As discussed in the PneuNets bending actuator documentation, materials stiffness defines the amount of pressure required to actuate and the output forces attainable. Low durometer (high strain) materials will bend at lower pressures but will produce lower output forces.
We have found Elastosil M4601 silicone from Wacker Chemie AG or Dragon Skin 30 from Smooth-On Inc. to be useful for the core bladder of the actuator. Lower-durometer materials could be substituted to change the behavior of the actuator.
For the outer skin layer, which is applied to hold the reinforcements in place, we use a lower durometer material such as Ecoflex 20 or Dragon Skin 20. Using a higher-durometer material for the outer skin would make the actuator stiffer and require higher pressures to actuate.
Radial constraint options
|During the development of these actuators, various methods of adding radial constraints have been tried. For example, metal pinch rings can be used, but this leads to bulging in the actuators.|
|Thread wrapping, though more labor intensive, allows for the most customization. It is possible to use different thread materials, but Kevlar is preferred for its strength.||
Inextensible layer options
In this documentation set we use fiberglass fabric as the strain-limiting layer. However, this can get messy, and in cases where the fiberglass is molded concurrently with the main chamber, stray fibers can create leaks. Any thin, inelastic material should work, including office paper or Tyvek. However, as these materials are less porous than fiberglass, they do not embed into silicone very well. To solve this, you can cut holes/slits into the material so that the elastomer can reach both sides.