pic: We've got balance, how bout' you?

[Kevin Sevcik]

Originally Posted by DonRotolo

Adding weight to both sides will not help. The addition of springs, or bungee cords, or similar, and fine tuning it with the battery test should make it react like a competition bridge.

I disagree. Adding weights in the right location is the best way to simulate the competition bridge.

Firstly, adding weight DOES make the bridge more stable and less sensitive. The CoM is the weighted average of the bridge's CoM and the batteries CoM. Heavier bridge means the batteries move the overall CoM less. I proved that to another mentor tonight with a scrap pie of plywood adding weight to the bridge and a battery barely balancing it. Pick up the plywood and down goes the bridge.

Secondly, the moment of inertia of the bridge could definitely matter to balancing and knock down mechanisms. A heavier bridge is going to have slower dynamics than a lighter bridge. It will accelerate and decelerate more slowly, which may affect dynamic balancing systems. Bungees add no mass, and thus leave a lighter, more lively bridge system. Similarly, lack of care in locating your added weights could leave you with a more sluggish bridge than you'd face in reality.

Long story short, there's no substitute for the real thing. If you can balance the super sensitive bridge, you'll likely only need a little tweaking at competition, but you should expect tweaking to be necessary.