There are 2 main ways to make the actuator body: we can design a chamber and then multiply it in a linear pattern, or we can make a long rectangular solid and make several linear patterns of cuts. Here we will use the first method as it involves less arithmetic. [Video: Making a chamber unit]
Using the Extruded Boss/Base feature, create a 8x15x15 (mm) solid block.
Now we need to cut out the inner cavity of the chamber. Select the Extruded Cut feature, and make a sketch of a rectangle on the bottom face of the block. Using the Smart Dimension tool, set the offset from the block edges to the appropriate wall thicknesses.
Since we want the top wall thickness to be 2mm and the block is 15mm tall, we will make the extruded cut 13mm deep. (Alternatively, instead of a Blind cut, use Offset From Surface and set it to be 2mm from the top of the block.)
Now we need to make a strut between each chamber and the next. It will be 2mm thick, since that is our desired distance between chambers. To determine the height, we need to make sure that it is tall enough to allow room to cut out the central channel. Since the channel is 2mm tall, we will make the spacer 3mm tall.
Once again, use the Extruded Boss/Base tool and extrude a spacer block from the side of the chamber.
Now the chamber is complete. In the next step, we will create multiple copies of this chamber and combine them to create our actuator