If you had to choose between wood and aluminum where both would cost the same and have the robot ready within the same period of time, which would you choose and why?
Please don’t vote for either and just say “because it looks cooler”, I’d really like some technical answers to this to give the team all the information they need to make a good decision.
I would personally go with aluminum from the stand point that if your robot does get rammed alot during competition you have the ability to beat it back into shape where as if you have it made out of wood it will chip away and become irreplaceable
Aluminum is much easier to work with in my opinion and it is much lighter and comes in many more different shapes. Also in some tight situations, if you really need to, you can feed your wires through aluminum if you are using box aluminum. It is also a little more flexible from my experience.
The only downside is that on wood you get splinters and with aluminum you get huge slices on your fingers with sharp parts if you aren’t that careful but overall aluminum wins by a landslide.
Pavan.
Aluminum is usually a better choice, as you can do more with it. An aluminum tube can withstand a very large load, and weigh very little compared to a solid wood board of the same strength.
Wood may be easier to work with if you have few machine tools, although clever design can get you very far with sheet, angle and tubular aluminum and a few hand tools. Rivets are strong, light and inexpensive. If you have access to a sheet metal shear and brake, you can make many aluminum parts that are strong, light, and rigid. As an example, we made a prototype ramp section that would weight less than a pound per linear foot, and can support 400 lbs over a two foot span.
Both wood and aluminum have been used very successfully to build airplanes, so it should be obvious that they both can be used to build strong, light structures, if the necessary design work is done.
Aluminum provides much greater flexibility in your design. Aluminum comes in many stock shapes and varieties, and can be used for just about anything (frame, axles, gears, rivets, bolts, sprockets, wheels, etc.). Aluminum can also be bent and re-shaped, while wood breaks. Aluminum also provides more options for mounting, such as welding and riveting.
aluminum
ever tried to make a wooden sprocket?
Well, I’m sure someone has, I was mostly referring to the robot frame and arm though.
The only use I can think of for wood in robotics is to offer a noncunductive surface for mounting electronics.
For everything else, aluminum. (2024, 7075, and 7068 are hard to beat, as well as the alloy everyone loves, 6061)
Gabe, my welder hates you. Seriously, any of the aircraft grades are nigh impossible to weld well. Thus we use 6061 for the majority of our parts. We’re actually looking at thin wall steel for next year to make the welding even easier.
At any rate, on topic, wood is just too fracture prone under shock loading for my taste. Aluminum will bend, but might be usable or salvageable after it yields. Wood doesn’t yield, it breaks. That said, it can have its uses in structural parts of the robot. Contrary to the prevailing opinion here, I think wood is a rather lot easier to work with than aluminum, as it is amenable to all sorts of hand tools and, well, woodworking tools. The strength to weight ratio of wood is more or less comparable to aluminum as well. So understanding the main limitations of wood, there are still places on a robot where it might be preferable to other materials.
Which is better? What I think you should be asking is “what am I building”
There are plenty of good uses for wood, and if used correctly it can offer comparable strength and durability to aluminum.
Our team needs to make a fairly large 5/8" thick plate this year for our tube grabber. After extensive discussion we determined that Baltic birch plywood (a marine grade plywood) would be perfect for this application. The wooden plate would be lighter then the aluminum and would offer reasonable strength and rigidity.
For many applications, aluminum can and should be the preferred choice.
However, I can think of several circumstances where high-quanity wood can be successfully used on the robot, and might even be a much better choice than aluminum. I can think of a few prominent teams who use wood chassis’ with great success. 
Each has their uses, but if we had to choose just one then I would go with aluminum for many of the reasons listed above.
Fortunately I don’t and we have used wood for everything from a chassis (2004) to an arm (2005) that was 5’ long, weighed 3 pounds and supported two PNW regional judges as well as the Xerox Creativity award they gave us for it, to the CNC machined turret, hand-turned 8" loader pulley, and maple bearing blocks and mini-bike motor mounts we used last year.
This year… well… it is definitely coming back in our lift and end effector… but now that the challenge has been raised… hmmm… wooden sprockets… where can we fit one of those in to the design?
Don’t be too quick to write off wood… when dealing with solid circular or rectangualar cross sections (no hollow tubes, etc.) it has one of the highest stiffness to weight ratios of any material, and in structural applications it is more fire-resistant than steel. (Uninsulated steel, that is… it gets hot and goes soft while the outside of the wood chars to form an insulating jacket.)
But yeah… for the robots… Aluminum if I had to choose.
