Newly Developed Chassis

Hi everyone,

Team 418 and team coach Tony Bertucci have been hard at work returning to our roots, and we’ve designed an improved (simple, lighter, and more robust) chassis for the '09 season!

Without further ado, here are some specs:
-6 wheel drive, lowered center wheels
-7 pounds, 16 ounces (9 pounds lighter than our chassis for Overdrive)
-#25 chain runs from the center wheel to the front and back wheels
-It currently has kitbot wheels, but those can be modified
-Chain tensioners built-in
-Supports the weight of various team members

For comparison, here’s a picture of this year’s robot:
ZePHyr
and…
Pictures of the new one(they’re a little grainy since they’re cell phone images, but this is still a work in progress; I’ll post better ones once it’s done):
Picture 1
Picture 2
Picture 3

Feel free to ask questions/voice opinions/concerns.

Wood Coast Drive?

I dig it!

that is pretty amazing!!!

It looks really beautiful as well. Awesome.

That is really cool! How do you think the wood is going to survive impacts by other robots? I can just picture it snapping.

You could always make it out of the strongest wood in the world.

Very nice. I <3 wood :slight_smile:

I might suggest wrapping it in fiberglass. Done correctly, it will remain light and the beautiful wood will remain visible. Fiberglass will dramatically improve the flexibility (wood usually cracks instead of flexing) allowing it to survive most impacts.

I’m also not crazy about single motor drives. We tried one motor per side this year and we lost a LOT of acceleration. Maneuverability and speed will be improved with two additional motors.

Very nice! It’s great to see creative designs that use materials in clever ways.

I don’t know about the strength of wood as compaired to something like aluminum 1/8" box extrusion that everyone uses, but I’d guess that it’s a better material for the base frame. Wood has the wonderful property that it doesn’t get dented if you hit it really hard; it flexes and then returns to it’s original shape. It makes sense to me to use something like wood for the drivebase, which gets beaten around a lot during competition.

That’s why we use fiberglass extrusion; it can take a beating and won’t get bent!

Very nice! I’d suggest making the front and rear crossmembers go past the wheels, so you can attach bumpers to them, and add blocks between the wheels to support the middles of the side bumpers.

http://photos.project1726.org/albums/userpics/10011/normal_DSCN1732.JPG

shows kind of what I mean…although we added a vertical piece of 1/8" x 1-1/2" alumimum angle at each corner later to support the ends of the side bumpers.

Also I am not a big fan of using a single material for the entire robot, it seems to me that it’s wise to select the best material for each part (within the constraints of your fabrication abilities and budget).

Thanks everyone-

Our plan for this version of the chassis is actually to make it a test “mule” for our electronics team and to allow our drivers some practice. Our coach decided to surprise the team with this chassis after jests from a couple team members that there was no way he could build a wooden frame that could stand up to the beatings of other robots. At first, many thought he was building a rocking chair…

As for the single motor on each side, we just went with what we had available-all of our CIMs and dewalt transmissions are currently on our other robots, so we just used our fisher-price motors from previous seasons.
Glad to see that you like the woodwork, though-I’ll pass it along to our coach.

You need to get Woody to sign it!

I agree with glassing it though, that is a really slick look. It looks pretty strong, amd with bumbers it wouldnt be much of an issue at all. Now I want to see a bamboo robot…

Oh man, you shoulda seen the look on my face when i first saw my coach walk in the door with this thing! ridiculous!
It is incredibly strong; made from red oak and with some neat joinery. I actually took a sick of the scrap left over, approx 1" square, and did a little stress test with a hammer, comparing it to some 1" box alum. this stuff is strong! it withstood 3 smashes with the sledge before snapping, while the aluminum didn’t even survive the first blow!. I’m a believer :stuck_out_tongue:

another feature is that it is incredibly lightweight, somewhere around 8 lbs for the base frame itself (not including wheels axles etc.)

i think this thing will qualify as an antique in 50 years, assuming it lasts that long.

ps: don’t tell my team, but i want to put a steam engine on this thing and turn it into the worlds first Steampunk FIRST bot…:cool:

there is one team in LA that make a robot out of bamboo… their team name was the bambots i think. ill see if i can find a pic.

heres their team profile on tba there are a few vids of the bot:http://www.thebluealliance.net/tbatv/team.php?team=848&year=2008

I think you might be familiar with Steampunk robots from CrabFu

Material selection is a lot of fun, and there are strengths and weaknesses to all materials. The weaknesses of solid wood (in robots) are that it has low impact resistance at the point of impact – the fibers in the wood can crush or get gouged out, and that the joint between metal fasteners and the wood can be a weak point. The good things about wood are that it has incredible strength in compression (think “tall tree”) and is light for its stiffness. Dave Gerr in his book “The Nature of Boats” has several chapters on the different common hull materials for pleasure boats: fiberglass, wood, steel, and aluminum. You’d like the book: the title of one chapter on materials is “Even From Cheese Whiz (Almost),” in which Gerr posits out that the important thing is matching the material to the purpose, not picking “the best” material, which he claims doesn’t exist.

