Structural System

The structural system is comprised of the legs of the football launcher, as well as the shelf to hold the electronics. 

The stand of the football launcher is made of 1" aluminum tube stock. We were looking for three pieces of tube stock that were at least three feet long to make a tripod. This would provide the correct amount of kinematic constraints to our system as to not over constrain our system and introduce area of wobble of our system. The tube stock is welded to a piece of square aluminum tube stock. The square tube stock has mounting holes for the mounting rail of the launcher system to interface with. 

The stand angles the launcher at a 28 degree angle. To view our rational for choosing that angle, see our launcher subsystem section.

With the stand, we were most concerned with the static load it would undergo due to the weight of the other components, as well as ensuring its center of gravity would allow it to not tip over during operation.

Our shelf is made of 1/8" aluminum sheet and sits eight inches above the ground. It is designed to support the mass of the battery and it's accompanying electronics. The position of the stand allows the center of gravity to be moved lower, increasing stability. It is welded to attach to the legs of the structure.

A key analysis for the frame was ensuring the center of gravity (the black and white circle shown above) remained within the legs of the tripod. This consideration helps to ensure stability both during static operation and under launching recoil. We considered multiple designs to push the CG further in, but landed on this one because it balances stability, simplicity, ease of manufacturing, and ease of assembly well. Keep in mind that the addition of the battery will further lower the CG, and, depending on placement move it closer to the center of the launcher.

Another relevant analysis for this frame was ensuring the thin aluminum tubes that in the base would not yield under the force generated by a launch. To test this, we performed FEA on the structure with a simulated load of 200 Newtons (our calculated force that a launch would generate) applied, with 100 Newtons applied on each of the bearing mounting blocks. The maximum stress on the structure was an order of magnitude below the yield stress, so we proceeded forward with our structure design.