Week 5

     This week we received the items we ordered for our shakedown testing (our constant force springs and elastic bands). We decided to go to the engineering lab and start constructing the wooden "arm" described in the Week 4 blog post. As we are not technically certified to work on our own in the lab yet, we had Wes help us.

The wooden boards modeling the upper and lower arm were cut to be roughly the same length as Isaac's arm. 

Wes helped us construct the model.

A hinge was used to connect the two boards. Small holes were cut out so that the hinge was in the center of the boards, rather than sticking out. This mimics a natural elbow joint.  

We also drilled holes on the top of the boards at 2 cm intervals. Currently we are using eye hooks to guide the string and act as anchor points, and the different holes allow the placement of the anchor points to be adjusted. 

Wooden boards connected by a hinge.

This picture shows the holes drilled in the two boards.

Once the "arm" was built, we attached the spring system. Our constant-force spring was housed in a 3D printed casing, and the end of the spring could be pulled out (similar to the way that tape measures can be used). One issue we found is that the spring can recoil on itself and then not return to the casing. This issue seemed to be mostly resolved when we attached the spring to the board, but bears further testing, as this may be a potential issue that causes us to move away from the design altogether.

Example of the spring recoiling and getting jammed. 

The spring system was composed of two springs, acting opposite each other (such as two opposing muscles). In other word, as one spring was "contracting," the other one was lengthening. Parachute cord (or paracord) was tied to the end of each spring and threaded through the guide holes until they were anchored. As stated before, screw eye holes were used to provide the guide holes and anchor points. The spring casings were taped to the end of the "upper arm" board, as their placement on the actual body would likely be near the shoulders.

Constructing the model.

The final model of the spring system.

We finished building the model for the spring system. Rather than having to deconstruct the system whenever we wanted to test elastic bands, we constructed a second "arm." We did not yet attach the elastic bands, as we are considering testing their pull profiles first, but we will do so next week.
     Next week, we will use the force transducer to test the moment generated about the elbow joint for both models. We will also test how changing the anchor points affects the moment and attempt to find  comfortable (natural) neutral points for the user.

Materials to be used for shakedown testing.

    The rest of the week, we worked on the mid-semester presentation and packet that are due on Monday. These are essentially summaries of our problem, what we have done to this point, and our future designs.

This is our presentation cover slide.