We are trying to use pneumatics to make the mechanism show below slide out of the robot.
We were thinking of doing something likethis but with only one piston.
Another thought we had was to not even attach the piston to the thing that slides and and just giving it a good shove. The issue with that is that we are concerned about the fact that we can’t get it to slide smoothly and we are not sure it will push it out all the way.
So any suggestions?
The pictures are not loading for me.
Here are his two pictures:
That looks really long for the pneumatics to push all the way out. If it only has to go out and not back in maybe you can setup something with rubber bands to shoot it out and latch closed. You would still need a motor, server, or pneumatic to release the rubber bands. Just a thought, but others might have better ideas.
good luck making a piston do that
on the other hand, if you rubber band it and keep it latched with something else for maintaining starting position it would work way better than a piston
one way to hold in the tensioned slide would be to have standoff on the arm or something prevent the slides from moving out and when the arm lifts up it releases and the rubberbands expand the system.
It’s better to use rubber bands because they operate on a wider range of motion and you can put as many as you want for as much force as you want. In addition holding in rubber bands and releasing them using the method above does not take much force. So i guess an analogy would be that it’s very cost effective versus wasting a piston on one task.
From the pictures, it looks like you would have some amount of weight on the end of that. With any weight hanging on the end of the structure cantilevered like that you will run into issues, the biggest being instability and possibly even the slides popping out of the metal rails. However, even if that is fine, the force will result in the sliders not sliding well in the rails, which is why you were having trouble getting it to slide out smoothly.
If it is necessary to have something hanging out to the side like that, it might be better to put it on a turntable and have it rotate out with pneumatics/elastics/both.
If you need it to slide out, maybe it would be possible to add a wheel that supports the weight rolling on the ground. Pneumatics would be hard to push it out due to the distance, so it might be easier to use elastics and a pin to release them, but once again the long distance might make it challenging.
Just some ideas to consider. Whatever it is you are doing, it sure seems interesting, and I really want to see the final robot.
Ok, does this mechanism need to go back in during the match? or could it simply slide out and latch?
If it only has to extend, my way about it would be to LOAD it up with rubber bands, and have it held back with a ziptie connected to a different moving arm. That way, the slide is held in place by the ziptie, but you move the second arm and the ziptie falls off and the rubber bands shoot the sliding arm out.
Kevin_Team 472 is correct, you would also need to do something that slides out with the C-channel that would help support it from sagging.
Okay, but… uh… whatever you do make sure it’s NOT going to fly out and take somebody’s finger off.
My kids had built a claw deployment that was quite impressive, but it also required somebody to have their face right down in front of it to spring load the thing. Consequently, it was perfectly designed to flip up, tear off their safety glasses and rip out both eyeballs in under 0.1 second, all in one, swift motion. It was a safety nightmare, so I made them take it apart and they hated me for that.
You evil evil person.
Are you saying these were dangerous?
https://www.youtube.com/watch?v=6QiBkeUyaiU
Not even close. Neither of those comes anywhere close to the eyeball-ripper-outer my kids came up with. Too bad I didn’t make a video of it. It was like something out of a bad dream.
lol yes I meant for it to be done safely. Let’s keep all limbs, eyeballs, and other parts intact please ������
Having rubber bands/latex tubing would probably work well. We would probably release with the piston though because it would be pretty simple and not using the piston at all would be wasteful because we already have the piston. Using a motor would not work well because we already have 9 and we need the remaining port for something we have planed for the robot at worlds.
we do have a lot of weight at there but we have a lot of steel to put on as counter weight. as for sliding out, we have nuts sticking out at the end of the slides and I don’t think anything we will build will be strong enough to go through that. The issue with not sliding out smoothly we believe is cause by the fact that we can’t line the green slides 100% perfectly, this causes friction which is solved by using only one slide, but then we give up stability. The power that a pneumatic piston has is the reason why we wanted to use it, we didn’t think it would have any trouble pushing. Having it swing out on a turn table would require us to raise the whole mechanism because other wise we hit the skyrise base an that would make it difficult to stay in size. Though you do have some good ideas.
it never has to go back in. We might try something with this, I think it might be a bit easier to use a piston to release though. As for stability, with 3 slides we have no problem, it’s really solid.
I see evidence of this on your profile photo 
After reading these posts, I think we will probably use a lot of rubber bands and a piston to release. If that for some reason doesn’t work we might do what Jared suggested and have another mechanism pull the release, and then if that doesn’t work probably something similar to the pneumatic engine I linked to in the first post. Well before we work on this we need to fix some things on other places on the robot.
thanks everyone for your suggestions, later I’ll tell you how well this mechanism is working.
What I meant with popping out was the green slides actually coming up and out of the rails. The outer slides do this very easily, but with a lot of force it might happen with inner slides. But it will probably be unlikely with 3 rails and slides, unless there is a ton of weight on it.
The alignment of the slides will also give a lot of friction. One thing that might help is loosening the screws on the slides so they can move a bit, however that might reduce the stability. The torsion (i.e. the front pushing down and the back pulling up) that will be on the slides can also give you a ton of friction, sometimes even to the point of them not moving at all. Just put a plate onto a slide and try it out by hand to see what I mean.
I loosen the slides, then put the rail on, and then have another team member tighten it back as I move the slider back and forth. This usually allows them to work fairly well together.
we have never had any issues with being able to do it by hand, going in or out with it. The friction isn’t super bad enough that a 393 motor can’t push it (I think) though regarding future design a 393 would not work for us.
However, it is bad enough that in order to use elastics we will have to use a lot, fortunately there’s no limit to how much you can use in VRC, as long as what you are using is VRC legal. I’m also not terribly concerned about them popping off. This thing that slide out have a arm that’s on a turntable. When we spin the turn table with just one slide to where there is lots of weight on one side of the slide it doesn’t pop out, at this point there is also torsion because we push the sliding thing out by hand. I don’t think it was very good for the linear slides but it didn’t pop out.
That’s a great idea! We must try it!
Wee have this working fine with rubber bands. We got it working awhile ago but I keep forgetting to report it.
Anyone have a good design for a pneumatic catapult??? Thxx.
You might try by searching for Vex Toss Up Catapult. The game of Toss Up generated lots of catapult designs.
For example:
