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Unread 01-09-2005, 11:33 AM
greencactus3 greencactus3 is offline
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Re: Tetra Manipulators

Quote:
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..

Last edited by greencactus3 : 01-09-2005 at 04:43 PM. Reason: right triangles have 60 degree insides not 120
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Unread 01-09-2005, 12:12 PM
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Re: Tetra Manipulators

Quote:
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.
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Unread 01-09-2005, 03:50 PM
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Lightbulb 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
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Unread 01-09-2005, 11:24 PM
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Re: Tetra Manipulators

Quote:
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.
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Unread 01-09-2005, 11:35 PM
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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)
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Unread 01-10-2005, 12:37 PM
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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.
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Unread 01-10-2005, 12:58 PM
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Re: Tetra Manipulators

Quote:
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
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Unread 01-10-2005, 05:42 PM
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Re: Tetra Manipulators

Quote:
Originally Posted by Wetzel
The tetras are glued together and the bolts in them have loctite. This should not be a problem.

Wetzel
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.
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Unread 01-10-2005, 06:53 PM
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Re: Tetra Manipulators

Quote:
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.
Quote:
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
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Unread 01-15-2005, 11:07 PM
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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?
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Unread 01-15-2005, 11:32 PM
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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.

Last edited by oreocookeee : 01-16-2005 at 08:20 PM.
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Unread 01-15-2005, 11:38 PM
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Re: Tetra Manipulators

Quote:
Originally Posted by Kelvin Ng
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.

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
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Unread 01-16-2005, 12:02 AM
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Re: Tetra Manipulators

Quote:
Originally Posted by n0cturnalxb
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
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.).
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Unread 01-16-2005, 06:15 PM
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Re: Tetra Manipulators

Quote:
Originally Posted by 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.
I answered your 4-bar question here (I hope)

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

Quote:
Can you elaborate as to how to we can make sure it will work?
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.
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Unread 01-17-2005, 11:45 PM
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Re: Tetra Manipulators

Uhmm... can you say, Gun Rack?
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