Hi Mohsen,
Ralh is right.
But why not calculate it? Because there are so many factors involved, and they are unique to your specific printer setup, and some factors will be unknown - and change with speed.
- The torque of the motors varies by speed as shown below (different for every motor model), and is also related to the motor current
- The mass you are moving is unique to your printer, and may be different by axis
- The friction in your printer is unique
- The moment of inertia for the lead screws, etc., etc.
This site has all the formulas. Very complex.
So this is the way I did it.
1) I first determined the maximum safe travel speed my motors will reliably produce without resonating or missing steps. My printer's move speed is not limited by my controller (32-bit Smoothieboard), but if you have an 8-bit controller then that may limit the max speed. Since I have a delta printer I used moves out near the edge of the print area where one of the motors must move the fastest. You can create a macro in Pronterface to test move speeds with moves to different X/Y coordinates formatted like this: G1 X0 Y0 F4000, where F is the feed rate in MM/min. Then I set the max speed in firmware.
2) Then I increased the acceleration in firmware, testing with the same script, until it started having missed steps. Then I backed off the acceleration by about 15%. Over time I lowered the max allowed speed (in firmware) just slightly - mostly relying on the acceleration setting. You can also set acceleration in a test script using the
M204 gcode.
3) After you have set your max acceleration, - if you use Slic3r - you can different accelerations for different kinds of moves. For example:
For this I would use the max acceleration for moves (default), Infill, and First layer. Then I use a lower acceleration for Perimeters to control ringing, and you could use a lower acceleration yet for bridging (that would give the pressure time to build so the beginning of the bridge does not fail).
The bridging acceleration above is just an example, I use something more complex with my post-processor.
Hope that helps.
My printer: Raptosaur - Large Format Delta - [
www.paulwanamaker.wordpress.com]
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