# How is your team pushing the bridge down?

Hey guys!

My FIRST team recently has brainstormed on ideas for how to lower the bridge so you can get on it. We’ve come up with a couple of ideas, including wedges, big arm that just moves out and pushes down, and some kinda of non-motorized peg wheel to catch it.

However, we’ve got a couple of questions that we’re stuck on. It would help us if we knew the thickness of the bridge along with how much force is needed to move them.

With them being double hinged, it appears that you will need more energy to push it down, against the hinge that wants to right its self and the weight of the other side rising up. The rule book, from my reading and reading dosen’t explain much on them.

Does anyone know of a palce to get that info? Also, for simply brainstorming ideas, how is your team planning to do this, and if not, why?

Good Luck with the Seson!

Check the Field Drawings for info on the dimensions of all of the field parts.

We built something similar once before. It has an axle that runs the length of the front of the robot. Several wheels (or rollers) are on said axle. The whole contraption is lowered in front of the robot by means of a hinge actuated by a window motor or pneumatic piston.

The thought behind this is to put wheels or a skid plate in front of the bumper to push the ramp down.

As far as the ease of tipping the ramps, the ones at kickoff (which I assume are stiffer) can be pushed down very easily if you attack it at the right angle. If you have the resources, build a bridge and then try a few different ideas by building them and driving/ pushing the kitbot around on it.

Good Luck

Make sure you consider the geometry of driving up and over the bridge when thinking about manipulator to push the bridge down. A bridge “level” should be a foot off the ground, while a bridge tipped the other way is two feet off the ground. Are you planning on pushing it down to drive over for yourself or do you also intended to be on the opposite side manipulating it for another bot on your alliance to drive up it?

If you build the team version of the bridge it should run you less than \$150 in plywood, 2x4s, hinges and plastic sheet to simulate the actual bridge surface.

We put one together the other evening, it is heavy and it does take up a bunch of space.

I have an idea for a belt that runs vertically with flanges on it so when it runs in one direction it lowers the bridge and when run in the other direction raises it when pushed next to the bridge. The problem, though, is that it would be a bit on the fragile side and would be outside of the bumper zone.

According to our calculations and field mock-up, you need 16 pounds of force applied at the very edge of the ramp to push it downward.

-Brando

I talked to a guy at the Manchester Kickoff, and he said it was 11 pounds. I could be wrong though.

I take it that’s a directly downward force vector? Do you have your calculations? We’re looking at driving at it with a 45deg angle plate (and our bridge isn’t done yet).

If there is empirical data from a Manchester field element I would tend to trust that more.

I will gather the calculations and show them, they are quite simple.

We based them off of the youtube video on Bridges. They explain about using 2 batteries to test your own bridge to mimic the dynamics of the field.

-Brando

Any I dea ion how much the bridge actualy weight or that not of any relevance?

do you mind elaborating about driving at it with a 45deg angle plate?

I heard 18 lbs from a good source at the Manchester field. Whichever number you use, I suggest a significant factor of safety. I don’t know how these hinges will vary or wear from event to event.

My team thought of doing this too, but because of the location of the bumpers, it isn’t possible: the bumpers would have to be above the height of the brige (12") to be able to go at it with an angled plate, when their max height is 10". They get in the way, it can’t be done.

Ah ok, I thought it was based on your bridge. I did the calcs off the video as well. We’ll test on our bridge (when it gets done…). You’re right, I think the next-best thing is Manchester data.

45deg is a semi-arbitrary starting point (which I think is probably incorrect). We’re testing what happens when you tilt a plate that starts inside the bumper perimeter out to some angle and drive into the bridge. We’re considering any time of active conveyance on the front as well, not sure without a bridge to test on.

Untrue. You need only to put the plate where the bumpers are not, i.e. 8" in from the nearest exterior vertexesm and ensure the plate doesn’t run the bridge into the bumpers (again, 45deg is a pre-analysis & testing arbitrary initial guess)

We have 3 bridges in our lab that were used at our local kickoff. Once I saw that video published by FIRST

displaying how to test for matching dynamics, we tested ours. Based on the numbers FIRST
provided in the video, we calculated 16 lbs, straight down, at the end of the ramp. Thats what we’ve been tweaking our bridges to mimic.

Somewhat related sidenote: I will almost guarantee that when you build your bridge it will require tweaking to mimic FIRSTs video.

-Brando

In the demo video, it took two batteries at one side to make the bridge fall.

Not a lot of force is needed to push it down.

Tend to agree. We just built ours.

We’ve got some competing ideas about floor loaders, but one of them could be a pivoting arm that could also be used to push down the bridge, sort of like the redabot that gets pushed around by Dozer in the animation.

I know this wasn’t addressed to me, but I felt compelled to link my response in another thread about the difference between the home-made bridges and the actual competition bridges:

http://www.chiefdelphi.com/forums/showpost.php?p=1102267&postcount=52

Brandon, can you update us on any best practices for the required modifications? What kinds of things have you tried doing to the bridges to make them better mimic the competition bridge?