Actual speed on my Delta



  • I think I need so additional education. In an earlier discussion (https://forum.duet3d.com/topic/328/max-speed-at-different-microsteppings/3) it's mentioned that 16x micros stepping Duet can only do up to 100mm/sec. I've been running my Delta at different speeds

    80mm/sec 1200 acc
    160mm/sec 3000 acc
    240mm/sec 4000 acc
    320mm/sec 6000 acc
    400mm/sec 8000 acc

    I understand that most of the time 240, 320 400 will not be printing at that speed due acceleration and jerk but even at the higher speeds the interface does show it reaching these speeds once in a while.

    has something changed (the mentioned post is 2 years old) or am I reading things wrong?



  • @core3d-tech Yes, you've misread that post of Davids. He said " For example, if you have 80 steps/mm at x16 then you will have 1280 at x256".

    So that's 1280 steps per mm using 256 X micro stepping and then he goes on to say "which implies a maximum speed of around 100mm/sec to allow for 2 motors running". So 100mm/sec @256 X micro-stepping, not at 16X.

    Things have moved on a bit as DC said in that post and for multiple motors, the step pulse frequency is around 180kHz rather than the 130 kHz that he used. So if you divided that by your steps per mm, it'll give you an idea of what you can expect. Using the example in that thread of 1280 step per mm (using 256 x micro-stepping) then you ought to get in the region of 140 mm/sec (180,000/1280) but when you drop to 16X micro stepping the calculation becomes 180,000/80 (steps per mm at 16x micro-stepping) = 2,250 mm/sec!

    That ought to be adequate ☺



  • Thanks for that. Out of curiosity, what is the interface showing when it states requested speed 320 and top speed 320? Considering the top speed constantly fluctuates I assumed it was actual reached speed but clearly it can't be (I was running at 16x with 256 interpolation). I'm going to run some test at 16x no interpolation now to see what happens.



  • Interpolation is done by the drivers, there will be no difference.
    It is the acceleration that limits the max speed in most scenarios. High acceleration is they key to fast prints unless you print really big models.
    Step rate is very rarely an issue when you have a Duet. It easily became a problem on those nasty 8-bit boards that have been the standard for far too long.



  • @core3d-tech said in Actual speed on my Delta:

    Thanks for that. Out of curiosity, what is the interface showing when it states requested speed 320 and top speed 320? Considering the top speed constantly fluctuates I assumed it was actual reached speed but clearly it can't be (I was running at 16x with 256 interpolation). I'm going to run some test at 16x no interpolation now to see what happens.

    Yes, the displayed speed is correct but it doesn't update as quickly as the carriage moves, so at high speeds, it's more of a snap shot. 16 x with or without interpolation makes no difference as far as the firmware is concerned. The duet sends the same pulses to the driver chip but when interpolation is active, the driver chips sub dived the micro-step pulses into 16 smaller segments. That's how they interpolate to 256 x (16 x 16).

    In actual fact, it's not true interpolation because the duet cannot send a fraction of a pulse. So from a resolution point of view 16x with or without interpolation are exactly the same thing. When interpolation is active, the driver chip sends out 16 smaller pulses for every single pulse that it receives. The net result is that motion might be smoother and quieter but resolution is exactly the same.



  • @bondus said in Actual speed on my Delta:

    It is the acceleration that limits the max speed in most scenarios. High acceleration is they key to fast prints unless you print really big models.

    Actually, it's the filament melt rate that limits the maximum print speed for the vast majority of people.



  • Thanks, I just verified (visually) that interpolation is indeed moot. my settings:

    M350 X16 Y16 Z16 E16 U16 I1

    and printing a circle at 400mm/s indeed runs at 400ms (ish). replaying the video it seems to be running at 384ms (acceleration/jerk )



  • @deckingman said in Actual speed on my Delta:

    Actually, it's the filament melt rate that limits the maximum print speed for the vast majority of people.

    That's very true. That damned plastic refuses to behave 😉

    But acceleration can keep your average speed high, even in the detailed sections of the prints.


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