It’s interesting that Gerr says that when you remove cost of construction (where fiberglass wins), and maintenance (where aluminum is best), the material that works the best for boat hulls in the yacht range is Douglas fir, when looking at strength and stiffness per pound of material. When we built the FRC robot “Wooden Thunder” four years ago, we created side bumpers out simple 2x4 Douglas fir boards planed down to 1.25" thick. We took some terrific bashes from other robots, including one that gouged out a chunk of wood an inch long and a half-inch deep, without any damage that would have actually hurt the robot.

A single layer of 6-ounce woven fiberglass cloth, or even better 12-ounce biaxial fiberglass set in epoxy on each side of the frame will increase the breaking strength while adding very little weight. My #2 son did a middle-school science project which consisted of cutting 1x6 “white wood” boards from Home Depot into blocks, and then gluing the blocks together. He then tested the glued joints to destruction using a mechanism we built together. The results were kind of fun. As you’d guess, superglue was terrible on wood. The joints failed before the material in nearly every sample. “Gap filling” superglue was just about as bad. Polyurethane glue (“Gorilla Glue”) worked well when the blocks were clamped very tight. In some samples where the clamping wasn’t perfect, the glue lines failed, and in other samples the wood split before the glue line. Yellow carpenter’s glue and epoxy joints held perfectly – the material failed before the glue line. The fun samples were the ones where he used epoxy, and then epoxied a single layer of 6-ounce fiberglass cloth on both sides of the joint. In the reinforced sample, the wood broke at the edge of the cloth in every case, and we had to add so much weight that we nearly broke our test mechanism before the wood broke. If I remember correctly, the super glue joints failed at about 40 pounds of applied force, and it took more than 150 pounds before the reinforced blocks broke – and not in the reinforced area. Six-ounce cloth is called that because it weighs six ounces per square yard, so the builder could reinforce that frame with a lot less than a pound of 'glass and epoxy. (When I quote weight, we were applying the force along a very narrow edge pressing directly on the joint with a lever arm holding 5-gallon paint buckets into which we placed rocks as weights – the weight is the weight of the rocks, not a scientific “pounds per square inch” measurement – it was middle school.)

I buy most of my marine epoxy and glass from System Three (www.systemthree.com), but there are several good brands. Stay away from polyester resins, which simply don’t hold as well as epoxy. Make sure you keep the epoxy off your skin by wearing long sleeves and gloves and if you do a LOT of epoxy work, you might want to wear a $25 respirator. Partially cured epoxy can be BAD to sand, as the particles easily trigger skin allergies. If you want to sand your 'glassed and epoxied frame after construction, wait as long as you can before sanding it (like a week or longer), and wear long sleeves, long pants, a respirator, gloves, and use a sander hooked up to a shop vac. Epoxy WON’T cause cancer, as far as we know today, but it can trigger allergies, and the more often you have contact, the more likely you are to get a reaction. I’ve been doing epoxy boat building and maintenance (hobby, not pro) for about five years and I sometimes get a little redness on my skin for a day or so, and I have repeated contact and am careful. Like any other construction method, learn about and follow the safety rules.

Anyway. Using lumber (instead of plywood) for the frame of a robot is a terrific idea. It’s nature’s own composite material, and the way that frame is laid out makes good use of its strengths. If it was me, I might use lumber with a lower specific gravity than red oak, and then not drill speed holes, but I have nothing against the one in the pictures. Please tell the woodworker that it’s pretty.

Will do!

Many thanks for your informative post, you may have just ended our own debate on the subject. we are really in the weeds on our chassis and drive train for next year, and will probably make several prototypes by the end of the summer.

the question is, what is really the most effective material for a FIRST Chassis?

strength? flexibility? yield strength? compression strength? rigidity? weight?

Very interesting observation. Thanks for sharing. What you have described confirms what we learned this year.

After bending up a 1/8 " sheet of aluminum that was the front of our robot and then bending up a 2x4" piece of aluminum angle that we added in addition to the other 1/8th inch piece, we ended up putting a 1" by 4" by the width of our robot piece of wood up front also. That piece of wood seemed to take the shock of collision very nicely. If they ever make bumpers optional again, we are putting a 1" thick piece of lumber around our entire robot just to absorb the shock.

Here is a comprehensive list of wood properties:

The super exotics like bulletwood (or “beef oak” sometimes for its red color, the most desirable material for ship’s masts in the days of yore), or kaneel heart are about twice as strong as teak, but normalized for density, they are about the same. Normalized for density, high performance woods are as strong as all but the exotic aluminums alloys.

We gave plywood a try, rather the Chinese stuff that masquerades as plywood, 2 years ago. General durability was more than sufficient; my one complaint was fastener holding. If I had listened to my gut and used the much harder Ipe (the most readily available of the high strength timbers in the US, pronounced ee-pay, called Brazilian cherry by the flooring industry), I think I would have had a much easier time. One of these days I am going to convince the team to make an Ipe plywood robot, and use one of the various bonded aircraft nut plates to make the threaded connections.

Travis

Wood is an excellent material for a robot chassis, just ask Team 173 (Rage).

Try jarrah some time. I think it must be 50% titanium by weight. (<-- humor)