Arm Designs
 

I know there is a very similar thread already out there, I just wanted to get some input specifically related to the arm design. What kind of design would work better, fork lift or a bending arm? Ideas? Post away.

Re: Arm Designs
 

I'm not sure how well a forklift would work given that the maximum height of the robot is 60" and the goals with a couple tetras on them would be too high.

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If you've ever watched forklifts before, you notice that on some, they dont extend upwards to just the top of the vertical segment. It's like a telescoping pole. the segments in front of the first vertical piece start extending from the top of that point (for our purposes 5') and allow you to reach a much higher height

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One thing about being a 14 year team is you get to see alot of previous design that could work with this year's game and I think we found a good one today.

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I'm a fork truck driver (narrow aisle) and the front end of the truck is heavy and needs to be counter balanced or it'll tip over. I would assume the same would apply to the robot if something similar was made (I think the robot would end up way overweight and also easy to tip over).

Re: Arm Designs
 

But our forklift doesn't need to be on the front of the robot. It could be right in the middle: simply drive underneath the large tetra and deposit your small tetra. That's the advantage of just having tetra frames. You can be inside the big tetra while you cap the little one.

This however, only removes the need for a counterweight, and if I hit you with your center of gravity really high you're going to go a-tumbling.

Re: Arm Designs
 

Forklifting can be worked nicely as can an articulating or telescoping arm. But why would some one on 177 mention that? :D

The history section of our website should inspire some of you.

http://www.swindsor.k12.ct.us/Highsc...s/clubs/first/

Pete

Re: Arm Designs
 

Because I'm a rookie and don't remember last year :D

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I think using the arm is better since you can grab the tetras anywhere around the robot; whereas, the forklift requires you to be in a specific position to grab them. However, with an arm, it's harder to control your robots balance n might tip over, but you may be able to use your arm to pick yourself up.

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What specific arm designs would probibly work best for manipulating the Tetras?

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The teams ive been on have done both an elevator system and a stereotypical arm design. Both have worked to some extent. The standard arm design is easier to design and build, but i feel the elevator design is the easiest for the drivers to handle. The most important factor in the design is ultamately how much thought and detail goes into it.

Re: Arm Designs
 

You're right, an elevator design probably would be easier for the drivers to handle. but depending on which way you make the lift mechanism, you might be limited to coming at the tetra in a specific way. Either design you use is goign to require a lot of practice though. Manipulating those tetras will be no piece of cake.

Re: Arm Designs
 

Something to consider though about going into a goal structure and then pushing the tetra up is that you risk dislodging the already stacked teras (incuring point penalties and losing posession permanently for the goal to the oposing alliance), there could be tetras inside the goal that impede your movement, and you have to be able to get over into the goal structure without tipping (topheaviness could become an issue). Hope that helps you guys fine tune something to meet your objectives. :)

Re: Arm Designs
 

we've had considerable success with a few kinds of arms but all 'bending arms'? i think you might call them? our best one was this year's occra one. which wouldnt be too useful in this year's first game but it was a nice 4bar crossing linkage thing.

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My first impression is that (sorry Pete) a forklift would work better. Besides being a lot easier for drivers to use, it's easier to get multiple points of contact on the tetra with a forklift than an arm. If you try to grip a tetra with an arm that only makes contact at one point, you need to make sure you have it gripped hard enough to keep it from rotating. But if you make contact at multiple points it's harder for the tetra to move.

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i would go for a cross design. The vertical would press on one edge of the triangle. The horizontal would go through two holes somehow. Then sort of pick up using the pivot points, then that would lift the triangle up at an angle, making it easier to put the tetra on the goal

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Has anyone considered a three pronged hand at the end of an arm? Any point of contact would result in the tetra being grasped in some way. What do you think?

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When I was on team 535 (2001 rookie year) we had a robot with a forklift mechanism. With our arm we could lift the large ball 11' into the air every time :ahh: And we were able to keep it within the 60" spec.

Wayne Doenges
CAD Mentor

Re: Arm Designs
 

wiat... are you referring to your forklift as the arm? and if you have any pictures please, dont refrain from posting them.

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My fear is that when you are trying to place the tetras and when your arm or forklift or whatever is at its highest point, a little bot will come over and knock you over. Due to your arm being high up, you would be very vulnerable. Besides, when you stack those tetra's you have to remember that the height of the stack will be increasing and you have to make you sure your bot can go higher than the height of one tetra stacked.


GO 1403!!!

Re: Arm Designs
 

That is exactly what i have been thinking. It would seem like it is impossible to miss the Tetra because no matter what you can get it. It would also allow for a greater percent error as far as control is concerned because you'd have a greater chance of getting something.

Re: Arm Designs
 

Arm design this year is going to be much more important. Having a robot that the controller can use to react quickly to the game will be cruical this year. Ease of use and fast response times will be very important issues.

