Lignin fiber matrix (wood) as a chassis material
 

We have built our frame from wood for the past three years. In the past, you couldn't really tell it was wood because of the finish we applied. This year we decided to leave it natural so that it was obviously wood. At Peachtree, most people were familiar with us and I heard no negative comments on the wood frame. At STL, I heard several people comment that our robot must not be very good because the frame was wood. Even the judges pretty much ignored us. No judge came by our pit to speak with the team until one of the kids asked them to. Then they just came by, asked a quick question or two, then left. There was a pervasive feeling that wood is an inferior material for construction, and that we must have used it because we couldn't do any better. This is not the case. One of our sponsors is a laser cutting operation that can cut anything we want from wood or aluminum. We have built aluminum frames in the past, but we have had such good success with wood that I see no advantage to aluminum. I won't say that wood is the best possible material for all robots or all teams. I can't guarantee that we will build a wood robot next year. I do believe that for the last three years, wood has been the best choice for our team. I wouldn't do it different if I had the chance. Here is a brief history of our wood chassis and how they have done.

In 2009, Sean Cantrell, one of our college mentors, suggested building our frame with wood. I was not really in favor of the idea. He made a good case about the weight, strength etc, and the kids decided to give it a try. So we used Okume marine plywood (very expensive), laser cut the parts to fit together like a jigsaw puzzle, and glued it up with marine epoxy. The frame turned out beautifully. It was light, very strong, and incredibly easy to work with. Need a fastener here? no problem, drill a hole and install a tee-nut. Need an opening there? no problem, grab a hole saw and zip, there you go. No worries about aluminum shavings shorting out electronics, no problem with the frame being a conducting path for shorts, no dents or bent parts ever. The kids decided to give the frame an automotive paint job (gloss black) and nobody knew the frame was wood. We played over 60 matches, were the # 1 pick at Peachtree, Palmetto, Curie, IRI and GRITS. We won Palmetto and GRITS, and did very well everywhere we went. If you look at that robot today, you will see that the aluminum parts are beat all to hell and back, bent, straightened, re-bent. You can now tell that the frame is wood because the paint is all beat up and worn off, but the only damage is a few wood fibers pulled up where most of the impacts occurred. Since then, we have been wood all the way. Last year we decided to go with baltic birch instead of Okume because it was much cheaper and more readily available. We used wood-woking glue and a brad nailer. Again, I was pleased with the results. We built an 8 wheel drive, 6 motor, high traction pushing monster. We won Peachtree, and played in the quarterfinals on Galileo head to head against 217 in two very aggressive matches (at one point both us and 217 were almost vertical, with no wheels in contact with the floor). We held our own, but our alliance went down in two. Several times during the event I went by 217's pit and observed the work they were doing repairing the bent aluminum sheet metal on their frame. Our wood frame sustained no damage. It remains pristine to this day. This year, Sean decided to help out 2415, but we stayed with wood. Again, we had great success. We won Peachtree again, and were seeded #1 on Galileo. We used a Banebots 775 for our elevator drive. I don't know if we ever had the famous case short issue (we didn't when we installed it), but even if we did, it couldn't cause problems with the control system because the chassis is not conductive.

If we had built our chassis out of carbon fibers laminated in a matrix, it would be considered high tech and cutting edge. Instead, we used lignin fibers laminated in a matrix. For some reason that was considered low tech. Again, I can't say that wood is the best possible material for all robots or all teams, but for us, it has worked well. I saw that 829 built a wooden frame similar to ours this year. I didn't see any of their matches, but they made it to the semis at Smokey Mtn and Boilermaker. If anyone wants advice or info on wood as a robot material, contact me, or I would bet that Sean would answer any questions you may have.

Re: Lignin fiber matrix (wood) as a chassis material
 

Our wooden robot from 2009 (your long lost clone) was by far the easiest robot to build and maintain that I've ever been involved with. When I think back on the robot design that year I don't know how we would have gone about it with a different material... it wouldn't have been pretty.

You bring up a surprising point about the judges ignoring a robot with a wooden finish. We threw a few coats of Krylon spray paint on ours in 09 to make it look fairly nice, and we managed to bring home the quality award at AZ. A lot of people didn't even realize it was made of wood. I wonder if things would have turned out differently if we didn't take the time to put on some cheap paint.

(by the way, still searching for a picture of your bot this year... I didn't manage to stop by at champs!)

Re: Lignin fiber matrix (wood) as a chassis material
 

You do know that the battle of Britain was largely won with plywood airplanes. ;) Combined with modern fibers & resin matrices (IE fiberglass) plywood is incredibly strong & light. Not to mention that it can be worked with primitive tools for those of us that do not have access to laser cutters or water jets. Great shock & fatigue properties as well.

