pic: Team 1511 Prototype Drivebase Mk. II

[Electronica1]

What thickness sheet metal are you using? Also, do you need the outer wheels to be live axle, or would dead axle work?

[Abhishek R]

Originally Posted by notmattlythgoe

What about single acting cylinders? They would spring back up when not pressurized.

I agree, this seems like it would be a good use for single action cylinders, defaulting to the retracted position for cautionary purposes so you never get stuck. You would save air as well.

[MrBasse]

If you do decide to actuate feet rather than the belly pan, a simple hinged element would remove the possibility of side load on your cylinders. Think of a see-saw where the cylinder pushes on a side that isn't in contact with the ground at all.

Also, I agree on this being a perfect place for a single acting cylinder. If you don't have any, a simple spring placed over the rod and one port vented to atmosphere can make a double into a single. You get the unique option of having the opposite direction of your typical single acting cylinder as well.

[asid61]

Originally Posted by MrBasse

If you do decide to actuate feet rather than the belly pan, a simple hinged element would remove the possibility of side load on your cylinders. Think of a see-saw where the cylinder pushes on a side that isn't in contact with the ground at all.

Also, I agree on this being a perfect place for a single acting cylinder. If you don't have any, a simple spring placed over the rod and one port vented to atmosphere can make a double into a single. You get the unique option of having the opposite direction of your typical single acting cylinder as well.

Or an over-center linkage might work if used correctly.

[Greg Needel]

Pneumatic cylinders directly acting on a plate with a short throw will be fine, no reason to over complicate it with a linkage.

Our brake last year was 3x 1" pancake cylinders all attached to a 20x14 plate covered in rough top. Worked great without ever bending the rod on a cylinder.

I will say that you should consider pancake cylinders instead of regular ones from a packaging standpoint they are much nicer for this kind of application.

[Vespasian]

Originally Posted by Electronica1

What thickness sheet metal are you using? Also, do you need the outer wheels to be live axle, or would dead axle work?

Most of the sheet metal is 1/8" with the exception of the cylinder mounting brackets and the bracket between the inner flanged sheets and the front/back 1x2" tubing (.090"). The outer wheels could be dead axle, we actually did so for the earlier version of this design (which we built: http://www.chiefdelphi.com/forums/sh...readid=131485).

I'm thinking keeping the axle type consistent would be preferable for machining purposes, but that does mean a bit more mass is being directly driven by the transmissions.

[Vespasian]

Originally Posted by Oblarg

How much chain wrap are you getting on that center sprocket if you only have one run of chain per side? That kind of design worries me.

They are not shown here, but we plan on using tensioners between each wheel to increase the total chain engagement on the center sprocket. I discussed this with a few of our mentors, and they didn't seem to be concerned. Can I ask what specifically is worrying about that style of chain? I am a bit skeptical of it since we have not used it before, but I don't want to discount it if the concept is valid.

[Vespasian]

Originally Posted by MrBasse

Also, I agree on this being a perfect place for a single acting cylinder. If you don't have any, a simple spring placed over the rod and one port vented to atmosphere can make a double into a single. You get the unique option of having the opposite direction of your typical single acting cylinder as well.

Thank you to everyone who suggested the single acting cylinder, to be honest I didn't know they existed! This is our team's first time using pneumatics in quite some time.

I just looked up what they are, and it seems they would be perfect for this application.

[Arpan]

Originally Posted by Greg Needel

Pneumatic cylinders directly acting on a plate with a short throw will be fine, no reason to over complicate it with a linkage.

Our brake last year was 3x 1" pancake cylinders all attached to a 20x14 plate covered in rough top. Worked great without ever bending the rod on a cylinder.

I will say that you should consider pancake cylinders instead of regular ones from a packaging standpoint they are much nicer for this kind of application.

I'd still use some kind of linkage. It doesn't add that much complexity, and for something where the failure mode is being stuck for the rest of the match, you want a lot of safety.

[Greg Needel]

Originally Posted by Arpan

I'd still use some kind of linkage. It doesn't add that much complexity, and for something where the failure mode is being stuck for the rest of the match, you want a lot of safety.

I guess....but wouldn't your linkage be just as susceptible to failing in the down position? Call me old fashioned but, I would rather stick 3x 1/2 steel shafts taking the brunt of the impact than some aluminum linkage bracket. Also 1 degree of freedom vs 2+

[Arpan]

Originally Posted by Greg Needel

I guess....but wouldn't your linkage be just as susceptible to failing in the down position? Call me old fashioned but, I would rather stick 3x 1/2 steel shafts taking the brunt of the impact than some aluminum linkage bracket. Also 1 degree of freedom vs 2+

When the half inch steel shaft bends just a little, it gets stuck. The proper linkage with a robust hinge can be bent and still retract.

The other option here is to incorporate some kind of shock absorption system that absorbs impact. I recall doing something like that on our 2013 robot when we didn't want cylinder shafts to bend as we ran into the pyramid to start our climb.

[Vespasian]

Originally Posted by Arpan

When the half inch steel shaft bends just a little, it gets stuck. The proper linkage with a robust hinge can be bent and still retract.

The other option here is to incorporate some kind of shock absorption system that absorbs impact. I recall doing something like that on our 2013 robot when we didn't want cylinder shafts to bend as we ran into the pyramid to start our climb.

What about gimballing the cylinders? is there any easy way to do so? Just a thought, it could be used as a form of shock absorption.

[Arpan]

Originally Posted by Vespasian

What about gimballing the cylinders? is there any easy way to do so? Just a thought, it could be used as a form of shock absorption.

That sounds like a good idea. Your cylinders are in a corner, do using a clevis to mount the cylinder end and tying each cylinder into the corner with something slightly elastic (rope) could help dissapate those impacts.

[Arpan]

For this complexity, though, I'd just build in 2" vexpro wheels with blue nitrile and a pneumatically locked idler.

Edit : 2" wide.