3D adaptable arm. This is the piece that the other connections on the page attach too.

Here is the stl file for any confusion.

Final Adaptable Arm.stl
Download View in 3D

Step 1: Make a Cylinder

From the tool bar on the right, drag out the cylinder shape: 159 mm in length and 97 in width, or to fit the persons arm

Step 2: Insert Cylinder Hole

Make another cylinder smaller than the one you just previously made. Make it a hole, and place it inside the previous cylinder. Make sure the hole cylinder does not come out of both sides of the original cylinder. Only one side will have a hole, leaving about 2mm at the top.

Step 3: Insert Hexagons Into Cylinder and Side Slits

First you want to drag out the hexagon shape and make it a hole. Then copy that design by right clicking, you will need a total of 3 hexagons. Now insert the 3 hexagons on the side so that they are going on opposite sides of the cylinders, three in a row. Then insert a rectangle and make it a hole. And create a slit going all the way through the cylinder, on the opposite side of the hexagons.

Step 4: Insert Cylinder

Insert a smaller cylinder the same width as the previous cylinder but length about 20 mm.

Step 5: Connection

Drag out a cylinder and place two rectangles on the the side. This will be the connecting piece you add to other adaption to fit into the arm. The cylinder should be 23.73 in length and 33.38 in width. The retangles housl be placed the base of the cylinder and the dimension are: height: 12.09, width:10.17. These are exact so they can fir in correctly.

As for what this slides into. Into the top cylinder that is closed, place a hole that is that is 1mm in dimension bigger than the measurements above. Place this half way into the cylinder. For the turning aspect, place rectangular hole on either side so the piece will rotate 90 degrees.