Stepstick jumpers

If you want to change step or microstep size, read on.

If you have a Mini Gerbil V2 or V2.1 then refer to the diagram below:

Photo shows jumper labels for an A4988 stepstick

That’s the MS3 on the left, followed by MS2, then MS1.

What are these mysterious MS1, MS2 and MS3 labels on the photo? They’re the jumper positions such configuring the relevant pin on the stepstick HIGH. If the black jumpers aren’t in place, then the stepstick pin is set to a LOW level.

So let’s say you’re sticking with the standard A4988 stepstick, look up the product details on a website such as https://www.pololu.com/product/1182 Under the heading that says Step size, you can see that for the HIGH, HIGH, HIGH combination, the steps are 1/16th size. That’s how your Mini Gerbil gets nice smooth steps straight from the Awesome.Tech factory.

Knee bone connects to thigh bone

If you’re replacing the A4988 stepsticks with a DRV8825 stepstick, then you’d refer to https://www.pololu.com/product/2133 It turns out that for a DRV8825, HIGH, HIGH, HIGH corresponds to 1/32 steps. You’d need to change to LOW, LOW, HIGH to retain 1/16th settings. But a DRV8825 has M0, M1 and M2 labels instead of MS1, MS2 and MS3…. I don’t know why! So look up the electrical pinout of the 8825 stepstick relative to the A4988 pinout and confirm that:

  • M0 corresponds to MS1,
  • M1 corresponds to MS2, and
  • M2 corresponds to MS3

They do, so that’s promising

Caution!

Now compare the other pins: the only difference is the A4988 requires a 5V VDD supply, whereas the 8825 has a _FAULT_ output (active low). So this should be a red alert that the pinout is incompatible, until you read further down the DRV8825 description (‘Key differences between the DRV8825 and A4988) and find out the DRV8825 Fault output has a 1.5kOhm resistor in series, to limit current flowing from a 5V VDD supply in the event an active low _FAULT_ output. Phew!

Now you’d need to check your replacement stepstick’s other relevant features, such as how to set the vRef, because it differs to the A4988. And if you don’t want to keep 1/16th step settings, then you’d need to change

More Caution!

We’re not huge fans of non-standard stepsticks, because it’s easy to get out of your technical depth for little benefit. We don’t want to be dream crushers, but…

  • If you’re hoping to supply more power with an alternative stepstick, don’t! The power for your stepper motors doesn’t just depend on the stepsticks, it depends on the Mini Gerbil, and the K40 power supply, both of which are limited. So if you want to seriously upgrade power, then connect your MG to external stepper drivers and use an external power supply.
  • If you’re hoping for more speed, that means more power, see above.
  • If you’re hoping to get ‘better performance’ from other stepsticks, tell us why in the comments below, we’re honestly interested in what specific benefits you are hoping for

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