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-   -   Need help, Titanium / Carbon Fiber / Aluminum (http://www.chiefdelphi.com/forums/showthread.php?t=65644)

R.C. 09-03-2008 21:22

Need help, Titanium / Carbon Fiber / Aluminum
 
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

geeknerd99 09-03-2008 21:28

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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?

Woody1458 09-03-2008 21:30

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.

EricH 09-03-2008 21:30

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.)

clydefrog88 09-03-2008 22:01

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.

R.C. 09-03-2008 22:07

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.

clydefrog88 09-03-2008 22:11

Re: Need help, Titanium / Carbon Fiber / 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

R.C. 09-03-2008 22:13

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
Thanks, but our mentors want to use one of three mentioned. I wanted to use expanded aluminum.

sanddrag 09-03-2008 22:34

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
Quote:

Originally Posted by geeknerd99 (Post 715384)
Ti is extremely lightweight, but also pretty darn expensive. It is probably the strongest of the 3.

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).

MrForbes 09-03-2008 22:39

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.

Jimmy Cao 09-03-2008 22:53

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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,

David Brinza 09-03-2008 22:59

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.

clydefrog88 09-03-2008 22:59

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.

R.C. 09-03-2008 23:34

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
here's the pic
http://www.chiefdelphi.com/media/img...7ba7059d_l.jpg

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.

clydefrog88 09-03-2008 23:42

Re: Need help, Titanium / Carbon Fiber / Aluminum
 
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.


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