Platform building experiences

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

--
(Replies: cleanse my address of the Mark of the Beast!)

Teleoperate a roving mobile robot from the web:
http://www.swampgas.com/robotics/rover.html

Coauthor with Dennis Clark of "Building Robot Drive Trains".
Buy several copies today!

"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 :-)

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

How nice, I didn't know of the existance of this club. Will definitely take
a look (and probably become a member)

tks


Padu

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

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