Disable Axis Travel Smoothness

[pouryatorabi]

Hi,
I'm working on a project that is very sensitive to axis speed, so I don't want the Duet to alter the speed or apply any smoothing. Whatever speed I set should be maintained consistently over the entire travel distance. I tried increasing the acceleration, but I still notice some speed variation. What is the best way to achieve this?

[dc42]

@pouryatorabi it's physically impossible to accelerate a mass from rest to some speed instantaneously. There will always have to be an acceleration segment at the start of the move and a deceleration segment at the end of the move, even if these are very short. You can set the acceleration in M201 as high as the mechanics can support.

What acceleration did you try, and what speed variation did you see? Are you using any sort of bed compensation?

[pouryatorabi]

@dc42 I know what you mean. I thought there would be some kind of smooth transition, rather than just simple acceleration and deceleration. I tried setting the acceleration to 10,000, and the speed was around 800 mm/min. I'm trying to dispense a material through a nozzle, so I aim to keep the dispensing rate stable, but the smoothness affects the width of the dispensed line.
So if the smoothness is only a simple acceleration, what is the maximum acceleration that I can set?

[dwuk3d]

@pouryatorabi i presume you already have the feedrate set at 800 before the extrude move - otherwise if its was previously a different speed I believe it will gradually accelerate up or down to 800 throughout the move.