Tetra Manipulators

[greencactus3]

Originally Posted by n0cturnalxb

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.

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..

[leo_singer]

Originally Posted by greencactus3

so if you get a small grabber that will grip one side of the tetra tightly enough so it wont slip or spin

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.

[ShadowKnight]

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)

[Gary Dillard]

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.

[Wetzel]

Originally Posted by ShadowKnight

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)

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

Wetzel

[greencactus3]

Originally Posted by leo_singer

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.

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.

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.

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

[Kelvin Ng]

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?

[RONALDO!!!]

Originally Posted by Tytus Gerrish

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?

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.

[IA-Howitzer]

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

[Cyberguy34000]

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...

[Ianworld]

Originally Posted by IA-Howitzer

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

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.

[Ductapemaster05]

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

[Bernardo F]

Originally Posted by Tytus Gerrish

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?

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.
I think. After that, CG is what we have to worry about.

[Rick TYler]

Originally Posted by Bernardo F

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.
I think. After that, CG is what we have to worry about.

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.

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

[Sachiel7]

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.