The Barrier Thread
 

So lets talk about the barrier. The thing is a lot taller than you would think at first glance; 4". The 6" standard 6WD can't get over it, it would seem, though I would like to see someone do the math. Can the kitbot get over it?

Anyhow, how important do people think going over the barriers will be? And how do they plan to do so?

Re: The Barrier Thread
 

Reaction while watching animation: "Pssh, it'll be easy, no different than going over the bump/ridge that divides tile and carpet(If that makes any sense)"

Reaction after ::rtm:: : "So let's get to work on deciding our bridge-going over mechanism"

Re: The Barrier Thread
 

A kit bot with 6in wheels could get over it if you had some spacers between the wheels and frame. This would raise the frame just high enough to let it get over. Not sure how bumpy it would be but it could work.

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Actually you can get a 6" wheel over the barrier if you have the momentum and tread to do so.

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Well if you have all six wheels driven and a full weight robot I think it would be quite easy. maybe not very effective. Heck it might damage the wheels after repeated use.

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While I cannot give any proof on this, I can fairly certainly say you do not want to brute force over the hump; i feel you could have serious damage to your wheels. I saw teams break their wheels coming down from hard landings in breakaway.

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We are thinking that with big enough wheels the barrier shouldn't be to rough. I think it will be important to avoid traffic jams at the bridges but not important enough to warrant another system.

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Yep, our 2010 robot broke one of her wheels.

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Breakaway was a much higher drop, though.

EDIT: How would we do the math for this?

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look at my signature link click on update 7 and see our video of what we were trying to do today.

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But you had that little thing in front. Do you think something similar will go through inspection?

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But what if you load your robot with an extra 90 lbs?

EDIT: And it also breaks the bumper rules; those are uncovered corners.

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It will be underneath our bumper.

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Is that even steel that you're running over?
And the other two are correct; you're violating bumper rules and your robot is very lightweight. In addition to this, because the person on the left didn't hold onto the strip, your robot is not taking as much force. Also, the repeated attempts will put a large wear and tear on your wheels/robot.


How would you manage to put the bumper around that while still having an effect?

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it is a prototype on the first day and we have other thoughts of getting over the barrier.

come on we have not thought of everything yet just wait in the next couple days we will have something.

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To everyone who thinks you can cross the bump unaided (that video shows what lifting the robot before the wheels hit can do) with 6" wheel, I'm fairly sure that is wrong. The center of your wheel is 3" off the ground and as such you would ram flat into the metal. MY guess is that you'd break the wheels or send your robot hurtling head over heels before it would go over the bump. Even a 8" wheel would be sketchy, because it is level with the top of the metal. To be certain you would need 10" wheels.

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or you can have pneumatic wheels

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I believe what you're looking for is shear stress analysis.

If the side-profile of your robot is trapezoidal-esque - that is, you have powered wheels elevated above the ground - you'd be able to do so with 6" wheels.

I don't personally believe that people will break their wheels by anything, including driving into the rail (which is steel, as can be confirmed by the CAD) - if they do, it'll be because the wheels will have already experienced heavy damage - but I do expect to see wheels damaged by collisions and impacts. Plactions will crack very easily if you abuse them enough.

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My question on math was how we would calculate if a wheel can climb a surface, my bad.

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Then you'd be comparing the net upwards force (acceleration and friction) to gravity.

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Alex,

If you actually do the math and check your geometry, you will come to the conclusion that a 8wd 6" wheel will definitely clear the 4" "Bump". Also there are a lot of ways with 4"-6" wheels you can clear it. 10" wheels would be a bit overkill.

-RC

Re: The Barrier Thread
 

I was thinking about this too, the 8 inchers from AndyMark are lookin' especially nice right about now...

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Yeah, our feeling is that just throwing more wheels at the problem would be more effective than massive wheels.

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FRC gamers are so used to nice flat surfaces (for the most part) we hardly ever think of a standard vehicular feature ---- suspensions. I'm looking forward to see what the 6WD fans do for this year.

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Sorry, but I have to disagree. I can even do it with 4" wheels.

As a trivial example, imagine a wooden 'ramp' at the front end of the robot (inside the bumper perimeter), starting at 5" and ending at 2". Hitting the barrier at speed will launch the bot over.
As for high-centering, if you use Gates Belt instead of chain, it can act as a tank tread for between the wheels.

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Key word in the post you quoted was "unaided". Take away the wedge and try again. ;)

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I bet our 2010 robot could make it over with no problems!
http://www.chiefdelphi.com/media/photos/35272Some nice 10in pneumatic tires!

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We're planning on using the slants in front of our robot along with the 8" pneumatics from Andymark. Deflate the wheels a tiny bit, and they become instant shock absorbers.

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No one was dragging you down for not considering the entirety of a design; they were just pointing out the possible flaws before you found them later on...

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I think he was being slightly sarcastic.

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If you had 6 inch wheels, you would still be able to drive up the rail like this.
http://www.youtube.com/watch?v=3qWYAOGZVM4
Not necessarily recommending it, but it is using small wheels to drive up a large obstacle.

If one was to use Gates belts, would tensioning them be a problem when the barrier pushed into them?

I think high centering could be a large problem. Could this be solved if you had a convex bottom part of your frame so it had a turtling effect (not stable so it doesn't balance when resting on the frame between the wheels)?

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If anything, it would increase tension, possibly to the point of failure. Technically, this would be a "tensioning problem", but not the one people normally think of, also, it could easily be reduced by adding idlers to the belts where they are exposed so that the belt is pushed into the idler rather than into nothingness.

