Machine Shop I
Welcome to the second lab in E5, where you will learn your way around the Machine Shop in the basement of Papazian (next to Hicks). You will be using the shop to fabricate subsystems for the musical instrument class project, but first you must learn the basics of how to use the machines correctly and safely. Our machinist is Grant Smith, who goes by the name of Smitty. Please pay attention to his overview of the machine shop during lab period this week and next.
For the musical instrument project, I have put you in the following lab groups based on the interview information you obtained in lab last week:
|Lab A||Lab B||Lab C|
The subsystem you design will be played by computer using servos and solenoids. Servos are motors that rotate through a total angle of approximately 180° to a specified angular position (-90° to +90°), as determined by the temporal length (duration) of a square-pulse voltage between 0 and 5 volts. For instance, a pulse of 1.52 ms (milliseconds) duration, repeated every 14 to 20 ms, will cause the arm of the servo to remain at the 0° position; one of 0.6 ms will cause rotation to the maximum counterclockwise position (-90° as seen from above); one of 2.4 ms will cause rotation to the maxium clockwise position (90°). It is up to your group to design a linkage that will translate this motion into something useful as regards your subsystem. Next week, Prof. Orthlieb will spend much of Tuesday's lecture discussing possible mechanical linkages you might employ.
One issue regarding servos is the torque, or axial force, that a servo can produce. The greater the torque, the heavier (and more expensive) the servo. Response time to a change in pulse duration is a second factor, related to the first insofar as greater torque usually means slower response time, and may have bearing on the speed with which the instrument can play different notes or beats. We will discuss servos in class and order ones that meet your group's needs.
A good reference to the MIDI standard is available at http://www.borg.com/~jglatt/tech/miditech.htm
A group that uses MIDI controllers on each instrument has its website at http://lemurbots.org/
As you may be aware, solenoids are coils of wire in a housing that, when energized, produce a magnetic field that drives an armature forward. The ones we will be using are described in the links below:
Solenoid data sheet
A link to a supplier of various solenoids we could use
The circuit to connect a controller to a solenoid is shown below (also shown is the simple circuit for a light-emitting-diode (LED) and how to connect the analog inputs, should you have any in your design.