Tetra Manipulators
 

okay, this is personally my biggest concern. Designing an Appendage witch is Gracefully Powerful and proficient in handling the tetrahedrons. From the grabber mechanism to the arm Assembly or tentacle or whatever. What are your thoughts?

Re: Tetra Manipulators
 

I've been giving it some pretty heavy thinking(seeing as its the only field element) and i think tetra grabbers are not going to be anything fancy. To lift one all you really need is a swinging pole with maybe a hook on the end and a stopper to stop the tetra from falling too far back down the pole. Thats about as simple as you can get, but even the best shouldn't be too much more complicated. I'm thinking something akin to a fork lift with no powered grabber, just the up and down motion of the fork lift prongs. Anybody any ideas that more clever than that? (not that its particularly clever or anything)

Re: Tetra Manipulators
 

YAY! people who did OCCRA this year just might have a bit of an advantage! tubies and tetras heh. close enough lol.
well stacking them on a goal is pretty simple once you figure a way to grab and lift that high. because the tetras can be placed with any side facing down.... well except the vision ones im guessing?
well anyways. if you can think of a strong reliable way to actually grip the pvc securly. maybe a simple claw. but i dunno.
is flinging these tetras against the rules? im not sure... because if you can make a backboardish thing, flinging these wouldnt be too hard.. dangerous yes. so if you can get a consistent arc with no spin, youre a winner.
ok ignore me.

Re: Tetra Manipulators
 

here's a place to look for ideas-

in 1997 the playing pieces were inner tubes hung on a rack or topping a pyramidal goal. The grabbers from that year would be very similar-

look for the designs from Toroid Terror

WC :cool:

Re: Tetra Manipulators
 

yes, it is. i can't quote you the section in the rules yet, but i remember it was one of the questions during the "quiz show" at the end of the webcast. you were correct, it's just far too dangerous to send those objects flying.
i agree with you Ian, simple ideas do sound good right about now!

Re: Tetra Manipulators
 

just to second that it was said multiple times that flinging, throwing and tosing of the tetras is not allowed... so basically no projectiles.

Re: Tetra Manipulators
 

well man, from what i can tell the actual construction of an appendage to lift the tetrahedrons, but rather the effect that having such a long endefector, or the power necessary to power a platform or forklift type object for lifting and stacking the tetrahedron will have on the 'bot's center of gravity.

Re: Tetra Manipulators
 

Uhhh, if u make a ski-like design with a pole about 2 ft down, u can keep the tetra from sliding down the pole and the ski-ended part will keep the tetra on and allow it 2 b easily unloaded onto the large stationary tetra.

_______L_____¸,. <---Ski

Re: Tetra Manipulators
 

Obviously the problem with the arm isn't going to be grabbing the tetras, parsay, but getting them up high enough. It would be pretty sad to get to a match where every robot was only designed to just put one tetra on top. Imagine how much fun that would be for the one robot that could stack higher...

Re: Tetra Manipulators
 

As stated before, it throwing the tetras is not allowed. The rule is G23

Wetzel

Re: Tetra Manipulators
 

In addition to getting the tetras high enough, there's half a million ways to get a little bit of extra height out of your arm component but The arms can only get so high.

I think grabbers than can get a little extra height with the tetras are going to come through in the end of matches to get some final rows in where grabbers that are simple and work quickly might not. Where and how you grab the tetra has a big effect on wether or not you can put on the highest tetra.

Tetra Manipulators
 

Howabout a forklift that had an arm extending out with a ball jointed grabber hanging on it to grab tetras? Kind of like one of those stuffed animal claw machines.

Re: Tetra Manipulators
 

the problem with that is that then you have to get your arm on top of the tetra. Something that can hold the tetra flat (like it would rest on a flat surface) by one of the bottom corners, or pvc pipes is going to work best as far as height.

Re: Tetra Manipulators
 

Or pick the tetra up from the bottom PVCs and hold it tilted at an angle towards the robot. That way, you wouldn't have to get the tetra as high up as the goal, just almost.. and then tilt it away from the robot, lower the tetra however low it must go, and then move away.

At least.. in theory, that works. I'm working with 6 unsharpened pencils, put together like a tetra with scotch tape .. and two other, separate pencils with a part of an unused row of small staples taped to them to test out my grabber ideas :P

Re: Tetra Manipulators
 

If I learned anything from a late-night 1257 brainstorming session, it's that straws and tape work best.

