Chassis Material/Construction

[Jeff Waegelin]

We like steel. Our two most successful robots have hade a steel frame. We used aluminum, too, for our mast in 2000, but 2002 was all steel. It was ridiculously heavy, but for our simple but effective design, it was perfect. We took a heavy beating, but the only damage was superficial damage to our Lexan paneling.

We've done wood and aluminum, too. Our 1998, 2001, and OCCRA bots are all wood/aluminum hybrids. We make an aluminum frame and put in a wood base and side walls.

[MacZealot]

When I heard chassis I thought it was a computer chassis or such.

DUH!

Anyway, aluminum tube, it's stronger and lightweight.

[maclaren]

Some of you said that polycarb was brittle and or shatterd easily, those people are confuseing polycarbonate(aka lexan) with acrylic. Acrylic is very brittle, which was best demonstrated at the seatle regional when a team had a scoop made out of acrylic and the opposing alliance threw a ball into play, and it hit the scoop, the scoop shattered. Polycarb on the other hand is extremly tough in fact it is used instead of plate glass in prisons and things of that nature. I saw a demo of polycarb on TV where they invited members of the LA SWAT team to try and break the stuff. The SWAT team tried to break it with sledges, axes, pipes, and crowbars and failed miserably. So they came back with their automatic weapons and fired on the stuff with MP5 sub-mchine guns (NO JOKE) and the polycarb stopped every bulleto a full 30-round mag!! So polycarb(aka lexan) is extremely tough and has no problem holding up to any and all FIRST applications.

My team used extruded aluminum for our base in the form of a "c" shaped structure which was temporaily bolted together for testing and then was TIG welded at the end of testing. Then we built up from there with alum. angle. Then a plywood base to mount ball gathering mechanism and electronics. Why did we use plywood you may ask, because it as avalible and it is so much easier to work with then metal will ever be. Even though it is ugly as can be. On top of the plywood we used alum angle for the ball hopper which filled out the maximum allowed space.

[JVN]

Originally posted by maclaren
Polycarb on the other hand is extremly tough...

Unless you effect it chemically. In 2001 my HS team had forklifts made out of 1/4" lexan. We spray-painted them so that the drivers could easily see them from the booth. Late in the day at Long Island, we had a minor collision with 263 (they blasted right into us coming into the endzone) and the forklifts shattered.
Near as we can figure, the Lexan was weakened by the spray paint.

Moral of the story:
Don't paint Lexan. It can weaken it greatly.

[maclaren]

That is a very good point to not paint lexan. Generally plastics dose not like to be sprayed with solvents(which spray paint is). They tend to weaken them by eating little holes in them. Thus, as you know, they become weak and brittle. 1/4" Lexan is about the weakest lexan you can find. The lexan used in the demo was most likly of 3/4" to 1" thick lexan.

[patrickrd]

Originally posted by JVN


Unless you effect it chemically. In 2001 my HS team had forklifts made out of 1/4" lexan. We spray-painted them so that the drivers could easily see them from the booth. Late in the day at Long Island, we had a minor collision with 263 (they blasted right into us coming into the endzone) and the forklifts shattered.
Near as we can figure, the Lexan was weakened by the spray paint.

Moral of the story:
Don't paint Lexan. It can weaken it greatly.

Are you sure this was Lexan? I have never heard of Lexan shattering, but acrylic would do exactly what you say. Certainly spray painting could have surface effects but by the molecular nature of polycarbonate I don't see how it could shatter, even if the surfaces are eaten away a little.

[sanddrag]

First of all I don't see why you'd ever want to spray paint lexan as it's crystal clearness is beautiful as it is. Perhaps a custom airbrush job but I'll save that topic for another thread.

As for the lexan shattering, this is completely reasonable given the circumstances. The spraypaint acts as a solvent and attacks the lexan making it brittle. Pactra and Parma both make paints safe for lexan. They can be found at your local hobby shop. Here's the link for the Parma paint http://www.parmapse.com/faskolor.asp

[JVN]

Originally posted by patrickrd


Are you sure this was Lexan? I have never heard of Lexan shattering, but acrylic would do exactly what you say. Certainly spray painting could have surface effects but by the molecular nature of polycarbonate I don't see how it could shatter, even if the surfaces are eaten away a little.

Positive. It was the real stuff. It took quite the hit to break it, but still.

[Jeff Waegelin]

Originally posted by sanddrag
First of all I don't see why you'd ever want to spray paint lexan as it's crystal clearness is beautiful as it is. Perhaps a custom airbrush job but I'll save that topic for another thread.

We painted our Lexan panels last year. That's how we got the black color. We dented it a little, but it never broke (and it took some big hits, too).

[maclaren]

The lexan that was spray painted and shattered was 1/4" thick this is important. Lets say that the paint eat away at the 1/16" deep(very conservative estimate) on all painted sides that leaves 1/8" of untainted material left to hold up to an impact. since the imapct was on there goal grabber forklift and it most likly was nt supported except on the end and it was probably over 10" long that leaves an 1/8" thick 10" long piece of unsupported lexan collideing on edge with an unforgiving piece of metal(most likly). Shattering sounds like the logical solution.

If you want to make your forklift visible I would have used a bright shinging tape. Like a neon yellow tape or what ever would match your bots color scheme.

[Clark Gilbert]

Here is a pretty good website w/ Metric and English properties of polycarbonate (aka lexan).

http://www.matweb.com/SpecificMateri...&group=General

[JVN]

Originally posted by maclaren
If you want to make your forklift visible I would have used a bright shinging tape. Like a neon yellow tape or what ever would match your bots color scheme.

This was the solution we came up with for Nationals.

[PMGRACER]

We'd love to use all Ti plate and tube, but C & A might balk at the materials bill! So instead we've used the 1.5 x 1.5 extrusion in the past. There is a considerable weight penalty once you add all the hardware to put the frames together. I like how the Huskie Brigade designed this years bot. Using the shape of the Huskie as the primary structure. I also likes the Killer Bees chasis. Standing .156 plate on edge, connecting the plate with tube is strong and light. And as their leader says "some chasis flex helps keep the wheels on the floor.." Working with sheetmatal most of the time, I appreciate Wildstang's bot as work of art. It is amazing how strong thin sheets of aluminum become once you start putting bends and beads in them. The benfit of the extrusion is the rapid build and ease of maintenance once the bot is together. The trick now, is to use the modular concept for ease of assembly and modification, making the components durable enough for the application, but light as possible....I still want an all Ti bot....

[Steve Team 311]

.09" Sheet metal, oh yeah.

[John Schineller]

We plan to use some of the aluminum extrusion in the kit this year. Has anyone found a marking on the box extrusion or a spec for the exact alloy of aluminum used. We need this for a compatible weld material.
Thanks