02-05-2010 19:44

Dkt01

Re: pic: Rastogi 8wd Iteration 1.2

Looks great. If I didn't know better, I'd think you had built it already and this was a picture of it.

02-05-2010 19:49

gyaniv

Re: pic: Rastogi 8wd Iteration 1.2

Looks great!!!

I have couple of questions for you:...

Does the 4 outer wheels raised?

If the wheels are raised why not going for 8WD instead of 4WD?

Why did you decide to use 4 dual-nano (have no idea what it is but i figured it is a gearbox) instead of 2 gearboxes and using chain/belt to convert the power? might save some weight over there.

I don't know much about sheet-metal drive-train but wouldn't it be wiser to bent the sheet-metal towards the robot instead outwards? My opinion is that it will be much safer, more easy to work with, and stronger. But as i said, i don't know much about sheet-metal drive-train, so i also want to hear an expert on that question...

Thank you

02-05-2010 19:58

Brandon Holley

Re: pic: Rastogi 8wd Iteration 1.2

Why are the hex shafts so long? Just curious, I'm sure its just something you haven't gotten to yet.

Looks good. Designing in sheet metal is a very good thing to learn if your planning on becoming a mechanical engineer of some sorts. I cannot tell you how many sheet metal parts I've designed for my various jobs I've had. It comes in handy for other parts too that aren't necessarily made of "metal" (ie: polycarb, other such plastics) which may be created using the same techniques as standard sheet metal parts.


Also very handy with sheet metal are PEM fasteners. If you can master their usage, you can create really sleek sheet metal designs.


Have you done any FEA on the frame? Its sometimes difficult to gauge the "strength" of a design from sheet metal, especially when first starting to design in sheet. My only comment would be to add a cross member lower on the frame to add another axis of stability, however it may be unnecessary, thats what analysis is for!

Brando

02-05-2010 20:04

jamie_1930

Re: pic: Rastogi 8wd Iteration 1.2

I immediately questioned why the metal was bent out and all though I don't have his answer to it in my opinion it is better to bend out because when you bolt things to the top it allows easier access to the nuts than reaching your hand around to the inside.

02-05-2010 20:12

apalrd

Re: pic: Rastogi 8wd Iteration 1.2

With little experience designing sheet metal chassis, I will share my opinions anway.

1. Any reason for folding out instead of in? Without that pesky bolt heads frame perimeter rule, there should be no reason to cover the bolt heads.

2. What material is the dead axle? I assume a 3/8" pipe, taped at the end, with a bolt holding it in.

3. Again, why the dual-nano?
3a. You could alternatively make the distance between the two side plates exactly the width of an AM Shifter, then put an AM Shifter inside (with the chassis sides as the side plates). Or, you could just use an SuperShifter or Toughbox as you do now, with a live axle, then chain the other side.

4. Why the bump-climbing notch? Assuming there is less terrain then this game...

5. I like the render. Looks very real.

02-05-2010 20:18

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

Yup, just didn't get to that yet, its just the standard AM model length.

I haven't learned proper testing, that's a big part of CAD I plan to learn shortly.

I'm not sure what you mean. The center 4 wheels are lowered 3/16" for barely a rock.

I'm just trying out new nano configurations and it decreases chain usage. I haven't calculated how much power I'm getting to the wheels as apposed to using a single gearbox with dual CIMs per side.

This is a question I have for the experts too. Right now I'm just creating "shells" for the main structures as I've seen done with team 1902's 2008 and 2010 frames. I assume it is actually easier to work with the frame pieces this way because you have more access to the open surfaces of the material.
I definitely like this idea. Right now I was just going for something that is direct drive, but I'm liking the built in SuperShifter idea a lot.

Thanks for the questions. More suggestions and advice are welcome and appreciated.

02-05-2010 20:18

Chris is me

Re: pic: Rastogi 8wd Iteration 1.2

edit: akash is a ninja delete plz

02-05-2010 20:25

sgreco

Re: pic: Rastogi 8wd Iteration 1.2

I would say you're fine for powering from four separate locations as opposed to one central spot on each side. If it shortens the chain runs and makes maintenance easier, it's a good trade-off.

I can't see the stress tests for this, but as a typical rule of design you want the most support in the middle, as that's where it'll break first. I would take out some of the pocketing in the middle, it'll likely only add fractions of a pound anyway.

