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Originally Posted by Gunnar Frahm
1) We used a handheld digital tachometer to measure each motors RPM individually at free speed. The RPM hovered in those ranges for each motor.
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The free speed of a CIM is not 63 rpm. What exactly were you measuring?
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5) We were not using PID at all. Just normal select triangles for buttons to create an output.
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The free speed of each motor being slightly different does not mean the motors are "fighting" each other when physically connected to the same shaft and being given the same open-loop command. Each of the motors is trying to lift the load. One is not "dragging" or "fighting" the other.
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4) The arm we are moving is a "boom-like" structure 48.5 inches long and made out of aluminum. The fulcrum where the motors (connected by the shaft) are an inch from the end. Just moving the arm is heavy enough, but it is more so when there is a load on the end of it.
2) The shaft is in fact twisting a bit. We are worried that the couplings are going to break as a result of this.
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Not good.
Did you use the JVN spreadsheet to calculate how much torque that 48" arm is exerting on the shaft (and on the gearbox output stage?). If not, I recommend you go back and do that before doing anything else.