Swapped ethernet cables keep belts from extending. Why?

Troubleshooting
1

I’ve been trying to troubleshoot the 15mm error that seems to occur consistently to me. One test I wanted to attempt is swapping the TL and BL motors and TR/BR motors to see if my 15mm and Encoder read errors stayed with the motor or the controller port. I expected swapping those two would simply make the machine travel a vertically mirrored path.

However, what I found is that when swapping the cables in the controller ports, I could no longer extend the belts more than an inch. When returning the cables to their original ports, I could again extend the belts fully. This was consistent and repeatable. I made a video here (video link) to show exactly what I did. I first show that the machine would retract and extend normally when the cables were “normal”. When I swapped them to be “goofy”, I could retract but extend would barely allow them to move. Swap back to “normal”, do retract and extend and they move freely again.

@bar, why would that be?

2

Have you tried swapping them diagonally? Maybe the ports are not wired the same but symmetrically? Does that make sense?

3

I don’t think so. Imagine if I dissembled and reassembled everything. Which motor I place in each position doesn’t matter. When I move a cable to another motor, it doesn’t appear any different to the controller than if I’d reassembled using the motors in a different order. I would expect it should still work the same.

1 Like
4

That’s interesting, but what does the br and bl motor do when you try to extend, since that is the wires you switched them to?

5

None of the 4 motors will extend more than a fraction of an inch.

6

Did you try power cycling? I am guessing since those are servo motors maybe they don’t like being plugged into a motor that is in a different position? Just a guess as I have limited understanding of how exactly servo motors work.

I believe retracting them works on a turn on and pull until max pull force is achieved which doesn’t care about motor position, vs. extend which is a command to extend belts a certain distance. The new motor has a different starting value then the old motor, and therefore is confused? Just a guess.

7

note that you have to move both the motor power and the encoder cable to have
things work.

extending works by detecting encoder movement and powering the motor.

David Lang

1 Like
8

That makes total sense. I thought for sure I did do a power cycle in my initial testing but I’ll test again today.

9

That makes sense. The part that I think is confusing is that it moved at all.

The servo is a closed loop system so it’s taking feedback from the encoder and using it to drive the motor. With the cables swapped like that you have feedback from the top encoder driving the bottom motor and vice versa so the machine is going to get all confused.