arm design

[NotaNerd]

I agree with Zippiot. While pneumatics are easy to do and install, its all or nothing with them. In or out, not halfway. Motors allow that option. And they don't just randomly burn up or catch fire. Only if they are overworked/ overstressed. You just need to check the loads on them. Plus, pneumatic tubes can get pinched. In addition, what happens when your air tank runs out? You have to wait for it to reload. And in a game where defense is key, that could cause you capping points. Just some words for thought...

[Adam Y.]

Originally Posted by Zippiot

pneumatics are more powerful but its an all or nothing solution. you can't stop them halfway through, so if a tetra is just out of place then it may be difficult to pick it up

Whatever happened to the method in which you could stop a pneumatic cylinder anywhere you want to. Can you still do that?

[cadman2k5]

Team 637 is going with a motor driven arm. yet no articulation.

[Rickertsen2]

We have a single jointed arm with a second joint controlled by a four errr... three link. The whole thing is mounted on a stationary tower and folds up nicely inside it. On the end of the arm we have a pneumatic gripper somewhat akin to a stuffed teddybear grabber from hell. The arm will probably be powered by two fp motors if anyone ever takes the initiative to design a gearbox for them.

[web2linc]

our arm is made out of carpet

[Bcahn836]

We are using pneumatics and something else but it is a secret, lol

[Andrew Schuetze]

This is our last area of design need. A multiposition pneumatic would do the job just perfectly. Barring the use of a second solenoid to meter the exhaust, it is not possible. To be able to use the metered exhaust will likely require a human touch that an auto program cannot handle consistantly.

I did have an idea to gang two cylinders in series. Have something like an 8 inch throw connected to a 12 inch throw gives you four positions. All in, 8 out only, 12 out only, all out....


Anybody considering something like that? Our engineering crew is meeting with the students on Thursday and then we have a Saturday build session planned where I hope to put the wraps on this last design item.

[Zippiot]

its actually quite simple to make a pneumatic cylinder that can stop at any point. all you need to do is attach another solenoid to the exhaust of the cylinder's solenoid. it's very hard to describe, and i may draw up a pic in the next few days, but essentially u make it so that at any point in time you can cut off the exhaust of the cylinder, so both sides will fill with air, effectively stopping the piston in its place (or very close to it). but the purge can be very violent, otherwise all you need is enough buttons to manage it. if this was too complicated i can try to make it more clear just ask.

[Zippiot]

another way to make multiple points of stop for pneumatics is to use many tiny stroke pistons. this is expensive and complicated but it is just as strong, can be much faster (instead of slowly filling 1 large piston you can slowly fill 2 small ones, tripling or doubling the speed depending...). the only issue is keeping stability constant, to do this i recommend a sliding arm action, and i haven't seen a design of that yet that doesn't compromise the integrity. a good part about pneumatics is that, for what i know, there is no limit to how many pistons that you can use, the only issue is how quickly it takes to charge them all. problem is that generally speaking pneumatics are much heavier, considering the pistons tanks compressor tubing and connections.

[ngreen]

Originally Posted by Andrew Schuetze

To be able to use the metered exhaust will likely require a human touch that an auto program cannot handle consistantly.

I agree with you generally. But it also depends greatly on a the complexity of your movements. In most cases using pneumatics that stop midstroke are similiar to dead reckoning programming. With adjustments and fine tuning you can get good results for simple, broad movements. But for complex, precise movement you are generally out of luck.

An example of this was my teams 2003 robot. We had two cyclinder lifting our stacker. As part of our autonomous we would lift our stacker part way up. It came to the same position almost everytime. But it wouldn't work well it if had to be precise.

This is where some design comes in. IF you design a robot that is able to pick up tetras with broad movements, you would likely be able to tune a program to do it in automounous (thinking about things like air pressure, piston speed, what the tetra weight will do). If it must be precise in it's movements (move two inches, then one inche, and so on) it will likely be hard for autonomous and equally so for the driver's and any programming in user mode.

[Zippiot]

an interesting thing that i designed and tested was a joystick controlled regulator with psi relief valve. the more forward i moved the joystick the more pressure was allowed in, and if i back out the joystick pressure would be relieved. this made it so that with a load on the piston you can precisely position it where you wish, but it takes some practise.

[Anchi]

keke, we are goin all the way with ours, pnumatics, ball screw, and gears. every section and pivot uses a diffrent one.

[danield710]

we're usin pneumatics and motors for our arm

[Ianworld]

i just don't understand how you all are going to get the necessary travel out of a pneumatic? Does anybody have any examples how they are accomplishing raising a tetra a pretty large distance using a pneumatic?

[BoyWithCape195]

Originally Posted by Ianworld

i just don't understand how you all are going to get the necessary travel out of a pneumatic? Does anybody have any examples how they are accomplishing raising a tetra a pretty large distance using a pneumatic?

How did they do it last year with pneumatics.....?