How much Bridge Space does your robot need?

[Wayne TenBrink]

How do you decide whether or not to even try for 3? Unlike the coopertition bridge, there are no consolation points for trying. Its all or nothing.

You won't get any practice during qualifications. Perhaps your alliance can spend some quality time on the practice field with tethered bots while everybody else is eating lunch - You and the other 7 alliances that won't have any experience doing this either.

How much time would you need to balance 3? 30 seconds? If you have a lead at the 30 second mark, why bother? You can balance two and leave your best shooter on the field with lots of balls and nobody defending it - they should be able to put up at least 9 points in that time. Now, if you could do it in 10 seconds with high confidence, that would be a different matter.

I don't expect to see a lot of success with the 3-bot balance. I hope I'm wrong. It could be a game changer and will certainly be a crowd pleaser. We look forward to trying it with the right partners.

By the way, we need 34" if we're in the middle, about 22" if we're on the end.

[Doug G]

It is for many of these reasons we choose to build a platform bot to carry a third bot onto the bridge in Elim's. You can build the the best offensive shooter, but if you can't guarantee the coop bridge, there's no telling where you may be ranked come Saturday. So by building a platform bot, we feel that even if we are ranked outside the top five, we can help guarantee the 40 points in Elim's, no matter the size of the bots in our alliance. Our strategy in Elim's will be simple... make our two shots in auto, go to the other side of the field and steal balls. Then after a minute or so we begin to stack a robot, leaving our most offensive bot to get on the ramp with 15-30 sec to go. By starving the field of balls for half the match we can better our chances of winning the Elim's with a 3 bot balance. Also seeing a bot carry another bot when balancing will hopefully be worth an award of some kind!

[Chris Fultz]

=Swampdude;1135220]Good points made. We are currently just under 100lbs, and around 123 with bumpers and battery. So we figured a nominal 145 lb bot needed to have it's CG less than 19" from the other end of the bridge. Which should be easy and should only require a driver to move as far as they can out to the end. I'm hoping and in theory this should be quick and easy. If there were still a weight issue there's a few pounds to play with but I think we're good as long as we balance with 115+ lb bots.

Can you share your math and some of the details?

I am assuming your robot is 123 pounds and all of the weight is at the end of the bridge - 44" from the center of the bridge. (is this correct?)

If so, then the center of a 145 pound robot needs to be at 37" from the center of the bridge, so only 7" from the edge.

I am taking 123 * 44 = 145 * x.
solve for x = 37.

[Lil' Lavery]

Chris, keep in mind that the bridge "wants" to remain balanced due to the double hinge mechanism. You simply solved for keeping the CG of the robots at the center of the bridge, but it doesn't actually have to be dead centered to keep the bridge balanced.

[Swampdude]

You have to sum the moments in both directions considering the 3.5" hinge offset from center on either side (2 fulcrums). You also have to take the weight of the bridge and combined weight of the bots into consideration being applied in-between the 2 fulcrums. You can play with the attached spreadsheet if it makes sense to you. This might be helpful for anyone. You can vary the CG location and weights of 2 or 3 bots on the bridge.

The first case is for placing the CG of a 3rd bot left of center and the bottom case is for a 3rd bot right of center. So usually you would have the top case due to bot sizes.

[Chris Fultz]

Thanks for the response and your spreadsheet.

My question is more about when there are just 2 robots so I wil play with it.
Or, is your plan to be on the bridge when there are just 2?

[Swampdude]

You can set the robot 1 field to 0 to simulate 2 bots (1 on each end). My hope is to typically help 2 bots balance during quals (by acting as a ramp) then go to the coop bridge last and already have 1 bot balanced, connect and then have them move out to the end of the bridge. Then 3 bot balancing in elims. Usually we'd prefer bots were already balanced rather than have anyone climb our ramp but it depends on their CG, wheel base/type, ground clearance and driver skill.

[Bjenks548]

Very interesting that so far 42.36% of teams are 30" or over. This doesn't allow 3 of their robots on a bridge, let alone room to balance. An alliance looking to balance 3 on the bridge might be able to have 1 of these robots if they are a good scorer or defensive robot but 2 is really pushing it.

[RRLedford]

Originally Posted by Bjenks548

Very interesting that so far 42.36% of teams are 30" or over. This doesn't allow 3 of their robots on a bridge, let alone room to balance. An alliance looking to balance 3 on the bridge might be able to have 1 of these robots if they are a good scorer or defensive robot but 2 is really pushing it.

No, perhaps these teams were smart to assume that there would be other teams like us that can balance on the bridge by HANGING OFF the SIDE!
Only ~10 inches of our bot + ~3" of bumper, for total of ~13" overlaps with the side of the bridge, and we are near to a max. KOP size at 27"x37" We can drive the bridge end-to-end, balancing along the rail, while occupying only 13+ inches of its width. We weigh near 120 lbs and can both balance it in 3 seconds from first wheel up, or hold the position alone on bridge to keep it lowered. This leaves slightly under 35" of bridge width fully clear for our two long bot alliance partners to keep shooting until the last 10-20 seconds, at which point they can then just drive right up the PRE-TILTED (by us) bridge, which we, having already finished our defensive role duties, have already occupied and lowered for them, so that they just need to align themselves and roll smoothly right up without any jarring edge impacts or lowering delays.

So, if they can roll up the bridge aligned in a nearly bumper-to-bumper fashion, and then both stop with each on either side of center, we will quickly finish the balancing of the bridge.
We estimate under 10 seconds for our alliance to complete a 3-bot balance is easily possible with our bridge side overhang scheme, since having all three bots close to the center of the bridge makes the balancing process a lot easier and quicker. This means max shooting time for our partners and, with reasonably precision up the bridge driving accuracy by them, our alliance can count on a near certain +40 point bonus every match.

-Dick Ledford

[Bjenks548]

Week one is done and we have seen tons of robots. 148 and 33 both brought "stingers". Anyone see anyother techniques to eliminated space needed on the bridge?