Our final design functioned as desired; however, there is still work left to be done before this mechanism can be useful to someone for daily wear. The final prototype heavily used PLA and ABS because they were cost effective and readily available building materials; however, in the long run, these are poor choices for daily use.

Slider

The slider wheels on the prototype are made from PLA and will wear away very quickly. We would recommend that the wheels be remade with nylon to provide a smoother sliding contact and a longer wheel lifespan without adding significant weight to the slider.

Guide

We 3D printed the helical guide rail along a wrist brace because fabricating such a small helical profile from metal was not practical for a prototype. The consequence of this was a bulky, unattractive wrist brace. This may be heavy for some users and does not breath well. After a short period of wear, the user will quickly start sweating. The 3D printed helix was also not desirable from a manufacturing perspective. It takes 13 hours per brace to print and the helix requires high precision printing to be an effective guide.

In addition, the current helical guide configuration considerably limits the range of motion of the user's elbow. This is because the analysis we performed did not account for the considerable size of the slider. By the time the user's wrist has gone through a quarter rotation, the user's elbow only goes through a 90 degree bend. This may be desirable in some cases, but in others, the user may feel overly confined by the mechanism. It would be prudent to consider the needs of the specific patient when designing future iterations.

Lastly, we need some way to prevent the slider from sliding off the railing. We considered adding stoppers at the ends of the helix, but this was left out for now to provide the prototype with as large a range of motion as possible. For users who are not able to finely control their arm motion, the slider could easily slide off without some restraint on the slider motion.

Upper Arm Connection

The connection for the upper arm does not provide a true “ground” for the mechanism. As the user flexes his/her arm, the bicep will expand and contract beneath the upper arm connection. Also, the current version of the connection grips the arm too firmly and shifts up and down as the arm flexes. This is uncomfortable for the user and could potentially pinch on the sides of the arm. This could be fixed in the short term without remaking the upper arm brace (the yellow piece on the prototype) by simply adding more foam padding. A long-term alternative would be to wrap the user’s arm in foam and then fit it with a larger version of the upper arm connector. This would ensure the user is comfortable and reduce shifting of the connector.