strong composites for belly pan

[Jon Stratis]

Just to throw another idea in there... what about making the bellypan in pieces? With out design last year, our pan had to be pretty deep to hang off the frame like we wanted. As a result, we couldn't make it out of a single sheet of aluminum - we ended up bending up two sheets, and pop-riveting them together down the middle of the robot. It worked great, and was plenty strong. So if you can work smaller pieces of aluminum and build the pan out of 2-3 sheets instead of one, that could be a viable alternative.

[JamesCH95]

A couple ideas:

Carbon Fiber with balsa core.
Carbon Fiber with honeycomb core.
Fiberglass with balsa core.

You can find almost any composite/core combination you'd like. We used a piece of fiberglass/honeycomb core for our 2005 robot electronics board. It is very stiff, light, and strong. Can be a little pricey though. Taking the 1/2" balsa-cored carbon fiber as an example, it has a density of 0.0125lb/in^3, about 88% less dense than aluminum.

If you get a little ambitious you could make this sort of stuff yourself, it's not terribly difficult.

[Madison]

Any thoughts on perforated plastic sheet (e.g., McMaster-Carr 9293T56)?

[EricH]

I don't know about perforated plastic sheet, but corrugated plastic is fairly strong and fairly light. If it's properly supported (around the bottom of the frame, say) it can hold a full-weight robot. I don't remember what thickness we used on our ramps in 2007, but I don't think it was more than about 1/4"-3/8", on about a 3' square.

[JesseK]

In case honeycombed composites are considered...

Our electroncs boards have been made from honeycombed fiberglass made by PlasCorp since 2007. The combination of a stiff board, insanely light weight vs. square footage, and insulating factors made it ideal for us to use. We even mounted the compressor and battery on the material for 2010.

The material is somewhat easy to cut with hand tools, but I would recommend a table saw and/or band saw. It is extremely easy to drill through, and not too difficult to punch through with a hand punch + hammer. Finally, spraypaint works great for color.

However, I would not recommend using it for a belly pan that provides support to the frame. The gaps from the honeycomb structure are not strong enough to withstand the implied lateral forces. I also recommend against mounting the board vertically unless the bottom edge has a lateral support since gravity will have the same lateral-force effect.

[svenw]

You might ask yourself if the belly pan needs to provide rigidity, or if it just needs to house electronics. In the past years, we have always used a box al welded frame and 1/8" lexan. The frame is solid without the lexan.

Because this is our first year welding aluminum we would like the belly pan to provide a bit of support incase our welds are not as strong as they should be. We are welding with our schools millermatic 180 with a spool gun for aluminum, and have been getting some fairly decent welds, but not perfect.

As per your techno, if it is similar to the new one we got here, it can cut aluminium using a carbide endmil

We actually had these guys cut on a 4x8' Techno Router

I figured that the router would be able to handle aluminum, and have been talking about it to our shop teacher about it. Apparently our school board is scared that the school might catch fire if we use a "wood working" tool to cut aluminum, we might just have to do it late on night when no one is around .When routing aluminum do you use 6061 vs a 5052? I think i read somewhere that routing a harder aluminum works better because it does not gum up the router bit.

carbon/s2 glass plywood panel for a robot bottom can be done for relatively cheap

We actually do have a bit of experience working with carbon fibre, we purchased a vacuum pump as well as a sheet of glass, and made some side panels out of carbon fibre last year. It was fairly brittle however, but this could just be because we did not do enough layers, how many layers of cloth would you recommend, and what exactly is S2 glass?

I don't know about perforated plastic sheet, but corrugated plastic is fairly strong and fairly light.

corrugated plastic is fairly strong when pushing it in the right direction, however when you push on it from the side would it not fail fairly easily?

Sven

[Jeffy]

Originally Posted by svenw

When routing aluminum do you use 6061 vs a 5052?

We have routed 1/8" 5052 al plate and 3/4" 6061 aluminum. 6061 clearly machines easier, but 5052 can be machined too.

[JamesCH95]

If you decide to lay up your own panels the number of layers will be determined by the weight of weave you use, the type of weave you use, the type of material (carbon, kevlar, glass, blended, etc).

For a good mix of aesthetic, coolness, and strength I would use something like this colored/blended fabric and do either 5 layers alone, or 2-3 layers on top and bottom of a core material (just from the seat of my pants) and definitely use epoxy for the medium. Don't forget to do a multi-angle layup.

[DonRotolo]

Originally Posted by JamesCH95

2-3 layers on top and bottom of a core material (just from the seat of my pants)

You mean they should cut up a pair of your pants? Hopefully not while you're still wearing them...

Seriously: Good advice. A lightweight but low-compressibility core will enhance the stiffness of the layup by bringing the tensile fibers (fiberglass or kevlar) further from the center of bending. Balsa is good, high-density styrofoam (expanded polystyrene) works very well, even 1/4" luan plywood is good. 1/8" is a good thickness to experiment with.

We've made some experimental layups using 1/16" aircraft plywood and 2 layers of 3 oz fiberglass, laid up at a 45 degree bias using marine epoxy and pressed tightly for cure using a heavy weight (iron barbell weights), the stuff was incredibly strong. Only problem is finding large sheets of 1/16" plywood, we used small pieces made for the hobby market.

[Jay H 237]

Originally Posted by Chris is me

Lexan can be used for an electronics belly pan at 3/32 or 1/8th. However, unlike an aluminium belly pan it won't provide much structural reinforcement / rigidity to the chassis, as lexan is very flexible.

1/4" polycarbonate can be used, and will work for mounting of electronics. It's thick enough that it can be tapped and can be heated, bent and hold it's new shape.....plus won't shatter on impact.

Not good for heavy assemblies mounted to it but it may work for a basic belly pan/skid plate set up.

[JamesCH95]

Originally Posted by Don Rotolo

You mean they should cut up a pair of your pants? Hopefully not while you're still wearing them...

Seriously: Good advice. A lightweight but low-compressibility core will enhance the stiffness of the layup by bringing the tensile fibers (fiberglass or kevlar) further from the center of bending. Balsa is good, high-density styrofoam (expanded polystyrene) works very well, even 1/4" luan plywood is good. 1/8" is a good thickness to experiment with.

We've made some experimental layups using 1/16" aircraft plywood and 2 layers of 3 oz fiberglass, laid up at a 45 degree bias using marine epoxy and pressed tightly for cure using a heavy weight (iron barbell weights), the stuff was incredibly strong. Only problem is finding large sheets of 1/16" plywood, we used small pieces made for the hobby market.

Thanks. Have you ever used those plates on your robot? It does sound like very durable construction.

OP, FWIW: typical commercial wood-cored composites orient the wood grain normal to the surface of the plate, typically called "end grain" orientation. This orients the core in a way to take maximum advantage of it's shear strength, the skin will support tensile/compressive loads.

[Mike Q.]

I may be a little bias because they are one of our sponsors, but plascore is some pretty cool stuff. http://www.plascore.com/