Jason
P.S. Why, YES… my favorite airplane IS the Mosquito! How did you guess?
There have been many highly successful robots that are made primarily out of wood. Contrary to popular opinion, the wood doesn’t ‘just break’. It will flex a great deal before deforming. When it does deform, it is typically a very localized thing. Imagine ramming an aluminum bar hard enough to plasticly deform it. The entire bar is now bent. Ramming a piece of plywood might dent, even break through, the area that was hit, but the rest of the wood will not be affected.
Is it the right material for every application? Of course not. But it does have it’s uses, and for the team with limited tooling it’s a godsend.
Team 95 has been using wood, mostly 1/2" Baltic plywood for years with great success. Heres a sample of four 95 robots, 1998 through 2004 that used at least some wood.
http://www.lrt-uppervalleyrobotics.com/newphotos/FRC/2004/pages/page_1.html
http://www.lrt-uppervalleyrobotics.com/newphotos/FRC/2002/pages/page_17.html
http://www.lrt-uppervalleyrobotics.com/newphotos/FRC/2000/pages/page_3.html
http://www.lrt-uppervalleyrobotics.com/newphotos/FRC/1999/pages/page_2.html
http://www.lrt-uppervalleyrobotics.com/newphotos/FRC/1998/pages/page_1.html
Many of those robots all preformed a similar task; picking up up balls off the ground. Rather then reinventing the wheel, the team chose to adapt an old design. By 2002, it had been pretty well perfected and the ‘popcorn popper’ was the result. A few more similar robots have been made since, all with the same frame layout and materials. The wood allows for a frame that is quick to produce, protective and just the right amount of flex. It could have been done with aluminum, sure, but plywood did everything just as well.
Use the material you are most comfortable with and best able to manipulate.
-Andy A.
I heard what you said about not just saying “it looks cooler”, but I do consider that to be a factor as well. Both aluminum and wood can make sucessful robots, but I think that most people think of metal as being stronger than wood. With this in mind, I think that if two robots had the same skills, and the same W-L record, an aluminum bot would be picked for an alliance over a wood bot.
i would choose aluminum because although it may cost more, it is easier to fix if bent than wood chipping…:]
^Totally agreed.
I have to lean towards trusting welds more than trusting screws or nails, when it comes to either assembling the lower flame, or when it comes to attaching upper frame pieces. Also, if you made it so the two frames would way the same, that would be some awfully thin and unstable wood. 3/4 inch square aluminum is plenty strong for most frames, and is very light.
I have used wood on 10 of the 12 robots built. The right wood works great. Due to the high impact it will take without breaking. Team 61 robot has been know to hit a lot of robots. But the robot frame has never failed. A wood frame works great to start from due to you can place any part on it with out a lot of work. Just pick a spot and put it there. where the Aluminum you need to do a little more work to make it fit.
Wood and the parts it take to put on different devices are cheap. The hardest thing with wood is knowing how to use it in the best way to get the most from it.
This is my first year NOT working with wood for a drive base, and I must say I don’t really have a favorite.
Wood is, for the most part, easier to work with. With little to no resources you can cook up a pretty solid base in less than a day. Electronics mount up nicely to it, and you can even give it a slick automotive paint job. Beyond that, with the proper reinforcement you can slam the thing into walls all day and not have to worry about it bending or breaking.
Aluminum is a bit lighter, and more customizable. You can get some pretty unique shapes and work motor mounts directly into your parts.
I don’t really see a big difference in terms of strength (for the purpose of a drive base) between wood and aluminum. Wood has the tendency to gouge, which isnt all that pretty, but for the most part it holds up quite well.
So, I guess its all a matter of personal preference and experience. YMTC.
Here are some useful properties of Birch (home depot grade plywood material, aircraft grade is void free with superior propeties at about 3X the cost) and 6061-T6 aluminum (all in KSI):
aluminum wood
tensile load at failure 45 10
modulus of elesticity 10,000 2,000
Here is that same table adjusted for density:
tensile load at failure 16.7 16.7 (ahhh perfection)
modulus of elesticity 3703 3333
Price of a clamp = $5, price of a square wave TIG machine = $1500. Home depot grade wood glue can acheive 80% parent material strength with much less skill then welding, and you don’t have to heat treat glue joints for full parent properties. Anyone want to race me to install a new limit switch with 2 wood screws vs tapping holes? How about hand jigsawing 10 linear feet? With a rookie team (3rd in a row for me), 6 weeks, and no money, I got wood on the brain.