For our bot’s arms, we wanted a highly flexible structure, so puppeteering them with rods would be straightforward and wouldn’t resist motion much. However, we also wanted our arms to look like they were being controlled by actuators on the robot and not just some magically bending tube – this effect would partially rely on nonfunctioning mechanisms and partially on restricted axes that would give the movement a more rigid and blocky feel.
Our first and only prototype consisted of drinking straws (chosen for its hollow form, ready availability, and low cost), styrene rod (chosen for versatility and strength), and lead solder (chosen for its minimal resistance to bending). The styrene rods were hot glued partially inside the straws, and the two styrene rods were linked by a piece of solder glued between the tubes. We were very pleased with the appearance of the mechanisms when they weren’t moving, but when they moved, their appearance and functionality faltered.
While the new rods to accent the robot’s arms helped the appearance move past Wacky Waving Inflatable Arm-Flailing Tubeman and more towards a machine, the constant length of the pieces meant that when bending the tube, it would be met with fierce resistance from the rods. We needed a system that would allow for the rods to change in length to facilitate arm bending. Additionally, the bent rods didn’t add the feel of piston actuation – it just looked like a weird, crooked staff when moving.
A minor change we made from the prototype was the use of 24 gauge insulated wire instead of solder for the joint. The big change we made was no longer attaching one of the styrene rods to its straw, allowing it to move unrestricted with piston-like action. The result of these changes was something we were incredibly pleased with. The arms were now unrestricted from bending at the elbows, and the bot looked as if it was driven by machine, not dragged along by rods.
These new arm pieces were attached to a corrugated tube that we touched up with silver paint by spraying some into a paper towel and firmly rubbing the towel across the tubes high spots. If the area was too shiny, we used a dry towel to knock some of the paint off. The styrene rods and straws were hit with a heavy coat of silver and later weathered with the rest of the bot. We left the insulated wire black for contrast.
The mechanism you use to move an object and the appearance of how that object is driven can be completely separate systems. Moving parts make all the difference in defining dynamic systems. Implied forces and actuation through sliding objects give the appearance that the arms are driven by pistons rather than what is really occurring – the pistons are driven by the arms. This experiment in faking mechanisms was a massive success, and I would highly suggest others play with the concept as well.