pic: Another Cheap Wood Frame Idea

[MrForbes]

Originally Posted by artdutra04

If you are going with dead axles, why don't you just support the axle/bolt from both sides with two chassis rails on each side of the robot chassis? This would take a lot of the stress off the single hole and spread it out between two holes.

That is another way to build the robot, and if you feel like making up a sketch or Inventor rendering of it, that would be great! It sounds like what team 173 has done in the past.

The cantilevered axle design has some advantages and some disadvantages. One advantage is that it's pretty easy to work on it, another is that the holes don't have to be aligned, another is that it saves the weight of the outer piece of wood, and since there's a bumper there anyways that piece of wood is kind of redundant. On the downside, it takes a bigger axle with a strong attachment to equal the strength of a non-cantilevered design.

We used a chassis layout almost identical to this one last season, with pultruded fiberglass C channel for the side and end rails, and sheet aluminum for the bellypan and gussets. Axles were 1/2" threaded rod with big flange nuts holding them to the fiberglass. It worked well, and we felt it was easier to work on the drivetrain with this design, than with the double-supported dead axles we used the previous two years. Also, building the chassis took less time. We are beginning to think that getting a chassis built and running quickly is a good thing, so the team can concentrate on the game-playing parts of the robot. That's one reason we are taking a lot of time playing with new chassis ideas now, hopefully we'll have enough design ideas ready to go that we can pick one and built it by the end of the first week.

[gorrilla]

Originally Posted by squirrel

The cantilevered axle design has some advantages and some disadvantages. One advantage is that it's pretty easy to work on it, another is that the holes don't have to be aligned, another is that it saves the weight of the outer piece of wood, and since there's a bumper there anyways that piece of wood is kind of redundant. On the downside, it takes a bigger axle with a strong attachment to equal the strength of a non-cantilevered design.

of the two, which do you think is the easiest to build and most durable?

and were do you guys get pultruded fiberglass channel

[MrForbes]

I think we got the fiberglass from Creative Pultrusions, we bought a bunch our rookie year. I think that cantilevered axles are easier to build, but do need to be made stronger since they are only supported at one end.

[gorrilla]

Originally Posted by squirrel

I think we got the fiberglass from Creative Pultrusions, we bought a bunch our rookie year. I think that cantilevered axles are easier to build, but do need to be made stronger since they are only supported at one end.

on a 6wd base, why not just direct-drive two of the wheels on each side(using say, a bb transmission), then run a chain the the last one? that way you would only need to really make one dead canilevered axle

Originally Posted by gorrilla

in my expeireance with it, fiberglass only becomes brittle if you dont mix the resin right, or wait to long to apply it,


they switched to epoxy resin in surfboards because, polyester resin dosent stick to the new type of foam most companies use.


you dont even have to use the fiberglass mat, you could just take a paintbrush and dip it in the resin and "paint" it around the corners and edges


we're getting off topic now.......

My experience with composites is mainly in the realm of Longboarding, and building customs out of most available types of composites. Most new users to fiberglass end up with a goopy, brittle mess, assuming they just lay the fabric and slap some resin on. You're correct about using Epoxy resin, it's much stronger (and more expensive).

Originally Posted by Rick TYler

Generally, I'd avoid Kevlar cloth (it fuzzes and is a pain to sand smooth), or carbon-fiber cloth (very hard to work with, fuzzes, and supernaturally expensive) (unless you make carbon-fiber poles as arm material, in which case I'd like you to send me pictures). Other cloths like Dynel are more for abrasion resistance than strength and will do nothing for a robot chassis than add weight.

I've had nothing but success with both Kevlar weave, as well as Carbon Fiber. Granted, these are in Longboard applications, but those tend to have a little more force involved (a 200lb rider going through a 90 degree turn at 60mph). As long as you take the time to lay out all your steps right, and then don't dawdle when working with the actual glass, you'll be fine with both these materials. If a team has the budget, there are some IMPRESSIVE things that can be done with composites. Heck, I'd LOVE to build an entire robot out of the stuff. Foam molds and vacuum bags galore!

[Rick TYler]

Originally Posted by CraigHickman

I've had nothing but success with both Kevlar weave, as well as Carbon Fiber. Granted, these are in Longboard applications, but those tend to have a little more force involved (a 200lb rider going through a 90 degree turn at 60mph). As long as you take the time to lay out all your steps right, and then don't dawdle when working with the actual glass, you'll be fine with both these materials. If a team has the budget, there are some IMPRESSIVE things that can be done with composites. Heck, I'd LOVE to build an entire robot out of the stuff. Foam molds and vacuum bags galore!

My background is in amateur boat-building where the object being made is too large to bake and usually wildly impractical to vacuum bag. If I needed the penetration protection of Kevlar, I'd cover it with a layer of glass cloth to prevent surface fuzzing, or, even better, get an expert to design a layup schedule that included some biaxial cloth for strength mixed with Kevlar. Usually, in amateur boats you find carbon fiber cloth in spars and blades -- not usually in hulls. Longboards use a lot less material. Carbon fiber in quantities big enough to build 20- or 24-foot boats is really pricey. Carbon fiber is also a pain to cut, it floats in resin (which is why it is usually vacuum bagged), and fuzzes if it's on the surface. The carbon fibers are usually considered dangerous to breathe, so you want to wear a respirator or at least a NIOSH dust mask when cutting.

I do think carbon fiber tubes are The Bomb for robot arms, but haven't had a chance to try it due to the famously conservative students on the FRC team with which I used to work.

We need some pictures of your longboard(s). Here's a link to pictures one of my boats: http://www.jemwatercraft.com/images/...ahPictures.htm, made from 4mm okoume and 6-ounce fiberglass. And other stuff!

[MrForbes]

This discussion is making it look pretty sensible to just cut up some plywood on the table saw, and glue it together!



The carbon fiber tube idea is nifty, but kind of pricey for those on a limited budget.

http://www.carbonfibertubeshop.com/large%20tubing.html

[Rick TYler]

Originally Posted by squirrel

The carbon fiber tube idea is nifty, but kind of pricey for those on a limited budget.

Make your own! Still pricey, but about 50% cheaper: http://boatbuildercentral.com/products.php?cat=36.

[MrForbes]

Interesting stuff, we'll have to look into it.

Back to the Quick Affordable Wood Chassis....Gary finally came home and made a sample cantilevered dead axle. Yeah, it's pretty simple, a dollar and a half for a bolt, hacksaw the head off, drill a 1/8" hole for a cotter pin to retain the wheel.



Hopefully he'll get some Inventor work done and show us what the chassis with the axles and Toughboxes could look like.

[Matt C]

Carbon Fiber?
http://www.inlinewarehouse.com/descpage-NB95SHI.html

[gorrilla]

did you just glue the bottom panel on? or is stapled also?

[s_forbes]

Originally Posted by gorrilla

did you just glue the bottom panel on? or is stapled also?

The bottom panel is glued and stapled.