dc motor control for a balancing platform (segway)

Posted by Boniq on August 26, 2009, 2:53 pm

I have just bought an arduino microcontroller and as one of my first
projekts I would like to make a small self balancing platform like
segway (but tiny one). There is a dc motorcontroller add on to arduino
that lets me control two motors (a motor shield). It seems to me that
the only thing you can control with any of the shelf controllers is
motor speed. But if the platfor is a bit out of balance a would like
to stter the motor torque to get it back in balance. Not the speed.
The speed would naturally follow. Does that make sense? But how do you
control the torque output of (any) dc (brushless?) motor?? Or am I
way of here...

Boniq

Posted by D Herring on August 26, 2009, 9:28 pm

Boniq wrote:

> I have just bought an arduino microcontroller and as one of my first
> projekts I would like to make a small self balancing platform like
> segway (but tiny one). There is a dc motorcontroller add on to arduino
> that lets me control two motors (a motor shield). It seems to me that
> the only thing you can control with any of the shelf controllers is
> motor speed. But if the platfor is a bit out of balance a would like
> to stter the motor torque to get it back in balance. Not the speed.
> The speed would naturally follow. Does that make sense? But how do you
> control the torque output of (any) dc (brushless?) motor?? Or am I
> way of here...

I think you're on the right track. If you can calculate the angular
offset from vertical (e.g. with an ADXL accelerometer), then you can
calculate and apply a correcting torque.

These links show the sensors and control strategy used by another
balancing bot.
http://coecsl.ece.uiuc.edu/ge423/spring04/group9/objectives_sensors.htm
http://coecsl.ece.uiuc.edu/ge423/spring04/group9/technical_control.htm

- Daniel

Posted by GregS on August 27, 2009, 9:10 am

>I have just bought an arduino microcontroller and as one of my first
>projekts I would like to make a small self balancing platform like
>segway (but tiny one). There is a dc motorcontroller add on to arduino
>that lets me control two motors (a motor shield). It seems to me that
>the only thing you can control with any of the shelf controllers is
>motor speed. But if the platfor is a bit out of balance a would like
>to stter the motor torque to get it back in balance. Not the speed.
>The speed would naturally follow. Does that make sense? But how do you
>control the torque output of (any) dc (brushless?) motor?? Or am I
>way of here...

Torque is controled by the drivers. if the motor has its own
drivers, you have little control or a fixed amount of available drive.
A DC brush motors torque is controlled by the loop gain of the drivers
assuming you have plenty of drive. The loop
is the driver, motor, and position feedback.

greg

Posted by Boniq on August 28, 2009, 6:05 am

Thank you very much for valuable feedback :-) Its great to be able to
aske people.

There seems to be something called a "torque motor"
also that might be useful. Lets say if one stand still in a slope on a
segway the motor must be able to produce constant torque even in it
doesnt turn.

Boniq

Posted by D Herring on August 28, 2009, 9:37 am

Boniq wrote:

> Thank you very much for valuable feedback :-) Its great to be able to
> aske people.
>
> There seems to be something called a "torque motor"
> also that might be useful. Lets say if one stand still in a slope on a
> segway the motor must be able to produce constant torque even in it
> doesnt turn.

Torque motors are good, but generally expensive. They aren't needed
for most systems like this. Just don't stop on steep slopes. :)

- Daniel

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