Anyone do work with composites?

"TheOnelectronic" (theoneelectronic)
09/22/2013 at 18:52 • Filed to: halp

long story short, I coach a FIRST Lego League robotics team, and for practice we use large, ~3'x8' tables made of wood. One was built by an engineer out of 2x4's and plywood. The other was built by a dad out of 2x4's and particle board. This second one is too large for the game mat, and also extremely heavy. As there are many days where I'm the only person above 120 lbs, I frequently have the JOY of carrying this thing into the room. Here's a partial shot of two tables next to each other.

So we mused about making a new table, and I thought "Why not fiberglass?" (I then thought "Wait. No. CARBON FIBER!" but that's quite pricey for the amount I'd need.)

I read a book once on laying fiberglass, and I know bits of the theory behind it, but I've never actually done anything with it. My main concern is that it would need to have fairly square inside corners, and from what I know, fiberglass and other composites don't tend to like 90 degree bends. A small amount of curvature is acceptable, but it's important that the robot could not drive up the walls. I included a picture for reference.

Is this doable for an amateur? Is it doable for a shop?

DISCUSSION (15)

Mattbob > TheOnelectronic
09/22/2013 at 18:59

I think fiberglass would really be way too much hassle for what you need. How rigid does the bottom have to be? Could you make it out of 1/4" plywood and some 1x4's? depending, on if it is already laying on a flat surface you might even be able to get away with that foam insulation board and make it super light. Perhaps coat the sides with something to toughen it up a smidge. But really, what are your requirements for sturdiness, and what are the critical dimensions?

TheOnelectronic > Mattbob
09/22/2013 at 19:01

It needs to be rigid enough to not sag when supported from either end longways, and anything that could dent or deform wouldn't work well.

Mostly the fiberglass was for weight purposes, as these are seriously heavy.

Mattbob > TheOnelectronic
09/22/2013 at 19:04

fiberglass is going to take some work to get an area that big to be nice and flat, and might end up being heavy anyways. I would really just use 1/4" ply and maybe a supporting runner or 2 along the back. Add some handles in key places, and maybe make it come apart into multiple pieces if possible. Anyone else have ideas?

twinturbobmw > TheOnelectronic
09/22/2013 at 19:05

I was part of a Lego Robotics team a few years ago. Very fun! Our theme was the "Food Factor" and before that something about the human body/health. We actually did pretty well.

TheOnelectronic > Mattbob
09/22/2013 at 19:13

You may have a point there. Going with thinner wood more cleverly structured might be the best bet.

TheOnelectronic > twinturbobmw
09/22/2013 at 19:15

Food Factor was my first year. Last year's was "Senior Solutions" which was horrifically dull. This year is "Nature's Fury" which promises to be pretty interesting. I mean, there's a zipline airplane and cylindrical tsunami waves!

Firewrx234 > TheOnelectronic
09/22/2013 at 19:20

Y not plexiglass???

Also I was a part of FLL for 3 years from 2001-2003 then FRC from 2004-now. Loved every minute of it!

TheOnelectronic > Firewrx234
09/22/2013 at 19:23

Plexiglass? Seems like it could be pretty heavy. The main goal is weight savings, really.

Firewrx234 > TheOnelectronic
09/22/2013 at 19:29

Plexiglass is pretty light, it's a clear plastic... You don't need it to be really thick

Phyrxes once again has a wagon! > Firewrx234
09/22/2013 at 19:43

FRC mentor here, plastic may be acceptable but make sure it doesn't shatter. I suspect you will have better and cheaper luck with a thinner hardwood plywood. Having moved a bunch of the "standard" FLL tables I wouldn't want to even consider picking up a particle board one.

I know some FRC teams have fabricated sheet metal tables through sponsors but I'm not sure if one of those would be lighter.

Firewrx234 > Phyrxes once again has a wagon!
09/22/2013 at 19:48

Plexi is a whole lot more sturdy and doesn't shatter like acrylic. It's some good stuff. Used it on our robots for years and never had one fail.

Phyrxes once again has a wagon! > Firewrx234
09/22/2013 at 19:52

Polycarbonate or HDPE (High Density Polyethylene) are likely to be "inexpensive" choices. Though trying to make it out of one sheet that you are sourcing "locally" you may be stuck with Home Depot or Lowes prices on polycarbonate.

MrGuy > TheOnelectronic
09/22/2013 at 20:15

I might go for wood-foam composite panels, which you can get pre-made from Kerfkore for example. The thickness from the foam adds strength without too much weight. You can also get honeycomb-cored panels which should also be pretty light. As long as you have a compatible glue, you could even make your own thin plywood-foam composite, but pre-made would be easier and stronger. Then you could just use the existing 2x4 edge and support, which should keep it light and simple.

JEM > TheOnelectronic
09/23/2013 at 10:50

I work testing composite material design software and this is totally doable in CF.

You will have a small radius curve in the inside edge but done right this should be no more than a centimeter or so radius.

Check the area you're in, there may very well be small shops that work in low volume CF and maybe they would like to sponsor you?

TheOnelectronic > JEM
09/24/2013 at 13:33

We're in a fairly large university town (Champaign, IL), so I wouldn't be surprised. The FSAE team could probably help out but they're famously snooty.