Overall it looks great though. Your rendering and designing skills have gotten really good, great job.

02-05-2010 21:01

Jamie Kalb

Re: pic: Rastogi 8wd Iteration 1.2

If you've got PEM nuts inserted in the flanges to bolt things to the top, you never need to reach under the flange to hold a nut...

*hint - Akash, PEM nuts are good - hint*

Looks really good, though. Really imposing. Keep it up!

02-05-2010 21:14

Chris is me

Re: pic: Rastogi 8wd Iteration 1.2

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.

02-05-2010 21:15

RMS11

Re: pic: Rastogi 8wd Iteration 1.2

Where here would you attempt to use PEM nuts. I was looking at them on mcmaster, and they look cool, but pressing all of them seems time consuming when you could just use rivets or a nut and bolt instead. In the long run it might save a bit of time though... Any other big advantages of them? thanks!

02-05-2010 21:17

rulesall2

Re: pic: Rastogi 8wd Iteration 1.2

Something I've noticed, only because we ran into the same problem this year, is that you have effectively created a giant piece of C-channel. Moving those cross-braces down to form an I-beam shape or adding ones near the bottom should strengthen the design a bit. Just some thoughts, but I like where this is heading.


.

02-05-2010 21:22

Andrew Remmers

Re: pic: Rastogi 8wd Iteration 1.2

Being on 1902 I can say that when the flanges are facing outward it is significantly easier to run maintenance on the drive train. Considering that the space you are working with is already very small it is difficult to get to all the components even on the robot we have this year. I can only imagine what it would have been like if it were the other way around, having that "obstacle" in the way would have made some points of repair for us very difficult especially when we had a master link failure at Florida.

Also what I think with the flanges facing inward towards each other means you would have to design enough space for your chain/belt to run depending on your configuration. Which means you might have less space elsewhere for another mechanism or something like that.


BTW very nice render It has inspired me to get finished with my school work faster so i can finally get around to designing my own sheet metal drive train!

02-05-2010 22:17

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

Ah thanks for the insight Andrew.

You might also like this. I tried to copy it from one of the pictures that was posted of your 2010 bot.

02-05-2010 22:41

Andrew Remmers

Re: pic: Rastogi 8wd Iteration 1.2

:O that looks strangely familiar! you did this in solid works right? (i need to find a copy of that...) I'm still using inventor and a little bit of Pro-E.

02-05-2010 22:57

Jamie Kalb

Re: pic: Rastogi 8wd Iteration 1.2

I'm not good at judging measurements from pictures, but it looks to me like the current flanges aren't big enough. But if the flanges bent off the main body of those enormous side plates were wider (or is that longer?), you could punch holes in them and press the PEM nuts in. As far as I know, many sheet metal shops can do this in-shop. Check out the 217/148 Sheet Metal video. It shows them pressing PEM nuts at about 5:05 in the video. Not time-consuming at all. Compare the ~1 second per insert to all the time you'd spend fumbling for a nut ... total. For a season.

Whenever possible, I like to add threads to a part (tapping or threaded insert) rather than using a nut. One less piece to worry about, one less piece to come loose, one less point you have to reach for assembly/maintenance. Plus installation and removal now only takes one hand!

But Andrew's 100% right about this:

Having the flanges bent in rather than out definitely does make drivetrain maintenance harder. It's possible to make the plates modular enough to justify this, but you're probably better off just keeping them facing outwards.

03-05-2010 02:18

R.C.

Re: pic: Rastogi 8wd Iteration 1.2

Nice Render,

Slightly curious what's the weight?

-RC

03-05-2010 03:33

Re: pic: Rastogi 8wd Iteration 1.2

Looking good.

Also, I'll second (third?) the recommendation for using PEM nuts. We use them at my work on our sheet metal chassis, and they're wonderful to deal with. Out of 75 robots, we had one PEM nut pop loose, and the shop that pressed them fixed it for us in less than 6 hours. PEM nuts are the way to go.

How many parts in there are standardized? It's always easier for a sheet metal shop to punch out and break more similar parts than differing ones.

03-05-2010 15:47

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

I'll definitely check out PEM nuts.

There are only 3 different parts here. All sideplates at the same, all cross members are the same, and brackets in between plates are the same.

