Motor springing back on one motor

Hi Guys,

wonder if anyone can shed some light on this or point me in the right direction,

recently built and one motor on one axis is skipping backwards at the same point on the rail.

Its a mini rambo board and the motors are wired together (edit: in series) . I noticed the x axis was running smooth as but one motor on the y would stutter a little at the same points down the rail. I first of all took it apart and made sure everything was square and then replaced the motors with new ones and we had the same problem. Ive switched the x and y on the mini rambo and the problem persists on the same motor (now it would be on the x axis though). I then upped the current to the motors but that only seamed to exaggerate the problem (though its now clearer to see whats going on)

Heres a link to a vid of whats going on

(I know it looks a bit of a mess, it was all tidy until i started pulling it apart to try and fix it)





Take the belts off and see if it still happens and make sure they are all moving.

Whoa. Interesting. That is quite a jump. Like half a turn. It is only one side?

Are the motors wired in series or parallel?

The exposed wires also kind of freak me out, but I’ll try not to look at them.

Ryan’s suggestion is a good debugging step.

It looks like you’re turning the knob when the jump happens. What commands are you running from the LCD? Stock V1 firmware with normal menus?

hi guys,


thanks for the responses, so it seams to work fine with out the belts on. theyre wired in series and the the other axis which works fine is wired up the exact same way. its all stock and im just running move axis 10mm from the lcd





Is it both motors on that axis or just the close side?

When you ran that test, how long had the machine been on? One minutes? Ten minutes?

If the current was too high, the driver could have overheated. When that’s happened to me they took a lot longer to restart though.

I was going to guess that it was noise affecting the DIR pin, but since this is a mini rambo, and it goes away without the belts, that doesn’t make sense.

Maybe it’s just binding in that part of the machine and it’s skipping steps. That doesn’t explain why increasing the current makes it worse.

Maybe it’s getting out of square when it slips and that’s causing it to be able to fit?

Are the X sides the same length? Maybe you’ve got a trapezoid.

Or roll it by hand without belts on and feel if something catches. Make sure the roller tension bolts are loose.

As you can see without us being there we will just keep guessing so it is best if you tell use what you have and have not tried.

Take a new video and post it with audio. that might give some clues as well.

Hey guys!

turns out im an idiot (not for the first time in my life lol) , its a 32 tooth pulley causing the problem, dont even know where its come from. Swapped it for the right one and its perfect!

its been driving me mad for longer than i care to admit.

thanks so much for all your help though, much appreciated.