Since we want our CVT to be a product that is as affordable as possible, it is critical to maintain the building cost of the bike CVT within a reasonable budget. A detailed cost estimation is provided below in the figure above. As seen from the table, the largest spending in our project is purchasing the bicycle and the CVT assembly itself is relatively inexpensive to fabricate. Our total spending is 640.72 dollars, which is significantly lower than the 1000 dollar limit. Therefore, monetary wise, the proposed design is well within the budget limit by a 35.9% margin.
For the vast majority of bicycles, to maintain a constant speed, the resistances on the pedals of the bike are constants. This is because most bicycles have a constant gear ratio throughout the entire pedaling cycle. However, for our design, the gear ratio of the bike is periodically varying. This interesting phenomenon occurs due to the fact that each connecting rod moves the lever arms in a sinusoidal motion, and the two lever arms act out of phase by 180 degrees. A motion study is performed using SOLIDWORKS and the results are shown in the figure below. In the SOLIDWORKS simulation, when the input crank angular velocity is set to a reasonable value of 60 RPM, the figure above shows the rotational speed of the output crank speed as a function of time for different percentages of lever arm extension. It can be observed from the figure that in any given pedaling cycle, there are two maximums and two minimums of gear ratio.
The result of this effect is that upon pedaling, there are points where the user would experience increased resistive force, and points where there is a decrease in resistive force. The two lever arms are made to move in phase with the pedals so that the maximum resistive force occurs when the pedals are parallel with ground, and the minimum resistance is felt when the pedals are normal to the ground.
This pedal timing is chosen because the maximum applied force to the pedals is at the horizontal position, when the operator is able to apply their entire body weight to the pedals for maximum torque. Furthermore, when the pedals are normal to the ground, although the user can still apply maximum force to the pedals, the applied torque is very low. This maximizes the use of torque in the design, and would give the user a new and interesting feel to the pedals, and a unique riding experience.
After our team has the CVT mounted onto the bicycle, our team members have tried to ride the bicycle in order to get a feel of the riding experience. As we have expected, the bike indeed have a different and unique feel when pedaling. When the two pedals on both sides of the bicycle are in a position parallel to the ground, it is very obvious that the pedaling resistance felt by the rider is truly significantly larger, whereas when the two pedals on both sides of the bicycle are in a position normal to the ground, the pedaling resistance felt by the rider is indeed significantly reduced. Also, when comparing the feel of pedaling at large lever arm extension with the feel of pedaling at small lever arm extensions, we are also able to sense a significant difference. Therefore, through the riding experience test, our team is able to demonstrate that our CVT design indeed has the desirable characteristics outlined in the design overview section.