Motor Shield V2 Low Voltage Output

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shadowck5000
 
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Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

I purchased the motor shield V2.3 (https://www.adafruit.com/product/1438) and am having unexpected voltage output when driving a DC motor.

I am using USB power for the Arduino and a variable voltage/amperage lab PSU to drive the motor shield. I have confirmed the input voltage is 12v, however the output voltage is only ~4.5v.

I am just running the sample code to drive one motor at 100% found here: https://learn.adafruit.com/adafruit-mot ... -dc-motors

Am I doing something wrong or is there a problem with the shield?

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adafruit_support_bill
 
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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

Please post some photos showing your soldering and connections to the shield.

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

Thanks for assisting.

Here are some photos: https://goo.gl/photos/1SerdwDoSi1n8bqh7
Please let me know if you want different angles or something more specific.

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adafruit_support_bill
 
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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

That all looks OK from what I can see. What is the motor you are trying to drive with this?

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

I have a number of motors I am trying out, however it is not specific to one. Measuring the voltage right at the M1/M3 headers I get the 4.5v instead of 12 without any motor attached.

Example motors:
https://www.amazon.com/gp/product/B01KTZXZMK
https://www.amazon.com/gp/product/B01N0UUMUW
https://www.amazon.com/gp/product/B00EDMIH7E

I had measured M1 and M3 thinking that maybe there was a problem with the M1/2 headers but both have the same issue.

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adafruit_support_bill
 
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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

Unfortunately, the specifications for those motors omit the most important data point. We need to know how much current they draw at 12v.

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

Sorry about that, for one of the 12v motors, it draws .05A no load, and .25A under load. Measured hooking directly to the PSU.

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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

OK. That should be no problem.

With the 12v supply connected, measure the voltage between the left side "VIN Jumper" pin and GND.

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

I get 4.41v across VIN and GND regardless of if the PSU is on or off and the Arduino is on, and 0v when the Arduino is off.

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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

Hmmm. And what do you measure between the right-side VIN jumper pin and GND?

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

Was not entirely sure what VIN you were referring to, so here is a diagram of what voltages I get where, and if the Arduino is powered by USB or not.
Let me know if there is a measurement I missed.

To confirm my understanding of the VIN jumper, it should not be connected when using a different PSU for the motors correct?
adafruit_motorcontroller_voltages.png
adafruit_motorcontroller_voltages.png (835.02 KiB) Viewed 874 times

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adafruit_support_bill
 
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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

OK. So you are getting 12v through the reverse voltage protection MOSFET. That sounds normal.

Looking back at your earlier post...
I am just running the sample code to drive one motor at 100%
Can you post the code you are actually using? This code:

Code: Select all

myMotor->setSpeed(100); 
Is not 100%.
To get 100% duty cycle, you need to do:

Code: Select all

myMotor->setSpeed(255); 
setSpeed(100) would give you about 39% or 4.7v.

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

Wow I think I am about to feel silly. I was using myMotor->setSpeed(100); not 255.

Is it using PWM to reduce the average output to 4.7v? A guess my DMM is just reading that as the average.

At work right now, but will confirm this when I get home later.

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Re: Motor Shield V2 Low Voltage Output

Post by adafruit_support_bill »

Most DMMs will integrate over a few hundred milliseconds, so a less than 100% PWM duty cycle will just appear as a lower voltage.

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shadowck5000
 
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Re: Motor Shield V2 Low Voltage Output

Post by shadowck5000 »

Thank you so much for the assistance you provided. You were correct, once I changed the motor speed to 255 from 100 I was getting the full 12 reading and driving the motor at full power.

I would recommend potentially changing this value in the example docs to something besides 100 to avoid this confusion, but carefully re-reading the docs would have also solved my problem.

You have certainly earned one long time customer because of your support.

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