it goes bezerk.
After hours and hours of trying different servos, different controllers, different wires, different voltage regulators and power supplies, etc. I finally decided to experiment dropping the voltage. I have an adjustable voltage regulator with an LED readout of the voltage. When I dialed it down from 7.2 volts to 5.9 volts all of a sudden the problem went away. Oh and something I neglected to say is it always works with vex batteries. So maybe the batteries aren’t 7.2 volts after all. I also tried 6.1 and 6.2 and that seemed to work but what I know for sure is an external power source of 7.2v is not liked by vex controllers using more than one servo.
I just thought I’d pass this along in case anyone else had to deal with this very strange problem