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Fine Tuning for A4988 on 2.1?

Posted by dlamet 
Fine Tuning for A4988 on 2.1?
December 02, 2022 12:25PM
Hello. I'm just setting up a RAMPS 1.4. board with my first axis (Z). Is it possible to fine tune behavior to a motor with the A4988 driver? Parameters such as steps / mm, acceleration, and holding torque?


Re: Fine Tuning for A4988 on 2.1?
December 02, 2022 06:32PM
Parameters like steps per millimeter, and acceleration, are set in the configuration.h and configuration_adv.h files used to compile Marlin. If the A4988 drivers are in sockets and can be removed (they should be on a RAMPS), there are 3 jumpers under the drivers that set the microsteps. When all three jumpers are in place (as they should be, unless you have odd requirements), the microsteps are set to 16, which Marlin will need to know.

Make DAMN sure you plug the A4988 back into the RAMPS the correct way, or it's toast!

The A4988 motor drivers are not configurable via software or firmware, so things like drive current and holding torque can only be adjusted with the tiny trim-pot on the A4988 board itself to set Vref appropriately for the stepper being driven. This should be checked anyway, as the settings are unique for each motor type. A good place to start is 50% to 75% of the stepper's rated current. You will also need to know the value of the Vref resistor on the A4988 board, as it is critical for calculating the correct Vref value, and the resistor value varies between A4988 driver board manufacturers. The tiny trim-pots tend to be wickedly sensitive, so take your time.

Part numbers for the steppers, and the value of the Vref resistor (or the name and source of the A4988 board manufacturer) would help us make specific recommendations for setting Vref.
Re: Fine Tuning for A4988 on 2.1?
December 02, 2022 06:33PM
"steps / mm, acceleration", yes

"holding torque" not with firmware for a4988

All you realy have is setting the current via the variable resistor

Edited 2 time(s). Last edit at 12/03/2022 06:27PM by Dust.
Re: Fine Tuning for A4988 on 2.1?
December 03, 2022 01:09PM
Great answers, folks. I didn't see anything in the config files, but was sure something for the A4988 had to be there. I guess not. Now considering whether the pots & jumpers are sufficient but also looking at the TMC2130.

Much appreciated !
Re: Fine Tuning for A4988 on 2.1?
December 08, 2022 12:47AM
The TMC2130 is a great choice because it is a SPI stepper driver which allows comfortable plug-in onto SPI stepper driver compatible boards and configuration in firmware. But the RAMPS 1.4 is not a SPI stepper driver compatible component. Please consider the SPI compatibility of your mounting board before you pick a SPI stepper driver!

Martin Turski, company owner of EirDev

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