Summary

This project utilized three different mechanisms, a cam, gear system, and four-bar linkage, to achieve motion of a cyclist riding a bicycle through scenery. With a constant input velocity, theoretical velocities and accelerations of all components are smooth. However, these velocities and accelerations start to have quickly changing magnitudes and direction changes once this input angular velocity becomes variable, which is more realistic to the motion of the assembly.

Challenges

The greatest challenge in building this paper assembly was that individual assemblies (cam, gears, bicycle) functioned well separately, but altogether allowed for very little movement. This was due to a number of reasons:

• For the cam, adding the grass to the top rod added just enough weight that the cam had a difficult time sliding side to side without getting stuck. 
• Connecting the cam assembly and the gear assembly with the bicycle on top made the input handle quite difficult to turn, as the torque required increased. If every edge was not lined up correctly, or if the weight of the bicycle was leaning more forward than backward, the input handle would not move.
• As for the gears, because I spun the mechanism many times during construction to confirm it was working, the paper gear teeth started to tear, and did not spin as well once they were taped back together. This was because the tape caused some teeth to bulge out more than they were intended to, so the teeth started to get caught on the sides of the casing or would not mesh well with the bicycle wheels. 
• Once the bike was connected to the intermediate gear, the added weight also made it difficult for the small input gear to turn all the wheels. This small input gear has a high speed and low torque, and thus had a difficult time moving all above components.
• The four-bar linkage assembly functioned well, however the knee could fall outward if the small nail that pinned the upper leg segment to the hip started to slip outward. 

Lessons Learned

If I were to re-construct this mechanism, I would make the following changes to improve its functionality:

• Two nickels were taped to the inside of the sliding cam piece in order to improve sliding, however removing some of this weight once the grass was added may have improved this motion.
• I would buy an X-Acto knife to be able to construct the baseline pieces, such as the cam assembly, gears, and input shaft, out of cardboard instead of cardstock or paper. Because the entire mechanism was made out of paper, its strength was low and easily susceptible to failing after too much wear, due to its weight. This likely would also solve the problem of the small input gear having difficulty turning the intermediate gear and bike wheels, as these could have still been made out of paper, and therefore would be light and have a low torque requirement to turn.
• I would buy some tacks or small pins that could more easily constrain the motion of the upper and lower leg segments to the sagittal plane only.