Springs

Crucial parts of our skateboarding robot that will perform a “bunny hop” are the springs that will create the vertical jump through the conservations of both energy and momentum.  In order to do this, two compression springs will need to be placed below the weighted mass on the vertical posts. The springs will be initially compressed providing maximum potential energy, and then when released all of the energy will be converted to kinetic energy in the weighted mass, driving the block upwards. When the block then hits the top of the structure, where there will be an ideally perfectly inelastic collision, momentum from the weighted mass will be conserved and therefore the structure will continue in the upward direction until the kinetic energy once again returns to purely potential energy at the peak height of the jump.

With all of this considered, I began my exploration of what characteristics the springs must have to allow for this movement by completing the energy and momentum analysis to obtain an equation that related the spring constant and spring movement length to the maximum jump height.  I then performed research on www.McMaster.com and www.Graigner.com to find various springs and plugged their various characteristics into the equations to determine which springs, when placed in parallel, would help us achieve our main need for a jump height of at least 20cm when using a mass of 4.54kg (10 lbs.).  Through research, I found the following springs to complete our goal:

Here is a table combining the pros and cons of each option:

Therefore, based off these pros and cons, I have chosen to use the 306 lb/in square wire spring made of tempered steel as it provides enough jump height while still being relatively easy to compress manually at a decent price of  $14.74 each.