# Weird flex but okay

The issue of centrifugal force

When you try to rotate at a relatively high speed, centrifugal force comes with the territory. The issue is that PCBs are not the most robust pieces in a mechanical system. We need to find a way to make them stronger to hold them in place so they don’t fly away and/or break and find their way into a bystander’s face.

We tried to figure out how much the PCBs would flex. Thankfully, Wikipedia exists and our problem is a classic strength of material case. We have an issue similar to beam theory’s cantilever beam case with a spread out force. Wikipedia has an article with the relevant formula giving us the information we need.

the last formula is the one giving the vertical flex in relation to x. In this formula, w is the force per length, E is Young’s Modulus for the material the beam is made of, I is the second moment of area for the beam and L is the beam’s length.

With this formula, we can deduce that a PCB will flex about 2.5cm if left on its own. Needless to say, in this formula, an assumption is made that it would not break. We need to find a way to reduce flex as much as possible.

A path to solutions

We explored ways to make the PCBs stronger. For now, the best solution we have is small steel beams on each side of the PCB. We estimate that flex would then go down to about mm. There might be a better solution but we have not found it yet and mm of flex over a cm PCB does not seem to be that much and might work.