pic: Rastogi 8wd Iteration 1.2

[roboticWanderor]

good work! i would put some wider cross bracings between the two pods, bend your flanges inwards and fiddle with your cheese holes a little. your lacking in some of the major stress areas and triangle departments. concept has some serious potential though. also if you run your cross braces to the outer plate of the drive pods they do a lot more for you.

take a good hard look at the slideshow in this :http://www.youtube.com/watch?v=_hTyXQUgYLE at how thier chassis is put together, pm or IM me if you wants some help with this.

[Akash Rastogi]

Thanks for all the new info

[NickE]

Originally Posted by Chris is me

6061 isn't very bendable at all, apparently.

6061 bends fine if you stay above the minimum bend radius. Our robot's baseplate this year was 1/8" 6061 with 3 bends (each had a 3/8" bend radius, which is above the minimum bend radius for 0.125" 6061).

However, the .090" 5052 sheet Akash is using allows for much smaller bend radii (3/32", according to here).

[roystur44]

Try to get rid of all those spacer plates between the side plates by incorporating them into the inner side plate by bending the flanges in from the inner side plate. Might also think of building a low profile drive base and bolting on a frame with the robotic mechanism built on the frame. Doing so you can reuse the drive base design and build out a frame with the other parts for the robot.

Consider a bent sheet metal tray instead of the cross braces to connect the two sides together. As shown all the forces will be at the corners of your robot. It will be hard to square up and maintain a rigid frame with the cross braces.

Take a look a some pictures of our 8 wheel drive sheet metal chassis.

http://www.spartanrobotics.org/galle...Season&bac k=


Roy

[DonRotolo]

Originally Posted by sgreco

I'm sort of in the process of leanring about the techniques of sheetmetal fabrication so I don't really know

Akash is doing this to learn more about sheet metal, and the quote above echoes a few posts (not much knowledge or experience with sheet metal), so I'll make you guys a super deal:

No matter where you go in the United States and Canada, there is a sheet metal shop within driving distance - often within bicycle distance. There you will find tooling of many types, and people with an awful lot of experience. Most will bend over backwards to help a high school kid learn about their business. So, here's the deal:

Find a shop and visit them during the day sometime.

Explain you're a high school kid, you are interested in engineering, and you are really interested in learning more about sheet metal. Like, for instance, how to bend flanges inside a cut sheet...

I GUARANTEE that 98 times out of 100 you will get a wonderful education that day. If you're over 18, maybe even a summer job...

Try it, see what happens, and let me know.

Originally Posted by AdamHeard

Buuuuut, after a few years you come to realize nothing beats good 'ol 2x1

At first I was thinking "no, that's why commercial products don't use 2x1 much..." but, thinking about it a little*, I came to realize the wisdom in Adam's post: Indeed, for FRC stuff, where you have relatively easy cost and weight constraints, and generally one-off designs, 2x1 aluminum extrusion is about the most versatile stuff there is.

Don

*Can't think much more than that...

[James Tonthat]

These parts could probably be replaced by a piece like this



The parts you have, difficult to assemble/disassemble and probably have less strength since they're putting tensile force on the fastener (and onto the flange). The replacement part above puts sheer force onto fastener and your largest flange face.



All these parts each have four flanges each and could probably be replaced by a simple plate similar to this.



This piece is a lot more simple and uses the existing flanges on the big side chassis pieces, removing redundancy.

Sorry if this seems kinda scrap together, I'm writing this pretty quickly because I have quite a bit of schoolwork to still do.

[548swimmer]

Originally Posted by Akash Rastogi

Solidworks 09-10 thanks to our Solidworks sponsorship through Marie Planchard.



Its .09" thick sheetmetal. I'm not totally positive what grade of aluminum most teams use in their construction so right now I just had it set to 6061 T6. Anyone want to answer that?

6061 T6 is crazy strong, and really expensive. Depending on where/how you guys machine you might look at a 50XX series alloy with a lower temper (T).

As for the flanges, putting them on the inside is the way to go. I was working on a kicker guide plate this year that had roughly 300lbf concentrated in the center. The plate spanned 16 inches from side plate to side plate and didn't bend at all. The flanges not only put the material under the type of stress it is strongest in, but also increases the second moment of area. This is the same reason why I-beams are so strong and that you should move the cross supports down some.

If at all possible, make the flanges continuious. Any gaps will concentrate the stresses in that area. FEA will be your friend in this endeavor, and I reccomend messing around with just a flanged strip of metal first with fixed constraints on the outermost sides. His will give you an idea of how much flanges help, as well as what happens when a flange is not continuious. If you can master sheet metal strengthening, your team will love you.

[James Tonthat]

Sheetmetal is generally 5052, it's able to be worked when cold.

1477 uses 5052.

Edit: Also, make sure your fabricator has "sectionalized dies" you have some inner bends.

[IKE]

Originally Posted by Chris is me

I'm of the opinion it would be faster to stress test a prototype then it would be to run complete and thorough FEAs on stuff like this anyway. We should just build one.

We have "prototyped" chassis out of posterboard in the past. If you do about 1/2 to 1/4 scale, you can cut fold and glue panels together. This softer material can help visualize where additional members may be helpful.

[JamesCH95]

Originally Posted by 548swimmer

6061 T6 is crazy strong, and really expensive. Depending on where/how you guys machine you might look at a 50XX series alloy with a lower temper (T).

6061 T6 is not terribly strong or expensive, relative to other aluminum alloys, though it is certainly more expensive than 5052, but 5052-H38 has the same yield strength as 6061-T6. Also 50xx alloys don't have a "T" temper because they're not heat-treatable, they are cold-worked (strain hardened) and have an "H" temper. Sorry 548swimmer, I didn't want to flame you too bad your other information was spot on.

Take a careful look at what sort of strength you actually need. Do you mind if a few small areas yield a little bit? It's probably okay if they do. Do you have a target stiffness for the chassis? If you make it out of .09" 5052 you can achieve the same strength, with lower stiffness, and half the weight, by making it out of 0.045" 7075-T6, if you can fit the required bend radii. Sure 7075 is more expensive, but the higher cost will be offset by using less of it. Making your frame half the weight has to be worth a decent chunk of money and is definitely worth considering IMHO.

[artdutra04]

Originally Posted by 548swimmer

6061 T6 is crazy strong, and really expensive. Depending on where/how you guys machine you might look at a 50XX series alloy with a lower temper (T).

It sounds like you've confused 6061 with either 2024/7075/7068. These are all much better than 6061 or 5052 in regards to hardness and yield strength. But like 6061, they need large bend radii and are thus unusable for many sheet metal components (which you are correct in that they're traditionally 5052).

If you have good suppliers and know where to look, small quantities (such as for personal project or a FRC team) of 6061 aluminum stock can be bought for as little as $1.50/lb. I bought a 15 pound bar of 6061 last year for about $25. I've also found 3/8" Hex bar made out of 2011 aluminum (easy to machine grade) for about $0.50/ft, which our team then promptly bought all 60 feet they had in stock for custom standoffs for the next few seasons.

[548swimmer]

JamesCH95, thanks for the clarification. I mostly just work on designing and a little fabrication, so I'm not terribly familiar with the various grades of aluminum sheet metal. Whenever I need to machine something I just walk over and grab the stock needed from where I was told to .