What is the maximum step rate of Duet-3 board?

psyblue

I know that the maximum step rate of Duet-2 board is 360kHz with just one motor running and 180kHz with 3 running synchronously. (https://forum.duet3d.com/topic/328/max-speed-at-different-microsteppings)

Is it the same on the duet-3 board?

Phaedrux

Currently unknown. https://forum.duet3d.com/topic/13737/duet-3-rated-stepper-khz?_=1585872190584

It should be faster than the duet 2 due to the faster CPU, but I don't think final measurements have been done yet.

psyblue

Thank you very much for fast reply. I'm watching the link you gave.

dc42

Maximum step rate of Duet 2 using current firmware is lower than 360kHz/180kHz because we disabled double/quad etc. stepping in later firmwares. The reason was that they upset step-servo drivers, and probably don't play well with interpolation in Trinamic drivers either. I may re-introduce it as a configurable M569 option in a future firmware revision.

nhof

@dc42 Since 360kHz/180kHz isn't current, what's a good new value for max step rate/axis?

deckingman

I've just run a little experiment. My Z axis uses fine lead screws so the steps per mm are 3200. The Z motor is connected to a Duet 3 expansion board and I'm running very old beta firmware (2019-12-29b1) so none of what follows this might be relevant. However....

I took the belt of the Z motor so that it's free to spin with no load and I added a couple of noughts to the maximum speed setting in config.g to ensure that it wasn't being limited. Then I issued G1 Z Fnnn commands. The motor spins at G1 F values up to 1500 but makes load buzzing noises with no visible movement at F=1800. So if my maths serves me correctly, 1500 mm/min = 25 mm/sec. Multiply that by 3200 steps per mm and I get a very disappointing step pulse frequency of 80kHz.

It may even be lower because there might be hiccups even at 1500 mm/min speed but because I am still on a Beta firmware, I can't get reliable hiccup data for an expansion board.

If this 80 kHz figure (or less) is indeed valid, this is going to cause big problems with my mixing hot end because I need to run the extruders at high micro-stepping to get the desired resolution when mixing ratios might be down to single digit percentages, but I still need to retract at reasonably fast speeds.

dc42

The maximum step rate on expansion and tool boards was improved in one of the 3.01RC releases.

deckingman

@dc42 said in What is the maximum step rate of Duet-3 board?:

The maximum step rate on expansion and tool boards was improved in one of the 3.01RC releases.

Thanks. Can you put a number to it?