03-05-2010 17:31

Re: pic: Rastogi 8wd Iteration 1.2

Wonderful! Keep up the awesome work!

03-05-2010 17:32

AdamHeard

Re: pic: Rastogi 8wd Iteration 1.2

Why not connect the two side assemblies along the bottom?

03-05-2010 19:34

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

Can't see it, but there's one along the bottom on the other side. The near side is open because I was working on a 148/217 style cam kicker for fun.

03-05-2010 21:51

DonRotolo

Re: pic: Rastogi 8wd Iteration 1.2

I disagree. The sideplate will tend to be pushed inward by any contact from other robots or field elements. In such a case, your flange will tend to be in compression. Such a small flange will buckle. If the flange was on the inside, it would be in tension, a mode that is far stronger than the compression mode. Try it yourself with a piece of angle.

Second, you might consider putting flanges on some of those inside cutouts. Yes, it ends up a little heavier, but because the outer flange is not continuous you will suffer from low rigidity (and low resistance to bending) at certain points; use flanges to compensate.

Akash, when you're doing your analysis, be sure to model loading from another robot hitting you from the side at several locations.

03-05-2010 21:55

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

I was thinking about this for a while, but I am not familiar with capabilities of sheetmetal manufacturing.

Could you, or anyone else, elaborate on what types of places flanges can be made on a part like this? I wanted to add flanges on some of the inside pockets but wasn't sure if that was easily possible. Like I said, I'm looking to learn about this as much as possible.

Thanks.

03-05-2010 22:05

Jamie Kalb

Re: pic: Rastogi 8wd Iteration 1.2

You're right; I didn't think about that. You definitely want flanges like that in tension.

And, How would you bend a flange out from an inside cutout? Would you just use a really small (short) set of jaws on a brake, or is there another tool to do that?

Thanks!

03-05-2010 22:19

artdutra04

Re: pic: Rastogi 8wd Iteration 1.2

The same as they would with an outside bend; they just move the bending dies around and leave gaps where there is material that should not be bent.

This past year, 228 used a bunch of these inside bends on our GUSwerve modules to mount the lower bearing plate on. Here's a photo:

03-05-2010 22:23

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

Excellent, I'll definitely be changing things around a lot then.

03-05-2010 22:26

Jamie Kalb

Re: pic: Rastogi 8wd Iteration 1.2

Ohhhh! Gaps in the die! Duhhhh! Now I get it. Thanks. (the picture helped)

Hey, Akash, you can bend flanges from an inside cutout!

04-05-2010 07:22

sgreco

Re: pic: Rastogi 8wd Iteration 1.2

I'm sort of in the process of leanring about the techniques of sheetmetal fabrication so I don't really know, but right now this is a fairly straightforward part to make, especially if you have a laser cutter. What I don't know is will adding those inner flanges add significantly to the fabrication time? I would imagine if in fact more strength was needed it would be easier and more robust to just add more cross supports between the inner and outer plate.

04-05-2010 07:37

Re: pic: Rastogi 8wd Iteration 1.2

I'm not an experienced sheet metal designer, but what CAD program is that in?


Thaine

04-05-2010 09:52

JamesCH95

Re: pic: Rastogi 8wd Iteration 1.2

I would add in some triangulation in the x-y plane. Other than that I think it looks solid.

What material were you planning on making it out of?

04-05-2010 11:40

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

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?

04-05-2010 12:30

R.C.

Re: pic: Rastogi 8wd Iteration 1.2

Akash,

Sheet Metal is usually 5052, John or Art can confirm that (or anyone with sheet metal knowledge). 6061 just isn't that great for bending. Btw how much does this DT weigh?

-RC

04-05-2010 12:41

Re: pic: Rastogi 8wd Iteration 1.2

We use 5052.

(edit: Just checked the BOM at work... Turns out I was a digit off. Whooops.)

04-05-2010 12:42

Chris is me

Re: pic: Rastogi 8wd Iteration 1.2

Every sheet metal place I've called up (now why would I be doing that? lol) uses 5052. 6061 isn't very bendable at all, apparently.

04-05-2010 12:55

JamesCH95

Re: pic: Rastogi 8wd Iteration 1.2

KOP stuff is 5052 from AM (iirc), our other sheet metal parts were also 5052. 6061 likes to crack when it's bent parallel to the grain structure. I have also done sheet metal work with 3003 and 1100, which are very easy to bend, but weaker than 50xx aluminums.

