Newly Developed Chassis

[roboticWanderor]

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

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...

[lynca]

Originally Posted by roboticWanderor

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...

I think you might be familiar with Steampunk robots from CrabFu

[Rick TYler]

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.

[roboticWanderor]

Originally Posted by Rick TYler

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?

[SSMike]

Originally Posted by roboticWanderor

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

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

This really depends on what the game is. If you are trying to design a chassis for a pushing game, like Rack and Roll or Aim High, you'll probably want a material that is strong, tough, rigid, yet still has some "give" to it (meaning it won't snap in 2 as soon as its hit). However, for a game like overdrive where speed was a much bigger factor than torque was, a chassis that is light yet still is strong enough to withstand high speed collisions is needed. We usually end up using some form of aluminum or a similar alloy for our chassis; a little heavier than wood, but it seems to work for us.

And of course, you can't forget weight constrictions, those little nuances that FIRST throws at us to make us use our brains even more. Always fun to deal with

[AustinSchuh]

Originally Posted by Rick TYler

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.

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.

[travis]

Here is a comprehensive list of wood properties:

http://www.fpl.fs.fed.us/documnts/fp...tr113/ch04.pdf

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

[Rick TYler]

Originally Posted by travis

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.

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

[Matt C]

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

[tim_reiher]

Well, we've made our chassis out of plywood for god knows how long (way before my rookie year, probably from 2002). It has been reliable for us, with the Europly we use tending to maintain strength and flexibility. But hardwood... hmmm... gonna have to check that for next year...

Originally Posted by Matt C

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

Yeah, we got the whole wood chassis idea from RAGE; they were something of a parent team to us a few years back. We've built a RAGE chassis for a few years (We really are trying to phase out with some creative ideas, though. Not saying that those RAGE chassis don't work great, it's just about time we tried something new, I think.)

[,4lex S.]

Our practice robot was built from 3/4" ply. Beyond strength, it turned out to have a convienient bendy quality. Since my team used a holonomic drivetrain, we were assured maximum wheel contact with the ground.

Wood seems like the optimal frame material for capable teams, but I still gravitate towards aluminium for asthetic reasons...

[Gdeaver]

Good post Rick. The System3 is a good link. They offer a trial kit that offers a good sample pack of epoxy and laminating materials. Included in the kit is their epoxy hand book that is worth the price alone. Working with composites is not hard but takes practice. Week one is not the time to dive into composite construction with no practice. Now WOOD be a good time to get some materials and research for some summer practice. There are 2 types of fiberglass. E and S2. When ever posible I WOOD use S2 glass cloth. It can give up to 30 percent better performance for a little more money. Many FRC teams are stuck on AL because it's what they know. This summer is the time to experiment with other materials.