Microstepping and speed limits

dc42 · 18 Jan 2017, 17:14

You should preferably limit the step rate to about 100kHz per motor. For a Cartesian or CoreXY printer, the step rate is your steps/mm multiplied by the travel speed in mm/sec. So here is a table giving maximum recommended speeds when using 20 tooth pulleys, GT2 belts and 1.8deg motors:

Microstepping, steps/mm. max speed
16x, 80, 1250
32x, 160, 625
64x, 320, 312
128x, 640, 156
256x, 1280, 78

For 0.9deg motors, divide max speed by 2. For other numbers of pulley teeth, multiply max speed by pulley_teeth/20.

On the firmware work list is to implement variable microstepping, so that you can configure 256x but it will be reduced automatically at high speeds.

InSanity · 18 Jan 2017, 17:14

@elmoret:

I didn't come up with it, it is explained in the link I posted.

My bad, didn't notice the link. Interesting..very interesting. Looks like 1.8 deg with 16 tooth and 256 stepping I'm looking at 150mm/s perhaps more as I think those charts are for a delta. I'm running 17t as well so yah maybe 150+ mm/s.

Thanks,

Jeff

deckingman · 18 Jan 2017, 17:16

@(In)Sanity:

@elmoret:

http://reprap.org/wiki/Step_rates

Assuming a 20 tooth pulley, 1.8deg stepper, max speed is 187mm/sec at 256x. If you change to 0.9deg steppers, then about 93mm/sec.

Thanks I'm actually running 1.8 deg motors with a weird 17t pulley setup. So I'm loosing a little speed with a little better resolution. Where did you come up with your value ?

Jeff

May I ask what are your steps/m for X and Y?

InSanity · 18 Jan 2017, 17:19

@dc42:

You should limit the step rate to about 100kHz per motor. The step rate is your steps/mm multiplied by the travel speed in mm/sec. So here is a table giving maximum realistic speeds when using 20 tooth pulleys, GT2 belts and 1.8deg motors:

Microstepping, steps/mm. max speed
16x, 80, 1250
32x, 160, 625
64x, 320, 312
128x, 640, 156
256x, 1280, 78

For 0.9deg motors, divide max speed by 2. For other numbers of pulley teeth, multiply max speed by pulley_teeth/20.

On the firmware work list is to implement variable microstepping, so that you can configure 256x but it will be reduced automatically at high speeds.

Thank you sir, looks like I should stick with 64x or 128x , perhaps 128x as I still can hear a little singing with 64x, not too much..but a little bit. 32x just drives me nuts. Hmm, I do once in a while print at 150mm/s when I need junk quickly.

Jeff

InSanity · 18 Jan 2017, 17:21

@deckingman:

@(In)Sanity:

@elmoret:

http://reprap.org/wiki/Step_rates

Assuming a 20 tooth pulley, 1.8deg stepper, max speed is 187mm/sec at 256x. If you change to 0.9deg steppers, then about 93mm/sec.

Thanks I'm actually running 1.8 deg motors with a weird 17t pulley setup. So I'm loosing a little speed with a little better resolution. Where did you come up with your value ?

Jeff

May I ask what are your steps/m for X and Y?

Sure, here is my current setup

M92 X94.12 Y94.12 Z400 ; set axis steps/mm
M92 E200.7238:200.7238 ; set extruder 0 and 1 steps/mm

M350 I1 X64 Y64 Z64 E256:256 ; set microstepping

dc42 · 18 Jan 2017, 17:23

Does the 64x sing less if you enable interpolation? The TMC2660 datasheet doesn't make it clear whether interpolation works at microstepping other than 16x.

InSanity · 18 Jan 2017, 17:25

@dc42:

Does the 64x sing less if you enable interpolation? The TMC2660 datasheet doesn't make it clear whether interpolation works at microstepping other than 16x.

You know, my mind wants to think so…so I leave it on. I've not done any real serious testing. I'll have to do so.

