Circular Bumpers

[brrian27]

Okay so we are doing a circular base. But one roadblock we have is how to do the bumpers.

Per R-21A the bumpers must be backed by plywood, but this would be difficult on a circle.

I know some teams did this last year, so any suggestions/input? Thanks!!

[mrnoble]

I'm going to assume that your team chose the circular base for valid reasons, ones which overcome the multiple other reasons why a square or rectangular base would be significantly easier to construct; bumpers being one of many I can think of. Would you mind articulating some of your reasons?

If you're absolutely set on the round base, I think it is more likely that your frame will be constructed as a decagon or other polyhedron. You will just need to cut plywood pieces to fit each side, with a matching angle, and put the pieces together with brackets (which you will probably need to manufacture or modify).

[mrnoble]

By the way, loved your wheeled shooter prototype! Very inspiring.

[FilthyArgonian]

You could modify your frame to be hexagonal or octagonal, which would make bumper fabrication exponentially easier. or you could find a way to bend your plywood into a perfect circle.

[Phyrxes]

While use of a steambox and a form to shape the bumper plywood into the appropriate diameter circle, that seems be a significant amount of work even before dealing with pool noodles and fabric.

Given the right expertise and equipment this is certainly doable, can't say I would recommend it though.

[MechEng83]

While I can't comment on the merits of this specific team, a circular robot frame allows the maximum area inside the perimeter limits, which also allows the maximum area for a catcher.

Soaking the plywood in water overnight and then clamping it to a form and allowing it to dry would be a way to construct the curved plywood. Pool noodles and fabric are flexible, though attaching would still require some work (think attaching fabric on a round seat cushion)

[Nate Laverdure]

You could vacuum-form your bumper backing around a cylindrical mandrel. You'd have to build it one ply at a time, up to the full thickness.

[pntbll1313]

Originally Posted by MechEng83

While I can't comment on the merits of this specific team, a circular robot frame allows the maximum area inside the perimeter limits, which also allows the maximum area for a catcher.

IMO with the 20" extension rule this year I don't think there is much gained by building a round robot just to maximize the catcher. Just doing some quick math I got that a round robot could have up to 4492.6 inches sq to catch in, and a square robot would have 4280 inches sq. That 5% may make the difference but I doubt it. You're losing 2 inches of reach in the corners and gaining 3.8 inches of reach on the edges if building round over square. Hopefully your 6 foot wide catcher will do just fine without those few inches.

[brrian27]

Thanks for the tips everyone!

A circular base is pretty important to certain factors in our design. But perhaps we can make it hexagonal or octagonal, or figure out bending the plywood.

[Dad1279]

You could try bending thinner plywood, like 1/4", and glue it together around a form.

There is also a bendable plywood, called 'wigglewood' but I'm not sure it has the strength needed for bumpers. http://www.woodworkerssource.com/mm5...y_Code=plywood

[Whippet]

Originally Posted by Dad1279

You could try bending thinner plywood, like 1/4", and glue it together around a form.

There is also a bendable plywood, called 'wigglewood' but I'm not sure it has the strength needed for bumpers. http://www.woodworkerssource.com/mm5...y_Code=plywood

The wood on the bumper backing is required to be 3/4" thick. It can't be any other thickness, or you will not be allowed to compete. This caused us a lot of difficulty at comps last year.

[Dad1279]

Originally Posted by Whippet

The wood on the bumper backing is required to be 3/4" thick. It can't be any other thickness, or you will not be allowed to compete. This caused us a lot of difficulty at comps last year.

I said glue it together, but should have been more specific. Glue up 3 layers of 1/4", or 2 layers of the 3/8" wigglewood. Both should be bendable in the radius required.

[Mr V]

The team that had a round robot in our area last season laminated their own bent plywood. I think they used 1/8" so it was easier to bend, more likely to hold its shape and was most like commercially available 3/4" plywood with is usually 5-7 ply. If you really want it replicate commercially available plywood and its strength don't forget to alternate the direction of the grain.

I believe they did their bumpers as two semi circles to make it easier to build and handle.

[JamesCH95]

You could cut out a number of 3/4in thick arcs from plywood and glue them on top of each other to make your bumper backer.

Similar to how this furniture is made: http://inhabitat.com/images/sande.jpg

A CNC router would be a big plus here.

[MechEng83]

Originally Posted by pntbll1313

IMO with the 20" extension rule this year I don't think there is much gained by building a round robot just to maximize the catcher. Just doing some quick math I got that a round robot could have up to 4492.6 inches sq to catch in, and a square robot would have 4280 inches sq. That 5% may make the difference but I doubt it. You're losing 2 inches of reach in the corners and gaining 3.8 inches of reach on the edges if building round over square. Hopefully your 6 foot wide catcher will do just fine without those few inches.

I didn't say it was worth the trouble