Plastics

[yash101]

Originally Posted by CalTran

I cant recommend using this for a bellypan though, that stuff is heavy. We used hdpe on year and man did it weigh in.

Yep. That is a drawback of delrin, however, if you need a smooth surface, delrin will cut it, most of the times!

[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. We used this material for our belly pan, so the solution to the point loading was to use c'sink head screws, and they would self-countersink as we tightened them up, being careful not to over-torque them. Velcro also worked well to avoid the issue.

We also used it for our shooter deck sandwich. It was light and lent itself well to waterjet cutting. Later, we found that there is a solid polyethylene core version called "Alupanel". It solves the point-loading problem, but is a good bit heavier than the corrogated core. Both are available through sign shops (always ask for donations, they may have cutoffs) or online.

[thefro526]

As others have said so far, Delrin (Acetal), Lexan (Polycarbonate), and ABS are all pretty common plastics that are fairly easy to work with. Composites like Fiberglass, Garolite, etc are also well within the range of most FRC teams but require some special considerations when being machined and used, specifically ventilation, etc.

My personal method for deciding whether or not a part can be made out of plastic is based on a bit of previous experience and some guessing. One of the biggest considerations is the purpose of the part and how strong it needs to be. If it's something that needs to hold relatively precise geometry, but doesn't necessarily need to be strong, Plastics are a pretty good option and can be easier to work with than Aluminum. The common trade off is that you're going to need more (thicker) material to get a part that is strong enough, which means that you could get into situations where a plastic part is the same weight as a part made of Aluminum and is as strong.

One of the other nice things about plastic is that they're really useful when something needs to be a specific thickness for one reason or another. We've done bearing blocks and things along those lines from 1/4" Delrin before since they didn't need to be strong, but did need to keep the bearing flush with a surface.

There's also the added bonus of elasticity, should you need to have a part that has a known amount of 'give' or impact resistance before it permanently yields. Both lexan and delrin are pretty handy for this purpose, since they're fairly good at taking a beating if they're outside of the frame perimeter.

[protoserge]

Also, pay attention to the possibility of ESD when using plastics for electronics mounting. A fellow inspector and I witnessed a team last year at Chesapeake having strange issues caused by their mounting board.

A sheet of 0.063" aluminum with some dimple dies may be lighter and thinner than a plastic of the same stiffness and load capacity.

[Bald & Bearded]

Like many of the posters above have stated the exact application drives the plastic would want to use.

For electronics this year we are looking at HDPE and similar sheet plastics that we can mill easily. We also 3D print small parts in ABS.

In the past we have used corrugated fiberglass sheets for many applications including drive train pans, electronics, and one year ramps for other robots to drive onto. It has good stiffness but one needs to be very careful in mounting it using washers and other things to make sure stuff does not pull through.

[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