Lignin fiber matrix (wood) as a chassis material

[timmmoore]

Jason, we should have shown you our spare arm at Seattle, it had a clear coat finish. We used that version at St Louis, see
http://www.popularmechanics.com/tech...c=rss#fbIndex5

We used wood glue except when glueing to non-wood, for the same reasons you stated.
We took a major hit on the arm in St Louis, a rough estimate was a bot hitting our arm moved our bot ~12" sideways, a bit of glue and we were good to go for our next match.

[Gdeaver]

Good. First teams have had a metal addiction for years. I've been trying to get teams I've work with to vary their robot diet to include some fiber. Plywood is a very viable construction material for first robotics. But, mentors should not stop there. Our students do not get a traditional shop education any more. Tech Ed has turned into an arts and craft experience. We need to expose students to the many material choices we have available and teach them how to work with them. Why don't you over the summer put together a white paper on wood and robots construction techniques. Your design and joining methods are why the robot holds up. Share your design methods. This year we used some Birch 5mm plywood and laminated it with 5.7 oz. carbon. We have several students that are now proficient in vacuum bagging. It's not that hard. We also use thermoplastics that are thermo formed and vacuum formed. ( polycarbonate and polypropylene). Fiberglass pultrustions were used for the 4 bar arm. I'm very happy that in a 6 week period our students received the shop education that they should have had in school.

[FrankJ]

Wood is well used in small boats & small airplanes were weight & strength is important. Lots of good information can be found by Google. West marine is one source among many. It is amazing how strong a joint is made by laying over a strip of fiberglass & epoxy.

One wood bot is kinda weird.
Two wood bots is a cult.
Three wood bots is a revolution
Vivia la Revolution

[AdamHeard]

I agree with all of your points except for the lightweight aspect.

If aluminum is used properly in efficient frame design, it is definitely coming in lighter than wood. No doubts.

The past two seasons, the sum total weight of all frame members (upper and lower) was around 15 pounds. this includes bellypan and bumpermount.

[MrForbes]

You might be right Adam, but I will point out that most aluminum robots do not have very efficient frame designs.

Designing a light, strong, robust wood robot takes some effort. Building it can be relatively quick and easy, but only if you put in the time designing it well.

I wouldn't build a wood robot just to have a wood robot. There are many considerations when choosing a material. I like to use the "best" material for each part. That could be plastic, wood, aluminum, steel, fiberglass, lexan, titanium, etc. My idea of what's "best" usually is based on obscure factors such as material availability, tools, working knowledge, cost, toughness, etc. Ultimate tensile strength is pretty low on the list for most parts of the robot.

[EricH]

Adam, have you ever seen an R/C aircraft built mostly out of aluminum? (I have, but it was a custom build for SAE Aero Design--and that particular airplane was still about 1/2 balsa.)

My contention is that it's not about what material you use, it's how you use it. Build the robot out of steel, but mess up something, and it will break. You could also build out of mainly plastic, and have it never break (1714, for example), because you did it right.

[AdamHeard]

I wasn't criticizing wood, just clarifying a point. Too often I see students on here catching onto phrases/ideas they've seen and repeating them without ever questioning their validity (the drop on 6wd is awful, etc...).

Personally, when I look at a team the thing I admire most is that team using their unique resources as best they can to create the best machine they can. If a team can build a better robot out of wood, cool! Just because aluminum is the best choice for my team (and I'd wager a good deal of teams), does not mean I'd claim it's the best choice for all teams.

I'd stress that young designers focus more on GOOD design than material choice. There is no magic material out there; every material has a useful application, and what will determine success of a design far more than material, is the quality of the design itself.

330 and 1726 have both made machines and mechanisms I thought were awesome out of wood; and it was what their resources dictated. Good move!

Originally Posted by EricH

Adam, have you ever seen an R/C aircraft built mostly out of aluminum? (I have, but it was a custom build for SAE Aero Design--and that particular airplane was still about 1/2 balsa.)

My contention is that it's not about what material you use, it's how you use it. Build the robot out of steel, but mess up something, and it will break. You could also build out of mainly plastic, and have it never break (1714, for example), because you did it right.