Re: Tetra Manipulators
 

right. so if you get a small (Well doesnt have to be small) grabber that will grip one side of the tetra tightly enough so it wont slip or spin, then you can use a 4 bar or anything w/e to lift it vertically .. and then have a bit of or wait a second... since the sides of these tetas are uhhh 60 degrees?or a bit less i think... since its not a pyramid. dont feel like looking up geometry dimensions now.. well anyways,,, if you get a grab on this at one side from a 120?60?(where am i measuring from?) angle,
like
.............o.......
............//....
.......a..//...arm
.......^//
...../....\....
..../.......\.....
.b.--------.c
...tetra

(o is the arm axis)

and then rotate the arm up so itll look like
.......b
.......^.
...../....\....
..../.......\.....
.c.--------.a
...........\\
.............\\
...............\\
.................o

then you will have a 'holding as if it were flat on the ground" even though the
arm has rotated.. makeing full use of the tetrahedral shape... little problem with the vision ones tho im thinkin..

Re: Tetra Manipulators
 

Thats what i was thinking. If you don't drive into the large tetra stacks (over the pvc bars and such) your robot will have to reach about 2 feet in to get it over the top of the stack. But after that just lower your arm/forklift/whatchamacallit down and i'm pretty sure the tetra will sort itself into a nice position.

I guess the question is, are other teams going to be knocking tetras from your grasp. Without an actuating grabber your tetras could easily go flying.

Re: Tetra Manipulators
 

i thought that it would be a good idea to have an arm the has a 60 or so dergee angle on it so you can hold two of the base sides for a better hold then have it clamp down on the pvc, and lift it up like a fork lift
___ <-- fork lift type structure
|| <- arm
||
/\

/\ <--tetra, with out the third side

imagine it from looking down at it, also imagine that the arm has about a 60 degree angle on it because if i remember right tetras have 60 degree angles. then have it drive up to it get it with in the arm angles and then with the two grabbers on each end clamp down and use the fork lift mechanism to lift it up and cap the goal

Re: Tetra Manipulators
 

Exactly how tight is that? Maybe it might be easier to handle a tetra if you grab it from a vertex, or from two edges.

But I do like the idea of taking advantage of the tetrahedron's rotational symmetry.

Re: Tetra Manipulators
 

Well, looking at one of the posts, I noticed this: "And one other thing about the tetras that may or may not be addressedsoon...holding some of them, a loose nut in one piece of the pipe will cause that part to spin around. Know that if you're planning on building a one-pole grabber." This could be another problem similar to somwhat deflated blass and deformed balls at competition in '04. It wouldn't surprise me if this was considered part of the challenge. If in fact though the edges can spin, then any height advantage gained by grabbing an edge would be lost. (your arm has to extend to a little less than 9 feet, if you're doing an arm that pivots at the base of the robot)

Re: Tetra Manipulators
 

Wow, 3 people able to draw their designs using text in a script processor program. I guess I wasted my time learning all that CAD software :)

I've got an idea for a grabber Ty - you may recognize it from Fluffy.

Re: Tetra Manipulators
 

The tetras are glued together and the bolts in them have loctite. This should not be a problem.

Wetzel

Re: Tetra Manipulators
 

I'm not sure I would count on that keeping them from rotating. Regardless of them being glued together and having loctite on the bolts, each leg is an axis that is held by a single bolt at each end along that axis. What keeps the bolt and leg from spinning in the hole in the end connector? I wouldn't rely on friction, and any loctite in that hole won't cut the kind of moment induced from swinging a 9 pound tetra.

Re: Tetra Manipulators
 

well thats where you have to fing the best gripping material against the pvc. spongy rubber most likely, im thinking maybe bicycle brakes. but we dont really want to take forever in aiming it correctly either. or crack a pipe.
you're right. so maybe once someone builds a tetra correctly and rightly abuses it, see what happens. but we still hafta think about the IFs. sooooo.... what now :rolleyes:

Re: Tetra Manipulators
 

me, my father and our team have all brainstormed a whole ton of grabber ideas: first of all, it is our first year and that i'm unfamiliar with alot of terms that you guys might use...a 4-bar? ??? thats an example.

1) pincer - just a pincer with rubberized grips that hold onto one pole.