I do not if we will ever use it, but it has a lot of great properties.

Re: Lignin fiber matrix (wood) as a chassis material
 

I have to say sorry to 1771, our team was confused by your use of wood. We had no understanding of how well engineered its construction.

There was a team in Archimedes that also had a wood robot. I forget their number but their arm was fairly obvious that it was really well made and an enormous amount effort went into it. That robot changed out perspective on what you can do with wood. From the description of your chassis construction, so have you.

This is a lame excuse for casting judgment before knowing the truth, in my past encounters with wood robots, I have seen their frames battered and broken. I have seen their frames split apart at the joints. This was before bumpers, so maybe having bumpers helps. Though I think the real reason was they were nailed together instead of having proper glued joints.

I have to agree, that paint helps any robot look better.

I find this amusing in retrospect, I observed my students hesitance to use wood even in prototypes, its amazing how they go immediately to the polycarbonate sheets.

Thanks for sharing this information. Any chance you have pictures of your frame?

Re: Lignin fiber matrix (wood) as a chassis material
 

I don't yet have many pictures posted, but here is a picture of several of our frames. Two copies of this year's frame can be seen, one on either side of the 2008 sucker-bot. I will try to get some picture uploaded soon.

Re: Lignin fiber matrix (wood) as a chassis material
 

Do you have an estimate of what the cost would be to do this without having a sponsor to laser-cut it? i.e. How expensive would it be to laser cut all the pieces.

Re: Lignin fiber matrix (wood) as a chassis material
 

I don't really have a feel for cost per hour on the laser, but I do know that the cut speed for wood is slower than for aluminum. I would imagine that it takes 1-2 hours to run our wood parts on the laser.

Re: Lignin fiber matrix (wood) as a chassis material
 

We built our 2009 robot Major Tom using common woodworking equipment. Laser cutting is not necessary! but if you have a sponsor who can do it, go for it.

Re: Lignin fiber matrix (wood) as a chassis material
 

Do you have any guidelines as to tabsizes and design considerations? Or is there a proper name for tabbed construction that I could look up to find guides on this type of construction.

I have liked the idea of a well built wooden robot for a while now but have never pursued it. I am in the process of starting a new rookie team and depending on resources a wooden robot may be the easier and more reliable option. I do feel however that it will be necessary to sell the team on the idea so I was thinking building a simple chassis this summer may be an interesting project.

Re: Lignin fiber matrix (wood) as a chassis material
 

Mark, we (1899) were probably the team you are thinging about, while our frame was aluminum, the arm was all wood. We did get a lot of visitors to the pit looking the arm. Interesting enough our spare arm, hung at the back of the pit was painted and most people assumed was metal (I had several questions as why we switched from alum to wood), whereas the one on the bot was unpainted. A photo of the arm is

http://www.popularmechanics.com/tech...c=rss#fbIndex5

The truss section weights 2.5lb (wood only), the arm including motors, wiring, preloading, etc weighs < 19lb.

Re: Lignin fiber matrix (wood) as a chassis material
 

Martin, Mark --
As timmmoore mentioned in the previous post, here are some photos of the arm during build season.

The claw/gripper was eventually replaced with an aluminum one, once our kids were able to get some time in the school's metal shop.

http://www.flickr.com/photos/saintsr...57625889648895

http://www.flickr.com/photos/saintsr...57625889648895

http://www.flickr.com/photos/saintsr...57625889648895

http://www.flickr.com/photos/saintsr...57625889648895

Re: Lignin fiber matrix (wood) as a chassis material
 

We are planing on at least using Baltic birch for our prototypes next year(and our whole robot if we like it enough). I was wondering what fastening techniques work well, and ones that allow quick dis-assembly. I also would like to see some pictures of the 2011 robot and how you accomplished a wood arm.

Re: Lignin fiber matrix (wood) as a chassis material
 

The fact that the judges ignored your wooden drivetrain rather surprises me. The quality of work needed to design and build one made out of wood, is imho, far greater than that needed to make one out of aluminum. Nonetheless, I'll never be as confident in a wooden one as an aluminum one (we've experienced too much chassis damage and warping for me to be comfortable with wood), but that's just me.