Does anyone have any ideas about a non-forklift style arm that could be useful?

Re: Arm Designs
 

That's what 1474 has been looking at for a design. I'm not sure exactly how it'll all work out but we're hoping for the entire arm to be able to rotate around the chassis of the robot.

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Our team seems to have decided that the bendable, traditional arm would be better than a forklift in that it allows for more precision than a forklift type arm would.

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it depends on the chassie but my preference is a lift because it doesn't move the cg out it just moves it up a little. that is just my opinion.
hope u do well see u at the comp

Re: Arm Designs
 

For arm design I was tossing around the idea of something similar to a bucket truck arm (that's a bending arm isn't it?). My team hasn't taken much fancy to it but I think that it could give a lot of flexability in motion when the tetra is so high in the air.

Here's an Example of what I was thinking (This isn't a robot picture, just an idea). Just my thoughts though :)

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After my earlier post I took some time to think and came to my senses: an arm's the way to go. If you've got a forklift then you need to be right next to a goal to score, so a robot could just get between you and the goal. But if you've got an arm you can reach over another robot if it's in your way. The hard part is going to be designing a mechanism for the end of the arm to effectively pick up and score the tetras.

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our team did some calculations and discovered that with a folding arm, there is a tremendous amount of torque placed on the main joint while carrying a tetra. :(

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reaching over a 38" long robot and then reaching 10-14" into the goal (assuming you hold the tetra from about the end) is going to put your CD pretty far forward. Don't expect to be safely reaching over an entire robot without something to stabilize you.

Re: Arm Designs
 

There is a lot of geometry here to play with and work out. I wouldn't rule out anything just yet. Every year I see some one else figured out how to do the killer strategy that I couldn't figure out how to accomplish.

Also tetras aren't had to pick up. Play with them for a couple minutes. It took us all of 5 minutes to come up with a K.I.S.S. method for doing it once we had a couple made.

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I really like the forklift idea, I can see a robot driving over the flat side of the base of a goal tetra to the point where the scoring tetra is over the point of the goal tetra. Then just lower the forklift onto the top of the goal tetra. You may also be able to articulate the "tower" the the forklift is attached to to lean the tower forward, enabling the bot to be further away from the tower. This would raise the center of gravity, but I see it as a last ditch effort.. I also see the scoring tetra hanging from a hook or something like it on the bottom of the forklift. I think this would be easier to place on the goal. Thoughts? Opinions?

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cd? cog? or am i mistaking sumthing?
but who said it had to be one joint.

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Hey, how about that arm on the blue robot in the new game animation? You know, the one that extends about 20 feet?

I'm glad Dave and I share a common sense of humor.

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My team doesn't have a favorite idea yet for an arm, but I'm looking forward to go to competitions and see all the different designs people come up with.

Double-jointed is looking good for us, though.

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We were discussing a forklift today, but we found out that it would require a long prong to reach the top end of the goals, causing massive balance issues... A forklift elevator combined with an arm of some sort... hmm...

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Yeah, for anything short of a verticle lift you're going to have some massive torques on the arm. The tetras are heavier than the big ball last year and heavier than the boxes from stack attack. You also need to reach rather far into the goal which can add two to three feet of extra torque on any type of arm, verticle(forklift), extending or swinging. Getting the tetras on top of the center goal is proving to be much trickier than at first glance.

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undefinedundefinedundefined I know i am new at all of this but would somebody please tell me how to start a thread i have no idea and spent 2 hours trying to find it . Thanks :ahh: :ahh: :ahh:

Re: Arm Designs
 

You would not necessarily need a long heavy forklift we discussed that a couple of days ago but a forklift elevator combined with some sort of arm would be ideal

Re: Arm Designs
 

so how about instead of an arm, you do a escaltor type deallie, have a concave tetra style figure at the base of your bot and then with like a couple of belts drive it up and deposite on top, we had something like that last year except it went the opposit way. i dont see why that wouldnt work

^/|
/ |
^/__| kinda sorta :D :confused:
you get the idea, im trying to think outside the box

Re: Arm Designs
 

I think a "bending arm" would accomplish the task better because it has more ranges of movement vs. a forklift. Forklifts simply move up and down. Although simple is sometimes good, this year I think the more complex arm designs will win.

A "bending arm" also allows the robot to stack tetras on a goal at a greater distance than forklift, due to the fact that forklifts have to be under the goal and be perfectly aligned the properly stack a tetra.

As far as CG is concerned, simply change where you mount your arm in relation to the robot.

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But you have to reach 7 feet and up ( if you wanted to stack more tetraes on)!!

Won't height be the biggest problem for every team????

