pic: Drivetrain Concept

[MrForbes]

I've been discussing this with some of the students and Steve, here are a few more comments. The plan for the sides was to use a hardwood such as oak. I'm sure we'll get the "that's way too heavy!" comments...that's ok...last year our robot with it's way-too-heavy drive base was still 10 pounds lighter than it could have been, and it never wanted to fall over. Hardwood has the advantage of being dense, so it won't let the bearings open up their holes too much, and it should hold screws better than a lighter wood (although putting the screws in would be more of a challenge). We used .060" 3003 aluminum for the belly pan and corner braces last year, it worked fine, it's pretty easy to rivet to the fiberglass channel to make a strong structure.

One interesting point about this design is that it uses three quite different materials for the chassis structure, and each material is used in that place where it is most effective.

[sdcantrell56]

I do like the way that you are using multiple materials and your use of fiberglass has actually gotten me thinking about incorporating it possibly. I do think that fiberglassing the side rails and bonding the whole thing together with epoxy would be your best bet. Your frame would be indestructible. Also for all the naysayers, oak is much less dense than aluminum and stronger as well for the weight so go for it. I hope you guys get a chance to prototype this and post it up on here. Maybe we should see who has a prototype frame done first

[Jonathan Norris]

I think the wood will work fine for the overall stress of the base, but I worry about how about the stresses at the axels and how you are attaching the bearings. I could see big issues with however you attach the bearings for your cantilevered wheels (can someone rationally explain to me why everyone likes to have cantilevered wheels??? seriously...). I see the wood warping at the bearings (even hardwood), unless the bearings are very securely supported. For this reason it just makes more sense to me to go with two 1/8" plates on both sides of the wheels with cross-bracing.

[gorrilla]

cantilevered wheels have benefits that i am not aware of and i will let them explain




its like the wood trim in cars, noone knows what it is but its red so they call it mahogany

[sdcantrell56]

The 2 major reasons for cantilevering wheels is to ease wheel replacement, and to maximize your robot's footprint. Many teams are able to change a wheel on their cantilevered system in a matter of seconds by removing a snap ring such as 254.

[s_forbes]

Originally Posted by Jonathan Norris

I think the wood will work fine for the overall stress of the base, but I worry about how about the stresses at the axels and how you are attaching the bearings. I could see big issues with however you attach the bearings for your cantilevered wheels (can someone rationally explain to me why everyone likes to have cantilevered wheels??? seriously...). I see the wood warping at the bearings (even hardwood), unless the bearings are very securely supported. For this reason it just makes more sense to me to go with two 1/8" plates on both sides of the wheels with cross-bracing.

If all we had to worry about was the strength of the chassis, then I would agree with you. Unfortunately other factors come into play, like build time and ease of maintenance. Our 2007 chassis was a good example of a solid 6wd base with dead axles that were supported on each side. It was very strong, but building it took forever and it took a lot of effort to replace a wheel.

[gorrilla]

Also how(if you decide to use this system) are you thinking about attaching bumpers, I remember on this years robot we had a nice 6 or 8 bolt attachment system but we dident factor in wrench space and ended up taking all the bolts off and putting two screws on each side in between our first and second quarter final matches

[s_forbes]

I don't have any decent pictures of it, but last year we simply attached the bumpers on the corners and braced them in the middle with a couple of standoffs. We learned a while ago that putting bumpers on with little tiny bolts that you can't get to is a lot of work, so we used coupling nuts instead.

[BoyWithCape195]

For the wood, I would suggest Baltic Birch.

[MrForbes]

Why would you suggest Baltic Birch?

(I cannot seem to find any engineering data for Baltic Birch, although I can for Yellow Birch....how different are they?)

[sdcantrell56]

Baltic birch would be good for plywood but not for solid wood. A good oak or mahogany would be better suited for solid wood although you could go exotic and get bloodwood or something.

[MrForbes]

That sounds reasonable. One advantage of using oak is that it's easily available.

Also the configuration of the wood side members in this design is such that a solid hardwood would be a good choice over plywood. For other designs, plywood might be better.

[gorrilla]

wood is good for lots of things, but im starting to lean back towards metal side rails because thats somthing you dont want to ever have problems with

if only metal was lighter



does anyone know what a side rail size peice of 1/8th inch alluminum would weigh


also when i was at TNT I dont remember what team it was but they had a a piece of channel on each side and one on the bumpers and they drilled holes in both and just had pins to hold them on, it looked really nice and was very simple

[MrForbes]

Aluminum weighs about 1/10 of a pound per cubic inch. So, if you had a 3" x 1/8" x 36" side rail, without any holes, it would weigh about 1.3 lbs. Two would weigh 2.7 lbs. That's not very heavy. But they probably ought to be made of an extruded or bent shape, such as channel or tube, to have the necessary resistance to bending.

[gorrilla]

yes, but would a having it be channel make it hevier or lighter?

that way you could mount things easier(like bumpers)