Pololu stepper driver board
- Please note: Pololu stepper driver boards has 0.05 ohm sense resistors instead of StepStick 0.2 ohm.
Pololu driver boards (8+8 pins):
- Pololu A4988 stepper driver - A4988-based; equivalent to A4983-board but offers overcurrent protection. If the boards get too hot, they will interrupt the current until it cools a bit. If the current is too high for the heat sinking, the motors will pulse as the current is interrupted and restored. See http://forums.reprap.org/read.php?4,116813,116832,quote=1 and its video. Try reducing the current until the pulsing stops.
- Pololu A4983 stepper driver - A4983-based; (discontinued).
Pololu driver boards with Voltage Regulators (longer boards - 8+14 pins):
- Pololu A4988 Stepper Motor Driver Carrier with Voltage Regulators - A4988-based; equivalent to A4983-board but offers overcurrent protection.
- Pololu A4983 Stepper Motor Driver Carrier with Voltage Regulators - A4983-based; (discontinued).
As Nophead has pointed out, that Pololu driver is a nice design, but with one big shortcoming: it will run hot, and is difficult to cool because it's so small. So what I've done is to design the electronics in such a way that they both perform their function and act as a physical duct for the flow from a fan to direct their own cooling. A happy side-effect of this is that the resulting PCBs are very simple, and can be made single-sided without any thin tracks. That is is why RepRap itself can make them. We must walk before we can run...
Tuning
Per the A4988 datasheet [[http://www.pololu.com/file/download/a4988_DMOS_microstepping_driver_with_translator.pdf?file_id=0J450, the calculation for the maximum trip current is:
I_TripMax= Vref/(8*Rs)
With Pololus, the sensing resistors are Rs=0.05 ohm, so a Vref of 0.4 should produce a maximum current of 0.4/(8*0.05)=1A.
As another example, aiming for 50% temperature rise on 1A rated steppers by using max 0.7A, so rearrange it as:
Vref = I_TripMax * 8 * Rs or
Vref = 0.7 * 8 * 0.05 = 0.280V
With a measured Vref of 0.273V, I should expect 0.6825A, and I measured the current through one coil as 0.486A in full step mode, which should be 0.7071 of the full trip current, or I_TripMax= 0.486/0.7071= 0.687A, which seems close enough.
The Vref signal is accessible as the "VREF" pin on the carriers with voltage regulators, as the through-hole via on the carriers without, and also as the wiper on the trim pot itself on both carriers.
For StepStick, the Rs=0.2 ohm, so you'd get 4 times the Vref at the same current.
