HAptic GUidance System (HAGUS)

The HAptic GUidance System (HAGUS) is a device that I designed and built for my Master's thesis at the Media Lab.  It began as a re-thought and re-designed version of the FielDrum, but ended up as a separate project.  The underlying idea is the same as with the FielDrum: to explore the effect that physical guidance has on motor learning, but the devices are quite different.  Whereas the FielDrum uses magnets for actuation, HAGUS uses a servo motor.  There were a number of reasons why I decided to switch to a servo-based system, the most important of which was accuracy.  I found it extrememly difficult to get the kind of control and measurement precision using electromagnets that are relatively easy to get out of a servo, encoder, and gears.  

HAGUS was designed to be used in a set of experiments to be conducted this summer.  It can "record" and "playback" single-axis rotational motions that approximate those that the wrist is involved with during percussion performance.  The design is fairly straightforward.  A smallish servo motor (40W) turns a shaft which runs to an electromagnetic particle clutch.  The clutch is needed for "recording mode" where you want as little mechanical impedance presented to the user as possible.  Particle clutches are a nice solution since they're electromagnetic and can therefore be operated with control logic and they offer a consistent and predictable (and linear) holding torque profile.  The output of the clutch then runs through a high-precision (2000 line quadrature = 8000 ticks per revolution = .045 degree resolution) optical encoder and on to the drive gear.  The 20 tooth drive gear then drives a section of 80 tooth gear which is connected  to a drumstick.  In "playback" mode, the encoder is used by the control electronics (motion control hardware from Jeffrey Kerr, LLC) in the PID feedback loop.  In "recording" mode, it's simpy used to read the position of the drumstick at a high sampling rate (60Hz).

This shows the drumstick, gearing, and optical encoder.	The entire actuator (drumstick, gearing, encoder, clutch, and servo motor.	The control electronics (SERVO-SC board, SSA-485 serial adaptor board, and the 24V 6.2A power supply.
Here's an early diagram of how I envisioned HAGUS.  The design obviously changed a bit (still need to build the wrist cradle), but the underlying ideas are there.	Here's a screenshot of the software I wrote to interface with the motion control hardware.  It's pretty basic, but it provides a convenient means of setting PID values, dealing with log files, etc.