Chassis Material

Our team is considering making a custom chassis for the first time and is debating what material would work the best. We are considering aluminum, fiberglass, and wood. Here are some pros and cons that we have come up with:

Aluminum Pros:
We are very familiar with it
It’s possible to weld it
Its strong

Aluminum Cons:
It’s heavy(.098 lbs/in^3)

Fiberglass Pros:
It’s lighter than aluminum(I read somewhere that it is about 70% of the weight, I don’t have exact details though)

Fiberglass Cons:
Not as strong
Can’t weld it
We’ve never used it

Wood Pros:
It looks really nice
We’re from Oregon where logging is a big industry so we would kind of be representing our area
It’s light, I got a density table:
http://www.engineeringtoolbox.com/wood-density-d_40.html
and if I calculated correctly Douglas Fir, which seems to be about average for the different types and is a common tree in our area, is about a fifth as heavy as aluminum, .019

Wood cons:
It’s not as strong
You can’t weld it

Any more thoughts would be greatly appreciated. Again, it is our first year making our own chassis so we don’t have any experience with this kind of stuff.

Glass-reinforced (structural) fiberglass is definitely tough, rigid stuff, and is roughly half as dense as aluminium. It makes for a pretty beefy chassis that you can lighten easily enough with a hole saw. You can use wood tools to cut and play with it.

The main drawbacks of fiberglass are that cutting it makes a nice, incredibly irritating powder that’s pretty itchy if you get on your skin. Inhaling the stuff is also bad. In addition, it’s commonly available mainly in thicknesses greater than you might need for your application so lightening is something you’ll definitely be doing.

I’d recommend sticking with what you know during the build, and using the off season to experiment.

Does anyone know what the forces the robot absorb are, compared to the strength of wood? If the wood is capable of taking all these forces, it seems like it would be better since it is so much lighter.

Also if someone knew the strengths of fiberglass compared to the other material too that would be good.

The strength of your chassis’s cross section is in general a lot more important than the yield strength of the material you are using. It’s not really a matter of how much load an arbitrary piece of material can take head on.

That being said - one of the reasons aluminium is so popular is that you can use it in a number of “strong enough” ways.

We’ve always used aluminum from the AndyMarks manufacturers. It is a bit heavier than say, fiberglass or polycarbonate, but it’s strong and is especially good for first-timers, because it’s pretty easy to work with. Here’s what we always use:
http://www.andymark.com/ProductDetails.asp?ProductCode=am-0202
It’s nice because the holes for nuts and bolts and whatnot are already there, and it’s easy to cut with a basic cutter.
Hope this helps! Good luck from team 3397!:smiley:

does anyone know any teams that have used wood frames in the past?

12mm baltic birch plywood is much stronger than the same weight aluminum and can easily be fabricated using wood tools and attached using wood glue.

Based on the information that I found on the internet, I have found that aluminum is much stronger than any wood. Although, I could be wrong :slight_smile: how much stronger is baltic birch plywood compared to aluminum?

If you have used this for your frame before, can you send me some links to pictures of your robot or explain how you used it effectively? thanks

It’s hard to compare the strength of these materials fairly if you just go by the tensile strength rating. You need to consider the strength to weight ratio, for the complete frame structure. Since you design the frame based on what material you’re using, you will have a different frame design for each material.

Wood works, fiberglass works, aluminum works, steel works. We’ve used them all except aluminum before, but we might use the kit frame this year.

As mentioned, at this point in the build season, you’re probably better off using what you know how to work with.

That’s why the search button was invented. :yikes:

But here are two links you can start looking at:

http://www.chiefdelphi.com/media/photos/tags/wood
http://www.chiefdelphi.com/media/photos/tags/frc173

@Squirrel. What do you mean by this point in the build season? It has just started?

If you were to go with aluminum would you use 80-20 or C-Channel or would you fork out the money for Carbon Fiber?

Carbon fiber is not aluminum, and it’s way down on the list of materials I would use. 80-20 is also way down on the list of shapes of aluminum that i would use, it is not really the right shape to make a strong, light structure. Thin wall rectangular tubing, or channel, would be more appropriate.

We’re already a week into build season, we don’t have a frame design or even material selected yet…but we do have experience with 4 different materials. When we’ve used new materials, we’ve always done some experimenting first to get a feel for it, and worked out some preliminary designs before build season. But you do have the resource of CD to give you ideas of how to build using new materials, and you can get quick advice about your planned design–take advantage of it, post the design for your chassis before you commit to building it, and let us see if we can anticipate any problems.

look up 1771’s robots from the past 2 years.

Our team uses 2"x1" rectangular tubing, 1/8" wall thickness. You can get it from Mc-Master. It’s cheap and easy to use.

We’ve used:

Baltic Birch Plywood: here, here, here, and here.

Maple and mahogany here.

Fibreglass sheets (we cast them ourselves on urethane foam cores), here, all the white sides are sheet fibreglass.

And thin walled 3/4" square aluminum tubing TIG welded together here. Oh, wait… there was baltic birch in that shot, too.

We’ve used the KoP frame in several years… albeit welded, chopped and otherwise hot-rodded, and I can’t find any quick photos of our nerf-ball shooter which was also 3/4" thin wall tubing.

So… yeah… they all work great, so long as the structure you use matches the materials you have. In general, though, I have found the aluminum tubing to be best for “space frames” that occupy a large volume, simply because you can build them lightweight yet rigid. I like the baltic birch for anything that allows you to get sufficient joint strength and will undergo massive abuse. The upper arm in that “Triple Play” robot with the red background could sustain two judges BOUNCING on it. (We had a display with a spare arm set up in the pit… it helped win us our first FRC award.)

Actually, now that I think about it, our overdrive robothad a lot of wood in it, too.

Thinking of the engineering and design awards that we have won, we’ve had our use of wood cited three times, our use of fibreglass cited once, and our use of aluminum never mentioned. Thinking outside the aluminum box has paid off for us, both in unique, functional, robots and in resultant recognition from the judges and teams in our area.

Jason

P.S. Ever thought about using Bamboo? Use some fibreglass tape and epoxy at the corners and you might have a good (mostly) biodegradable, eco-friendly replacement for thin walled aluminum tubing for use in space frames.