Fabrication

Fabricating a workable McKibben actuator consists of only 2 major steps. Refer to Bill of Materials for the supplies you'll need to get started.

1. Making the Balloon-Mesh Bladder

2. Setting up Circuitry and Pneumatic Systems

Step 1: Making the Balloon-Mesh Bladder

Select a balloon and inflate it all the way, checking for imperfections or holes. After verifying, nip the end and the open side such that the middle section is the part you use. Our balloon used had an uninflated length of 8 cm. Additional sections used on the barbs added another ~3.6 cm for a total of 11.6 cm length, as depicted below.

Place a plug and tube fitting at each end of the balloon. Secure the ends with tape around the barb such that one creates an airtight seal.

Measure the distance between the fitting barb and and the plug barb, and cut a length of mesh accordingly. Use a lighter to melt the tips of the mesh into a solid end such that they do not unravel in the future.

To fasten the balloon and mesh together, slip the balloon into the mesh and use zip ties to secure them to the barbs. This way, the mesh will not move. Make sure to secure the zip ties as tight as possible.

A number of precautions:

• Due to friction between components, adding too much material for inflation may reduce the number of cycles your actuator can run.

• Tape is used when assembling the balloon-mesh bladder to prevent leaks. The zip tie on its own is unlikely to create an airtight seal, so make sure to add at least 2-3 turns of tape.

Step 3: Setting up Circuitry and Pneumatic Systems

Our components in the Bill of Materials were chosen to match the dimensions of our chosen pump and solenoid valve. We chose this particular size to optimize for low-cost, but your design needs may differ. For upscaling or downscaling, just make sure that the width of tubing used matches for all components.

Set up the MOSFET circuit and wired components as shown in the diagram below:

Next, set up the air system, as shown below. Make sure to stabilize connections between the pump and solenoid valve, and ensure the connections are airtight. For the connection between the balloon-mesh bladder, make sure it is secured with a zip tie.

Now, your McKibben actuator is good to go!

Note: The wiring in these instructions will cause the pump to remain turned on, but it can also be done such that pump and valve are switched on at the same time. Depending on the pressure the pump can generate, this may increase the time it takes for the bladder to fill and contract, and slow overall actuation as a result.