Don't waste a day like I just did!

[Brian]

This afternoon I began the last phase of my V2 assembly, and I installed the belts. I went to install the end effector and arms and when I did that I discovered that my Z cheapskate was very hard to move compared to X and Y. I checked and rechecked the belt for rubs and interference and eventually I removed the belt and discovered that my Z stepper seemed to be defective. It was a lot harder to move than the others and it was very "notchy". It did not move as smooth as the others.

I decided to take the stepper off and swap it for the extruder stepper and if it was bad and needed to be replaced that I could tackle that without taking the whole machine apart. If it just worked, but was sticky for some reason, at least all of the arms would be the same and it wouldn't affect the positioning.

So, I took the bad stepper off the Z axis, and swapped in the extruder stepper, then put the sticky one on the extruder. I got my belts back on and tightened, and things seemed good. I then installed the extruder stepper and played around with it to decide if I should just get a replacement in case it was bad. While I was messing around I noticed that it began to loosen up and then it was totally free and easy to spin. Only then did a thought come to mind as to what was really going on.

On a hunch I took one of the other steppers and gathered the end of the wire together and tried to move the cheapskate. Sure enough, it's stuck like glue. Release the end of the wire, and it moves as free as can be.

I'm not sure if this is some common thing about steppers that everyone already knows, but it turns out that shorting the wires together can cause them to resist movement because some coils are inducing a current that generates opposing magnetism in the shorted coils and makes it resist moving. I never knew this, but I should have figured it out sooner. It turns out that the little female connector pins on my stepper got hooked together while I was building and it caused the cheapskate to feel sticky and waster my whole afternoon.

I'm not sure if anyone will benefit from my story. Perhaps a not in the manual explaining this effect might be helpful to someone?

[Polygonhell]

Yep, if you short the coil pair together they become very difficult to move, it's not a bad way to identify the pairs if you don't know the color coding.

[McSlappy]

Well that's useful to know!

[Tinyhead]

That is a particularly good thing to know. Like a hand-crank generator, if you have no load, you can spin the hell out of it, but throw a bulb on there for load, and suddenly it gets rather difficult. I take it the same is happening on the stepper. Tying the coil wires together is making a load for you. And that load is the area that makes it hard to turn the shaft/armature.

This is also why you don't want to move your cheapskates too quickly after everything is wired up. Moving the stepper shaft can actually induce a high voltage on the Rambo board.

Someone please tell me if I'm giving bad info...

[Polygonhell]

I commonly move my carriages by hand fast enough for the fan on the PSU to move, I've yet to damage anything. Having said that back EMF is never a good thing, so moving the steppers quickly by hand should be avoided, but I doubt you generate much voltage doing so (maybe a couple of volts).