24-01-2005 18:39

Bleric

Re: pic: 488 Arm Prototype

Wow, that looks really good.

You may be interested in this:

http://www.chiefdelphi.com/forums/sh...ad.php?t=23934

24-01-2005 19:09

Stephen Kowski

Re: pic: 488 Arm Prototype

you mention that the 24" is an air hog, but it may help if you put one of the regulators in front of it and run it at 20 psi (which i believe lifts 50 lbs but im not sure).....we used it last year at 60 and wow you are dead on that it is an air hog, but this year I imagine you aren't lifting the robot in the air just some tetras.....good luck

24-01-2005 19:35

Spikey

Re: pic: 488 Arm Prototype

It looks like a lot of teams will be using the big pneumatic cylinders this year. It will be interesting to see how well people manage their air.

24-01-2005 21:40

M. Hicken

Re: pic: 488 Arm Prototype

im sure im going to get chewed on for this, but there are the students?

BTW, the arm looks good. and yeah, the 24" is a big air hog, 3 years ago we had 2 of them. Needless to say we didnt do well, in fact, i dont think we ever used them both.

24-01-2005 21:52

Cory

Re: pic: 488 Arm Prototype

Adults are allowed to do things... just because there's no student pictured means nothing

24-01-2005 22:50

Mr. Ivey

Re: pic: 488 Arm Prototype

Just to re-state the obvious... that is a whole lot of air being used... just a suggestion, to take the other side of what Stephen Kowski said about lowering the pressure. You could lower the volume of what you have to fill. P1V1=P2V2 so you can change volume or pressure. Just a suggestion if you are worried about air problems, lower the pressure to say 40psi or so, and downsize the diameter of the piston. Sacrifice a little of both, just my two cents.
ivey

24-01-2005 22:58

Sachiel7

Re: pic: 488 Arm Prototype

Hmm...
That looks awful familliar...

24-01-2005 23:10

Madison

Re: pic: 488 Arm Prototype

Two tetras at the end of a 60" moment arm exert about 100 ft./lbs. of force and that's a lot like lifting a robot, actually. If your piston pushes against the arm anywhere within 12" of the point of rotation, it's actually more work than lifting a robot.

The students were probably eating lunch. Mentors don't have time for that.

This was the first iteration of a prototype that has since been reworked to require less air reserves for its operation as well as shorter stroke, smaller bore pistons. Also, we tried to take advantage of the implicit binary nature of pistons and use it to our advantage rather than pursue further complicating the mechanism by trying to stop pistons in mid-stroke.

I have Inventor models of the newest iteration that are incomplete, but perhaps I'll share those sometime soon so that people might see how the design is progressing.

24-01-2005 23:25

Mr. Ivey

Re: pic: 488 Arm Prototype

Awl come one... Please try and make it harder than it needs to be. Every year people go into a multi-staging frenzy, if you really want to multi-stage, just use two shorter pistons connected to each other. Just another suggestion, but I know you have already revamped your prototype...
ivey

25-01-2005 06:28

Jay H 237

Re: pic: 488 Arm Prototype

Nice job with the arm.

Are you planning on using a third cylinder or a motor (or motor and gearbox combo) for the wrist movement?

25-01-2005 08:07

Greg Perkins

Re: pic: 488 Arm Prototype

Hey It looks really good!!

Madison, you may want to contact my team leader, Dave Kelly(not from indiana) and ask him about our regenitive pneumatic circuit davekelly@cyberportal.net is his email

Basically when you extend your arm it will move reallllllly slow as the pnuematic extends, but when its retracted, it saves air and goes much faster...

give him a note..we did it last year, and worked wonderfully

25-01-2005 08:18

Zanella BR

Re: pic: 488 Arm Prototype

Interesting design!

25-01-2005 11:41

Madison

Re: pic: 488 Arm Prototype

We are trying to design a grabbing mechanism that minimizes the need for any additional motion. If we're successful, we will be able to use the motion of the arm to grab a tetra securely and will not need further actuation. We have one idea floating about that does that superbly while picking up tetras, but doesn't let go of them so well. We have a second idea that requires actuation, but releases tetras easily and accurately.

Thanks, Greg. I'll send him an e-mail today and see what more I can learn about this. I have real concern about the speed at which the pistons actuate and its effect on our center of gravity as well as how it minimizes control of the placement of tetras. This sounds like it may be a solution.

25-01-2005 13:21

Stephen Kowski

Re: pic: 488 Arm Prototype

I'm sure if they could they would but they can't so they won't.....24" is only available in the 2" bore size this year which does not make much sense, but whatever....

25-01-2005 13:46

Madison

Re: pic: 488 Arm Prototype

Again, I was able to redesign some parts of the mechanism so that a considerably shorter stroke piston is able to accomplish the same task. However, your general assessment is correct.

Two tetras at the end of a 60" arm produce approximately 100 ft./lbs. of torque. To lift that, you'd want a piston acting as far away from the pivot point as possible to minimize the force needed, but as that point of actuation moves away from the pivot, the length of stroke required to get the desired radial motion (~120*) increases. A 24" stroke piston is the bare minimum required as shown, as that allows us to act on a point approximately 12" from the pivot. 2" bore pistons are rated at 188 lbs. of force extended, but, that's assuming 60 PSI. It would operate at something less, but I wouldn't feel comfortable relying on its operation over and over without making the compressor do some serious work.

I shortened the piston stroke needed by moving the point of actuation a bit nearer to the pivot. This means, of course, that we'll need to be closer to 60 PSI to operate correctly, however, it also means that we need much less volume of air, as well; 50% less, in fact. Coupled with weight saved, it seems like a fair trade.

25-01-2005 14:24

Max Lobovsky

Re: pic: 488 Arm Prototype

Correct me if I'm wrong, but the weight neccesary for a given torque and range of movement is constant. Saving weight on the cylinder is possible, but you seem to be arguing that by moving the mounting point and changing the length of the cylinder, you managed to reduce the air requirement.