Re: pic: How It's Made: 148 & 217 Robots
 

Anything that is bent is most likely 5052 aluminum. 6061 does not bend very well and 7075 does not bend at all.

Re: pic: How It's Made: 148 & 217 Robots
 

Now that's what you call a teaser for sure!
How much for a laser cutter? Seriously.:D

Re: pic: How It's Made: 148 & 217 Robots
 

Awesome video. Awesome process. Awesome that you could share it.

Hmmm, Cyber Blue Road trip to IFI for a tour ... :)

Re: pic: How It's Made: 148 & 217 Robots
 

I've been up to Greenville myself, then came a second time with a small group of students. They all enjoyed it, it's well worth the 5 hour drive from The Woodlands.

Re: pic: How It's Made: 148 & 217 Robots
 

Same

Re: pic: How It's Made: 148 & 217 Robots
 

I think you'd be surprised at how little the total would come in at. The only big initial cost being set up. Considering there is very little time in the process for all those parts ( He mentioned ~ 24 hours ) just factor in an average machine shop time, that cost and material costs.. whamoo you have your answer.

Personal example, we used to have our drive train manufactured by a facility that was not well equipped to do sheet metal. ( Multiple CNC cutting centers no water jets or laser .. ) When we would ask for a quote for accounting / sponsorship letter the cost would often come in at 5000+ for around 10 pieces.

Now that we use a sheet metal facility that quote comes in for around 700 total, and we have 1-2 day turn around rather than a week.

On a side note, I am giddy like a school girl to see this video because of how important understanding sheet metal construction can be for Mechanical Design Engineers. I have been consistently inspired by 148 and 217 year in and year out. There competitiveness on
the field and GP off inspired 1902 to use these manufacturing techniques for many years and I think anyone reading this forum should take note.

Re: pic: How It's Made: 148 & 217 Robots
 

John- would it be possible for you to put on a presentation in Atlanta this year, or even a powerpoint presentation up here on CD, detailing your design process in Sheetmetal in Solidworks? This question is also directed to others who use sheet metal fabrication such as 217, 228, 1771, 1477, 1902 and any others I don't know of.

I've been learning the features in SW but I don't know what works or what doesn't in my designs when, hypothetically, I would try to get them manufactured at a fabrication site. Are there limitations using sheet metal during fabrication? What are the advantages? (other than speed of fabrication, weight, duplicates)

Great video, great insight into your process. Thanks to those who can help answer some of my questions.

Re: pic: How It's Made: 148 & 217 Robots
 

I'd also love to hear more about some of the details that need to be considered when dealing with sheet metal design. One of the things I find most perplexing is the tolerances involved with these kind of parts... Some things I've read online mention that large sheet stock (like 4'x8') can vary in thickness as much as .005" (thicker in the middle).

Separately, how tight of tolerances can the machines hold? For example, when bending a c-channel out of 0.125 thick sheet, how much does the outside flange to flange distance vary?

It seems like getting rivet holes to line up would be a nightmare.

Re: pic: How It's Made: 148 & 217 Robots
 

These are the same things I have been wondering. I've heard from some teams that after they made their parts in sheet, the biggest challenge was making everything line up perfectly.

Re: pic: How It's Made: 148 & 217 Robots
 

I don't have any specific numbers but I know on our sheet metal parts from last year specifically the shooter which was quite complex every hole lined up perfectly first go round. We are very fortunate to work with a super high precision sheet metal shop so I dont know if this is the usual.

Re: pic: How It's Made: 148 & 217 Robots
 

I've never had any problems with tolerances. The laser and punch tolerances are great. I had an argument with Paul a few years ago because the "promised" tolerances didn't meet his needs. I reassured him, they always under-promise and over-deliver. We're spoiled working with Metal Solutions.

Bend tolerances vary purely based on the skill of the break programmer and operator. I'm lucky to work with a group of absolute ARTISTS. For a long time I shied away from allowing for any bends to affect gearbox tolerances, but (in a typical role reversal) Paul has proved to me that these guys are getting things so close to nominal so consistently we shouldn't worry about it. For the first time ever 148 will be riveting our gearboxes together and spacing them with flanges instead of threaded standoffs.

