Adiel Fernandez

Interaction Designer & Developer

Feedback Gearbox for Linear Actuator


For the Spacetime Explorer project, I used a high-speed linear actuator to manipulate the spandex-covered table surface. Because I needed to know the absolute positioning of the actuator, I needed to build a mechanism that would give me precise feedback of the actuator's current position in space. While linear actuators can be purchased with internal feedback mechanisms, finding actuators that are also capable of higher speeds (80mm/s+ as needed by this project) was cost prohibitive.

The mechanism seen at left consists of a high-strength fishing line connected to the top of the actuator and wound around a spool inside the gearbox housing. To the left of the spool is a rotary spring that provides a biasing force, i.e. it keeps the line taught. Coaxial with the spool on the right is the first stage in a pair of reduction gears that translates 12 inches of actuator travel into a single rotation of a 10 kilo-ohm rotary potentiometer. By reading the potentiometer, the actuator's precise, absolute position is known, without needing to home the piston at start-up and keep track of steps/travel time.

All parts, with the exception of the rotary spring (re-purposed from a common tape measure) were designed and 3D printed at home by me.