Chief Delphi - FRC Bridge Weight

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ENeyman

15-03-2012 18:41

FRC Bridge Weight

Does anyone know the weight of the FRC bridge? Or how much force is needed to tip it.

Grim Tuesday

15-03-2012 18:48

Re: FRC Bridge Weight

22 lbs at the end is the number I've heard being thrown around. You should design with considerably more than that if you want to be able to push anywhere but the very end (really hard to hit it there), and do it quickly.

Suitster

15-03-2012 20:35

Re: FRC Bridge Weight

Get your arm up to the level where you worry about things breaking
we had a 14" am powered by two window motors that wasn't strong enough for competition
we ended up adding weight to the arm (a package of electrical tape) and we still could use more

Something we figured out works for the bridge at FLR was if you rock the bridge and keep hitting it when it is moving down, you can knock the bridge over fairly quickly

Rangel

15-03-2012 20:42

Re: FRC Bridge Weight

Quote:

Originally Posted by Grim Tuesday (Post 1144711)

Are you sure that it is 22lbs? I thought that it was supposed to be around ~16lbs.

slijin

15-03-2012 22:06

Re: FRC Bridge Weight

Quote:

Originally Posted by Rangel(kf7fdb) (Post 1144748)

Are you sure that it is 22lbs? I thought that it was supposed to be around ~16lbs.

This.

On another note, please use the search function to find this information in the future, rather than starting new threads.

Quote:

Originally Posted by slijin (Post 1139169)

The video said 28" to 30", so assuming 29" is the tipping point, 26" is the effective tipping point (CoG of battery isn't at the end). Keeping in mind that the bridge rotates on the edges of the bump and not the exact center, subtract another two more inches to get 24". Two batteries are 27 lb. That gives 27 lbf * 24" * (1'/12") = 54 lbf-ft = 648 lbf-in.

However, because of the double hinge, it's not a perfect lever, so aim for a bit more than that.

(88"/2) - 2" = 42"; 648 lbf-in / 42 in = 15.4 lbf, so approx. 16 lbf to tip.

EFastring

18-03-2012 10:31

Re: FRC Bridge Weight

After hearing the 16lb number, we designed an arm that could push down on our bathroom scale ~20 lbs (Banebots RS550, 64:1 transmission, ~15" length). At competition on practice day, we couldn't lower the bridge. We thought about adding weight to the end of the arm, but decided to swap to a locking wedge design instead.

A window motor at that arm length puts out about 4-5 lbs.

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