That's comparing apples to oranges. It's just as inaccurate as me asking if you have ever seen modern fighterjets or spacecraft made of balsa.

[Mark Sheridan]

Originally Posted by AdamHeard

I wasn't criticizing wood, just clarifying a point. Too often I see students on here catching onto phrases/ideas they've seen and repeating them without ever questioning their validity (the drop on 6wd is awful, etc...).

Personally, when I look at a team the thing I admire most is that team using their unique resources as best they can to create the best machine they can. If a team can build a better robot out of wood, cool! Just because aluminum is the best choice for my team (and I'd wager a good deal of teams), does not mean I'd claim it's the best choice for all teams.

I'd stress that young designers focus more on GOOD design than material choice. There is no magic material out there; every material has a useful application, and what will determine success of a design far more than material, is the quality of the design itself.

Just to elaborate on your point. If two frames that are perfectly designed, the aluminum one will be lighter than the wood one.

Now for teams, like mine, who don't have ideally designed frames, will have ones that are not lighter or stronger than the wood frame. This whole topic fascinates me because we build aluminum frames without a metal shop; yet we work in a fully equipped wood shop. We weld our own frames without a welding table, so there are quality issues. I realize that our woodshop is a powerful unused resource.

I feel there are a lot of teams that work out of a wood shop instead of a metal shop that ought to take a look at these teams.

[Ian Curtis]

Originally Posted by EricH

Adam, have you ever seen an R/C aircraft built mostly out of aluminum? (I have, but it was a custom build for SAE Aero Design--and that particular airplane was still about 1/2 balsa.)

Have you ever seen an R/C plane with even *close* to the same structural requirements of an FRC chassis? NO!

The great thing about aircraft is that most of the loads are pretty specific. An FRC base is going to get hit -- hard. An airplane is not. You build a nice sturdy spar (balsa is a great material, but there are many others) and then you put lots of ribs who mostly serve as a surface to attach a covering to. You build a nice sturdy wingbox, and hang a lightweight fuselage off it to put your payload in. You have a sturdy motor mount tied in somewhere, and a sturdy tailboom to hang a lightweight tail off of. You put in a couple of mounting holes for servos that weight less than a 1/10th of a pound, stick a receiver somewhere and you have an airplane.

When a balsa structure suffers an impact event, it is typically a total loss.

(I'd love to build a tabbed wooden FRC chassis though)

[Zflash]

We have used the tabbed base construction method since 2006 on 1319. When I was on team 507 we used it on our robots in 2001, 2002, and 2003. It is a great method of construction no matter the material. As many have mentioned it comes down mostly to design techniques and putting the effort there more than anything else. The chassis' have never had any failures we make them out of aluminum and weld up the tabs, this is most likely lighter than wood constructed in this manner however it requires a skilled welder.

As far as judges and awards. We have won many technical awards, a few events and always at least make the dance. Up until 2009 we have always spray painted our parts with paint purchased from Wal-Mart or Lowe's. We still paint some of our parts however our chassis' since 2009 have been powder coated by a gracious sponsor.

I have not seen 1771's robot this year however I have always admired your team's work since we first competed with you at Peachtree in 08. I am sure your team has something to be proud of but understand you wanting the validation a technical award can bring. We to did not score a technical award this year and we had several unique features that worked well. We wonder if we possibly looked to good with our powder coat and painted parts.

Hope to see the 1771 machine at GRITS and keep on with the wood since it is obviously working on the field for you where it matters most.

[Tristan Lall]

Originally Posted by Ian Curtis

Have you ever seen an R/C plane with even *close* to the same structural requirements of an FRC chassis? NO!

There's always an exception...I have.

Actually, I had a significant part in building one for a project as an undergrad. I had a less significant part in originally designing it, so I can freely concede that it could have been lighter. Nevertheless, it was a 14 ft span, 12 ft long, 80 lb operating empty weight/100 lb loaded weight aircraft, designed for a strange combination of aerial reconnaissance and parachute-based payload delivery.

It was built with a tabbed plywood truss fuselage (basically, a long box, tapered at the ends), with foam-cored, balsa-skinned wings with an aluminum spar.

