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Let's Talk About The Bridge:
Does anyone think an active balancing mechanism, like a moving heavy object, on the robot to balance 3 robots? My guess is, like most years, the majority of the robots will be around 120 lb and it would be relatively easy to balance one or two on the bridge. I had the idea of putting the battery and electronics on a platform that can be shifted from the front and back of the robot and anywhere in between to actively balance the robot. Having the weight shift back and forth instead of the actually moving the robot will be better when trying to squeeze 3 robots on the platform.
Any one have any objections to that? Relatively, it would only add a weight of a motor and the mounting. All the other weight will come from other necessary components such as the battery and other electrical components, perhaps even the shooting mechanism itself. |
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It'll be a whole lot easier to just move the base at a slow speed then to actively shift the weight in your robot.
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It would be very likely in your idea that the cord could get caught or yanked from the connectors. The battery alone could work well if nothing would tangle on its cord, but a dead weight (if the robot has weight allowance enough for it) would serve the purpose just as well. No math to back this up, but anything lighter than the battery may not be worth spending the weight or motors on.
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I was thinking of a lead screw with a "nut" that was just a huge chunk of steel with a threaded hole. But I also agree with BrendanB, that just careful driver control can be sufficient.
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I'll second Brendan. Why not just move the whole robot instead? You presumably already have that system on your robot and working. Why make even more work for yourself when you already have a shooter, pickup, and bridge slapper to design and build?
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In the eliminations how does the coopertition bridge play out? I can't find that anywhere. |
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I am wondering how robots are going to make the bridge go down form the neutral position. That may be hard. Is it just gonna be you run into it and it will move? or will we have to make a mechanism to lower it for us? Any thoughts?
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Last year our robot had a "finesse" mode, that literally slowed down the arm motors and the drive motors. I think a similar mode (that can simply be activated by a button on the joysticks or a toggle switch) could be highly beneficial when trying to just drive your robot to balance.
If your robot this year ends up with any kind of swinging chute or arm, then you could probably use that to effectively shift the center of gravity. ALSO: Quote:
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What about placing an accelerometer on the robot that allows it to autonomously balance on the bridge? You could have it detect when you are unbalanced on the bridge then press a button that activates the auto-balance and drives to correct the imbalance. Just tell whomever you are balancing with that you have this auto-balancing feature and you have yourself 20 points or 10 points and a 2 point CP bonus as the case may be!
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Please build a little robot like Team Thrust's in 2010, so we will all fit on our ramp during the match. Thanks 694 |
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edit: any legality on "latching" onto other robots? The "t-rex" arms to push the platform down can be used to latch onto robots. |
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I'm thinking "robot one moves onto the ramp, robot two moves onto the edge. Robot one stops moving, robot two balances with accelerometer or gyro assist."
If three robots, it becomes, "robot one moves onto the ramp, robot two moves onto the edge. Robots one and two creep forward until robot three can move onto the AAAAAAAAAAAAAAAAAAAAAGH! THIS IS SO HARD!" Should be awesome! |
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How much force is required to bring the ramp down?
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On the video on Youtube they stated that if you place 2 batteries next to each other, 28 inches out, the bridge should stay level. Move it an additional 2 inches I believe, and it would tilt. Use physics, convert and stuff, and there's your answer! :p |
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What about this scenario:
Eliminations, you have two robots on your alliance bridge and one robot on the coopertition bridge (and thus prevent your opponent from scoring on the coopertition birdge): You get 20 points for the 2 robots on the alliance bridge and 10 points for the robot on the coopertition bridge, meanwhile preventing your opponent from scoring 10 points because you prevent them from using the coopertition bridge. Unless your opponent could get 3 robots on their bridge, this scenario would come out the same as if you got 3 robots on a bridge and they got one robot on the coopertition bridge in terms of point differential. I think the bridge will prove to be pivotal because not only do I think the points are weighted more balanced than in past years (...minibots), but also because FIRST reserves the right to change the point values come Championships. |
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The Coopertition bridge scores no match points.
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So in other words, go big or go home.
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If you made a wide base robot you could have a larger intake and more easily fit 3 bots on a ramp.
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I think getting 3 bots on will work well if the last bot to get on has a bridge lowering device.
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just put your battery on a linear slider and rack and pinion...::safety::
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[G37] Final scores will be assessed 5 seconds after the Arena timer hits zero.
So, whatever you do to balance, make sure it stays in position after you lose power. |
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I guess this thread would be good to talk about how teams plan on moving the bridge from the static position down to court level so the robot can get on the bridge.
Are you going to stick a wedge on top of your robot to push it down on the other side for an alliance member? Are you going to build something that knocks it down on your side? Are you going to put legs on the robot so it can jump, or something else? |
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Some kind of deployable traction device would be desirable if these are used, of course. |
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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?
