Hissing sound on entering Lightburn after home

This issue does not affect operation, it is just annoying. Once my Cohesion 3D is fired up and I enter Lightburn, the laser head homes as expected in the upper left corner. There is a hissing sound that comes from that general direction. Saw this in the C3D forum but no real answer. Quite by accident, I was in the laser panal and clicked the STOP icon and the hissing instantly stopped. Also happens when RUN is clicked but not PAUSE. The hissing will not reappear and everything runs fine unless I actually power off the C3D board. The hissing sound does not interfere with the operation but something is making the noise! So now, on launching Lightburn, I just go straight to the laser panel and hit STOP. As I’ve read this reported by other users, just curious if there is a setting, or if the STOP command could be issued at Lightburn startup automatically in a setting?

This is just the sound the motors make when the drivers are active. It’s quite normal.

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Motors, when energized, “hiss” every time a force is applied on their shafts.

I use smoothieware M18 command to disable the motor when i don’t need them to hold position either in a macro command or Start/End Gcode commands.

I tried M18 earlier, it just returns “OK”. Doesn’t seem to stop the hissing. I was looking at the commands in the console to see what code was actually being sent when I pressed the “stop” button in the laser panel, but it shed no light.

Is there a way to adjust the idle or “hold” current of the steppers? You may find that a small increase or decrease in the current makes the hiss go away or be less (or maybe more) objectionable.

Yes, I saw some documentation ont the Cohesion 3D site. Haven’t tried it yet. Seems that if clicking the “Stop” or “Run” icon makes it go away for the rest of the session, there should be an easy adjustment somewhere.

Maybe check the C3d site and documentation as you suggested to yourself?

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I actually started there and I’ve read all, if not most, of the documentation. I’ll figure it out I’m sure.

As an update. Now that I am at home, have things sorted out, I started the Cohesion 3D board and then Lightburn. the hissing started on homing. I issued an M18 command and it instantly stopped, so you were correct! Is there a way to send that to the Cohesion 3D on software start automatically?

First you have to find out why your motors hiss in the first place and if yours hiss louder than normal. this can be due to mechanical issue which exerts a constant force on motor’s shafts like bad pulleys/bearings/belts/gantry/air assist tubing/wires/etc…

The stepper motor drivers on the C3D board can be tuned to reduce hiss:

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Only hissing while stationary so I’m thinking it’s motor noise from “hold in place” current. Issuing an M18 command disengages the motors. It’s not a loud noise, just annoining.

Thank you @TomWS for the link to Cohesion 3D and stepper tuning! This was very useful and helpful! Quick question however, If one chooses to leave the steppers in “spreadcycle”, will it adversly affect the motor life? If not, I can deal with the noise for better performance.

I don’t have any data specific to this question, but one of my first CNC routers (DIY) hissed for years and I’ve never replaced a stepper motor. In my experience, I’ve gotten hiss when using cheap stepper drivers. When I’ve replaced the stepper drivers with ‘decent’ ones, the hiss went away and performance went up. I am surprised the Trinamic drivers are causing hiss. They don’t on my K40 with a C3D board.

@TomWS , could be my version of K40. While it appears to be well built for a Chinese laser, OMT Preenex, it might have junky steppers. I did notice an immediate improvement in both precision and smoothness when I upgraded to the C3D board. Read on C3D forum, several others have experience the same thing. I noted above that issuing an M18 command disengages the steppers and they go silent. You can hear them “clunk” out as the drives are released.

Any stepper will do that if you instantly de-energize them after stepping. The motor is just moving into the nearest magnetic detent.

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