strong composites for belly pan

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.

If you decide you still want to go with a rigid “belly pan”:
I can give a +1 on garolite. I’ve always heard that it is about 90% the strength of carbon fiber. Machines just like carbon fiber or fiberglass in my experience.

As per your techno, if it is similar to the new one we got here, it can cut aluminium using a carbide endmil, and if you want some suggestions on speeds and feeds, I can give you first hand exerpience with a techno router. It’s not fast, but it can be done if you decide that is what you want.

One other thing I remember hearing while lurking the forums was a suggestion to use a high quaility 5 ply 1/2" plywood. It’s rigid and easy to work with.

The RAWC actually uses 1/8" 6061 Aluminum and gets it waterjetted/laser’d.

Sven, we’ve used belly pans like 254 did last year.

We actually had these guys cut on a 4x8’ Techno Router. Our team has owned one for about 3 years now. If you have any questions or need help, feel free to shoot me an email.


In my time on 330, we had some really nice plywood bottoms. 2005, we took aircraft-grade plywood, cut some pieces to match the openings in the frame that we wanted to cover, and cut a piece to match the entire bottom area to cover. Glued them all together, and had a strong belly. 2007, we looked solid from the top. The bottom of the belly pan (1/4" ply, I think) was a spiderweb of strength and thin areas. Attachment points were full thickness, supports for the attachment points were full thickness, everywhere else was thin. A skilled hand with a router was all that was needed.

McMaster is a bit strange with regard to shipping to Canada (provided nothing has changed in the last several months). They’ll happily and promptly ship to existing customers, but I’ve heard several times from potential Canadian customers that they’re being turned down.

Since you’re in Kincardine, maybe one of the Bruce Power folks can arrange for you to ship it to their dock? (Surely they’ve got a prior relationship with McMaster.)

As for belly pan materials, laminated carbon fibre and plywood was just what I was going to suggest. Companies like DragonPlate sell it, and it’s expensive but excellent. I’ve never been able to afford enough of it to use on an FRC robot though.

Garolite can work too, though I’ve never seen it laminated with a lightweight core. You may have to build your own using a high quality epoxy and some appropriately smooth plywood or other material.

With any of these composites, machining can be a bit of a pain (not to mention the dust is nasty). If you still have a way to get some parts cut on a waterjet, that may be the thing to do, provided that any wood core is marine grade (or similar) so the glue won’t dissolve, and doesn’t expand too much when wet. (I seem to recall that DragonPlate says they’ve tried this with their plywood-cored material, with decent, but cosmetically poor results.) Otherwise, they’re usually cut with a CNC router (but the material wears out cutting tools quite quickly).

I’d actually be interested in seeing how progressively-stiffer robots perform on the playing surface. There’s probably a point where more stiffness becomes inconsequential in any given design, and it might be worthwhile to experiment with several materials to try and find it.

One final thought: in most designs using one, the belly pan is probably most useful as something that keeps the frame rectangular, rather than something that keeps it from bending in the vertical direction. In that sense, buckling resistance in 2-D is probably more important—and that has a lot to do with the way you attach it to the frame rails. (Lots of rivets are good!)

G10 is incredibly abrasive and will destroy even carbide end mills/router bits in no time flat. You will probably want a diamond coated bit if you intend to do extensive machining to it.

The dust is very very nasty. If you breathe it, imagine essentially ending up with microscopic glass particles deep in your lung tissue. You want an appropriate respirator for sure, if you produce any dust.

G10/FR4 is not cheap. To make a full size carbon/s2 glass plywood panel for a robot bottom can be done for relatively cheap. 20$ for a 1QT. epoxy kit. 14$ for home center 1/4" plywood 4 x 4. About 35$ for Baltic birch. 8 oz. S2 glass about 8$ per yard. 660 KSI carbon about 35$ a yard. This is all you need to do a basic lamination using weight to smash it down. Better results can be had with vacuum bagging but, would require more investment in materials. A fine tooth metal blade will cut the finished product just fine. CONTROL THE DUST!! Do not allow epoxy on skin and ventilate well. Be aware that there are some people that have amine allergies. Laminating is not that difficult. The are many videos on your tube.

A 3x4 piece on mcmaster (with their high prices) of 1/16" g10/fr4 is only $60. We’ve been using it for years, that gets you a bellypan and plenty of spare material.

make the belly pan heavy, and you’re robot won’t be so likely to fall over…

But if you’re going to put electronics directly on it, then making it insulating is also a good idea.

We’ve used 1/16" aluminum and 1/8" plywood to good effect in different years. Aluminum is easy to rivet to the frame (assuming the frame is aluminum or fiberglass or similar), and wood is easy to staple/glue to a wood frame.

I’d still like to be able to use 1/4" steel plate for the bellypan…it’s a life goal…

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.

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.

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

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.

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.

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 :wink: .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?


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

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.

You mean they should cut up a pair of your pants? Hopefully not while you’re still wearing them…:rolleyes:

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.

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.

:yikes: 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.

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