Fabrication: 3D Printed Mold

This section contains step-by-step instructions for fabricating a fiber-reinforced bending actuator. If you are making a different fiber-reinforced actuator, e.g. one that twists or extends or combines different motions along its length, the overall steps will stay the same; the only changes you will need to make will be during the second step when the strain limiting layer and fiber reinforcements are added. This should be straightforward, using this page as a guide.

Because of the multiple molding steps, the fabrication of these actuators takes much longer than PneuNets. However, you can make multiple actuators in parallel.

There are two processes described in the following pages: the fast curing process and the slow curing process. The overall steps are the same, the only difference is the amount of time spent on curing. Leaving the cast elastomer to cure at room temperature leads to better bonds between layers, but takes about 12 hours. Alternatively, an oven can be used to speed up the curing process, but can lead to weaker bonds and can cause the finished actuator to have a pre-bent neutral position (as some of the layers contract when cured in the oven). Each of the steps described here ends with the elastomer being left to cure. At these points in the instructions, the relevant steps for each process are described.

If you choose to follow the fast curing process, please read the tips for heat curing first.

To fabricate our actuator, we will follow these steps:

  • Step 1: Mold the actuator body (a semilunar tube) out of Elastosil M4601 (image A above).
  • Step 2: Demold the actuator, but leave the inner rod in to hold the shape. Glue on the strain-limiting layer (B).  Wrap with Kevlar thread (C).
  • Step 3:  Coat an outer skin of Dragon Skin to hold the wrapping in place, then remove the inner rod (D) and dip the actuator in Elastosil to plug one end (E).
  • Step 4: Install a vented screw into the plugged end and seal with silicone glue (see image below). Plug the other end of the actuator.
  • Step 5: Seal the newly plugged end with silicone glue. Once this is cured, the actuator is complete. Attach the actuator to an air source and pressurize it to make it bend.