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.

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!)

You do know that the battle of Britain was largely won with plywood airplanes. :wink: 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.

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?

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.

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.

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.

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.

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.

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

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

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/saintsrobotics/5466649985/in/set-72157625889648895

http://www.flickr.com/photos/saintsrobotics/5467260648/in/set-72157625889648895

http://www.flickr.com/photos/saintsrobotics/5467264508/in/set-72157625889648895

http://www.flickr.com/photos/saintsrobotics/5466670979/in/set-72157625889648895

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.

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.

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.

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

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 'botup 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 epoxyas 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](http://www.chiefdelphi.com/media/photos/20483) 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

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

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.

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.

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

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.