Hello
I have three NEMA 17 motors 17HS3401 that need to run at the same speed. I use three A4988 Pololu drivers for them. They are mounted on an Arduino shield. The motor power supply is 12V.
I set the current limit on all three controllers to 1.04V (1.3A80.1).
The program is simple, set the same direction on all three motors, then enable and give them all identical clocks. The motors do not run at the same speed. Where am I wrong?
Sorry about my english.
Hello.
It sounds like you are setting the VREF voltage to 1.04V on our A4988 carrier, which would configure the current limit to over 1.8A! I’m not sure where the 0.1 comes from in your equation, but as mentioned on the product page, you can use the following equation to calculate VREF:
V_{REF} = 8 \times I_{MAX} \times R_{CS}
Where R_{CS} is 0.068Ω for boards manufactured since 2017. So, to set the current limit to 1.3A (which it looks like you’re trying to do):
V_{REF} = 8 \times 1.3 \times 0.68
V_{REF} = 0.7
However, please note that you should only set the current limit that high on our A4988 carriers if you are using full-step mode. (Otherwise, you should keep the current under 1A per phase for the original A4988 carrier or 1.2A per phase for the black edition.)
As for the problem you are describing, if you are stepping the boards at the same rate and the motors are going different speeds, then the three things I suggest checking first are:
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make sure the stepper motor drivers are properly soldered and making good electrical connections.
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make sure they are all in the same microstepping mode (some stepper motor shields might default to different microstepping modes for the different motor channels). The microstepping mode is set using the MS1, MS2, and MS3 pins as described on the product page.
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make sure the motors are not skipping steps (ramping the step rate up to speed and slowing down the maximum step rate could help).
If you continue to have problems, could you post more details about your setup (such as links to the stepper motors, shield, and power supply you are using) as well as pictures of your setup that show all of your connections?
Brandon
Thanks for the quick response!
In the meantime the problem has been solved, it was a defective Arduino UNO board.
Secondly, on my A4988 drivers the resistors are 0.1 ohm so that’s how I came up with the formula 1.3x8x0.1=1.04
Ok, now the motors spin correctly but I had another problem, namely when I reset the Arduino the motors shudder. I solved that by adding a 10kOhm pullup to Enable.
Now I’m satisfied, everything works OK for me.
Thanks again, you can lock the topic.