Motorcycle Case Study
For an assignment for class, I was given a 3D CAD file of a motorcycle, given its properties, and told to determine the characteristics of its shocks and suspension system in order to make it withstand a high speed landing with minimal jerk. In order to do this I used Creo (previously ProEngineer)’s mechanism suite to set up the landing on a track, set physical properties, and run simulations to get data. Using this I was able to set values for the spring and damper system, and check my solution to make sure it met the required specs.
Absorbing a landing
In order for the suspension to take the landing, I used Creo’s mechanism suite to insert shock absorbers onto the front and rear wheels. I first set up limits on the ranges of motions of parts (which are not initially set). One of the most important steps here was making sure parts wouldn’t pass through each other. After the assembly’s motion was made similar to a motorcycle’s, I added springs and dampers to the wheels. Material properties were assigned to the assembly, as well as overall physical properties, such as gravity and friction. I then set an initial condition that mimicked landing on a road at high speeds from less than a foot off of the ground. From there, I took a look at the data to see what I could learn about the landing.
Choosing the Right Shocks
Once the simulation was run, we could look at any data from any part of the landing. Some information that was important in choosing the correct shock absorbers: The angular velocity of the motorcycle’s rear wheel (which will tell us the tire’s velocity), the force on the spring during landing (which will tell us how much force was transferred into the shocks), and the angular velocity on the rear wheel frame, showing us how quickly the rear frame moved in the impact. Because of the low range of angular displacement in the frame, the movement of this part of the motorcycle affects the vertical motion of the seat greatly. If we want to minimize jerk, we want to use the spring-damper system to minimize the angular velocity of the wheel’s frame.
We want the spring-damper system to be underdamped, because an overdamped and critically damped system would transfer a lot of jerk to the rider because of the lack of oscillations in the seat. I used information provided to me, like the maximum allowable jerk, to help drive the changes I made to the shock absorber’s properties. Using data tables and plots from the simulation, I made quantitative decisions that adjusted the landing. Of course, I re-ran the simulation after every adjustment, to make sure the values reflected my calculations.