Acceleration settings

Machine: Custom build 1305x760mm

Board: LaserBoard

Firmware: Smoothie as shipped

Question: Is there any rule of thumb or way of estimating a good acceleration figure to start out with?

I’m stress testing my machine and want to push it to its limits, (no laser installed - just testing the mechanics), but I don’t have a good feel on how to adjust accelerations and what to look for when I do.

I have my max speeds set in the config file as 60000 mm/min, (although I’m not hitting that speed - maybe getting 20000 mm/min), and acceleration at the default 2500 mm/sec^2. I read one post where someone had their machine running at 550mm/sec with an acceleration of 10,000 mm/sec^2 so I should be able to get some more out of this I think.

What would a good process be for getting speeds and accelerations dialed in? I can send ever increasing feed rates in a G0 command at different acceleration levels, but what result am I looking for? What’s the consequence of too much or too little acceleration?

My ultimate goal is to find the maximum rates before my machine starts to complain, and then back it off with a suitable safety margin and program that in to the config file to give myself trouble free running.

And a follow up question. What’s the difference between the acceleration setting in the Planner module section and the individual axis configurations? It looks like I can set a separate acceleration rate for each of X, Y and Z, and then there’s yet another value for the Planner.

So I think I’ve answered this to an extent by testing. I have it running at 600mm/sec just fine, but if I use any feed rate above this it doesn’t get any faster. After finding this limit I upped the acceleration from 2500mm/sec^2 to 5000mm/sec^2. It accelerates fine at this rate, but while it’s not mentioned I’m guessing this is also the deccleration rate it uses, and this is just too much for my machine to come to a stop. :smiley: (Especially the Y-axis.) I’ve now set 36000mm/min and 3000mm/sec^2 in the config file and it seems to be happy at these rates.

I’d still be grateful of some further explanation / advice / suggestions in this area and an answer to the Planner vs. axis configuration. (I have both set the same right now.)

I think you were right to use trial and error to determine those values. A lot of them depend on the individual stepper torque curves, gantry/carriage weight and whatnot, so it’s going to be different for each machine. I’m sure there’s a mathematical formula that can be derived from several inputs here but I’d be lying if I said I know what it is! That said, you have it moving pretty fast - congratulations!

As far as to the planner vs. axis configuration - I unfortunately don’t have an answer for you there.

Here is a blip on Minimum Planner Speed.

http://smoothieware.org/motion-control#maximum-speeds

Thanks! That was useful reading. I think my issue is that my machine isn’t rigid enough yet so that while I can accelerate better than 3000mm/s^2 I can’t decelerate at that rate without overshooting. I have managed to improve the overall speed by adjusting the micro-stepping I was using and today I’m working on making my machine more solid. When that’s done I’ll try tweaking the acceleration rates again and keep going around the various options until I find the best setup.

If you really want to test machine speed, setup a 45 degree 1/4” wide zigzag pattern and see if your machine shakes. There is also another variable that controls the Deceleration at direction changes. It’s called junction deviation. If your trying to push your max speeds, this is one you should be aware of

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