Slow G1 Move Possible? (<0.5mm/sec)

ben_van

Re: Unable to get slow G1 + English/metric questions

Just wondering if anything to allow movements slower than 0.5mm/sec has been changed in the latest firmware release (2.02)?
I am currently running my duet 2 Wifi in laser mode on a modified microscope where very fine/precise movements are necessary. The main issue is the heavy gearing on the Z axis (~16000 steps/mm with 1/16th micro stepping) making even 0.5mm/sec movements way too fast for the system.

To solve this for the time i have converted the Z axis steps/mm to really be steps/micron, however this doesn't make previewing gcode very nice and requires fixing any gcode i didnt generate myself for all Z moves/feeds to also be in microns.

I would really like all the gcode to be in mm, and still allow moves as slow as 1mm/min, if this can easily be achieved?

Any help is appreciated.
Thanks!!

RCarlyle

Do you need finer motion resolution or are you just hitting a minimum speed floor?

Some not-great solutions:

Switch the driver to true 1/256 instead of interpolated 1/16 so it runs at 1/16th nominal speed
Add another gearbox to the drivetrain

ben_van

Hey thanks for your suggestions
Yes, I'm simply just hitting the minimum speed floor. Anything less than an F30 the firmware will ignore..

I don't understand how switching the microstepping would change anything other than the number of step pulses required to achieve the same motion?..

I could change the gearing from the stepper motor to the focus on the Z axis however I can't change the gearing in the internals of the microscope whithout major work.. Which is the issue. Regardless of other gearing those internal gears will spin at the same speed to translate a 0.5mm/sec move to the microscope stage and spin too fast for comfort.

I have been able to achieve the slow speeds I need so I know the duet is definitely capable, it just makes writing gcode very non conventional.

Physically I have 16000steps/mm but I have set it up as 16steps/mm in the firmware. So now when I want to physically move 1mm in the z axis, my gcode would look like (G1 Z1000 F1000) as feeds and speeds are now in microns.
What I really want to do is simply say G1 Z1 F1, but the F1 command will be ignored and I'll get an F30 instead..

fcwilt

Hi,

You mention "heavy gearing" - what do you mean by that?

Thanks.

Frederick

ben_van

Hi,

I just mean that large motions of the stepper motor produce very small motions of the Z platform, through planetary gears (1 rotation of stepper = 200micron)
I do not mean to say that the gears are heavy in mass, or that they are hard to turn...

fcwilt

@ben_van said in Slow G1 Move Possible? (<0.5mm/sec):

Hi,

I just mean that large motions of the stepper motor produce very small motions of the Z platform, through planetary gears (1 rotation of stepper = 200micron)
I do not mean to say that the gears are heavy in mass, or that they are hard to turn...

Thanks that is now clear.

Changing the gearing on the stepper won't solve the problem as you would end up having to enter a larger value for steps/mm if you wanted Z100 to be 100 mm.

Hopefully dc42 will reply on this issue.

Have you looked through the source code to try and determine where the F30 limit appears?

Frederick

ben_van

@fcwilt
Yes.. But coding is definitely not my strong point. I was hoping someone here could point me in the right direction if it comes to recompiling some custom code

fcwilt

Hi,

Perhaps simply post a request for slower movement in the section for firmware requests?

Normally dc42 is very good at responding here.

Frederick

dc42

Yes I can reduce the minimum speed allowed. I may make this a configuration option, because it's easy to confuse a low speed with the system having crashed/hung/stopped. How low do you need to go?

ben_van

@dc42
Yes i completely understand your reasoning for having the limitations, and would be perfectly fine if my setup/needs were not so abnormal..
I need to go as slow as 1mm/min (0.0167mm/sec)

Thankyou!!