Re: Lignin fiber matrix (wood) as a chassis material
 

The arm consists of 3 types of wood, the struts are straight grain spruce, it was 1 piece of rough lumber cut up on a table saw.
There are 2 types of plywood - aircraft grade okoume and marine grade. This was cut with a table or scroll saw and sometimes scissors (the okoume for the truss re-enforcing is very thin)
Mostly wood glue is used to glue everything together (titebond III), some 2 part expoxy used when gluing alum to wood (e.g. ends of the gripper), plastic to wood and a few wood to wood bonds when we couldnt be sure of a close mating of the wood surfaces.
The corners of the struts are re-enforced using small pieces of okoume. There are pieces of plywood at each end of the truss for the joint to the gripper and to the boom. The boom is a box structure of plywood and spruce also glued. The back of the box is screwed to allow the back to be removed to get into the box (it contains gas struts for preload, window motors, timing belts, etc). No nails anywhere, lots a clamps when glueing.
The gripper is controlled with a banebot motor into a drill gearbox, mounted at the top of the truss with wire running down inside the truss to the gripper. The truss and boom are controlled using window motors and timing belts.

Re: Lignin fiber matrix (wood) as a chassis material
 

Yep, it was you guys. That is a mighty impressive arm.

Re: Lignin fiber matrix (wood) as a chassis material
 

I see several posts here from my fellow long-time "wood evangelists" here on CD. I'd be happy to put our baltic birch breakaway 'bot up against pretty much any aluminum frame and see which one comes away damaged and warped. We've built aluminum frames for years, but we've never built one as stiff and sturdy as this 100% wooden one.

Wood has turned out to be a very appropriate material for students to use, for many of the reasons listed above... and you don't need a laser cutter to do a nice job of it. Although we do have a CNC router, which makes some tasks easier, the majority of our construction is carred out using traditional wood shop power tools. Check out the guts of the machine here, and you'll see that there are no fancy joinery, tabs, or epoxy... just a bit of carpenter's glue and some screws. Our practice bot didn't even have the carpenter's glue... it was just screwed together, and held up just fine (although it was considerably weaker than the glued competition frame). On a related note, I'd question the need to use epoxy... my lab tests confirm these made by Fine Woodworking Magazine, that standard white or yellow PVA glue actually outperforms epoxy as an adhesive for wooden joints. Not to mention it is cheaper, easier to clean, and much less messy to work with. The only time we use epoxy is for the occasional quick repair at an event. (Hmm... another advantage of wood... no trips to the machine shop.)

I am really surprised that you got a negative reaction to a wooden frame. We've received outstandingly positive reactions to our use of wood since we used it for our "unbreakable" three pound arm in 2005. I have to say that a clear coat of laquer (with perhaps http://www.chiefdelphi.com/media/photos/32608) gives it that finishing touch. We've had our use of wood cited as a contributing factor in three design awards and one judge's award over the course of six years at three different events.

Even when we don't do the whole chassis or frame or drive module out of wood, we still made it a prominent part of our lifts and mechanisms. We are very proud of our use of wood, and recognize that their will be "doubters". That's why when we built our three pound arm, we brought along a spare for the judges to JUMP ON. That was a key to our very first FRC award, and the beginning of our team's minor reputation for using wood.

Equally significant from the point of view of myself and the other mentors is the outstandingly positive feedback that we have received from other teams, and the knowledge that we have inspired others to consider using a biodegradable, low cost, environmentally-friendly material as part of their design. It is especially cool to see that now that our team is no longer around that others are doing an even more impressive job of creating wooden wonders. Check out 1899's arm if it had been clear-coated instead of painted it might have been the single most beautiful arm I've ever seen at an FRC event. (It's still up there, though... I just like to see the grain.)

Wood is good. Go for it!

Jason

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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!



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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

Our bot had a plywood eboard and a plywood elevator. We painted it green and many thought it was aluminum. Finalists at Duluth MN as well as judges award.

Re: Lignin fiber matrix (wood) as a chassis material
 

I've always been interested in using wood as the primary building material for a robot. However after kickoff the designs almost always go to aluminum.

Though you might be interested in this:

Splinter - Supercar made mostly from wood.
http://www.joeharmondesign.com/index.html

Re: Lignin fiber matrix (wood) as a chassis material
 

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)

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

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

Hung tubes beautifully.

Re: Lignin fiber matrix (wood) as a chassis material
 

I should know better than to speak in absolutes. :o

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).

Re: Lignin fiber matrix (wood) as a chassis material
 

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.

Re: Lignin fiber matrix (wood) as a chassis material
 

I sorry the STL judges were not impressed. I was your inspector at Peachtree and I was very impressed. You had one if not the best designed and it was very well executed. Your robots bordered on being elegant.

I talked today to one the inspectors at STL and he was of the same impression.

You robot has also made us question our entire design approach. We are currently working on designs using both plywood and a wood truss with gussets. Think DeHaviland Mosquito, Bellanca and Morgan. We also are on the fourth version of a wooden wheel with pneumatic tires.

Thanks for the inspiration.

Re: Lignin fiber matrix (wood) as a chassis material
 

FRC 195 has made beautiful, competitive, and winning wooden chassis' as far back as I remember.