Fabricating the Kinetic Sculpture

Dec 17, 2017 00:30 · 530 words · 3 minutes read Design Fabrication

After prototyping fabricating a small version of Presence to test the design and physical mechanics, it was time to build the real thing.

I decided to go with a design of 21 tubes arranged tightly together in a curve.
They would be mounted on long piece of arcrylic attached at the bottom to a piece of CNC routed plywood:

For the sides, I designed walls with small .2” deep x .72” tall (the thickness of the plywood) pockets to make sure the horizontal pieces would fit in seamlessly and straight. For the bottom, I added a pocket for where the power supply and servo controller would go with sizes based on their datasheets:

Now it was time to take these designs to the Mastercam, the CNC Router, and Fabricate them:

To assemble this all together, I used L-braces. This would allow the piece to be dissassembled for easy transport at a future date:

Then it was time to laser cut the servo mounts. Because the bed supported only 32” length, these were cut into 2 pieces with a diagonal divider to make sure the fit exactly into place:

The servos mounted nicely into the acrylic:

these mounts aligned nicely to the holes that were cut by the router into the plywood:

Now it was time to attach the mounts to the frame:

All 21 tubes would have end caps at the top and bottom. The ones at the bottom would be be attached to lightweight servo hubs, and would have a small pockets to fit the center of the servo hub to make it align perfectly. The ones at the top would have small holes that would allow a pole to lightly hold the the the tube into place in the center and easily pivot around the pole. These caps would be cnc routed out of plywood, with a combination of 18” and 12” router bits.

Lightweight servo hub purchased from servocity.com

Lightweight servo hub purchased from servocity.com

Design for the endcaps, with depths for the cnc router

Design for the endcaps, with depths for the cnc router

To make 21 pairs, these were laid out in a grid, sent to Mastercam, where the depths were specified, then cut on the cnc router:

I then sanded the caps at the corners to create a chamfer that would allow the caps to slide into the tubes easily.

Then the servo mounts were attached to all of the caps.

To make the tubes, I used white shipping tubes, and wrapped electrical tape in a spiral around 180 degrees of the tube. This would allow one side of the spiral to be visible when the servo was at 0 degrees, and the other at 180 degrees. To guide the tape along the spiral I cut a stencil out of paper and lightly taped it to the tubes:

With the tubes fully inside the wood frame, there was friction that prevented the servos from turning. To fix this, I offset the tubes from the bottom of the end caps, by glueing them halfway in and clamping them to make the glue strong:

And finally, I attached these to the servos, by first zeroing all the servos, then aligning the bottom of the spirals to the zero position of the tubes: