Servo - October 2008

the following commands:

• Wait for servo 3 to finish movement

• Move servo 3 to +90° over two seconds

This will rotate the wrist back as soon as it stops, but the arm will still stop lifting in another second, so we need to tell it to lower as soon as it finishes rising:

• Wait for servo 1 to finish movement

• Move servo 1 to - 22. 5° over two seconds

• Move servo 2 to - 67. 5° over two seconds

We can then repeat these back and forth movements until the waist reaches its destination:

objects on the Propeller Object Exchange at http://obex. parallax.com/. If you have any questions, ideas, or other points to discuss, please post them in the Propeller Chip forum at http://forums.parallax.com/forums/default. aspx?f= 25.

With eight processors on the Propeller, there is still plenty of power left for other tasks. Next month, Kevin McCullough will add stepper motor control, and after that Chris Savage will be back with PWM control. This will only be the work of three people, but the best part about open-source projects is that the work is done by the community as a whole. I have more features that I would like to add, but my question is what will you make it do? Post your ideas and additions, and let’s see what develops. SV

• Wait for servo 3 to finish movement

• Move servo 3 to -90° over one second

• Wait for servo 1 to finish movement

• Move servo 1 to - 67. 5° over one second

• Move servo 2 to - 22. 5° over one second

• Wait for servo 3 to finish movement

• Move servo 3 to 0° over one second

By programming the servo controller to postpone some commands until others have been completed, all of the timing can be performed internally. As an added benefit, the microcontroller sending the commands does not need to send them as often, and as long as the queue is not depleted, the timing of the servos does not need to be based on when commands are sent.

The servo controller firmware, its source code, and a more detailed description of the commands are available from Parallax’s website at www.parallax.com/tabid/666/ Default.aspx. I will also post related

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Resources

Project Page — www.parallax.com/tabid/666/ Default.aspx

Parallax, Inc. — www.parallax.com/

Propeller Object Exchange —

http://obex.parallax.com/

Robotics Discussion Forum —

http://forums.parallax.com/ forums/ default.aspx?f= 10

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