Motor Shield V2

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zachary3352
 
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Motor Shield V2

Post by zachary3352 »

Hi Everyone,

I am building a 3D scanner for my school. Currently, I am building a machine to move my laser pointer up and down. I am using a Nema 17 stepper motor. It is a Kysan 1124090, and it is available here: http://printrbot.com/shop/large-kysan-motor/. I am also powering the project with an arduino uno.

The motor is 4.2 volts, and the page for the motor shield says that any motors used must be 5 volts or above. Does this matter for my project?

I would like to power two of these motors as well as an end-stop available here: http://printrbot.com/shop/18-end-stop/. The end-stop isn't needed, but I would love to be able to use it.

Is what I'm doing possible? If so, how would I do this? What code would I run on the arduino?

Thanks,
Zach

PS: I apologize if anything I wrote was not correct. I am inexperienced with electronics and trying to learn as much as I can.

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Franklin97355
 
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Re: Motor Shield V2

Post by Franklin97355 »

The current draw of that motor is too high for the motor shield. Something like this would be more appropriate https://www.adafruit.com/product/1750

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adafruit_support_bill
 
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Re: Motor Shield V2

Post by adafruit_support_bill »

Stepper motors with very low phase resistance such as that one are not a good match for a constant-voltage driver such as the Motor Shield V2. They require a current limiting driver to achieve good performance.
See this guide for more details:
https://learn.adafruit.com/all-about-st ... he-stepper

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zachary3352
 
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Re: Motor Shield V2

Post by zachary3352 »

Thanks for your replies!

Is there a different driver (maybe not so expensive) that Adafruit makes that could drive these two motors?

Also, I'm still confused about the voltages. Since I'm new to electronics, would someone please explain to me how 4.2 volts draws more power than 5 volts? That would be great.

Thanks again for the quick replies!
-Zach

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adafruit_support_bill
 
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Re: Motor Shield V2

Post by adafruit_support_bill »

Also, I'm still confused about the voltages. Since I'm new to electronics, would someone please explain to me how 4.2 volts draws more power than 5 volts? That would be great.
You can blame the motor manufacturer there. The specifications are somewhat misleading:

Rated Voltage: 4.2 V
Current / Phase: 1.5 A
Resistance Per Phase: 2.8 Ω± 10%
These specs describe a steady-state condition where you are delivering a fixed voltage to a purely resistive load.
And using ohm's law: V=IR, 4.2v does indeed equal 1.5A * 2.8 ohms.
However, the motor was not really designed to operate at that voltage and will not perform very well if you try. Motors in motion are not purely resistive loads.
To achieve the torque and speed that the motor was designed to deliver, you need to use a higher drive voltage. But to do it safely, you need to use a current limiting driver. What the spec says is that the current limiting driver should be set to 'chop' at 1.5A to avoid damage to the motor. In a 'holding torque' situation, that would mean that the driver is delivering 4.2v into a 2.8 ohm phase resistance for a safe current level of 1.5A.
The principles behind that are described here: https://learn.adafruit.com/all-about-st ... he-stepper

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zachary3352
 
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Re: Motor Shield V2

Post by zachary3352 »

Hi,

Thanks for the response!

Would you be able to help me find a variable voltage driver that would work with these motors? It also needs to work with an arduino or similar board.

Thanks again,
Zach

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adafruit_support_bill
 
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Re: Motor Shield V2

Post by adafruit_support_bill »

The Synthetos gShield recommended by Franklin in a previous post is a very good choice. There are also some good options form www.pololu.com

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