When our holes don't line up it is 99% of the time a designer's error. I'm always amazed how smoothly things "drop together." We always get exactly what we ask for (now, whether that is what we actually wanted is another question...)

I've also never heard of thickness variances like you describe, though it is possible I just never notice it.

Hope this answers some of your questions.
-John

Re: pic: How It's Made: 148 & 217 Robots
 

Hi Akash,
I already have two presentation proposals in for Atlanta this year, so a third may be a bridge too far. I will work on a whitepaper for this off-season, I'll be sure to pester Paul to help me with it (the two of us working on a paper together would be fun... I think.)

The main advantage in using sheet metal for me is the versatility in design. I use it in 2 major ways:

1. Custom "extrusion" type pieces. You'll see a lot of c-channels, hat sections, question mark channels, and angles on 148 robots. These are made exactly the size we want, with all the mounting and lightening patterns already included.

2. Custom "shell" designs. There are years where our entire robot is one giant box section. This allows for some very rigid, very light structures.

The general rule I tell my students is "get your strength from your cross section, not from your material thickness." This means that if you do it right you can get a LOT out of very little material. Now we consider 1/8" to be "thick". I remember back when I was on a team that made their side-plates out of 1/4"! I distinctly remember Raul looking at our robot at Championship in 2004 and shaking his head: "Why so thick? Just add a flange it'll be 10 times as strong!"

Want to get really good at sheet-metal design? Learn the basic things your shop is capable of. Now learn basic strength-of-materials (I took this as a sophomore MechE at Clarkson). Apply the principles you've learned and think outside the box (or welded tube)...

Take a look at the Tumbleweed and Tornado CAD models. You'll see a few of the ways we utilize this awesome manufacturing technique.

Feel free to PM or email me if you have any questions. Shoot me a design, and I'll be happy to tear it apart for you. Keep at it long enough, and you'll be finding all the times I got lazy in my designs... ;)

-John

Re: pic: How It's Made: 148 & 217 Robots
 

This video was really cool, but I'm looking forward to next week's episode on pick lists.

Re: pic: How It's Made: 148 & 217 Robots
 

Like John said, it is all about the geometry. There are three thicknesses we use: .0625, 0.90, and .125. I try to start with .0625 and only go up in thickness as required. For the last few years, the major differences in the basic sheet metal construction between 148 & 217 have been:

1. 148 used .090 for the drive base and 217 used .0625
2. 148 primarily used 1/4" rivets and some 1/8" rivets and 217 used 5/32" rivets exclusively.
3. 148 used flat plates with standoffs for the gearboxes and 217 used bent metal and rivets.
4. 217 got most of it's lightening from using .0625 with basic holes and trusses and 148 did it with .090 and a specific focus on visually appealing large lightening patterns.

This year, we decided to try each other' styles and mix and match:

1. Both 148 & 217 are using .090 fir the drive base.
2. Both 217 and 148 are primarily using 5/32" rivets, but using 1/4" rivets for main structural attachments and in place where we may need a bolt due to rivet gun access. We found a very inexpensive pneumatic riveter that can do 1/4" rivets with no problem. Each team owns 1.
3. Both teams are using a bent sheet metal gearbox for the drive directly riveted to the drive base. In addition, our other gearboxes are a combination bent meta / standoffs.
4. Both teams are using the 148 style of lightening.

One major difference between the two designs is the choice of fasteners. 148 uses English (where possible) and 217 uses metric (where possible). This posed interesting design challenges to make interface holes to handle English or metric on the few parts that were the same. We standardized on #10-32 (M5) and 1/4"-20 (M6). That has worked out much better than I planned.

I will probably do a joint white paper with John, but it will have to wait until the VEX stuff settles down as John and I are both extremely busy due to VEX's increasing popularity globally.

Re: pic: How It's Made: 148 & 217 Robots
 

Thank you John and Paul for the excellent info. I've been looking at the 148 models in solidworks (well, the tumbleweed model... I'm afraid if I open the 09 bot my computer will melt) to get a better idea of how you go about designing some of these parts. There are some parts in there that I wouldn't have even thought were bendable. Really awesome stuff!