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.

I would think that you need to enter how far the axis would move for one revolution of the pinion as your Leadscrew Metric Pitch.

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.

What are the actual settings you have at the moment?
Edit: I really should have said "could you post your .ini file"

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.

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.

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.