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Is there any risk of damaging stepper motors if I set too big travel speed? What is maximum safe travel speed?
My printer is a German RepRap Neo.
I currently use 120 mm/s. Is it safe to increase this value to 200 mm/s? What would my printer do if I set very big travel speed?
Short answer no
We use stepper drivers to limit the current, the travel speed is at capped by the amount of current supplied by the stepper drivers. This prevents the stepper motors from damaging themselves. You can set 200mm/s in the slicer, but you have no guarantee that that will be reached in real life.
One thing to keep in mind though is that setting your travel speed too high can induce artifacts such: shifted layers, ghosting, uneven extrusion, etc. So the best thing is to keep the speeds within the specified limits.
What would my printer do if I set very big travel speed?
If a speed is set above the limits of the stepper, the stepper will stop rotating or stutters.
Basically there are 2 limits, the first is the limit of the board to generate the pulses to the stepper and second, how these pulses are processed by the stepper.
The speed of steppers depends on several aspects, including:
This reference gives you some more background as well as a table (which is a little optimistic for Marlin firmware) with maximum speeds. Depending on the application in your printer (stepper type, pulley size and microstepping value), it lists some maximum speeds for various boards:
What is maximum safe travel speed?
In case of an Anet A8, 1,8°; 16-teeth-GT2-pulley; 1/16 microstepping, this leads to 160 mm/s on Marlin on an Atmega microprocessor (note this is optimistic).
I currently use 120 mm/s. Is it safe to increase this value to 200 mm/s?
That depends. If you work out the mechanical and electronic details of your printer, you could look up the value you could ultimately use.
Is there any risk of damaging stepper motors if I set too big travel speed?
No there is not, the stepper will stutter or stop. I've had this with too fast retractions on an extruder stepper motor.
Stepper motors contain permanent magnets, which are only really damaged by heat. The coils in the motor are only damaged by high currents that would happen at voltages above the maximum rating of the motor. While it is possible to configure a stepper driver to send enough current into a stepper motor to damage it (either due to heat or over current), desktop 3d printer drivers do not have enough current capacity to do such damage to those NEMA 17 stepper motors. The only thing bad that will happen is that you risk over heating the driver or the components around it on the PCB causing an early failure of the parts. (Google "Temperature Cycling and Fatigue in electronics").
That aside, the only problem that you are likely to encounter is stepper stalling.
A high speed is unlikely to be reached unless you also set a high acceleration, and acceleration is generally more likely to cause a problem (unless you reach the pulse rate limit of the drivers).
High acceleration will increase vibration, and critically requires higher torque from the motors. At some point, the torque will exceed the motor/drive current capability, and the motor will skip steps. As soon as this starts to happen, your print will become unusable.
Before reaching the point of missed steps, you're likely to see other quality issues, but unless you're in a very hot environment, unlikely to see damage to the motor. Depending on the quality and heatsinking of the stepper driver, you might see overheating here (you can check for overheating of the board though).
