Physical Computing: Servo Control

Published October 04, 2017

Over the course of this week’s labs, I made a simple mechanical linkage out of foam-core, hot glue, and a bit of metal rod which uses a servo to control the angle of a camera in the up-down direction.  What I discovered was that mechanical linkages are almost completely foreign to me.  Despite that our lives are filled with them, and I can name dozens of applications for mechanical linkages in my daily life, I have very little frame of reference by which to pre-visualize their operational characteristics.  It took some time, for example, to understand how to translate the servo’s limited rotational motion to the camera unit: the rotational motion of the servo becomes a linear motion of the connecting wire, which is then pulling on a tab set apart from the pivot point of the camera, and becoming a rotational motion again.  Depending on how near the pull-tab is to the rotational pivot point, the rotational motion is either amplified (if it is quite near) or reduced (if it is further away).

I am very inspired by the work of Theo Jansen – massive “Strandbeests” which walk along the beach using dozens of legs powered by the wind. These sculptures are capable of mimicking natural – though often not bi-pedal – gaits using mechanical linkages made from PVC pipe. Wind power is translated into rotational motion of a central shaft which powers the not-quite-linear motion of the legs. While the basic concept is simple, its execution reveals sophistication and experimentation in the path of leg transit and power-transmission from wind to leg all controlled by the lengths of various PVC pipes.