A4998 Driver Problem

hi guys,

I am using A4998 stepper driver to drive NEMA 14 stepper motor.

My problem is that when I touch the driver(probably crystal) my motor works, but after a few loop it stops and vibrates little, and stops until I touch again.It works unstable.

I use this instructions :
howtomechatronics.com/tutorials/ … d-arduino/

What can I do to solve the problem?

What are the motor specifications (coil resistance and coil current rating)? Can you post a link to the data sheet?
What are the voltage and current ratings of the motor power supply?
To what value did you set the current limit of the A4988?
Do you have all the grounds connected together?

This is the datasheet of motor: pololu.com/product/1208

I use 11,1V Lipo Arduino and Vmotor directly connected to battery.

I use 7805 for 5v, A4998’s Vdd port connected to 7805 output.

current limit is 500mA, i arrange it by setting vref 0,2v.

between Vmotor and ground there is a capacitor value is 50uf. GND is connected input of the 7805 board.
Other gnd which is near vdd conencted to output of the 7805 board.

I don’t see anything obviously wrong, but with that motor you don’t need to worry much about the current limit – it will draw about 500 mA even if you connect it directly to the battery. The current limit you set on the driver board may actually be a bit low.

The program on the web site attempts to drive the motor at 1000 steps/sec, which is quite fast without acceleration and may be too fast for that motor. Change the delays in the step loop to several milliseconds for testing.