We were wondering, which substance is lighter, stronger, and flexes back to original position the best. A list would be extremely helpful. Also what are your personal experiences with these materials.
Thanks
This all depends on its application. I’ll use bike frames and components, as that’s what I have the most experience with involving these materials.
Ti is extremely lightweight, but also pretty darn expensive. It is probably the strongest of the 3, but also has benefical vibration dampening features. It’s been said that it has the ride quality of steel, the weight of carbon fiber, and the durability to the elements of aluminum. I wouldn’t flex it though.
Carbon is really light, but often has no crush resistance. It might be a decent choice if flexing (within reason) is required.
Aluminum is light enough, strong, but does not fatigue well at all. When aluminum goes, it goes suddenly and often catastrophically.
I would generally pick Ti for the weight/strength ratio, but the addition of flex in your query makes it difficult. Could you elaborate more on what you need this data for?
this really depends what for. Chassis? Manipulator supports(arm tower)? Mainpulator (claw)? Motor mounts? the list goes on. Some other materials used on robots just fyi are fiber glass (like boat hulls), polycarbonate (plastic sheeting), PVC pipe, steel, and composite boards. I dont ever see that much of carbon fiber or titanium.
If you want flex, carbon fiber doesn’t flex much, if at all, once it has the resin in it. It’s pretty light and strong, but again, you need the resin. You may also need special equipment to work with it.
My experience: one attempt on 330, and now the Aero Design team I’m on is using it all the time (fuselage, special ribs, etc.)
i have experience with all three.
Titanium is very much cost prohibitive. For a FIRST related project I can’t imagine an application where it would be any better than any other material. Anything that’s titanium could most likely be steel or aluminum.
Composites such as carbon are excellent materials. The parts need to be specifically designed and molded for a purpose to reach their maximum effectiveness. What i mean is: buying a sheet of premade piece of carbon would most likely not be as effective as a custom fabricated piece. Using commercially purchased stock usually requires so much design compormise that you end up compromising performance for ease of construction (It’s not always true). I would really recommend custom fabrication if you want to use carbon. It’s not as hard as you might think. Cloth is available online and you might be able to find scrap cloth from a local manufacturer (Composites companies tend to regard relatively large pieces as scrap). Resins are not difficult to come by either. I have hand-laid with West Systems epoxy resin in the past. While its not the best in the world, it is comparatively cheap and easy to work with. The real failing points of composites for FIRST applications are repairability and ease of use. It’s one thing to bend an aluminum manipulator during a match and quite another to stress facture a piece of cf. If you have any questions about fabrication or implementation, send me a pm and I’d be glad to help.
In the end i think aluminum is almost unbeatable in every FIRST application.
If you’re looking for a composite that’s “springy” traditional fiberglass is the way to go.
the application is the bottom fingers on our hand. Aluminum is not strong enough because our hand needs a tad bit of flex, but has to be lighter and stronger than aluminum.
You should try out a section of a fiberglass fishing pole. (they’re cheap) The thinner sections can easily flex 180 degrees without breaking and they’re pretty stiff. I picked up one for my team to play with for $6 at our Walmart the other day.
EDIT: I just found its name, Its a Durango Panfish Pole made by shakespeare
Thanks, but our mentors want to use one of three mentioned. I wanted to use expanded aluminum.
It actually is not extremely lightweight at all. The density of titanium is approximately 0.16 lb/in^3 where the density of nearly all aluminum alloys is approximately 0.10 lb/in^3. By comparison, titanium is quite heavy. However, with higher grade titaniums (Grade 5 and Grade 9) you can get away with less material thickness in your part. However, grade 2 titanium is actually quite weak (40ksi yield). Some of the aluminum alloys such as 7075 and 7068 can have quite high yield strengths, in the range of about 63ksi and higher.
For your application though, I might suggest polycarbonate (Lexan).
Do you have some pictures of the hand so we can see just what it is you’re working on? It’s a lot easier to offer useful suggestions if we can see just what the problem is.
Well, i’m not a materials expert, but here’s what I believe.
There are differant types of stresses. Compression, torsion, and lateral load (i dont know what it’s official name is or w/e).