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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 |
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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. |
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You'd need something like this, and it would be pretty hard. Look at other '07 bots http://www.youtube.com/watch?v=zgHanZXFweg |
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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! |
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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. |
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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 :)
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Ah yes, I see you're right. I should have read the drawings more carefully. In that case I expect somewhat fewer tipped robots.
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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. |
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I am not sure that the new update precludes robot on robot. The bottom robot is touching the ramp and it is supported by the ramp. It doesn't matter that there is another robot on top of it. However, one could also argue that the upper robot must be supported by the ramp by default since it is on a robot completely supported by the ramp. Hmmmm seems more clarification is needed here for sure. |
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Completely unrelated to all of the posts in this thread so far, but I have a new question:
Do these measurements seem accurate? If not, are they close enough that it doesn't really matter? ![]() |
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OUr team was mulling over an idea like this. Two non driven wheels with no interaction with the drive train are on the end of a rotating arm of sorts. THis arm is left horizontal at the base of the robot within all wheels and bumpers while drivng. When robot is approaching the bridge the arm is pushed down, pushing the wheels onto the ground lifting the front end of the robot off the ground high enough to place front wheels on bridge. Back wheels can still drive robot forward to get front wheels over bridge edge. Then the arm is pulled back and the robots weight pulls the bridge down with the front wheels already on and alternate wheels stowed back below.
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IMHO, each robot should have a bumper grabber to aid in bridge balancing by latching on to their neighbor. You have a pretty good (but not perfect) idea where your partner's bumper will be so it shouldn't be too difficult. Perhaps not a top priority though. |
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the center of gravity of your own robots's a counterweight
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Based on the calcs that I have done (from the info the video provides plus the other data from the rules, etc.),
There's a lot to think about... ...fun fun fun... Joe J. |
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Thanks for the analysis Joe....
Do we know exactly how far the Bridge edge is from the wall. We have it at around 1 inch. Can anyone confirm this from taking measurements from the actual demo field? |
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Does anyone have the wieght of a battery handy?
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IIRC, they're ~15 lbs
Edit: looking it up, they're 6.2 kilograms = 13.6686603 pounds (from the datasheet) |
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[Semi-teaser] Once you realize that getting FOUR full size robots on the bridge is quite possible without them overlapping, then the ways for easily getting three on and balanced start to look a lot easier to accomplish.
-RRLedford |
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I would love to see if anyone builds "minibots". Yeah of you can get your robot down to 10x10 that would be intense :) but would probably not be very usefull so how about other weird sizes like 10x 20 :) I want to see something crazy like that designed for 3 bots on a bridge but still able to function during normal game play.
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While smaller robots would make it easier, it's not impossible with "normal" sized robots. |
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-RRLedford |
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i want to see your math. no really... 28*4=112 inches + bumpers=136 inches ok so how do we get 136 inches onto 88 inches??? finishies lolrage realizes we have three robots per alliance.........:mad: |
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I only said that four full size bots CAN be balanced on the outer bridges, and without overlapping each other In order to imagine what I am saying you will have to start thinking more "outside the bridge" Now that I consider it further, even five (5) full size bots can balance on the bridge -RRLedford |
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-DIck Ledford |
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Thus, theoretical maximums are not valid compared to the real world physics of making it happen. In fact, I believe we will see a number of rolled robots as in the elims as they try for 3 robot balances. Build your robot robustly :ahh: |
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Since we are able to hang off the SIDE edge of the bridge with less than 1/2 of our width located above the bridge, our partners can drive right past us, stopping near the middle. This lets all of three of us remain closer to the center of the bridge as we balance it, making the job much easier than if we had two bots hanging off the ends. None of our alliance needs to go anywhere near the ends to still have a 3-bot balance in elimination round, and we all have plenty of bridge length to work with as we balance it. -Dick Ledford |
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This is what I have observed about balancing after practice and going to a scrimmage: it is all about knowing when to just "stop driving". So far, I have consistently balanced the robot in 4 to 10 seconds every time. I realize that you just require a lot of that "gut feeling". You just have to "know" when to stop driving. Once you overshoot, it gets fairly hard to balance. Also, about balancing two robots, I found hand signals to be the best way to communicate with the opposing alliance; have the coach watch and do hand signals.
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We really had to get as much of our mass as possible assembled as far over to the right side as possible and we are still needing a bit more far right placed ballast to improve our bridge traction for the 2-3 driven wheels that remain in contact as we go up it. We will likely just keep adding weight there right up to the point where we hit 120 lbs. so we can max out our traction for the right side (on bridge) wheels. Our left wheels are just spinning in the air as we climb up using only the left <1/3 of the bridge. It is a very cool looking DOUBLE balancing act. -Dick Ledford |
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