Step Sale and Velocity

Hello All!

Thanks for taking time to read my post.

I have recently got my motors running and I have them tuned to what I believe is the right settings.
I have a DM542T at step time = 5050 step direction = 5050 direction hold = 500 direction setup = 500.

I had them sitting on the bench and they sounded beautiful, then i plugged them to my machine and they were very jittery with what I thought was the right step scale. However I corrected it by a factor of 10 and they ran absolutely beautifully.


The problem with this however is that I cant seem to run my motors fast enough.

In the PNCconf wizard with axis selected I cant set the default linear velocity above 1000mm/min and the max linear velocity above 2000mm/min however I would like to jog at 9000mm/min and cut up to 6000mm/min for 2.5mm steel (making a plasma cutter with PlasmaC).




IMAGES AND INFO.

motor steps per revolution= 200
microstepping= 2
gear reduction= 3:1
mod 1.5 20T pinion drive with 30mm pitch circumference.






So my step scale really should be 1200 steps/rev (of pinion) and 40 steps per mm but this doesnt seem to match up. I had to change my motor steps per revolution to 20 instead of 200 which is obviously wrong.


Any help is very much appreciated

EDIT: (01/02/2020) The questions above were solved thanks to amazing support. I also encountered error problems with a refurbished dell optiplex but this was solved by changing the servo thread to 1050000 and selecting the second core in the BIOS.

Thank you very much phill, that was what I needed to fix it. This gives me a scale of 13.33 steps/mm which I think is correct.

However this means I still have the problem of not being able to run the program faster than 1000mm/min in “axis” running the default Linux cnc program, far short of the 6000mm/min that I would like to get at a minimum. How do I change this in the settings?

I can change the velocity to whatever I like in each single “X, Y, Z” settings but not for the “axis” simulation.

Sorry I should have posted these to begin with.

I think your expectation of 5000 rpm is the issue That is unachievable. I could not get past about 750 RPM with a Mesa 7i76e and a Longs Motor DM542a.

So with 20t Mod 1.5 pinion you have:
20 * 1.5 * pi = 94.2mm/pinion rev
94.2/3 = 31.4mm per motor revolution
So with 2x microstepping, that means you have 400 steps per motor revolution
or 400*3 = 1200 steps per motor revolution
or 1200/31.4 = 31.265 steps per mm

Maximum speed = 750 * 31.4mm = 23550 mm/min. I'd mark that by 20% I'd set the max speed at about 18000 mm/min
If you do not run hardware stepgen, you might need to reduce the max speed I suggest. eg. I could not get past 400 rpm with an Arduino.

I'd try and increase your microstepping to at least 10:1 and adust the steps per mm accordingly (say 10x microsteping = 31.265 *5 steps per mm which will be about 156 steps per mm.

rodw wrote:

I think your expectation of 5000 rpm is the issue That is unachievable.

Thanks for your reply Rod,

Sorry, I meant a velocity of 5000mm/min, not 5000rpm, I know that is extreme.

Also, thank you for posting your calculation, I just realised that I forgot to put Pi into my calculations. Idiot. I thought that N x T gave the Pitch Circumference but its Pitch Diameter.

I will enter these values and tray again.

To change my max velocity higher than 2000mm/min though, do I have to do it in the ini file? because I am not able to do it in the PNCconf window.

phillc54 wrote:

In the [DISPLAY] section you have DEFAULT_LINEAR_VELOCITY=16.666667 and MAX_LINEAR_VELOCITY=33.333333 which are 1000 and 2000 mm per minute.

Thank you!

I got the 5000 RPM from one of your screen dumps.
You still need to do the maths as I did. The only thing that will change the STEPSCALE is microstepping. By my calcs you are still wrong in the INI file you shared. Follow the numbers I shared and make sure you understand them.
When I set my machine up never used PNCCONF and just edited files by hand.