Motorshield V2 Stepper Motors Skipping

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pyrohmstr
 
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Motorshield V2 Stepper Motors Skipping

Post by pyrohmstr »

I have one of these kits assembled and I'm fairly certain it's all put together correctly. http://www.lightobject.com/Lite-400600- ... -P715.aspx The serials on the steppers are 17HW4410N-01AD and 17HW4410N-02AD but I can't find datasheets for them online.

I also have an Adafruit Motorshield V2 which I believe is assembled correctly. I've checked every solder joint and it all looks just fine.

My problem is that when I upload and run a simple sketch to just run a single motor (the Y motor @ 1.2A) the motor will go for a few steps, stop, and then start again. It doesn't matter what motor block I use, both have the same behavior. The frequency of this start and stop cycle will increase over the course of about a minute. During this time, the power LED on the board is a solid, bright green and doesn't flicker. I'm powering the shield independently from the board with a 12V 3A wall-wart power supply.

The smaller X motor will run fine if it's the only one plugged in, but if the shield is holding the Y motor while trying to step the X motor the power LED will flash and the motors will just tick.

The controller ICs get VERY hot. They have small aluminum heat sinks on them, but they get too hot to touch in about 10 seconds (I mean hot enough that I reflexively pull away from them and they still leave burn marks on my fingers). I know the datasheet for these things say they'll get hot, but this seems out of the ordinary. I've checked and their connections to the board look good.

I've tried both motors on both controller chips and it doesn't seem to make a difference. I've also tried to step the motors as 1 step in a for loop and as a large number of steps in one motor->step statement, the motor seems to skip the same way. Changing the motor motor->setSpeed( ) statement doesn't seem to make a difference either.

So this seems like it might be an overheating/power issue. Can the shield, although rated at 1.2A, not really handle that? Could there be something wrong with the ICs causing them to heat up so much? Is it possible that I've burned out the ICs somehow by letting them overheat before I noticed an issue? Is a 12V 3A power supply appropriate here?

Basically I'm wondering if I should buy a replacement adafruit motorshield V2 (for instance if I broke this one somehow), or if I need to look to more powerful pastures for these steppers.

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adafruit_support_bill
 
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Re: Motorshield V2 Stepper Motors Skipping

Post by adafruit_support_bill »

(the Y motor @ 1.2A)
1.2A is only 1/3 of the spec. We need to know either the rated voltage or the coil resistance too. According to Ohm's Law: V=IR. Since the coil resistance is fixed, if you increase the voltage, the motor will draw more current. From the sounds of it, the motors are drawing more than 1.2A @ 12v.

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pyrohmstr
 
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Re: Motorshield V2 Stepper Motors Skipping

Post by pyrohmstr »

I measure the coil resistance as 4.3 Ohm for the motor rated as 1.2A and 18 Ohm for the .6A rated motor. I can see how putting 12V (or the ~10V after the power chip) to the 1.2A motor would be more than the rated 1.2A.

Am I looking at a gShield chopper driver here? Am I just trying to force this motor shield to do something it isn't designed for?

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adafruit_support_bill
 
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Re: Motorshield V2 Stepper Motors Skipping

Post by adafruit_support_bill »

I measure the coil resistance as 4.3 Ohm for the motor rated as 1.2A
Sounds like that motor was designed for high torque/high speed. To achieve that performance level, you need to use a constant-current 'chopper' drive that is configured to match. The motor shield is a constant voltage driver. It works well with a lot of the smaller, general-purpose or hobby-grade steppers with no special configuration. The gShield would be a better choice to drive your motor.

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