2) no name - a 2 pronged design that skewers the tetras, then expands (kinda like a pair of doors in an an entrance), eventually expanding to the bottom 2 corners of a tetra and holding them in place by pinning them against a barrier at the back of the grabber. hard to explain.
experiments with straws show that it is possible to skewer the tetras from a wide variety of angles, the tetras are held tight (do not move), and they are held from the bottom, so the arm doesnt have to be as long. my team doesnt like it, but i like it most.

3) 3 pronged grabber (fork) - 2 outer prongs move up and down, central prong remains stationary. central prong skewers tetra apex, the 2 outer prongs lower, making contact with the 2 sides of tetra.

comments?

Re: Tetra Manipulators
 

i was thinking of a hook like this:

\___
......\___
............\___
..................\___
........................\_____|

you could drive it straight into the tetra without worrying where it connects. when you lift it up, the tetra would slide down the incline to the stopper on the end of the hook. this way the position of the tetra on the arm will always be the same without have to control it precisely. the slant would not be steep, maybe about 10 degrees max, so that the tetra wont lose any height.

Re: Tetra Manipulators
 

Sounds nice.. just remember to try to test out the idea once you've got a scoring tetra built. The thing is pretty heavy, so .. make sure your design (if you end up using it) will still be able to work as it should in theory :)

Re: Tetra Manipulators
 

Can you elaborate as to how to we can make sure it will work? i read something about making prototypes, but schoolwork is heavy for many of us (physics, calculus, chemistry, english teachers assign as much as 1 to 1.5 hours of homework a day each. can't forget about time spent on the team. i've had at least 1 test every week for a while now, and in the last 5 school days i've had 2 quizzes and 3 tests.).

Re: Tetra Manipulators
 

I answered your 4-bar question here (I hope)

http://www.chiefdelphi.com/forums/sh...780#post320780

As far as prototyping your ideas, use PVC, galvanized pipe, 2x4's and plywood. Make it as close to scale as possible, but don't worry about the weight or the envelope - just make sure your actual design can meet the requirements. You just want to match the stiffness of the structure out to the grabber and the actual geometry of anything that will interface with the Tetra. This will flesh out alot of what works and what doesn't, and will certainly tell you if it's feasible before you go to the effort of full development.

Re: Tetra Manipulators
 

Uhmm... can you say, Gun Rack?

Re: Tetra Manipulators
 

awesome .. straw and tape prototypes, here i come!

... after finals week ends, that is :(

Re: Tetra Manipulators
 

One word:
Pole
;)

Re: Tetra Manipulators
 

OK, say we choose one of these several designs mentioned, what materials would be good for it; i mean besides just aluminum, the obvious answer, would some kind of layering system be beneficial? like maybe 2 pieces of aluminum sandwiching some fiberglass, perhaps?

Re: Tetra Manipulators
 

our team has a grabber that grabs UNDER the APEX of the tetra, can grab three tetras at the same time, then can be put up 12 1/2 feet, then telescoped another four feet. :ahh:
I think. After that, CG is what we have to worry about. :mad:

Re: Tetra Manipulators
 

Thirty pounds of tetras 12 or 16 feet from the ground (if I read your post correctly), held by an arm that has to weigh 20-40 pounds? Yeah, I'd do the CG calculations if I were you. :confused:

But if it falls over really dramatically, can you please post video? :)

Seriously, I expect to see a lot of robots s-l-o-w-l-y rotating to the ground, losing the CG war. I kind of expect to see some teams driving out from under their top-heavy bots. Let's see, applying a force at ground level underneath a structure 8 or 10 or 12 feet high, with a high polar moment of inertia...

- Rick Tyler
Old Guy with a Sticky Shift KEy

Re: Tetra Manipulators
 

I think we've struck a good balance with our arm. We've sacrificed being able to stack multiple tetras for speed. We don't shoot up our arm over 12 ft like many are trying, we are shooting for an arm height of 10.5 ft, which is great for our needs. We should (I'll post some video in a few days) be able to stack a tetra that is within 3ft of a goal, per se, onto the goal in (I'd estimate) 5 seconds (tops!)
This assists our strategy, which is focused a little more on the rows themselves, but still leaves the door open for quick loading of several tetras.
Our grabber this year is simple, as I posted above, we're currently just using a pole, probably with a divot cutout for the tetra to sit in (and rest on some digital sensors...)
We're probably just using some sched. 40 PVC, just like the goals. Perhaps aluminum, but I don't think there's really going to be a difference in our design.