When creating the wrist components of my gauntlet I ran into the problem of needing a slot for some of the connection points. In my first iteration of the design, I had a 4 pieces covering the wrist that all needed to be able to rotate relative to the wrist joint. As you can see in Figure 1 components A and B do not cover the entirety of the wrist so the two smaller components had to be connected to component C for support and the ability to rotate.
Figure 1: Assembly Used to create slot for wrist motion with labeled components
I wanted all the components rotation to be aligned to the rotation axis of the wrist but the smaller components only intersected that axis on one side so I had to creatively connect them to part C to allow each component to mimic the rotation I desired. Part A had a simple stationary pin connection to part C but in order to maintain the proper alignment and rotation of part B a slot had to be created for a pin to travel in while it rotated. For a better understanding Figure 2 shows component A rotating and the unique slot that needed to be generated for part B’s connection.
Figure 2 Animation of the rotation of component A with a focus on the slot needed to connect component B
To accurately model this custom slot I used SOLIDWORKS Motion to run a motion study, trace a pathway for my pin connector, and then generate a slot from that pathway. The first step in the process was to create a motion study and then constrain some of the degrees of freedom in that motion study. In order to simulate the motion I desired, I completely fixed part C and added concentric mates to the pins and holes connecting Parts A and C. I also mated the planes of parts A and B together so there was no relative motion between the two. This mating configuration constrained the assembly enough to not fly into space but had the degrees of freedom to allow the components to rotate in alignment with the wrist joint.
A motor was added to the pin of component A and was defined to have a prescribed rotation about the axis of rotation. I set the motor to rotate component A 15 degrees. After the motion simulation was completed I created a trace path to graphically show me the path that the pin follows. This is done in the results portion of the motion study under the displacement category. Figure 3 shows the output of the trace path as a black curve in the graphics area.
Figure 3 Animation of the motion study used to generate the trace path
This curve can then be exported from the motion simulation into its own part document or into the current document. I chose to import the curve into the current assembly and then reference it with the component that needed the slot. To create the slot I first had to activate the part editing mode within the assembly. I then created a plane in which to start sketching the slot and used convert entities to project the trace path onto my sketch. The converted entity was a spline so I made it construction geometry so I could reference it with the slot tool but it would not create any 3 dimensional geometry. I used the 3 point arc tool to create a curved slot that followed the converted entity and defined the diameter to give the pin the necessary clearance to move and be printed. Figure 4 is a screenshot of the slot sketch but I had to rotate my view not normal to the sketch plane in order to see the trace path as well as the arced slot. Since the trace path was an arc shape you can notice I was able to add coincident relations between the endpoints of the trace path and the center point of the slots arc even though the entity was a spline.
Figure 4 Sketch of Slot generated from the trace path with the view rotated not normal to the sketch plane so both are visible
The design went through a few iterations and I used this procedure to make some different slots. After I decided on a thumb piece that went around the entire wrist the direction of the slot changed. I also tried a design where the pin went through the entire part but felt it ruined the athletics of the piece. Figure 5 is an animation of the design iteration with an open slot.
Figure 5 Design iteration with an open slot and thumb piece that surrounds the wrist
I you like this blog please look out for part 5 to see the finished gauntlet and some more specifics about the 3D printing process with the new HP Jet Fusion 3D printer.