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

[Brandon Holley]

Originally Posted by Peter Matteson

We did some testing last night to see if that would fix our issue but it seems like we need to add ~50lbs to each side IIRC.

We think there are missing springs or something in the drawings that are supposed to be there.

The real field bridge is going to be considerably heavier than the wooden one I would guess. I don't know if its 100lbs, but that certainly can account for why the bridges do not act the same.

We used bungie cords underneath each side and tuned until the bridge matched the video.

-Brando

[BigJ]

It might be a slight angle on the photo but measuring with a piece of paper and a pen on the computer screen, it doesn't look like the same amount of bridge is on either side of the fuclrum-pivot-whatever.

[earlybird]

Our bridge turned out to be a bit more sensitive then the one in the video, but we still managed to write some autonomous code to auto balance as well as use our Kinect to drive the robot onto the bridge and balance.

http://www.youtube.com/watch?v=Vb7PVAy-a-o

[mdiradoorian]

Impressed.

[bearbot]

Originally Posted by earlybird

Our bridge turned out to be a bit more sensitive then the one in the video, but we still managed to write some autonomous code to auto balance as well as use our Kinect to drive the robot onto the bridge and balance.

http://www.youtube.com/watch?v=Vb7PVAy-a-o

dang robbie that awesome keep up the work i have seen our team grow over 4 seasons let go win a regional nice kinect looks so fun almost stayed up

[DonRotolo]

Originally Posted by notmattlythgoe

The bridge 2363 built is not acting like the one in the video. We tried the battery test and it is nowhere close to what the video shows. Is anybody else having this same scenario?

We saw a bridge constructed by another team, and it was WAY more sensitive as determined by the battery test.

Originally Posted by Peter Matteson

We did some testing last night to see if that would fix our issue but it seems like we need to add ~50lbs to each side IIRC.

We think there are missing springs or something in the drawings that are supposed to be there.

Originally Posted by Brandon Holley

The real field bridge is going to be considerably heavier than the wooden one I would guess. I don't know if its 100lbs, but that certainly can account for why the bridges do not act the same.

We used bungie cords underneath each side and tuned until the bridge matched the video.

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.

A more sensitive bridge is better for practicing balancing - it is more difficult, so if you can do it with a sensitive bridge, you will find it easy with a competition bridge.

But, if your mechanism to pull it down relies on the bridge to be very easy to pull down, in competition you may find that it doesn't work well.

[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.

[skimoose]

This was the first of four tests we were conducting on the triple balance end game. This was a test of three long/narrow robots balancing. The Lunacy robot in the center is a short/wide configuration machine which still had its hard wheels. So it was orientated sideways and pushed up to position by the third robot. We chose robots weighted to competition specs with bumpers at least at the key interface points. Remember bumpers add an additional 14" of length to your robot train. The frame dimensions on our robots are 1" under the maximum size allowed in both directions. The end robots are not propped up in any way. They were simply designed with the weight biased to the back two axles.

We have also tested;

long/narrow - short/wide - long narrow

short/wide - long/narrow - short wide

short/wide - short/wide - short/wide

arrangement.

These tests have helped us make drive train decisions. One thing that is clear to us, the first and third robots in this operation need to be fairly close to the same weight. Each arrangement has its own challenges which need to be mastered. We also learned a few other important things that will be incorporated into our final designs.

[JamesCH95]

Care to share some more of those results/conclusions with teams that may not have three extra robots kicking around to do the same experiments?

[bearbot]

have two of the student who weigh less than 120 lbs and have them balance with the robot like 2849 http://www.youtube.com/watch?v=W1O23...ature=youtu.be

[EricLeifermann]

Being secretive about good ways to get 3 robots on a bridge and balance it isn't going to help you in the long run because if you are the only team that can do it your screwed because you need 2 others to do it. So why not share so more teams can think about it and decide if they want to go the same rout? Helping everyone is really helping you this year....

[Drivencrazy]

Being secretive about good ways to get 3 robots on a bridge and balance it isn't going to help you in the long run because if you are the only team that can do it your screwed because you need 2 others to do it. So why not share so more teams can think about it and decide if they want to go the same rout? Helping everyone is really helping you this year....

Unless your particular strategy will allow three robots to balance independently of whether or not your alliance partners have the same idea.

If one had a strategy that would allow this then I think it would make them a very desirable pick.

[davepowers]

Originally Posted by EricLeifermann

Being secretive about good ways to get 3 robots on a bridge and balance it isn't going to help you in the long run because if you are the only team that can do it your screwed because you need 2 others to do it. So why not share so more teams can think about it and decide if they want to go the same rout? Helping everyone is really helping you this year....

