Output current StepStick A4988

[kf1965]

Stepper motors do not develop torque and speed (skip steps.)
It turned out that the board are 0.2 Ohm series resistor instead 0.05Om.
Uref(max =1.5V) raise 4 times with trim potentiometer also failed. Uref takes from midle point from max 8,6 kOhm to ground and 20kOhm to +5V.
ITripMAX = VREF / ( 8* RS)= 1.5/(8*0.2)=0.93A(0.65A in fullstep mode).Your board does not produce a current of 1 A, 2 A to the declaration.
How do I get at least 1.5A?

Konstantin.

[techsupport]

Hi friend

The standard A4988 stepstick has a 0.2 ohm sensor resistor MS1, MS2 instead of pololu step driver 0.05 ohm, according the equation below

VREF max = (TrimpotMaxR/(TrimpotMaXR+R1)) x VDD=5(10,000/10,000+20,000)=1.66
ITripMAX (effectively max motor current) = VREF max / ( 8 x Sense_resistor) =1

The result is that the standard A4988 stepstick with 0.2ohm sensor resistor will produce approximately 1A current maximum. The way to increase the current is decrease the value of R1 and sensor resistor.

Regards,
techsupport

[kf1965]

1. TrimpotMaxR = 8.6kOhm instead 10000( but I'm not extract Trim Pot)
2. In full step mode Iout = 0.7071Imax(page 14 Datasheet A4988)
result 0.6A

I'm soldering || 8.2kOhm to 20kOhm (in photo 822)

Konstantin.

[techsupport]

It seems to increase R1 to 30K ohm and decrease sense resistor to 0.1ohm is the best solution according to http://www.reprap.org/wiki/Stepstick