$1=255 Making motors hot while idle?

[Big Man Black T-Shirt(Patrick)]

This is probably just for Derek but if anyone else knows feel free to chime in.

I was reading the issues on the UGS GitHub page and I found this comment from a user. It was about the poster’s Grbl settings.

”Notice that your $1 is set to 255, that keeps your motors powered all the time and get hot even when they are not being used”. $1=255 (step idle delay, msec)

I, too, have noticed that my M3 motors are quite warm even when nothing has been run for a long while. I’ve often wondered if this was good for them.

What say you, Derek?

Thanks!

[Derek the Admin]

That's completely intentional. You want it to stay powered so it doesn't drift from position. It's okay that the motors get hot. They are well within normal operating range.

[Bruce]

Here's what the GRBL configuration page says:

github.com/gnea/grbl/wiki/Grbl-v1.1-Configuration#1---step-idle-delay-milliseconds

$1 - Step idle delay, milliseconds

Every time your steppers complete a motion and come to a stop, Grbl will delay disabling the steppers by this value. OR, you can always keep your axes enabled (powered so as to hold position) by setting this value to the maximum 255 milliseconds. Again, just to repeat, you can keep all axes always enabled by setting $1=255.

The stepper idle lock time is the time length Grbl will keep the steppers locked before disabling. Depending on the system, you can set this to zero and disable it. On others, you may need 25-50 milliseconds to make sure your axes come to a complete stop before disabling. This is to help account for machine motors that do not like to be left on for long periods of time without doing something. Also, keep in mind that some stepper drivers don't remember which micro step they stopped on, so when you re-enable, you may witness some 'lost' steps due to this. In this case, just keep your steppers enabled via $1=255.

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If you turn the motors off on a belt driven system you going to lose position on at least the Z axis, it will drop.  On the lead screw based system it may not be as much of an issue.

But it seems to me the potential for lost position by turning off the motors would diminish any return of reduced heat from the motors.  The motors are designed to handle the holding current and heat it generates.

That's just my 2 cents.

[Bruce]

I see Derek already posted an answer...never mind. 

[Big Man Black T-Shirt(Patrick)]

Thanks for the clarification! I figured there was a reason for it but as a electronics nerd I associate idle heat as a bad thing. Good to know all is within spec.

[Derek the Admin]

Good question though.

Cheers
Derek