4 z axis on 4 1HCL

HighFreq

I have a large gantry moved in Z by 4 screws driven by 4 1HCL all connected on same bus. Everything works but on large movements at F 5000 or more the speed of the axis is different, they all arrive at correct quote but at different times.
If i move the gantry slowly the different speed error is not visible.

All motors work in closed loop on each of the 1HCL.

Anything i could do to keep them in sync?

dc42

@highfreq what is the Z steps/mm on your machine, at x16 microstepping?

Are all the 1HCL boards using the same PID settings?

HighFreq

@dc42 steps/mm 320, yes x16 microstepping.

All 1HCL on default pids, all the same, all on latest firmware.

steps and microstepping should be all correct because movement of the gantry is very precise and repeatable on z axis, 0.01 (one hundred of a mm measured with a comparator) mm precision on a 700mm homing and back to position.
The problem is the different speed of the axis when reaching position.

dc42

@highfreq I can think if a few possible causes:

The maximum speed achievable by the 1HCL is one full step per PID loop. Movement at F5000 with that steps/mm requires 1667 full steps/sec. That isn't especially high as the PID loop normally executes much faster than that. Still, it's worth commanding one of those large fast Z moves and then getting a M122 report for each of those 1HCL boards, to check what PID loop rates were achieved.
The motors may not be able to generate enough power to move at the speed you want. Please use the calculator at https://www.reprapfirmware.org/emf.html to work out whether you are able to get the full motor torque at 5000mm/min. If you can't get full torque, your options are to limit the Z speed to a lower value, or use a higher supply voltage to the 1HCL (it can use up to 48V VIN). If the calculator indicates that you can get full torque at that speed, try increasing the motor current.
The default PID values may be a bad choice for your motors. Try running PID tuning, using the closed loop DWC plugin.

HighFreq

@dc42 thank you very much will try all you suggest.
closed loop plugin doesn't support multiple drives axis as i understand.
Motors already run on 48V

HighFreq

@dc42
How do i increase motor current??

dc42

@highfreq said in 4 z axis on 4 1HCL:

@dc42
How do i increase motor current??

Motor current is set by the M906 command, normally in config.g.