After Each Member of Our Group Synthesized a Linkage (All Four-Bar Linkages), Each Was

Phase 2

After each member of our group synthesized a linkage (all four-bar linkages), each was give a force analysis under an iterated method. This provided a comparison between all the linkages to determine which would be most practical to produce, which would have the best cost/performance ratio, which would produce the least forces, etc. Under the assumption that our rider was 300 lbm and our linkage was a disjointed design, we could conclude that each pedal was experiencing a maximum of 150 lbm. This force vector, however, changes continuously because of the dynamics of the running motion. The biomechanics shown in Figure 1, show that there will be and angle between the hip, knee, and foot (toe or heel). This non-co linearity will provide two resultant force vectors, and this significantly affects the dynamics of the linkage synthesis. It should be noted that “average” design parameters were not used, such as the weight of the occupant. Three hundred pounds is used as a safety factor, because the average rider will be around 150-250 lbm.

The first option we had was Figure 2. This choice gives very acceptable results, however, there seems to be only one peak of force and it occurs at sixty degrees. These results seem slightly off, and are suspect to slight errors. Intuitively we should see at least two force spikes (at the beginning and end of the stroke, where there will be the greatest acceleration change). The one advantage to this design is its simplicity, which could cut down on manufacturing expenses, but this come at the price of a path that is not as accurate at approximating the running motion.

Figure 3 has the same advantages and disadvantages as Figure 2, being that it sacrifices an accurate portrayal of the running biomechanics for a more simplifies design. These advantages will be looked at more thoroughly later on.

Figure 4 is the opposite to Figure 2 and 3 in that it sacrifices simplicity for a more tailored running path function. The one advantage of this design is that it contains two force spikes (which might be a little on the high side, but are still reasonable). The two spikes also occur at the upstroke and downstroke where the accelerations of the coupler point will be the greatest. Given that this machine was geared towards the enthusiast/training athlete, and was marketed for a upper class machine, I believe it is appropriate to sacrifice some simplicity (and hence manufacturing costs) for the added benefit of a more realistic simulation of the running motion.

Figure 5 also contains these benefits, but with larger normalized forces, so this might pose as a problem from an endurance/maintenance perspective. From all of the options available, I think it is wisest to choose Figure 4 due to the lack of excessive forces and cost justification. It should be noted that this design is just an approximation of the finished product. Many features such as the inward pronation of the linkages. the adjustable stroke length, or the pivoting foot platforms was not included in the force analysis due to complexity issues. These things should however change the force analysis and may alter the design slightly by the finished product.

As for the future plans of phase 3, several obstacles will have to be overcome. The first and foremost being extracting the skeleton of a linkage from Norton and incorporating it into a more realistic design assembly. This task includes accounting for things such as the 3-dimensional nature of the linkage, the bearings that might be used, different type of lubricants, different surface finishes, how the linkage will be attached to the resistance mechanism, how the integrated electronics and control system (resistance control) will be incorporated and implemented in the system, etc. All of these finer details will have to be thoroughly evaluated before Phase 3. These tasks will be broken down into Aesthetics/UI (User Interface), Structural, Control Systems, Integration, and Biomechanics/Testing. The Aesthetics/UI will be taken care of by Beth Miller. She will be responsible for determining how the user will interact with the machine, and how the machine will be presented to the consumer. Though these details might seem extraneous at this point in design, they are very valid marketing considerations. It is a proven fact that functionality is not the only factor in a purchasing decision (and it is sometimes not even the most important). A sleek, understated, user-friendly machine will be the goal and responsibly of Beth Miller.

The Structural design will be delegated to Matt Manzione. He will be responsible for a more thorough evaluation of the dynamics and kinetics of the actual linkage. He will also be responsible on how the resistance element will be integrated into the linkage design. His focus will be “cutting the fat” from the core design. I would like him to focus on maintaining a compact shape (through refinement), low weight (through a more extensive search of materials), and a reduction of complexity between the linkage and the resistance element. Again, his goals will be to focus on “less is more” while still achieving functional satisfaction.

The Control systems will be handled by Wesley Miller. He will be responsible for the electronics and the controls of the resistance element. The user should be capable of varying the resistance from the dashboard, and this will be left to Wesley Miller.

Integration will be taken care of by myself, Jeremy Molligan. I will be responsible for integrating all of the different parts of each team member and making sure that all of the pieces fall in line. From the control systems, to the electronics, to the structural integrity; these will all be integrated smoothly, while keeping any extraneous details to a minimum. This machine will pride itself in performing its intended function, nothing more and nothing less.

Due to Michael Manlove’s experience as a seasoned runner, he will be responsible for the biomechanic evaluation of the linkage. He must make sure that this design is indeed conforming to the natural form of a runner. If this is not so, then our assumption that Team 6’s biomechanics data is accurate will need to be reevaluated. He will offer his experience and expertise as a runner will provide a good perspective of our customers that will be using this as a training alternative.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5