Motion problems

I’ve got a Chinese blue-and-white with the Ruida RDC6445GZ controller.

The machine’s motion system left a lot to be desired, so a few days ago I pulled it all out and built a new one for it, essentially building an Acro system from Openbuilds inside the case. It’s belt-and-pinion driven with two NEMA17 motors on the Y axis and one on the X axis.

I just finished it up an hour or so ago and I’m happy to say that it moves very well. The problem is that it doesn’t move accurately or consistently. I’ve had several CNC routers so I know about calibrating steps per millimeter for accurate travel. It’s the inconsistency in this one that I’m confused on.

I marked a spot on the X axis rail and used Lightburn to tell the machine to move 100mm to the right and made another mark. Then I repeated that twice more, marking each point.

The first segment is 99mm long. The second is 102.5 and the third is 105. ?? If the steps are off, the distance will be inaccurate but it should be the same each time. It also doesn’t return to the same spot when I tell it to move 100mm right then immediately 100mm back.

Can anyone shed some light on possible causes for this? Any direction to take in troubleshooting would be greatly appreciated. Thanks!

1 Like

Maybe the speed of the stepper or acceleration is too high ?
What about the belt tension ?

I suppose any of those could be off, but I don’t see how that would make it move different distances each time? I’m new to belt drive, as all but one of my CNC routers used screw drive and I didn’t have the belt-drive machine all that long.

I tape a digital slide micrometer to the rail, open it up, move the laser head till it’s touching, zero it, then move a set number of mm.

Measuring with a stick is too granular.

I’m measuring with a ruler, and it’s not “too granular” when the measurements are off my 2-3mm each move. I’ll dial it in with a dial indicator when I get closer than 3mm.

The question was what could be causing it? Especially the fact that it’s not even moving the same amount every time. If it were a simple issue with the step setting the movement would be wrong every time but it would be wrong by the same amount every time, and it’s not.

I would suspect the drive train. Could you send a picture of it?

I’ll get one up on here when I get back from work in the morning, thanks!

I went to grab a couple of shots on the way out for you and when I was shooting the drivers I realized I had NEVER CHANGED THE CURRENT SETTINGS for the new motors. Those 2.1-amp motors were being starved at .6 amps! I changed the settings to the most available with these drivers (1.6A). I’ll have to test it when I get home in the morning. THANKS for making me look at them! :smiley:

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.