Parts needed

There are four basic parts that are needed for this system -

• Motor (to apply torque and apply tension on the string)
• Rotary encoder (to measure length of string)
• A stiff string
• A controller board (to control the torque with a computer)

The goal is to build the system as cheaply as possible. I called maxonmotors and just the motor and encoder cost $155 each! My goal is less than $100. Possibilites are -

Motor and encoder

1. Scavenged disk drive actuators

• http://www.epanorama.net/circuits/diskstepper.html
• http://www.storagereview.com
• Opening up a hard drive

String

1. Fishing cables
2. Guitar strings

Controller

1. Make your own board and connect it to your parallel port

This circuit has proven useful when interfacing my computer to home made robotics. It is easy to build and use and it can control two DC motors of any current or voltage rating, depending on the rating of the relays. The circuit also provides two shaft encoders for positional feedback to the computer.

Electronics Australia, October 1994, pp.51

• http://www.geocities.com/SiliconValley/Lakes/7156/articl2.htm
• http://www.epanorama.net/links/motorcontrol.html
  
• http://tos.maintree.com/titivillus/hardware.asp#hardware