Titanium outperforms both CF and Alu in all three fields. It’s also the lightest (if used properly but it should be VERY close to CF). That comes at a price however… lots and lots of $$$. Titanium is far from cheap… but it’s extremely strong! We used it one year on our electrical board (we actually used a titanium tennis racket… and it worked great). To make an entire robot from this would exceed the cost limitations.
Carbon Fiber, or CF, is also extremely strong in compression and lateral load. I dont think it’s very good at withstanding torsion though. Again, though, CF isnt cheap, and it isnt healthy. Cutting CF puts small fibers into the air that destroy your lungs =D.
Lastly, aluminum. Aluminum is the most heavilly used material in FIRST, by far. It’s lightweight, and relatively strong. It can withstand tremendous compression forces. It can also hold up to torsion quite well (well, at least Alu box and tube can). It will give quite easilly, though, if it is subjected to lateral loads with a long lever arm. Best of all, Aluminum is cheap, and easy to use. Additionally, it can be welded under reasonable conditions. Welding titanium requires an EXTREMELY controlled environment or the metal will burn. Welding CF is well… impossible. Welding Aluminum is easy (compared to the others. From what I hear, welding Aluminum is still significantly harder than welding steel because aluminum will still melt with relative ease).
For my team, we’ve always used mostly (prob 95%+) aluminum on our robots. We cannot afford to use Titanium, and we don’t see the benefits of CF. Another alternative, steel, which is also cheap and strong, is extremely heavy, so we cannot afford (the weight) to use it.
As for using expanded (extruded, i assume) aluminum, it will not flex back to the original position after it flexes to pick up the ball. CF wont flex either. Titanium will flex, and it has pretty strong memory, but it’s very expensive. Maybe you can try using some plastic material (like polycarbonate or delrin)
I hope that was useful (and correct). Take care,
You can get tremendous stiffness-to-weight benefit from carbon-fiber composites, but there are drawbacks. As already pointed out, composite structures are susceptible to impact damage. Assembly with composites can be a challenge. It’s rather difficult to use fasteners with composites. If you want to use screws, you will need to install inserts or have large nutplates bonded to the composite material. In order to use rivets, you will need to bond sheet metal to the both sides of the composite around the area of the rivet (directly riveting composite will just crush the material and result in a very weak joint). The preferred method of joining composites is bonded joints and to do that right, you need to control the bondline thickness.
That being said, there are some structures that can be effectively constructed from composites. High-stiffness tubular truss structures are a good candidate for composites. Holy Cow’s (1538) forklift arms in San Diego were a work of art, Unfortunately, I didn’t get a photo but maybe the San Diego Imagery Award winners can share this.
From cost, strength-to-weight, ease of fabrication, assembly and repair perspectives, it’s hard to beat aluminum for FIRST robotic applications.
http://www.chiefdelphi.com/media/photos/20217
Here’s an example of what I was talking about with the custom fabrication, our 2005 bot. My dad and I made a mold specifically for the second stage of the arm (c-shape). We laid two different configurations: a 3lb heavy duty, and a 1.5lb light duty. We had the weight, so we ended up using the heavier one. the arm though is indestructable. It’s great to see the reactions people have to me hitting the light arm against a brick wall without it even scratching.
here’s the pic
So is titanium(Grade 5/9) lighter than aluminum? I thank you all for the advice, we want to use titanium or carbon fiber for the fingers on the hand ( the part where the ball rests). What do you guys think? Also you have to consider the fact that at San Diego our robot hand got pounded and is bearly in one piece and that is why we want to upgrade. That is why I asked if titanium or carbon fiber flexes.
i think that unless you have the ability to make several sets, carbon would be a bad choice. though carbon would be significantly stronger, it would ultimately have the potential to break. for that application i think fiberglass is your friend. it offers greater flexibility and is easier to acquire.
I am not a materials engineer. I’m not a mechanical engineer. What I am is a hobbyist who has built several boats out of composite materials and a few robots. Here are some things you might want to think about in addition to “flexibility.”
