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I have an STP-42D132-01 stepper motor which I want to use with an A4988 / TMC2208.

So far the motor is rotating but only very very weak. There is almost no torque.

At the moment my PSU shows that the motor only takes ~300mA when driving without any load.

I was not able to find any datasheet or specs for the motor.

The only information I got is from the label:

1.8Deg/Step 12Ω

No. 20901 *

Shinano Kenshi co ltd japan

The motor is very small (3x4x4 cm) - If I assume it is a 12V motor what is a realistic drive current per phase?

Would this make any sense?

$${12\text{V}\over12\text{Ω}} = 1\text{A}$$

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  • \$\begingroup\$ "There is almost no torque" - how much torque is that, and how much do you need? What voltage are you running the TMC2208 on, and how is it set up (microsteps, hold current etc.)? \$\endgroup\$
    – Bruce Abbott
    Commented May 28, 2022 at 2:39
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    \$\begingroup\$ Similar motor but with lower resistance - jameco.com/z/… \$\endgroup\$
    – Bruce Abbott
    Commented May 28, 2022 at 2:48
  • \$\begingroup\$ Try running it at 1A and see how warm it gets (it will take a few minutes to warm up). If it feels too warm reduce current. If cool, increase the current. Motors of that size are usually good for 1-2A. \$\endgroup\$
    – Drew
    Commented May 28, 2022 at 5:59

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It is a bit crazy but it turned out that the wiring of the coils was mixed (1 off) and not connected to the correct 1A,1B / 2A, 2B pins. After changing the wiring I was able to run the motor just fine. I slowly increased up the voltage and around 6V the motor started spinning. I'll monitor current and temp to see if it can handle it.

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  • \$\begingroup\$ The A4988 has current control built in. Youd feed it your drive voltage (i believe it likes greater than 8v, i usually use 12v, and trim the current down) and set your reference voltage on the driver based on the motors spec. Or are you just running it by hand with a bench supply, and not gotten drivers yet? In which case Id advise against the A4988. There's nothing particularly wrong with it, if it's all you have it's fine, but it's like comparing a VW bug to a Lexus or a Porsche. Just spend the extra few bucks and get the Lexus. Or a closed loop s42c controller that mounts to the motor \$\endgroup\$
    – Tank R.
    Commented Sep 24, 2023 at 23:19

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