[dabird]

Hello All,

My son and I built a CNC of his design to mostly cut aluminum, and overall it works great with great accuracy. We have two motors in sync with each other driving the x-axis, so it's important that these always stay perfectly aligned with each other. Whenever we turn on the machine it seems like all the power hits the motors, and there is an audible sound from the motors. The problem is that we have seen that this sometimes causes the motors to turn ever so slightly, though have seen the two X Axis motors shift in opposite directions. We are looking for ideas on how to stop this from happening - maybe a limiter of some kind? It only happens when the power first hits the motors, then everything works fine. It's just that initial surge that may cause a shift that puts the motors out of alignment. I can provide additional information on the electrical setup if needed though wanted to see if anyone has had this issue and how it was solved.

Thanks in advance for your input.

[Jim Dawson]

The normal way to solve this is to have a home switch on each side. Then home the machine after power up to sync the motors. You might have to home the sides separately. Bring home until one motor hits the home limit, hold that motor, then bring the other motor into its home limit. You may have to write a software routine to do this.

[Al_The_Man]

By X motors in sync, are they mechanically coupled and are turning to the a physical limit due to backlash etc? or able to turn separately?
Does the power supply to the motors come on before the controller has booted up?
Al.

[dabird]

Yeah if we can't stop that initial surge we will probably look at the home switches. We tried to set it up to get power to the right places at the right time. We checked and the breaker/control boards is getting 5v of power prior to power going to the motors. We also make sure the computer is on and Mach3 is running, and this powers the UC100 connection from the computer to the boards, all before the motors get power.

[peteeng]

Hi Dab - The steppers will never by perfect in sync mechanically. When they are initiated they find the closest magnetic coil to their stationary position. One may go clockwise to this position the other anticlockwise, vice versa or they could be close. All depends on how and where they were shut down and how much "spring" is in the mechanical system as a whole.. This is the clunk on initiation. To fix this a home position is needed that can realign them to the mechanically correct position. If the clunk is severe and the gantry moves a lot at initialisation this means the structure maybe "sprung" or is poorly aligned. So firstly work through the structure and check its not loose, misaligned or twisted or whatever. A clue to this is if the system is off and you push one side of the ganty and it proceeds but the other side lags then you need to stiffen the gantry structure.

Another thing to try is to manually move the gantry to its stops (if you can do this depends on your drive system) and physically hold it to them at start up. This removes the compliance of the start up and they may sync better...if you can't do this manually then do it via software control then shut down and restart may learn something about the issue...or clamp them in place before startup...or clamp one and se what the other does etc Cheers Peter

You say one motor is in sync with the other? Is one "slaved" to the other in the controller? or are they being driven from one controller in parallel or series? cheers

[dabird]

Thanks for the thoughtful responses. One is slaved to the other, and the motion is just as you described. The 'clunk' can make the motors shift ever so slightly, but sometimes in the opposite directions. Looks like we need to set up the two home switches. Thanks again for all of the input.