How fast have you pushed your machine?

X-Carve
29

I just realized Phil probably has a 4-start lead screw, which maybe is how he is able to achieve 4x the max velocity? I had to dial the $112 down to 625mm/min because I was losing Z steps during 3D carves again, even after calibrating the motor current with a true rms multimeter. I originally set the current by the diagram on the PCB, but I was too high.

For the Xcontroller, the formula is I = Vref * 2.13. My steppers are 2.8A per phase, so I calculated the magic number to be 1.314V. I must have originally misinterpreted the diagram because at 3 o’clock I was reading 1.6V, which would be 3.5A (too high). The potentiometers are now back at 2 o’clock (1.3V), which was where they were in the first place.

I have a 3/8"-12 single start Acme lead screw on my Z axis. If I set my $112 to 1800mm/min and move 1 inch, the motor locks up and makes a horrible buzzing sound. Must I sell my soul to a cnc demon to achieve higher velocities? I haven’t tried cranking the Z all the way up to 4A, but how come the other motors are happy at 500mm acceleration and 8000mm max speed; while my Z chokes at 100mm and 1800mm respectively?

Edit: I realize the belt drive vs lead screw is the reason they’re different. Also I tried setting the current to 4a(around 1.8V at Vref) and it still locks up.

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30

Are you using a direct connect Z-Axis motor or are you using pulleys and a belt? If you are using pulleys and a belt, you can change the pulleys to a higher ratio instead of the 1 to 1 that is default on the original z-axis and a lot of the replacement ones.

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31

Brilliant! Yes I do have a GT3 belt drive on the linear Z axis so I’ll just put a huge pulley on the motor side and change the Grbl ratio. Thanks!

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32

Don’t forget, if you change the ratio, recalculate your steps and update the $102 in grbl.

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34

If you want more torque and willing to loose some precision you could always cut down on the micro-stepping.
Another thing worth keeping in mind amps = torque voltage = speed and x-controller to my understanding can do 24V and I believe x-controller can’t push nemas to 48V

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35

I ran into similar issues with my Z axis when bumping the speed up.

The issue is the torque of the motor is reduced with higher RPMs. The faster you turn, the less torque is available hence why you get stalling.

http://www.geckodrive.com/gecko/images/cms_files/Step%20Motor%20Basics%20Guide.pdf

That looks like a good PDF to help explain things.

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36

Doing some math (please check over it, I do make mistakes):

According to Inventables, 1 revolution of the Z stepper relates to 2.117 mm (approx 0.083 in).

For the Z axis to move at 40 ipm, that would mean the stepper is moving at 482 RPM (approx. 43% of max RPM, see below) and probably very little torque.

The default limit of ~20 ipm translates to 241 RPM.

Doing 241RPM with the X and Y steppers would be (40mm/rev or 1.5748"/rev) 379.5 IPM!

Most likely the torque curve means that anything above 241RPM wouldn’t have enough guaranteed torque to move around Z.

Does anyone know what the maximum steps per second/minute a nema 23 motor can go?

This site: https://www.electronicspoint.com/resources/stepper-motor-max-rpm.54/ puts some math to it.

Max RPM = 0.3 * 1 / (-L/R * ln(1-iR/Vb))

For the stock NEMA23 motors:

Steps/Rev = 200
L = 2.2mH
i = 2.8A
Vb = 24V
R = 0.83 ohms

Max RPM = 0.3 * 1/((-.0022/0.83)ln(1-(2.8(0.83/24))) = 1111.28.
Max IPM (Z) = (RPM * IPR) = (1111.28 * 0.083) = 92.236
Max IPM(X,Y) = (1111.28 * 1.5748) = 1750.04

Bump up the PSU voltage to 48V means max RPM goes to 2280.6 but the torque would also increase at the lower RPM levels (the Gecko PDF echos this).

I emailed Inventables to see if the Xcontroller has a limit on the power supply voltage without damage. The 5V regulator appears to have Vin max of 42V, which would become the theoretical limit. I guess you could step down a 48V supply with an auxiliary circuit before the 5V regulator or just go with a supply less than 42V. With your setup @PhilJohnson, you could just swap your power supply out to be 36V or 48V and you’ll see torque increases which generally will translate into faster and potentially deeper cuts.

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38

Depends on the stepper torque curve, which I don’t see published. Some of the curves I’m seeing online drop-off pretty quick so maybe not.

39

I got no time to read whole thing so I apologize if I missed it somewhere but what is your micro steps set to ?
At 1/16 that x-controller is set default to you are getting 10% of your torque you could easily go to 1/8 and get 20% of the nemas essentially doubling your torque.

41

Ah forgot we talking Z here

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42

Wow, lots of great info! My Z is at the stock 1/2 microstep. I just ordered a bunch of pulleys to experiment with: 20, 30, and 40 tooth XL because the linear rail currently has two 10 tooth XL pulleys. I imagine if I increased the ratio to 2:1, this doubles the resolution, so I could set to full steps (no microstepping) to re-gain some torque?

Edit: Actually I think doubling the Z motor pulley tooth count would half the resolution because one step would now move Z twice the distance. I would have to increase to 1/4 micro stepping to retain resolution.

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43

If the shaft diameters are the same just reverse the pulleys.

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44

Finally made one

IMG_0673.JPG3024×4032 1.92 MB
IMG_0674.JPG3024×4032 2.23 MB

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