I have to disagree, if a team has a way to balance three robots on the bridge that is extremely successful, it would be in their best interest to keep that a secret. Remember now this is still a competition. And if said team that has the good idea decides to use that in a competition, then I'm sure they will pick the teams that can be used in with idea and they can let the cat out of the bag and inform the other teams in your alliance when it counts.

-D

[skimoose]

Originally Posted by EricLeifermann

Being secretive about good ways to get 3 robots on a bridge and balance it isn't going to help you in the long run because if you are the only team that can do it your screwed because you need 2 others to do it. So why not share so more teams can think about it and decide if they want to go the same rout? Helping everyone is really helping you this year....

We're not being secretive, we're still working on solutions. Aren't you?

This picture explains an awful lot if you spend the time to analyze it. If we wanted to be secretive we wouldn't have posted a picture at all. There was quite a lot of chatter about whether three long robots could even fit on the ramp. this shows they can, if built with with biased balance points. You can see the margin for error with six wheel drive is 2-3".

Is this simple to do? Absolutely NOT!

Here are things that need to be addressed.

With 2-3" inches to spare this will take a HUGE amount of driver practice. This takes co-ordination amongst all three teams. Like last year's minibot end game if your team doesn't put in the blood, sweat, and tears to figure it out, you won't be rewarded at competitions.

You'll also need to consider the change in your CG as the bridge tips. How can you keep the robot from pitching off the end of the ramp as it descends? Inertia is going to want your robot to keep moving. Do you need some sort of braking system on your drive base? Something else? Suction has already been deemed illegal by the GDC.

With 2-3" of available real estate to move your robots in, is there a better ways to balance the bridge without moving the drive base?

Can robots mutually aid each other on the bridge? Yes. How? Still working on that. What ever the system is, it has to be independent of what other robots do. As shown in the Breakaway and Logomotion games, relying on a universal method of achieving the goal is not realistic. Very few teams adopted a universal suspension system or minibot/deployment system. If you limit your choices for alliance partners to only teams that have universal systems, you'll have few or none. You need a system that is independent of what other teams do and will work with all the strange shapes that FRC robots come in. This is no small feat, but if you can figure it out, you've moved up on my pick list. If I can figure it out, I just moved up everyone's pick list.

Since you can only extend off one side of the robot at a time, I think (at least currently) that you can only mutually aid one other robot. Assuming I can only legally help one of my alliance partners, at least one of my two partners better be able to aid a robot too. If you want to be a valuable addition to an alliance, you should have a way to aid another robot in balancing on the bridge.

Is there a preferred robot shape? I can't say. We've merely shown that what most felt was the least likely combination, long-long-long, can work. You should be able to figure out how the other combinations will vary. Robot frames have a maximum footprint, bumpers are a fixed size, and wheel base lengths can be figured out for 4, 6, 8, & 10 wheel drives. Can a 4 wheel drive robot figure out a way to cantilever two wheels off the bridge? Your team has evaluated the game. You've prioritized what parts of the game are important to you, and your team is designing accordingly. Our priorities might differ from yours so are the decisions we make relative or valid to your goals? I think its pretty obvious that we are looking strongly at the triple ramp and it will have some impact on our design.

Do you need to figure out how to do this? If you want to triple ramp, you'd better do your homework.

Originally Posted by JamesCH95

Care to share some more of those results/conclusions with teams that may not have three extra robots kicking around to do the same experiments?

I just did.

There's no magic to starting the triple ramp. It's pretty straight forward. One starts up the ramp, As One clears the end of the ramp, Two starts up right behind One. They don't need to be bumper to bumper at this point. Once Two has cleared the end of the ramp, Three gets bumper to bumper with Two and the bumper to bumper train takes over. Now it has to become a coordinated, bumper to bumper procession. We're still working on an effective process for the final balance.

You don't always need three robots. one or two 140 pound students should fill in nicely. Obviously the center robot in this operation is kind of along for the ride. Its between two robots and all of its wheels can be in contact with the bridge.

Now if you're one of the end robots, you are earning those points. being cantilevered off the end of the bridge is tricky. If you can position at the high or low end of the ramp, with your 1.5" of real estate to maneuver in, and stay there when then students shift their positions to balance the bridge, and you don't fall off, you've figured out the triple ramp.

What say you oh Car Nack, will the triple ramp be achieved?

[Aren Siekmeier]

Originally Posted by skimoose

What say you oh Car Nack, will the triple ramp be achieved?

It certainly will be on Einstein, and that's where we all want to be, so we're going for it. Besides the fact that it isn't turning out to be all that costly in terms of design time and complexity, so far.