Let's Talk About The Bridge:

[Dmiller28]

Iv got a question... are we able to grab onto the bridge and hold onto the side of the bridge opposed to driving onto the bridge itself?

[PAR_WIG1350]

Originally Posted by davidthefat

So at 1.5 feet out from the center, around 36 lb is required to tip it. How much does a battery weigh?

13-13.5 pounds

Originally Posted by Dmiller28

Iv got a question... are we able to grab onto the bridge and hold onto the side of the bridge opposed to driving onto the bridge itself?

[G10]
Robots may not grab, grasp, grapple, or attach to any Arena structure. (Robots may push or react against any elements of the Arena that is not protected by another rule.)
Violation: Foul

[Frenchie461]

Originally Posted by PAR_WIG1350

\

[G10]
Robots may not grab, grasp, grapple, or attach to any Arena structure. (Robots may push or react against any elements of the Arena that is not protected by another rule.)
Violation: Foul

This means you can still push down on the bridge though.

[Mr_D_Mentor]

Originally Posted by Marc S.

If you made a wide base robot you could have a larger intake and more easily fit 3 bots on a ramp.

Of course you make your robot more prone to tipping over if you want to go over the 4" bump.

[Tetraman]

Originally Posted by davidthefat

So in other words, go big or go home.

Taking from the new will.I.am song, you mean "You can go hard, or you can go home."

Anyway, here is a bit of thought that I'm sure many have thought about already: (please excuse the bad Sketchup drawing. I'm not finished with the final field.)

http://i48.photobucket.com/albums/f2...ingTheGame.png

Step 1: Carry Bot is on one side, with the other two on the other side.
Step 2: Carry Bot puts the Bridge on the top of their robot, allowing a robot to drive onto them.
Step 3: Carry Bot or the Third Bot moves the bridge down for the Two bots to get up.
Step 4: Two bots move to allow the Third Bot to get up.
Step 5: +40 Points.

[Kusha]

Originally Posted by Tetraman

Taking from the new will.I.am song, you mean "You can go hard, or you can go home."

Anyway, here is a bit of thought that I'm sure many have thought about already: (please excuse the bad Sketchup drawing. I'm not finished with the final field.)

http://i48.photobucket.com/albums/f2...ingTheGame.png

Step 1: Carry Bot is on one side, with the other two on the other side.
Step 2: Carry Bot puts the Bridge on the top of their robot, allowing a robot to drive onto them.
Step 3: Carry Bot or the Third Bot moves the bridge down for the Two bots to get up.
Step 4: Two bots move to allow the Third Bot to get up.
Step 5: +40 Points.

Heh, this came up yesterday.
You'd need something like this, and it would be pretty hard. Look at other '07 bots
http://www.youtube.com/watch?v=zgHanZXFweg

[MechEng83]

Has anyone built the "cheap" version of the bridge? Ours is pretty much built to spec but doesn't have dynamic properties coming close to the competition bridge in the FIRST video on their site.

Using 2 batteries, our bridge tips at about 15 inches out, rather than the 28" claimed. I did some math (explained below) and came up with a weight for our bridge around 70 pounds, whereas the competition bridge should be more like 170 pounds. Anyone else notice this, and what are your recommendations? I've thought about just adding 100 lbs of weights to the underside of the bridge, but didn't know if other people had more elegant solutions.


Math:
The hinges are 7" apart, meaning the pivots are 3.5" on each side of center.
Since the batteries weigh approximately 14 pounds each, and the center of gravity is approximately 3 inches inboard of that, we can calculate the balanced gravitational moment of the bridge and battery. For our home-built bridge, the battery side moment is (15"-3"-3.5") X 28 lbs. The balance bridge moment must be 3.5" X W[bridge]. Solving for W we get ~70 lbs.
Now, take the competition bridge in the FIRST video -- replace our 15" with 28" and you get 170 for W[bridge]. No wonder they said the field was particularly heavy this year!

[ThaneS]

I've just finished our bridge and I note the same thing. Ours tips with the batteries at around 13". However, we haven't put a sheet of polycarbonate over the top yet. I think this should make the bridge less prone to tipping, as there is more weight keeping it in the center position (if my brain is thinking about physics correctly). Getting a 4x8 sheet of .25" polycarb isn't the easiest thing for us, but another sheet of .5" plywood weighs about the same (50 lbs), so that's probably what we're going to try first. The only other discrepancy between our bridge and the plans is that the plans seem to dimension the nominal thickness of the plywood, and not the actual, easily available, thickness that we used (15/32" instead of 1/2").

On a completely different note, I haven't seen much discussion of robots falling off the bridge. There's no lip on the sides, and if a wide robot tries to go over it, there's only 5" of clearance on either side. I expect to see a lot of tipped robots.

[Djur]

Originally Posted by ThaneS

On a completely different note, I haven't seen much discussion of robots falling off the bridge. There's no lip on the sides, and if a wide robot tries to go over it, there's only 5" of clearance on either side. I expect to see a lot of tipped robots.

There actually is a metal bracket on the edge to prevent robots from driving off; it's about 1 inch high if I remember right.

[speedbuggy76]

We ran into the same problem with our inexpensive version of the bridge today as well. Let us know what you decide to do to fix it, we need to work on ours too. We figure if our programmer can get it to work on this more finicky bridge, it should be good to go for the competition one

[ThaneS]

Ah yes, I see you're right. I should have read the drawings more carefully. In that case I expect somewhat fewer tipped robots.

[MechEng83]

Originally Posted by speedbuggy76

We figure if our programmer can get it to work on this more finicky bridge, it should be good to go for the competition one

Another mentor on my team made that same point... on the other hand, the competition bridge will take significantly more force to push down than the economy model. These two features need to be balanced (no pun intended)

[vamfun]

Originally Posted by Tetraman

Taking from the new will.I.am song, you mean "You can go hard, or you can go home."

Anyway, here is a bit of thought that I'm sure many have thought about already: (please excuse the bad Sketchup drawing. I'm not finished with the final field.)

http://i48.photobucket.com/albums/f2...ingTheGame.png

Step 1: Carry Bot is on one side, with the other two on the other side.
Step 2: Carry Bot puts the Bridge on the top of their robot, allowing a robot to drive onto them.
Step 3: Carry Bot or the Third Bot moves the bridge down for the Two bots to get up.
Step 4: Two bots move to allow the Third Bot to get up.
Step 5: +40 Points.

We had the same idea.... seems like an interesting way to go. Need to get rule clarifictions about robot piggy backing.... I wonder about possible bumper zone violations for the upper robot.

If all robots can be designed to climb a 30 deg ramp... then they could just drive over the robot using 14in ramp extensions and then you don't require the use of a bridge to mount. This would have to be a very low profile specilized robot.

[Marc S.]

Originally Posted by vamfun

We had the same idea.... seems like an interesting way to go. Need to get rule clarifictions about robot piggy backing.... I wonder about possible bumper zone violations for the upper robot.

If all robots can be designed to climb a 30 deg ramp... then they could just drive over the robot using 14in ramp extensions and then you don't require the use of a bridge to mount. This would have to be a very low profile specilized robot.

See the rule updates, all robots must be touching the ramp to be supported by the ramp. So now you just have to build a robot that can lift itself high enough to allow a robot to fit underneath. Maybe some team collaboration is needed.

[Chris is me]

Originally Posted by Djur

Omniwheels wouldn't be too useful because they can slide very easily and don't have good traction; Mecanums are a bit more helpful because they don't slide as easily and have better traction; holonomic drive would be best because it doesn't sacrifice traction for mobility, but it's difficult to create. Just my 2 cents.

Holonomic drives sacrifice traction in the same direction mecanum drives do. Holonomic drives have just as little traction as a rubber wheel, in theory. In practice omni wheels don't have very much traction in any direction unless you double or triple them up. Combine that with a low friction well greased gearbox and you will realize the wheel wastes power scrubbing motion in the wrong directions with any holonomic system. I would not recommend one.