13-01-2012 09:50

Hallry

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

Two narrow front robots, and a wide front robot situated long ways...just shows that three narrow robots CAN in fact fit balanced on a bridge =P

13-01-2012 09:50

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

Oh shnap! Gus got balance! Now let's see you do that with all three robots being controlled, not just placed on a bridge!

13-01-2012 09:51

BrendanB

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

What are the dimensions on those robots on that bridge? Are there any supports/weights added to those robots? Did you drive these robots onto the bridge or did you place them?

Very impressed to see this!

13-01-2012 09:51

JamesCH95

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

Awesome.

13-01-2012 09:55

Chris is me

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

All it takes is for two of the three robots to have identical CGs. And none of them get to move.

I'd still say wide is the way to go.

13-01-2012 10:05

Brandon Zalinsky

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

Nice! Do you have any clue about how much room for error you have when balancing the three robots?

13-01-2012 10:06

JamesCH95

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

Could all three robots drive onto the bridge? Even if you just pushed them on I'd be curious.

13-01-2012 10:20

kwotremb

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

Thats what I was wondering as well. So you have the first two robots on, how then does the third robot then push down the ramp to get on? Or else the second robot will have to be pushed into place which will be hard with most 6+ wheel robots.

13-01-2012 10:42

Peter Matteson

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

Does your ramp actually act like the one in the field tour video?

13-01-2012 10:51

notmattlythgoe

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

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?

13-01-2012 10:59

Jon Stratis

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

With coordination, it's certainly possible. First robot drives onto the ramp, but doesn't go past halfway - the ramp is still down. Second robot drives up and bumps into the first. Together, they slowly start inching up. The first robot can go past halfway, so long as the second robot is far enough back to hold the bridge down. The third robot comes in and starts pushing against them, and all three start slowly inching their way up.

The only thing that worries me is what happens when they get to the balance point - suddenly the bridge will swing down to level. Will that motion be enough to throw the first robot off balance and tip it over? Even if it doesn't fall all the way off, as soon as part of it is being supported by the ground, the bridge is going to go back up to where it started, further tipping that unfortunate first robot.

13-01-2012 11:24

rees2001

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

We are having the same issues. It would seel like the low cost bridges are lighter than the actual bridges. We made shelves on the underside of the bridge and are working to add weight until is acts like the competition bridge. I hope this is accureate.

13-01-2012 12:54

Peter Matteson

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

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.

13-01-2012 13:06

davepowers

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

Who said they were placed? ;]


37 inches long for all of them. There are no supports or weights. And that's for you to decide. ;] We'll have some fun stuff up tonight. Thank you!


Who said that the two end robots have the same CG's? I'm fairly positive they both aren't exactly the same anymore, especially with lack of minibot ramp, paint, and electronics board configuration, they are fairly different now. I do agree with the none of them get to move though, regardless of weights and CG.


Fairly close to none.


Yes all three robots could drive onto the bridge with a little frame scrape, but did we drive them all together? You'll just have to wait and see.


As close as we could get it. A little tip for anyone building the bridge is you're going to need to add weights to each end. And quite a bit of it too.


-D

13-01-2012 13:44

Brandon Holley

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

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

13-01-2012 17:06

BigJ

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

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.

13-01-2012 21:06

earlybird

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

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

13-01-2012 21:12

mdiradoorian

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

Impressed.

13-01-2012 22:36

bearbot

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

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

13-01-2012 23:01

DonRotolo

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

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

14-01-2012 00:20

Kevin Sevcik

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

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.

14-01-2012 23:41

skimoose

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

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.

15-01-2012 11:48

JamesCH95

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

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?

15-01-2012 13:41

bearbot

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

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

15-01-2012 13:57

EricLeifermann

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

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....

15-01-2012 17:13

Drivencrazy

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

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.

15-01-2012 17:43

davepowers

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

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

15-01-2012 21:01

skimoose

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

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.

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?

16-01-2012 02:18

Aren Siekmeier

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

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.

16-01-2012 02:28

Aren Siekmeier

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

I think we need some physics. All that we are given about the real competition bridge is the field drawings (from which we could glean a lot of things) and the "battery test," which I would argue is all that matters. You absolutely can get a wooden bridge to pass this test by playing with weight distribution, but adding weight to each end doesn't accomplish this. In fact, adding equal weight to each end does nothing. When the bridge tips around either of its hinges, you are lifting all the weight on one side of that hinge while letting all the weight on the other side down, by more or less equal amounts. The parts of the bridge OUTSIDE the two hinges cancel, because they are equal (sort of, in the team drawings they aren't really), and they are still equal if you are adding equal weights to each end. It's the weight BETWEEN the hinge points, and to some extent the hinging geometry itself, that affects the "tippiness." So by adding weight between the rock points, you are adding weight that must be lifted when the bridge tips, making it less sensitive. By taking away weight in the middle, you lift less weight to tip the bridge so it tips more easily and more sensitive. I didn't actually do any really involved analysis of this problem (taking into account things like the varying distance of each end from the hinge point, how the cg moves and the weight distribution changes when it tips because of the height of the cg, etc.) but I consider these to be mostly negligible so hopefully my rough approximation for a first pass analysis is good enough.

16-01-2012 15:15

ez4nick

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

was anyone able to successfully balance a bridge with the battery test without any modifications to the bridge??

17-01-2012 09:42

lerikson

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

Pretty impressive.

17-01-2012 09:45

Jared Russell

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

We were not. It takes adding (quite a bit) of weight or bungees to get it even in the same ballpark.