Limited stroke?

[Brad Voracek]

Well, if I read the rules right, we are limited to only cylinders which you can order from free for bimba, I know you can order more, but only of those types, correct?

Our team is needs something around an 18 inch stroke, and there's nothing of this kind on there, and the jump from 12 to 24 on the 2 inch bore cylinders seems like a huge hindrance. Considering we'll probably have to work with the 24 inch cylinders, we'll figure out a way to get them to work I suppose.. And the question I was going to ask is there a way to shorten the stroke, or stop them short, like maybe a sleeve over it? I'm not sure and ideas would be nice.

It's for a scissor life by the way, and we have ideas going around for how to work the 12 inch ones and the 24 inch ones into our design, but really not having anything in between is tough.

[Joe G.]

If its for a scissor lift, I would reccomend this approach:

in the "slide" at the base of the scissor lift, put some kind of stopper that stops the moving half of the lift from moving at where the lift would stop using an 18 inch cylinder. Make sure it is firmly mounted, due to the large forces generated in a scissor lift.

[Brad Voracek]

Well, I drew up something in ms paint for what we were planning to do, as it seems to be the easiest way to move a scissor lift, as all the forces are vertical and you can collapse it very far.

http://img245.imageshack.us/img245/1225/liftqp7.jpg

obviously not to scale and sorry, I'm on a laptop. haha.

... but this extended is about an 18 inch stroke, which is giving us problems. We plan to have one end on top and one end on bottom fixed, with the other two on slides. Obviously supported very well.

[MrForbes]

Do you realize that the 24" cylinder including clevis is 31" long from pin to pin when collapsed?

This may affect your design, if you did not account for it already.

I think our catapult design is looking better and better :) assuming we can make it work

[Brad Voracek]

We realize that, I guess I didn't show it well enough, but we planned to mount to the end of the piston, and the bottom of the actuator. nothing says you have to mount from end to end. so in the collapsed position our two points would be within inches of each other, and extended they are very near 24 inches apart, or whatever the stroke is.


A catapult does sound pretty nice. =D. We just couldn't think of a way to do it.

[MrForbes]

I think there's a crude sketch on our forum, under the "Mechanisms" section.

Should be highly confusing, we spent several hours today trying to get everyone to understand it! so don't feel bad if you can't figure it out....

basically two 10" by 2" bore cylinders next to each other connect to two bars, that fling the ball up and out of the robot. The trick is the start out partly extended and under pressure, so there is lots of stored energy available to send the ball flying. The magic latch is not shown on the drawing, of course, and needs to be figured out! but we think we have several ideas that will work.

[Brad Voracek]

I think there's a crude sketch on our forum, under the "Mechanisms" section.

Should be highly confusing, we spent several hours today trying to get everyone to understand it! so don't feel bad if you can't figure it out....

basically two 10" by 2" bore cylinders next to each other connect to two bars, that fling the ball up and out of the robot. The trick is the start out partly extended and under pressure, so there is lots of stored energy available to send the ball flying. The magic latch is not shown on the drawing, of course, and needs to be figured out! but we think we have several ideas that will work.

just checked it out, pretty cool idea!

... another question I have, reading another thread here people said you can use the optional magnet to stop a piston short? True? So we could use them contracted and only extend to 18 inches, say? Eh. I couldn't find much information about those magnets, and I'd need solid information to convince our advisor/mentors ;P

[MrForbes]

The magnet sensor is an electrical device that can sense a magnet on the piston in the cylinder. You need to order the "M" option when you order the cylinders, so they wil put the magnet inside. You can move the clamp on sensor to wherever you want along the cylinder. And you can probably put a few sensors on one cylinder if you need to figure out just where the piston is.

However, you may have fun trying to control how far you move the piston, since air is compressible, and you have to play some games with the valve setup to make it be able to stop partly extended.

[Brad Voracek]

Ahh man, I figured that. Now I get to be the bearer of "time to do some redesigning" tomorrow.


=) oh well. nothing can be easy! this is FIRST =D

[Brad Voracek]

Ahah. good day today, problem solved, thanks guys. =)

we just decided to add an extra "row" to the scissor lift and then the 12 inch actuator does exactly what we want.

[Chris Fultz]

Well, if I read the rules right, we are limited to only cylinders which you can order from free for bimba, I know you can order more, but only of those types, correct?

You are correct. You can order as many as you want (3 for free) but they have to be the ones that are listed in the pneumatics manual.

[Al Skierkiewicz]

I am surpirsed no one mentioned putting two cylinders in series for the desired movement.

[SteveJanesch]

I can think of two possibilities, for future reference:

The first is in general to limit the stroke of a longer piston. This can be done by either not allowing it to reach its maximum length or not allowing it to reach its minimum length. We had excellent results last year limiting the travel of the piston that drove our claw using the latter method. We put several plastic standoffs along the rod, between the cylinder and the nut, and it worked great, plus we could have fine-tuned it with washers or sanding a little off the standoffs. In your case, though, adding an extra 6 inches or so to the mechanism might be difficult to fit into your design.

The second is to mount the shorter piston to points on the scissor with shorter ranges of motion - somewhere along the arms between the center axles and the outer axles. This adds the requirement that the arms be strong enough to take the additional force of the piston where it wasn't originally intended.

Best of all is the solution you hit upon, though. Good thinking.