-
Titanium is a pain to work with. It’s hard to cut, nearly impossible to bend, and has to be welded in an inert gas environment. It is springy, though, which meets one of your criteria. The chance of your robotics team being able to work with titanium is low, however, unless you have a mentor with real experience with the metal. I wouldn’t consider it.
-
The reason people like carbon fiber composites is that they are incredibly stiff, and light for the strength and stiffness. The thing that carbon fiber composites are best at – stiffness – is exactly what you aren’t looking for. It’s probably not your best choice.
-
I see a lot of stuff on this board where “fiberglass” is used in addition to “composites.” What is usually known as “fiberglass” is glass fiber matt, cloth, or biax held together in a polyester resin matrix. Generically, fiberglass is just one type of composite material. The way you normally experience it, fiberglass is not very stiff, not particularly strong, and heavy for the strength and stiffness. The advantage to fiberglass in boat building, for example, is that it can be laid up by fairly unskilled labor, and doesn’t cost much.
More advanced composites use epoxy (or sometimes, vinylester resins, but let’s keep it simple) to bind a material together. The materials used include glass fiber in a variety of orientations and compositions, kevlar, and carbon fiber. One of the best things about glass fibers is that they are available in a variety of pre-made types – woven glass (in the US, measured in ounces per square yard of fabric – 6 ounce is lightweight, 10 or 12 ounces is heavy), bundles of glass fiber held together in crossing orientations of different weights (called “biaxial”), and other things like mat or chopped fibers which are generally not used with epoxy. Matt and chopped fibers are used to bulk up thicker laminations used with cheap polyester resins.
Since epoxy is expensive, very strong, and impervious to moisture, it is usually laid up with a fiber over a core material. We won’t go over cores in detail here, but for amateur use it’s very popular to use lightweight, high-quality plywood as a core for structural use. Something like BS1088 meranti or okoume plywood is stiff, strong, and lightweight. Some very expensive, very impressive sail- and motor-boats are built up with multiple layers of biaxial fiberglass laid up in epoxy over a core of 1088 plywood.
For really, truly expensive boats (see “America’s Cup”) they will lay up carbon fibers over a foam core with a thermo-setting epoxy to hold the whole thing together. If you want a mind-blowing experience, start pricing things like carbon-fiber spinnaker poles for 80-foot racing boats. For us mortals, carbon fiber is not a great choice for large assemblies – it’s picky, brutally hard to cut, messy, and demanding.
With one exception, if you want to lay up a composites structure for a robot, I would stick to either woven or biaxial glass fibers laid up in epoxy. If you need to make a long, strong pole, you might follow the plans like this: http://boatbuildercentral.com/products.php?cat=36 to build a pole, which can then be bonded to attachment pads for assembly to your robot. This is what I wanted to do with the tetra game a few years ago, but the students didn’t want to mess with composites. By the way, it’s the availability of carbon fiber “socks” that makes this possible for simple CF composite poles. (That link is to a commercial Website to which I have no affiliation, other than as a happy customer.)
Probably more than you wanted to know…
Titanium will eat through most general tooling like there is no tomorrow if you aren’t very careful when working with it.
And there is a small chance, that if you aren’t milling it correctly, it can actually catch on fire.
Although if you want “springiness”, you can also try PVC pipe, a flat sheet of Lexan (polycarbonate), or even use aluminum with a pivot point and surgical tubing to give the springiness.
Mr. McGuire: I want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Plastics.
Benjamin: Just how do you mean that, sir?
Titanium is surrounded by this wonderful mythology that seems to supercede reality. It actually is not all that tough to work with. It just requires some appropriate knowledge and slightly different practices when you are working with it to get the results that you want. HSS tooling will work just fine, and carbide tools will do even better. Keep surface speeds low, feed rates high, and use lots of coolant. You want to keep the cutting edge very sharp, cool, and constantly moving to prevent work hardening and/or galling. Titanium machines extremely well (you can basically treat it just like any other high-performance alloy like austenitic stainless steel), and finishes beautifully.
-dave
A Uni-directional weave of carbon bent correctly will give you high stiffness in one bend direction, but a “spring” action in the other. Pre-preg is usually easier to work with, but has its own set of caveats in comparison to laying up your own.