CNC SHIELD + ARDUINO UNO + A4988 + NEMA 17

Hi and sorry for my English.
I tried this setup. I powered the CNC at 12V. The motors, without load, run regularly. If I try to connect a peristaltic pump, for example, they can no longer rotate. Can anyone help me solve this problem?
Thank you and good job to everybody.

Salve e scusate per il mio inglese.
Ho provato questa configurazione. Ho alimentato la CNC a 12V. I motori, senza carico funzionano regolarmente. Se provo a collegare una pompa peristaltica, per esempio, Non riescono più ad eseguire la rotazione. Qualcuno può aiutarmi a risolvere questo problema?
Grazie e buon lavoro a tutti.

What does it say on the rating plate of the motor?

@BigGiu

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BigGiu:
I tried this setup. I powered the CNC at 12V. The motors, without load, run regularly. If I try to connect a peristaltic pump, for example, they can no longer rotate. Can anyone help me solve this problem?

Please post a link to the datasheet for your stepper motor. There are hundreds of different Nema 17 motors.

...R

Post your code. Read the how get the most out of this forum sticky to see how to properly post code. Remove useless white space and format the code with the IDE autoformat tool (crtl-t or Tools, Auto Format) before posting code.

Did you set the coil current limits properly? This Pololu page shows how.

Are you using acceleration? Motors cannot go from a dead stop to higher speeds without acceleration.