04-05-2010 14:39

Brandon Holley

Re: pic: Rastogi 8wd Iteration 1.2

You will not be able to make nice sheet parts with 6061, it does not bend well at all.

5052 is the stuff for bending, as most of you have stated. Whatever sheet metal house is helping you guys out will tell you the same thing.

-Brando

04-05-2010 15:32

M.Wong

Re: pic: Rastogi 8wd Iteration 1.2

Just a question: Is a sheet metal chassis lighter than an 8020 or 1/16 aluminum square tubing chassis?

Also, is there any sort of guide on building a sheet metal chassis?

04-05-2010 15:43

sdcantrell56

Re: pic: Rastogi 8wd Iteration 1.2

Lighter than 80-20...most definitely! Just about any chassis short of one fabricated from steel is lighter than an 80-20 chassis. Of course this is a bit of an exaggeration but 80-20 is a heavy material.

As for the tube chassis, I would think that a welded 1/16" aluminum tube chassis would probably be lighter as well as a bit easier to manufacture than a sheet metal frame.

Sheet metal is nice if you have the resources and if you understand how to design to its strengths, but I dont see it as the miracle construction method that a lot of people on CD seem to see it as.

04-05-2010 16:03

Re: pic: Rastogi 8wd Iteration 1.2

Thanks. How friendly are they with sponsors? Because we have like three sponsors, and need to branch out more.


Thaine

04-05-2010 16:04

M.Wong

Re: pic: Rastogi 8wd Iteration 1.2

We've used 1/16 wall 1"x1" aluminum tubing with Nylon connectors for the past 4-5 years. Hopefully, we get access to our school's $2 million dollar tech shop (we've been working at a Magna Seating Facility), allowing us to experiment with sheet metal construction.

04-05-2010 17:27

Chris is me

Re: pic: Rastogi 8wd Iteration 1.2

The "miracle" of this construction process to me isn't in the actual fitness for an FRC robot, since it's good enough to work as well as other materials. The appeal of it to me is that fabrication with a cool sponsor is automated and fast, so you spend less time machining and assembling and more time designing and thinking.

... in theory.

04-05-2010 17:35

Andrew Schreiber

Re: pic: Rastogi 8wd Iteration 1.2

You can do that with a good tubular design too. Take a look at 2337's chassis, it was all bolt together using inserts into the tubes. Took a bit of time to do but was pretty simple. For reference, it was a combination of 1/8" and 1/16" thicknesses. The majority of it was 1/16" but the transmissions were 1/8" just to be safe.

04-05-2010 17:41

AdamHeard

Re: pic: Rastogi 8wd Iteration 1.2

For inexperienced and novice designers, chassis construction methods are far less important than actual design skills and features included.

You'll see crappy extuded tubing drives alongside crappy sheetmetal drives alongside great forms of both.

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

04-05-2010 17:54

roboticWanderor

Re: pic: Rastogi 8wd Iteration 1.2

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.

04-05-2010 19:25

Akash Rastogi

Re: pic: Rastogi 8wd Iteration 1.2

Thanks for all the new info

04-05-2010 19:33

NickE

Re: pic: Rastogi 8wd Iteration 1.2

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).

04-05-2010 20:51

roystur44

Re: pic: Rastogi 8wd Iteration 1.2

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

04-05-2010 20:58

DonRotolo

Re: pic: Rastogi 8wd Iteration 1.2

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.
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...

04-05-2010 22:53

James Tonthat

Re: pic: Rastogi 8wd Iteration 1.2

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.

04-05-2010 23:44

548swimmer

Re: pic: Rastogi 8wd Iteration 1.2

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.

05-05-2010 02:46

James Tonthat

Re: pic: Rastogi 8wd Iteration 1.2

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.

05-05-2010 08:41

IKE

Re: pic: Rastogi 8wd Iteration 1.2

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.

05-05-2010 10:58

JamesCH95

Re: pic: Rastogi 8wd Iteration 1.2

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.

05-05-2010 13:59

artdutra04

Re: pic: Rastogi 8wd Iteration 1.2

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.

05-05-2010 15:16

548swimmer

Re: pic: Rastogi 8wd Iteration 1.2

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 .