Acceleration limit?

3DPMicro

is there a hard limit to the acceleration value in the FW or electronics?

dc42

The acceleration limits are specified in the M201 command in config.g. The ultimate limit depends on your mechanics, stepper motors, and motor current. The speed up to which you can maintain that acceleration also depends on the driver supply voltage.

3DPMicro

Thanks David. While testing I was able to determine that accelerations above 6-7000 produce very small decreases in travel time at least at speeds upwards of 300mm/s and 100mm travel distance. Soon to understand those relationships at slower speeds and shorter distances.

dragonn

They is also an M204 command which could limit you acceleration. https://duet3d.dozuki.com/Wiki/Gcode#Section_M204_Set_printing_and_travel_accelerations

deckingman

@3dpmicro said in Acceleration limit?:

Thanks David. While testing I was able to determine that accelerations above 6-7000 produce very small decreases in travel time at least at speeds upwards of 300mm/s and 100mm travel distance. Soon to understand those relationships at slower speeds and shorter distances.

You can do the maths which will tell you why. Set up a spread sheet and plug the numbers in. The formulae you need are:

Max possible speed over a given distance is sqrt(2 x Acceleration x length/2) That's assuming you accelerate for half the distance, then decelerate for the other half.

Time to reach a given speed is (final velocity - initial velocity) / Acceleration. From rest, the initial velocity will of course be zero.

Distance travelled to reach that velocity is 1/2 x Acceleration x time^2

So with an acceleration of 6,000 mm/sec^2 the maximum possible speed attainable over 100mm (from rest back to rest) is 774.6 mm/sec. The time to reach 300 mm/sec is 0.05 seconds and the distance travelled during that time would be 7.5 mm. If you double the acceleration to 12,000, the time and distance reduce by half from 0.05 to 0.025 and from 7.5 to 3.75 respectively.

As you can see, there are diminishing returns. Doubling that acceleration from 6,000 to 12,000 reduces the time to get up to speed by 0.025 seconds so no wonder it's difficult to see the difference.

All of which brings me back to the perpetual question that I keep asking myself, which is "why is the 3D printing community so obsessed with reducing moving mass to miniscule values in order to attain ridiculously high acceleration rates which actually save very little print time?" But that's just me......

Anyway, plug those formulae into spread sheet and play around with the values.

HTH

3DPMicro

@deckingman my motives are slightly different than for the reasons you mentioned. I dove down the rabbit hole of the ball screw because early use of belts showed they were incapable of providing the accuracy/repeatability required for the extrusion widths I mostly run. I have concluded the ball screw is the clear winner for those requirements. Now its about collecting empirical data on a single axis test rig through the use of data acquisition with an accelerometer and high speed video measurement all in an effort to a) gain a better understanding of this type of motion system because the math doesnt provide us with the limits and b) to determine a optimum combination of motor, lead and settings for my application to maximize performance over the entire speed range.
I posted the initial question because the settings weren't inline with what the data logger was saying so I just wanted to make sure electronically it wasnt limited

BenDiesel

interesting. will you share your results when you get them? id like to know what you find out

3DPMicro

@bendiesel yes, I already have a thread on reprap for this topic http://forums.reprap.org/read.php?1,816864 and will probably post the end result there

BenDiesel

cool

i know this isnt related to your project but might be in your interest to see
https://www.youtube.com/watch?v=fXU3q_eBDlI

3DPMicro

@bendiesel I'm always amazed at the will we have , as humans to develop. What's puzzling about it is that there's really no logical reason from a survival standpoint