Plastics

[DELurker]

Originally Posted by HumblePie

We had good luck with a composite material that was 2 thin sheets of aluminum (about .010" thick), bonded to either side of a corrogated plastic core. The trade name is "Alumalite" and it is used in the signmaking industry. It was very light, and had good stiffness. The only downside was that the corrogated core would collapse under concentrated loads.

1370 used Alumalite for our shooter deck and some other portions this year. It worked very well, but, as HumblePie noted, the corrugations will crush if you get aggressive with the fasteners. Of course, we had some students crushing our 1x1x1/6 aluminum tubing in our frame, so a little plastic was no problem at that point.

I would not recommend Garolite (G10) or FR4 because of the health hazards and precautions recommended for machining them. If you are going to work with them correctly, you need ventilation for any dusts and masks/respirators for the operators. At the very least, that was why my former employer had outside machine shops make our G10 parts.

1370 used 1/8" thick High-Strength PVC (perforated) for our electronics deck this year and it worked out very well. We got ours from McMaster-Carr and it is p/n 92985T51. We got the idea from 1089 in 2012 who used perforated polycarbonate on their robot that year.

[techtiger1]

We use .125 aluminium composite material (ACM) for belly pans. The material is two sheets of aluminum sandwiched around a sheet of plastic. The plastic center allows the material to be easily routed and bent to our specifications. If you wanted to use plastic I would go with .125in thick lexan or uhmw polyethylene. AndyMark sells some perforated material that always looked cool to me as well for bellypans if you wanted to go that route. Of course if you really wanted to get fancy they do make honeycombed aluminum and plastic sheet material as well.

[Tristan Lall]

I've used approx. 3 mm Alupanel in an FRC robot for the structural belly pan. It was alright, but ultimately needed lateral ribs that the quasi-monocoque design didn't provide for.

Its stiffness was better than plastic of equivalent thickness, but quite substantially less than aluminum—and although the solid core made it easy to rivet down, it meant that the weight savings were quite modest.

It cuts decently well on a CNC router, which is what we used.

If I had to do it again, and I really wanted to optimize the part for performance, I'd find a suitable sheet of fibreglass composite sandwich panel (carbon fibre is perhaps too expensive for FRC), or make one from raw material. (There's a fair bit of up-front expense to make these, but you can always make tooling and refine the process in the off-season, and those costs don't count against the limits.) If you make your own, you can lay it up with a lightweight honeycomb core in the centre, and rigid plywood or foam cores where you need to attach mechanical fasteners.

More ideas:
http://www.chiefdelphi.com/forums/sh...d.php?t=121911
http://www.chiefdelphi.com/forums/sh...ad.php?t=98779

[Al Skierkiewicz]

You need to contact More Robotics in Milwaukee. They build the entire robot from plastics since a mentor/sponsor, Mike Whitman owns a plastics firm.

[Michael Hill]

I'm curious, what kind of loading dues the bellypan support in a traditional WCD? If I say the X-direction is the direction of forward travel, Z is up and Y is the cross product of X and Z. Am I looking at torsional loads in the Z axis or the X axis? (Or heck, even Y?) what kind of loads are typical?

I ask because we're exploring a WCD and I'm contemplating material choice for a bellypan. I've heard Travis say they use 3/16 Aluminum (I think it was a 5052 alloy). It looks like 254 just uses an 1/8" sheet of presumably 7075-T6?

We've got a couple sheets of .050" 2024-T3 and .090" 6061-O. I'm contemplating sandwiching them into a flanged isogrid, but now I'm wondering if that's even necessary. I would use the 2024 as my flanges because of the additional shear strength. The stack up would be 0.19" thick, but now that seems like a bit too much.

[Kevin Leonard]

Originally Posted by Al Skierkiewicz

You need to contact More Robotics in Milwaukee. They build the entire robot from plastics since a mentor/sponsor, Mike Whitman owns a plastics firm.

Not only does 1714 build their robots entirely out of plastics, they are also perennially successful. Their 2012 robot was incredible, and their 2013 robot was one of the more successful climbers in Archimedes this year.

[MichaelBick]

We use our bellypan for shear and torsional strength. We used 1/8" 6061, which worked well, but 5mm baltic birch should work just as well if you are looking to use less resources.

[sanddrag]

We used 1/8" 6061 aluminum sheet that we routered out in a rather minimal diamond pattern, leaving mounting locations for electronics and things, and it came out to about 3.7 pounds if I recall. It was quite stiff.

I like doing this because the bottom pan serves as the welding jig for the frame rails and crossmembers. It helps line everything up. We rivet the side rails and crossmembers to the bottom pan, then weld the joints.

In 2012 we used 1/8" ABS which was okay, but a little soft and flexible. We had to brace it.

[R.C.]

Originally Posted by Michael Hill

I ask because we're exploring a WCD and I'm contemplating material choice for a bellypan. I've heard Travis say they use 3/16 Aluminum (I think it was a 5052 alloy). It looks like 254 just uses an 1/8" sheet of presumably 7075-T6?

3/16" for a bellypan would be a bit overkill..

Also a 1/8" sheet of 7075 would be quite expensive (well maybe not crazy expensive, but you could probably get two 6061 pans for a 7075 pan price wise) and overkill. 254 and many of the westcoast teams use 6061-T6 bellypans pocketed @ .125" Thick.

971 does a cool job of utilizing a turret punch to make their belly pan:

https://picasaweb.google.com/1177698...001343255 282

I believe its .060 or .090 5052 AL. Travis/Austin/971 can clarify.

-RC

[Michael Hill]

Originally Posted by R.C.

3/16" for a bellypan would be a bit overkill..

Also a 1/8" sheet of 7075 would be quite expensive (well maybe not crazy expensive, but you could probably get two 6061 pans for a 7075 pan price wise) and overkill. 254 and many of the westcoast teams use 6061-T6 bellypans pocketed @ .125" Thick.

-RC

Thanks, I just assumed they were using 7075 because they use it for so many other things

[Michael Hill]

Originally Posted by MichaelBick

We use our bellypan for shear and torsional strength. We used 1/8" 6061, which worked well, but 5mm baltic birch should work just as well if you are looking to use less resources.

Torsional strength about which axis?

[anthonyttu]

Originally Posted by mman1506

G-10/FR4 is a fiberglass composite that is light weight and stiff (a poor man's carbon fiber). I believe 973 used it one year for an electronics bedpan

I would not advice anybody to use/machine G-10 unless they really had a need and that it is the best material. For FRC robots poly carbonate works for most applications.

From the G-10 MSDS:
“Dust generated during grinding, cutting, or drilling fiber glass reinforced plastic produces respirable fiber shaped plastic (organic) particles whose concentration increases proportionally with dust concentration. These particles are not classified as carcinogenic by IARC or NTP. However, prolonged inhalation of dust can produce lung disease.”

[MichaelBick]

Originally Posted by Michael Hill

Thanks, I just assumed they were using 7075 because they use it for so many other things

7075 isnt used that much. Mostly in places that steel would be used in industry like gears and shafts.