Friday, March 31, 2006

Get your motors running...

Servo-Motor Prototype

To test the mechanical system using a servomotor as the means of motion, I first had to program a PIC 18F542-ip with a basic pulse width modulation program. To that I added a pot to stand in for my IR sensor. The pot makes it easy to control the servo, and therefore the action of my quills. The linkage is a bit kludgey, but I was able to get a good feel for the potential of the servo.

In comparison with the selinoid, the servo obviously offers a greater range of motion, but the conversion from rotary motion to linear adds a little more complexity to the system. I fear this complexity—it adds to the list of things that can potentially fail. The servo I’m currently testing with is also larger than desired, so I will be sourcing smaller motors, and Danny Rozin has graciously pointed me to some of his sources.

On the positive side, the ability to finely control the position and speed of the servo offers opportunities that the selinoid didn’t. Combining the analog input of the IR sensor with the servo, I can control the deployment of the quills to correspond to the interaction of the PSS and its surroundings: if the IR detects a slowly approaching person, the servo can raise the quills slowly; if the person approaches quickly, the quills are raised rapidly. If the person backs away, the quills can “relax” and lower. This might lead to a more interesting interaction, creating a chance to play with the boundaries of personal space. The servo also allows the quills to stay deployed for as long as needed; most selinoids have a very limited amount of time that they can be powered, therefore the quill deployment would be limited as well.

The prototype also revealed the limitations of my parallel plan concept for articulation. It might be worthwhile to investigate a hinging or axeled rotation.

ServoMotorMotion

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