Jeff

deckingman · 18 Jan 2017, 19:31

At 94.12 steps/mm 1 step = 0.01062734mm so at 16 micro steps 1 micro step = 0.000664046mm , at 32, one micro step = 0.000332023mm, at 64 it becomes 0.000166011mm and we need to use scientific notation for the higher micro steps.
Just thought I'd point that out.

InSanity · 18 Jan 2017, 20:22

@deckingman:

At 94.12 steps/mm 1 step = 0.01062734mm so at 16 micro steps 1 micro step = 0.000664046mm , at 32, one micro step = 0.000332023mm, at 64 it becomes 0.000166011mm and we need to use scientific notation for the higher micro steps.
Just thought I'd point that out.

The uneven ratio I know is a bit odd and could produce some possible artifacts, it's what the printer came with and is a bit of work to change out to 16t pulleys. 20t might actually be easier to switch to if they fit. I assume you were talking about the odd ratio, or perhaps just the resolution which of course can't be achieved? I can however notice stuff like the letters on the back of a 3dbenchy looking better at > 16 microstepping. It's subtle, but it exists. Mostly the higher microstepping is about noise level for me. I just can't live with 16x when I have that 1% chance of better results above 16x.

Jeff

InSanity · 18 Jan 2017, 20:35

@dc42:

Does the 64x sing less if you enable interpolation? The TMC2660 datasheet doesn't make it clear whether interpolation works at microstepping other than 16x.

It does seam to make a little bit more singing noise with interpolation off. I would say for those who are worried about such a thing to just leave it on, even if it does nothing more than make the end user think it does.

Jeff

3dprinting meathead · 2 Feb 2017, 03:53

@(In)Sanity:

@dc42:

Does the 64x sing less if you enable interpolation? The TMC2660 datasheet doesn't make it clear whether interpolation works at microstepping other than 16x.

It does seam to make a little bit more singing noise with interpolation off. I would say for those who are worried about such a thing to just leave it on, even if it does nothing more than make the end user think it does.

Jeff

Are you running 12v or 24v?
I heard that the tmc2100s were quieter with 24v, but not sure if it's true, and I'm not sure if it holds true with the tmc2660, which from th little information I could find, is a 2100 with higher amperage(?)

dc42 · 2 Feb 2017, 08:01

I've had confirmation from Trinamic that interpolation only works when microstepping is set to 16x.

The 256x interpolation modes in the TMC2100 and TMC2660 are similar, but as well as supporting higher currents the TMC2660 provides an SPI interface to control and monitor the chip, while the TMC2100 just provides some configuration pins instead.

InSanity · 2 Feb 2017, 14:19

I'm running 24 volts. So the finding on the interpolation match up with what I've seen, 32x for example is significantly louder then 64x with interpolation on.

So at the moment I'm running in 256x mode and can do travel moves at 200 mm/s and normally print at 80-90 mm/s. I've timed prints with 16x up to 256x and not seen any differences in completion time at all, so how does one know if you are being slowed down by using too high of microstepping values ?

Jeff

dc42 · 2 Feb 2017, 15:05

To check whether you have the combination of speed * microstepping too high, do some long, high-speed moves. Then run M122 and look at "MaxReps" in the Move section. Try to keep that value below 50, or 100 at most. The value is cleared out after it is displayed.

InSanity · 2 Feb 2017, 15:47

@dc42:

To check whether you have the combination of speed * microstepping too high, do some long, high-speed moves. Then run M122 and look at "MaxReps" in the Move section. Try to keep that value below 50, or 100 at most. The value is cleared out after it is displayed.

Ok, in geek speak what does this translate into ?

Thanks,

Jeff

dc42 · 2 Feb 2017, 16:16

MaxReps is the number of times that the ISR loops while generating step pulses, before there are no further steps due yet.

InSanity · 2 Feb 2017, 16:52

@dc42:

MaxReps is the number of times that the ISR loops while generating step pulses, before there are no further steps due yet.

Ahh, so kind of like the max length of the FIFO that was hit? I notice I hit 364 on my last print. I've stepped down to 128x and trying the print again.

Edit: Same print I got 17 now with 128x vs 364 @ 256x. Guess I'll stick with 128x.

Thanks,

Jeff