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In 2001 when I was on 177 we made a 14-foot telescoping arm to put the big balls on top of the goals. Granted we didn't need to worry about reaching very far from the base of the robot, and I don't think the balls were as heavy as the tetras are, but a long arm can be done.

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It's not so much height that is the concern, it's that the robot has to bend that arm over a greater horizontal distance than before with a heavier weight on the end. Again, height isn't the problem, tipping is, and not from jerking the robot too much. I think some teams will be using the edges of the goals as rests, to help aleviate the problem of tipping, or at least approach the goal from that angle as a safeguard in case they do in fact tip over. (that way they rest up against the goal with a lot less damage done to their bot and the possibility to right themselves)

Re: Arm Designs
 

The general consensus among the team leaders is that less is more... Less joints with more strength will give us a bit of an edge over some weak arms that can move everywhere in sight, but barely lift the Tetra. And let me tell you, we just finished constructing one of those things tonight, 9 pounds doesn't sound that heavy until you try picking on of these things up. Then thinking about moving it 8-9 feet away from the base of the robot... You get the idea. If you can, try building one of those Tetras as soon as you can.

Re: Arm Designs
 

Well, I mean that's kinda the point. I think that some people aren't quite realizing how far they are gonna have to lean out to cap. I would not be using a pnuematic piston to actuate the arm for that very reason. I just don't feel that it would respond quick enough under that kind of load (we use pnuematics last year to actuate our arm that capped and it was not incredibly responsive). We should be using motors to actuate the arm this year. (The new Fisher Price ,otors are looking promising for this application).

It's around 2 and a half feet horizontally that you have to lean out, assuming that your right there in front of it. In reality, it's gonna be a bit more, nearly as large as a bot footprint. Yes, the motor or pnuematic piston actuating that arm would have to mighty powerful to have any kind of dexterity when stacking.

Re: Arm Designs
 

we were just thinking of using a reverse wheelie bar on a long clyinder. I have the feeling that that issue is going to be a trial and error thing. Either that or our physics expert can get to work.

Re: Arm Designs
 

Hey anyone thought of using a lift and a arm/ wrist mechanism? I think that with the lift no matter where u put it in the tetra you will have a hold of it. But if someone could implement an arm and a lift in one i think it would be awesome.

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so i just came up with a most ingeneous idea to help solve the problem of stress on the robot arm if you use a jointed arm, springs, use something like a makeshift garagedoor spring and attatch it between, and im looking at my arm while im doing this, the wrist and the shoulderthat way the stress is limited on the arm, the only problem is gonna by the energy you get from it coming back, if you dont use a tremedously big spring then it should work.

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i have a design in mind. But does anyone have a good idea on how to extend a telecsoping tower? just thinking? im trying to aviod cables because past designs by my team have not gone well

Re: Arm Designs
 

We are thinking of a basic swinging arm mounted about four feet in the air and hanging down at starting. Hopefully it will be able to lift tetras from the ground and anywhere else (driving away or toward to get correct height of arm) and place then on top of a goal.

The only question is what to put on the end of the arm to grab the tetra.

Re: Arm Designs
 

BEWARE OF THE 2-JOINTED ARM!! its taken us 2 years in a row to get that message through our heads.. it didnt work the first time, and didnt do any better the 2nd time.. right now, were looking at a basic arm with a few ...features... built into it.. itll either be a piece of junk, or amazing
j

Re: Arm Designs
 

my team is new for this year, and after watching videos from last year i fear our bot will topple with our existing design. however, for a gripper, perhaps something similar to a 3 pronged fork? the 2 outside prongs turn upwards. the middle prong spears the apex of the tetra, the 2 outside prongs turn downwards, holding onto 2 sides of the triangle. it should be simple and secure. suggestions?

Re: Arm Designs
 

Our arm is a fairly common and simplistic design, following traditional 4-bar lift style.
Our possible tetra manipulator, however, is probably an idea that no other team has come up with though. But You'll just have to wait for our 2005 Reveal to see it, if it makes the vote :)

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sorry but can somebody explain to me what a 4-bar is? thanks

Re: Arm Designs
 

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I'm also worried about lifting those 9 pound tetras. Last year it was difficult to lift our 3 pound max hook with the van door motor (however, we had no reduction just a directly connected motor). Team 980 had a beautiful arm last year for lifting that large cap ball if you got a chance to see it. We want to design something similar to that. Where does everyone plan to get the muscle for that kind of lifting?

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You'll have to use a sick reduction if you're planning on lifting a lot tetras (3-4?). A lot of this game has to do with physics also, you simply do not want 10 pounds hanging 2-3 feet out while moving around.

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If you are looking for a good lift + arm combination check out Team 229's 2004 robot

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Some of mentioned the problem of tipping. Are outriggers legal? :rolleyes:

Re: Arm Designs