Is My Stepper Motor and Driver Compatible?

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JJMoney
 
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Is My Stepper Motor and Driver Compatible?

Post by JJMoney »

Recently, I bought a motor driver and stepper motor only to realize the driver wasn't rated for the required current of my motor. Before I buy a new driver, I would like to be extra sure my setup is sound! Links to my proposed setup are below:

Stepper motor
Driver

This will be used with a Raspberry Pi 3 Model B V1.2 and a power supply that delivers 12V at 2A.

Additional questions:
1. Is there a way I can calculate the RPM of my stepper with this setup? Keep in mind the 51:1 gearbox.
2. Are there any Python libraries that allow for easy interfacing with this stepper driver?
Last edited by JJMoney on Mon Dec 26, 2022 4:51 pm, edited 1 time in total.

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Re: Is My Stepper Motor and Driver Compatible?

Post by adafruit_support_bill »

Before I buy a new driver, I would like to be extra sure my setup is sound! Links to my proposed setup are below:
The Amazon link for your motor does not work. However, the current limiting on the Pololu driver is adjustable, so it should work with a wide variety of motors.
1. Is there a way I can calculate the RPM of my stepper with this setup? Keep in mind the 51:1 gearbox.
The motor specs should tell you how many steps per revolution for the motor (for a 1.8 degree motor, that will be 200 steps).
Multiply that by your gearbox ratio to get the number of steps per revolution of the output shaft (e.g 200 * 51 = 10200).
The final RPM will be the number of steps per second times 60, divided by the steps per revolution.
2. Are there any Python libraries that allow for easy interfacing with this stepper driver?
There are a few Python stepper libraries out there. We don't have any firsthand experience with the driver you are using. But the folks at Pololu may be able to point you to one that is known to work with their board.

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JJMoney
 
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Re: Is My Stepper Motor and Driver Compatible?

Post by JJMoney »

adafruit_support_bill wrote: Mon Dec 26, 2022 4:48 pm
Before I buy a new driver, I would like to be extra sure my setup is sound! Links to my proposed setup are below:
The Amazon link for your motor does not work. However, the current limiting on the Pololu driver is adjustable, so it should work with a wide variety of motors.
1. Is there a way I can calculate the RPM of my stepper with this setup? Keep in mind the 51:1 gearbox.
The motor specs should tell you how many steps per revolution for the motor (for a 1.8 degree motor, that will be 200 steps).
Multiply that by your gearbox ratio to get the number of steps per revolution of the output shaft (e.g 200 * 51 = 10200).
The final RPM will be the number of steps per second times 60, divided by the steps per revolution.
2. Are there any Python libraries that allow for easy interfacing with this stepper driver?
There are a few Python stepper libraries out there. We don't have any firsthand experience with the driver you are using. But the folks at Pololu may be able to point you to one that is known to work with their board.
Sorry, I fixed the link! This stepper looks like a 1.8 degree motor (without the gearbox). 10,200 steps per revolution seem correct with the gearbox then. Is steps per second a common metric found on stepper datasheets? I don't see it listed.

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Re: Is My Stepper Motor and Driver Compatible?

Post by adafruit_support_bill »

The steps per second is whatever you program it to be. The maximum achievable step rate for your system will depend on a number of factors, including motor, driver and power supply characteristics, as well as the load you have attached to the output shaft.

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Re: Is My Stepper Motor and Driver Compatible?

Post by JJMoney »

adafruit_support_bill wrote: Mon Dec 26, 2022 5:06 pm The steps per second is whatever you program it to be. The maximum achievable step rate for your system will depend on a number of factors, including motor, driver and power supply characteristics, as well as the load you have attached to the output shaft.
I see. Is there any way I can calculate the maximum step rate for my system? I know the required torque to perform the job is ~400 oz-in and I'll be supplying 12V at 2A. With these in mind, could I at least ball-park the maximum achievable step rate?

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Re: Is My Stepper Motor and Driver Compatible?

Post by adafruit_support_bill »

Is there any way I can calculate the maximum step rate for my system?
Stepper motor torque decreases with increasing step-rate. A complete manufacturer's motor spec will typically include a torque vs. step-rate graph. This will be calculated at a specific supply voltage. Lower voltages will result in less torque and a slower top-speed.

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Re: Is My Stepper Motor and Driver Compatible?

Post by JJMoney »

adafruit_support_bill wrote: Mon Dec 26, 2022 7:23 pm
Is there any way I can calculate the maximum step rate for my system?
Stepper motor torque decreases with increasing step-rate. A complete manufacturer's motor spec will typically include a torque vs. step-rate graph. This will be calculated at a specific supply voltage. Lower voltages will result in less torque and a slower top-speed.
One thing I'm a bit confused about when I look at this motor's torque curve is that the pull-out torque seems much higher than the motor's holding torque and max. permissible torque. Shouldn't the holding torque be the highest? Holding torque is the load the motor can support when it's not moving, correct? If I want to be sure of the torque this motor can handle when moving, which number should I be looking at?

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Re: Is My Stepper Motor and Driver Compatible?

Post by adafruit_support_bill »

Motor specs are sometimes ambiguous and often confusing. In this case, I suspect that the "Max Permissible Torque" is a property of the gearbox - not the motor itself.

The mechanical advantage of the gear reduction multiplies the raw torque of the motor. And with a 51:1 ratio, it is likely that the motor is capable of producing more torque than the output shaft can safely handle.

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Re: Is My Stepper Motor and Driver Compatible?

Post by JJMoney »

adafruit_support_bill wrote: Mon Dec 26, 2022 8:03 pm Motor specs are sometimes ambiguous and often confusing. In this case, I suspect that the "Max Permissible Torque" is a property of the gearbox - not the motor itself.

The mechanical advantage of the gear reduction multiplies the raw torque of the motor. And with a 51:1 ratio, it is likely that the motor is capable of producing more torque than the output shaft can safely handle.
Makes sense! So should I just assume that the 4Nm torque is what my motor is overall capable of?

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Re: Is My Stepper Motor and Driver Compatible?

Post by adafruit_support_bill »

That would be a reasonable assumption.

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