The Twiddler: A Haptic Teaching Tool: Low-Cost Communication and Mechanical Design

The previous haptic interface in the research lab was prohibitively expensive for distribution to a class of students and required a specialized Input/Output board. In order to solve these problems a new device was designed with the stipulations that its interface did not require an I/O board and that it have half the power of the previous device and cost less than \$400cdn. The resulting design is called the Twiddler. The Twiddler is a single degree of freedom rotary haptic device. An electronic box and an electric DC motor make up the Twiddler. The electronic box reads the current rotational position of the motor sends it to the host PC through the Parallel Port. The algorithm for the output force command as a function of the position is easily accessed and changed on the host PC to make prototyping and development simple. The host sends the command through the Parallel Port back to the electronic box. The command is converted to a motor driving signal and sent to the motor. This loop happens ever millisecond so that reliable haptic forces can be simulated on the rotational axis of the motor. The parts for the Twiddler cost approximately $400 and the peak torque output is approximately 0.04 Nm (or six oz-in). The software, mechanical and electrical designs are freely available for reproduction.