Platform building experiences

Let me share one thing that I learned these days. I'm a complete newbie in Robotics, and I'm working on a mobile robot that has a goal of traversing a
stretch of rough terrain autonomously. This robot is based on a 1/8th scale RC monster truck.
I've been looking for good materials for robot base construction, and I found that PVC Expanded Foam Sheets are very good for the task. I bought a couple of 12x12 sheets from BudgetRobotics, but I also found it (I needed a bigger sheet) on my local plastic reseller.
It is reasonably priced, for example I paid $12 on a 20x30 sheet, and you have a nice color selection to choose from.
I'm doing all my designs in Corel Draw first, and then I fabricate the piece and try in the rover. My first prototype can be seen here:
http://www.merlotti.com/EngHome/rover/rover_500.jpg
You can use regular hand tools to drill and cut.
Now the Colombo's egg. I found that for rapid prototyping and concept testing, it's much easier and cheaper to use foam boards. They are easily found at Target and WalMart, and you only need a scissor or a utiliy knife to cut it to shape.
Now I'm able to test a variety of shapes for my rover prior to cutting the PVC board. I bet many of you already use this technique, but I decided to share anyway.
Padu
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Padu wrote:

It's very good stuff -- I use it on all of my indoor platforms. Bear in mind, though, that the commonly available 1/4 inch stuff has a limited load carrying ability, and as others have pointed out can be brittle.
Not an issue on an indoor robot unless it takes a trip down the stairs, but if you expext to operate in rough conditions, bear this in mind.
Like most plastics, foamed pvc also tends to flex under load (at least the 1/4 inch stuff), so if you're carrying heavy batteries, you'll likely want to either reinforce it, or use another material. My robots tend to be multi-teir, with the bottom tier made of plywood (disguised by sanding, several coats of polyuerethane and metallic paint). The upper tiers and other parts are all foamed PVC, though. It's easy to drill and cuts nicely with a router bit. It can be formed using a heat gun, and pieces can be cemented together using commonly available pvc cement from the plumbing section of any hardware store.

And, of course, foam board can usually be scavenged from your kid's last science project.
Cheers -- tAfkaks
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(Replies: cleanse my address of the Mark of the Beast!)

Teleoperate a roving mobile robot from the web:
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"the Artist Formerly Known as Kap'n Salty"

Yes, ultimately, we will have to build the final version out of some kind of metal (alum, titanium) or composite. You mention it can be brittle, but I found it pretty flexible. I found that polycarbonate is more brittle than PVC foam.

The batteries are in the lower deck, in the RC car. I want to keep the heaviest stuff low to improve stability.

She's only 4 months old, I'll have to wait a while :-)
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Padu wrote:

Polycarbonate, sometimes erroneously called "bulletproof glass," shouldn't be brittle. The thin stuff may break with some effort, but it should provide very good impact resistance. Are you sure you weren't using acrylic? That plastic has some nice qualities, but impact and resistance aren't among them. SD Plastics sells polycarbonate under the brand name of Hyzod. See if you can get them to give you a sample piece or two. I wouldn't use anything thinner than 6mm.
There's a scrap metal joint in National City that sells inexpensive aluminum sheet you might be able to use. But I doubt you'll find titanium sheet there, and buying it new from a prime source is extraordinarily expensive.
If you can make it up to the next San Diego robot club meeting (first Saturday of every month, in San Marcos) I will give you a gratis copy of Constructing Robot Bases. All this stuff about PVC, acrylic, polycarbonate, etc. is covered in the book, but it's good you're experimenting on your own anyway. That's really the best way to learn. All of the members would love to see your 'bot-in-progress, as well. Check out http://www.sdrobotics.org/ for details.
-- Gordon
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How nice, I didn't know of the existance of this club. Will definitely take a look (and probably become a member)
tks
Padu
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Padu wrote:

Becoming a member of the SD robotics group means simply showing up!
There are a couple of foilks who come up from San Diego proper, so you might drop a line at the Yahoo group (SDRS) for the club. Might save some gas...
-- Gordon
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the Artist Formerly Known as Kap'n Salty wrote:

It depends on the age and the manufacture of the PVC, but most 1/4" sheets are anything but "brittle." Impact resistance of expanded rigid PVC is considered fair to good, compared to other commonly available plastics, like acrylic or styrene. Under continued load PVC will cold creep, whereas something like acrylic will just create stress crazing.
The thinner 1/8" PVC sheets can break more readily, but it depends on the manufacturer, age, even color. Darker pigments can cause changes in the cell structure of the plastic, causing them to break a little more easily. Lighter colors are tend to route and cut more smoothly.
Foam board is an excellent material for prototyping, though it's important to remember that 1/4" foam board is not the same thickness as "1/4" PVC. Almost all plastics are measured in metric sizes. Designs should accommodate for a little variance here and there for thickness.
Stuff called Gatorboard (different trade names) is also good for rapid prototyping. It's good for form fitting and sizing. I don't even bother drilling...I just punch holes through with a screwdriver.
-- Gordon
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