pic: Drivetrain Concept

[MrForbes]

Imagine a channel that was 3" tall, with a 1" wide flange on the top and bottom, again 1/8" thick and 36" long. If you started with a flat sheet of aluminum and bent it into the channel shape, it would have to start out being 5" x 36" in size, so it would be quite a bit heavier than just a flat side piece.

And if it were a rectangular tube, it would be even heavier.

[EricH]

Lighter or heavier depends on what you're comparing it to. A side rail like squirrel is describing is a plate, 3" high* 1/8" thick* 36" long. A typical drivetrain side using tubing has about the same weight, maybe a little more. Same length, but instead of 3" high, it's typically 1" to 1.5 " high, 1" wide, and 1/8" wall. So it will weigh a little bit more, as you effectively have to add an extra inch or two to the height of the 3" plate. Channel is lighter than tubing, because one of the sides is removed. This has other tradeoffs, though, because you lose all the support in the missing side along with the weight.

You'll end up about the same weight either way, due to holes and such like. If you really, really need the weight, a plate is easier to take material out of, but it's harder to get it removed from the right places.

edit: squirrel is right, for a channel that size. Most teams that use channel or tubing use smaller sizes or different materials.

[gorrilla]

i just had a quick thought, couldent you use lexan for a frame? that would be awsome it becomes very stiff once you bend it into a channel shape and it would be very light ,

it dosent crack or break normaly (in sheet format) at least i have never seen it

only problem i could see with this is it developing a crack where you drilled a hole for a axle or corner bolt and it just snapping after a while

[EricH]

Originally Posted by gorrilla

i just had a quick thought, couldent you use lexan for a frame? that would be awsome it becomes very stiff once you bend it into a channel shape and it would be very light ,

it dosent crack or break normaly at least i have never seen it

only problem i could see with this is it developing a crack where you drilled a hole for a axle or corner bolt and it just snapping after a while

Lexan has been done. It wasn't bent into a channel shape, it was built as a box by bending the edges and bolting. I seem to recall the 2007 design book saying that they used a Kitbot frame, or part of one, as reinforcement in the drivetrain. The team in question, IIRC, is 1714.

[gorrilla]

Originally Posted by EricH

Lexan has been done. It wasn't bent into a channel shape, it was built as a box by bending the edges and bolting. I seem to recall the 2007 design book saying that they used a Kitbot frame, or part of one, as reinforcement in the drivetrain. The team in question, IIRC, is 1714.

wow i had figured people would say thats crazy




and what do you mean design book?

[Greg Needel]

Originally Posted by EricH

Lexan has been done. It wasn't bent into a channel shape, it was built as a box by bending the edges and bolting. I seem to recall the 2007 design book saying that they used a Kitbot frame, or part of one, as reinforcement in the drivetrain. The team in question, IIRC, is 1714.

team 126 also made lexan frame in 2007

[EricH]

Originally Posted by gorrilla

and what do you mean design book?

FIRST Robots: Rack 'n Roll. Published in 2008. 30 FRC robots that won design/innovation awards. Sequel to 2007's FIRST Robots: Behind the Design, which was robots from 2006.

I only knew about 1714 because they were in the book. Something about a see-through robot. I don't recall seeing any pictures of 126's robot...

[AndyB]

Originally Posted by EricH

FIRST Robots: Rack 'n Roll. Published in 2008. 30 FRC robots that won design/innovation awards. Sequel to 2007's FIRST Robots: Behind the Design, which was robots from 2006.

I only knew about 1714 because they were in the book. Something about a see-through robot. I don't recall seeing any pictures of 126's robot...

Correct, 1714 uses primarly lexan as their building material. They built an omni-directional "kiwi" drive this year on a lexan frame. If I remember, I'll put some better pictures, if I have any, up tonight.

http://www.morerobotics.org/Pictures...robot%20sm.JPG
http://www.morerobotics.org/Pictures...0ball%20sm.JPG

[roboticWanderor]

Heh, okay guys, long time no see. But, since you brought up wood coast, I gotta speak, seeing as how we just about finished up building our own wooden robot prototype!

Oak is pretty much the best wood for a drive train, other woods compress and mar to easily to do any live axle though holes like you got here. bearings are under a lot of pressure, and they will wallow out of any softer woods.

To join the chassis together, it is recommended to use a type of cabinet or other type of joinery, these method range from the complex to the simple, and usually involve some combination of cuts, wood pins, screws, and glue, hardly any bolts. We used mortise and tenon (spelling??) joinery on the cross beams on our wood drive train and it holds up great.

the fiberglass seems to be unnecessary, wooden cross supports would work just as well with less bulk. I also think you got a little thicker wood on the side rails than you need. On ours were no thicker than 1.5 inches, and about 3 inches high, and PLENTY strong. I am sure with a little more work, you could easily cut the chassis down to about 20 lbs total.

[sdcantrell56]

RoboticWanderor could you post up some more pics of the woodcoast drivetrain. Also anymore information would be appreciated. Are ya'll planning on using wood in the coming season. How much testing have you done on the new base?

[roboticWanderor]

We have a fully functioning drive base using the wooden chassis, complete with a foam noodle rocket launcher turret! I will see what I can do about getting some pictures. we also used the new chassis to test chain tensioners and drivetrain layout, improving our motor mounts and the accessibility on the whole. Last year we had to rely on the smaller fingered girls on the team so they could reach into our chassis!
We really don't know what we are going to be working with for the '09 robot, and I am certainly not gonna tell if we did! We will be attending both the Dallas and Houston regionals this coming season, so everyone should have ample opportunities to come see what we have done.

Oh, and CAD work is gonna start up again here soon. keep your eyes peeled for some purple shiney!