POP-BOT motors rotate at different rates

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POP-BOT motors rotate at different rates

Post by marksmall » Fri Dec 04, 2009 12:57 am

Post by marksmall
Fri Dec 04, 2009 12:57 am

Hi,

I just recently bought this item from robosavvy, this is my first intoduction to robots. Anyway, the problem I'm having is that I followed the building instructions in the manual

http://robosavvy.com/RoboSavvyPages/Ine ... minary.pdf

Anyway, no matter what I do, the wheel motors do not spin at the same rate, making the bot veer to one side. It is the same motor, no matter which terminals I plug the connectors into or which way round.

Is this normal, if so, I'm suprised the manual didn't mention it and what I need to get to fix it.

Anyway, any help would be great, cheers.

MARK
Hi,

I just recently bought this item from robosavvy, this is my first intoduction to robots. Anyway, the problem I'm having is that I followed the building instructions in the manual

http://robosavvy.com/RoboSavvyPages/Ine ... minary.pdf

Anyway, no matter what I do, the wheel motors do not spin at the same rate, making the bot veer to one side. It is the same motor, no matter which terminals I plug the connectors into or which way round.

Is this normal, if so, I'm suprised the manual didn't mention it and what I need to get to fix it.

Anyway, any help would be great, cheers.

MARK
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POP-bot motor rates

Post by Sparky » Sat Jan 09, 2010 11:45 am

Post by Sparky
Sat Jan 09, 2010 11:45 am

I have also just bought a POP-bot and have found exactly the same thing.
Is it something to do with the accuracy of the PWM?

Anyone know a simple way to 'trim' the speeds so that the robot moves in a straight line?
I have also just bought a POP-bot and have found exactly the same thing.
Is it something to do with the accuracy of the PWM?

Anyone know a simple way to 'trim' the speeds so that the robot moves in a straight line?
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Post by PedroR » Wed Jan 13, 2010 5:21 pm

Post by PedroR
Wed Jan 13, 2010 5:21 pm

Hi Sparky

Please send me an email to pedro at robosavvy dot com with your order number so I can investigate your issue.

In the case of Mark, we have replaced his DC motor that was spinning slowly.

We may need to replaced yours as well.

It's interesting because we've sold plenty of those (and other models that use the same motors) but only now we have seen such an issue.
In any case let me know the details and I will get back to you.

Regards
Pedro
Hi Sparky

Please send me an email to pedro at robosavvy dot com with your order number so I can investigate your issue.

In the case of Mark, we have replaced his DC motor that was spinning slowly.

We may need to replaced yours as well.

It's interesting because we've sold plenty of those (and other models that use the same motors) but only now we have seen such an issue.
In any case let me know the details and I will get back to you.

Regards
Pedro
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Post by PedroR » Wed May 02, 2012 10:35 am

Post by PedroR
Wed May 02, 2012 10:35 am

Hi all

Just a quick stop to share an update and the work around for this issue.

The behavior where both motors don't spin exactly at the same speed when PWM'd with the same value is kind of expected in the POPbot (and for that matter in any Robot that uses DC motors without wheel encoders).

Due to the way DC motors are manufactured it is expected that there are small differences in speed between DC motors (that's usually why the specs are given" +- x%")

The way to work around the issue is to compensate the differences in code: if one motor is spinning faster than the other you can modify the code to reduce the PWM value of the motor that's spinning faster.
This should compensate and adjust the speed.

If the difference in speed is too large (let's say over 25%) than it may be worth contacting us to get a replacement.

Regards
Pedro.
Hi all

Just a quick stop to share an update and the work around for this issue.

The behavior where both motors don't spin exactly at the same speed when PWM'd with the same value is kind of expected in the POPbot (and for that matter in any Robot that uses DC motors without wheel encoders).

Due to the way DC motors are manufactured it is expected that there are small differences in speed between DC motors (that's usually why the specs are given" +- x%")

The way to work around the issue is to compensate the differences in code: if one motor is spinning faster than the other you can modify the code to reduce the PWM value of the motor that's spinning faster.
This should compensate and adjust the speed.

If the difference in speed is too large (let's say over 25%) than it may be worth contacting us to get a replacement.

Regards
Pedro.
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