Re: The Barrier Thread
 

Anyone thinking of using a 2 wheel robot? I mean huge wheels like 20 or 24 inch bike wheels. I would understand how to keep it upright during operation, but before the match? Little omni wheels to support might help, but will hinder it going over anything.

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yeah... after all of the people prototyping WCDs over the break, I wonder too... good luck using 4" wheels to cross the barrier...

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Our team installed aluminum wheels at the front, which were able to sustain the weight of our full-weight robot coming down from the bump.

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Our team is thinking of using four or six wheels, and using belts instead of chains. The belts will be backed on the bottom side by a flat panel, so that they can act as tank treads as they go over the barrier.

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I was thinking something like this: http://www.youtube.com/watch?v=Ktw6AZU2Wtk&t=0m36s whatever drive you'd like+ the threads in front that are shown in this video.

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One thing I noticed is the bumper rules this year. If I read correctly the bumpers have to exist somewhere between 2" and 10" from the ground. It seems to me there is only one location for the bumpers if you are trying to cross the bump. The top of the bumpers would have to be at 10" and going down to 5" off the ground. This is the only way that the bumpers won't hit the bump first. As well your frame perimeter would need to clear the bump as well so your wheels are the first thing to hit the bump. The KOP frame assembled with 6" wheels and per the provided instructions will NOT cross the bump even with brute force since the first thing to hit the bump would be either A) the bumpers if the lowest part of the bumper is below 4" OR B) the frame would hit the bump which would be flat vertical metal hitting flat vertical metal. The provided 6" wheels with no extra elevation of the frame would only lift the frame 3" off the ground (actually a little less than that).

Rookie teams please investigate this fully before putting together the KOP frame. You will only create extra work if you don't think about this before hand.

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Step one: buy a segway. Done

Or you could use the same concept Dean's wheel chair does where it starts on 4 wheels and stands up on 2.

My only semi seriou idea with this is tristar wheels, but I think even that is overkill. http://orionrobots.co.uk/Tri+Star+Wheels

I think my team is plannig to have a ramp at the front of the chassis and actually having a frame with low ground clearance so we slide along the bottom rails of the chassis across the barrier. We think driving six wheels will keep us from getting stuck, and sliding would decrease the impacts and jarring of the robot.

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This is only true in certain circumstances. It's not difficult to envision a situation where lower bumpers could be used, and yet the bump could still be traversed.

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Are you thinking of a mechanism that extends past the bumper perimeter, like a foot or a wheel or a wedge?

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It would be no fun if I revealed all my secrets... :)

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Awwww.... shucks.

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The last time I saw a mobility obstacle like this was in '04, I believe it was, when robots had to climb a couple of stairs to get up on to a central platform.

There were a number of ingenious solutions including some very nice treaded robots and the occasional one with some pneumatically activated "helper wheels" that would come down and lift the main wheels up on to the step.

But I agree that suspensions might be useful to have, too. I think that might be my first place to look.

Jason

Re: The Barrier Thread
 

Who said that a WCD has to have 4" wheels?

- Sunny G.

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This coming from an East Coaster, of course. ;)

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Go on the bump at an angle with 6" wheels and you can clear the bump without damage.

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Can you clarify and demonstrate that, please?

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I'm putting it out there and betting the majority of teams who weren't around for 2004 who try to climb over the barrier will end up like below.



You need to plan for worst case scenario, other robots contacting you and obstacles in your way as you try to traverse the barrier, if you choose to go that way. Trying to cross the barrier in your lab in a best case scenario would be as effective to your team as practicing your robot shooting at the hoops using a football.

Oh and for those of you who think you will not have damage to your robot if you just try to plow over the barrier at high speed, I suggest you do a real world simulation of this. Go find yourself some road hazard strips like this (or a simple curb) and feel the result of going over those even at 10 MPH. I think you will be surprised at the second thoughts you might have at just plowing into the barrier then.

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Well, automobiles have a suspension typically, and honestly driving fast over most normal speed bumps works just fine. I'm not so sure I'd do it with a curb, at least not in my own car. :D

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I think he means to drive over them with an FRC robot(?).

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No I meant in a car, because a car is designed to absorb and disperse the shock of bumps and you will still feel it. Now imagine the shock with no suspension or dampening and having very little clearance.

[Yes i know there are many other differences to take into perspective also, like weight, but this is just to get brains thinking more toward reality.]

Re: The Barrier Thread
 

Very good, then... I liken to ramming the 4" barrier with a 6" wheel to ramming a 20" curb with your 30" car tire.

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This is a terrible analogy, there is no connection between hitting a speed bump at 10 mph in a 4wd vehicle with suspension designed to drive on a mostly flat surface and hitting a 4 inch bar with a 120lbs robot that is being designed to do exactly that.

This just makes the analogy worse a standard car would clearly never climb a 20" barrier, that isnt what it is designed to do. A 6 or 8 wheel tank steer robot can easily climb over the 4" bar if the driver is smart about it and it the system is designed to do this. There will be a significant number of very good teams who stick with 6 or 8 wheel drive using 6 inch wheels. There will be less people tipping over due to going over the barrier than there were who tipped going up ramps in 2006 or 2010 or up the stairs in 2004. I would even guess that more robots will tip this season trying to go over the bridge than trying to climb the barrier.

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Sure, but I can see a relationship between speed and damage/wear here that's rather obvious if the system is not well designed.

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What are teams thinking to get over the bump, I am really confused as to how 6 inch wheels 8WD can do it w/out some sort of skid plate in the front to get off the ground, but then your climb becomes....ugly

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They are thinking about another way to get to the other side of the field whenever the bridge is being used or a robot died or something in that order. In my opinion it is a better choice to go over but every team has their own strength, weaknesses, and opinion for the features on the robot.