COACH Mechanical Design
Our COACH was modeled after the Gibson ES-345 electric guitar played by Marty McFly at the Enchantment Under the Sea Dance. (FUN FACT: While the dance takes place in 1955, the ES-345 wasn't actually made until 1959! Whoops!) The frontplate, pick guard, their corresponding borders, and the removable backplate were laser-cut from 1/8" acrylic. A 3-D printed casing for the reed switches was mounted to the back of the frontplate and was protected by a large window of clear acrylic. The box of the guitar was made from laminated 1/4" Duron, as were the neck and head. The neck-head junction was kerf-bent to better imitate the look and feel of an actual guitar. The neck was secured to the body with a generous helping of wood glue and epoxy, and a nylon guitar strap was added for comfort and extra support. The end result was a COACH that looked and felt surprisingly like a real guitar! (Furthermore, given the change in the dominant audible frequency that accompanied the PWMing of our thrust motors, it even sounded like a real guitar! Kind of. Unfortunately, none of us could successfully play a tune, but it was still pretty cool.)
The project specifications required at least three distinct sensing modalities on the COACH. To control the speed of the paired PLAYER, we used a SoftPot rectilinear potentiometer mounted on the neck of the guitar. The resistance of this device changes based upon the location of contact within the sensing region. The end result? As you slide your finger up the neck, the greater the (forward) speed value transmitted to the PLAYER! An FSR mounted at the base of the guitar head was used to transmit reverse speed commands. Kick commands were relayed to the PLAYER by triggering an array of reed switches with a magnetic guitar pick (i.e. a decently strong neodymium magnet super-glued to an actual guitar pick). Six reed switches were wired in parallel for two reasons: 1) to look kind of like guitar strings, and 2) to increase your chances of actually triggering a kick when you wanted to. To control orientation, we fed two of our three-axis accelerometer outputs to A/D pins on our COACH 'C32 and -- after calibrating on start-up -- were able to send turn commands based on the change in angle that we calculated in software. While it was definitely a challenge to drive most PLAYERs, you looked pretty awesome doing it...especially Ed.