And although it could have been lighter, one of the practical objectives of overbuilding was to minimize the impact of unusual conditions. It was one aircraft filled with thousands of dollars of stuff, and we were somewhat risk averse. Possible scenarios included payload failures (you wouldn't want a tangled chute to foul the aircraft and break an elevator off), rough landings (mostly avoided), and even being able to recover from skidding off of an iced runway (the taxi tests were harrowing: we didn't have any excursions, but we did manage to bend the landing gear). And yes, since this was the first time scratchbuilding an aircraft for just about everyone, nobody wanted the wings to come off in flight.

Ultimately, it's a convenient counterexample, but I do of course agree that ordinary aircraft don't need to be built to withstand FRC chassis loads.

[Kusha]

There was one team at the dallas regional that had a completely wooden arm. needless to say it won an award.

Hung tubes beautifully.

[Ian Curtis]

Originally Posted by Tristan Lall

There's always an exception...I have.
[snip]

I should know better than to speak in absolutes.

More on topic, the Riot Crew (58) has built wooden robots for many years. In recent years they've used a kitbot chassis with a mostly wooden super structure, and have been very successful (but as a 1 regional/year team, no one knows of them outside of Manchester).

Given the interest in various materials and their suitability, it seems odd to skip over what they are suitable for.

For items that are subject to purely tensile loads, it is desirable to have a material with a high strength to density ratio. It turns out that for common steels and aluminums these are almost the same. If the stretchiness (elasticity) is important, again common steels and aluminums are most the same.

Titanium is sometimes held as a miracle material, but its claim to fame is that its density is about that of aluminum with a strength close to that of steel. Check matweb to see if I got that straight. It's other nicety is that it does not lose strength as drastically as other materials do at higher temperatures.

If steel and aluminum are so similar why the preponderance of aluminum in aircraft?

The first good reason is that aluminum oxidizes so fast and the oxide sticks so well that further corrosion of the metal requires special circumstances - like a nearly closed lap joint with some salt and water. Common steels are either corrosion resistant and relatively weak or strong and tend to develop a flaky rust that does not protect against more rust.

The second good reason is based on this - roughly speaking, the resistance to bending of a flat piece of material is proportional to the cube of its thickness. A piece of aluminum 2 inches thick will deflect 1/8th as much as a piece one inch thick. Aluminum is about 1/3 the density of steel, so an aluminum part can be 3 times thicker for the same weight. It should deflect (1/3)^3 or 1/27th as much

Unfortunately, aluminum is 3 times as elastic as steel. so, in bending, the double thickness of aluminum is only 9 times as stiff as the same weight of steel.

One of the most important tasks a wing skin has is to not wrinkle. One of the best ways to not wrinkle is to have increased bending stiffness.

A similar effect is true when it comes to wood. Its low density can offset its low strength by allowing more thickness for a similar weight. Wood is more complicated because the strength depends on the direction of the load relative to the grain, but its properties in this regard is one of the reasons trees seem to have favored wood, rather than metal. Wood is also much better at avoiding fatigue cracking, a continuous menace in the world of metals.

Additionally, even though wood is combustible, a large wood beam in a building fire is a much safer beam because wood doesn't soften in the heat. The amount of beam remaining is a decent estimator of the amount of strength remaining. That said, fire in not a part of FIRST.

Remember - the largest wingspan aircraft built was built of wood. Yes the A380 wins on some scores, but not all. see en.wikipedia.org/wiki/File:Giant_planes_comparison.svg. Wood construction costs more and, while metal corrodes, wood can rot. Ask Knute Rockne about that.

Some of the most advanced materials today are fibers held together with resins, already mentioned as the way wood is built.

[Dick Linn]

Team 975's first robot was wood, even the drive wheels. Only cheap 1/2" plywood and 1" x 4" Pine (max) was allowed by the rules that year, IIRC.

We painted "Team 975 featuring W-Fiber" on a large piece of cedar siding. The field announcer would wave that around when our team was announced, LOL. I still have that sign hanging in the garage.

Thereafter, we had a saying, "Wood is Good". We tried to incorporate at least some wooden elements whenever possible.