pic: Cheap 6WD

[sdcantrell56]

I don't think using another tube in the hole will really help the problem. You need to have the bearings in some type of plate and then the plate fastened to the wood with bolts or t-nuts to spread the load. The best thing to do that I can think of is to have to plates of aluminum sandwiching the wood and then have them bolted together with bearings in each plate. Also, why use hardwood? Baltic birch is more than strong enough and is a lot more uniform than hardwood lumber. You can always layer 2 pieces of plywood to get a thicker piece.

On a side note. I have been designing a ton of drivetrains with wood and I just keep coming back to aluminum. Wood although cheaper, seems to be a bit more difficult to build and design with to get the same functionality. Maybe I just haven;t come up with the right thing yet but so far my aluminum designs are winning in my mind.

[AdamHeard]

Originally Posted by sdcantrell56

On a side note. I have been designing a ton of drivetrains with wood and I just keep coming back to aluminum. Wood although cheaper, seems to be a bit more difficult to build and design with to get the same functionality. Maybe I just haven;t come up with the right thing yet but so far my aluminum designs are winning in my mind.

Exactly, there seems to be a frenzy of people wanting wood bases because of how "Simple" and "Easy" they are. So far, I've yet to see a design or setup that really is simpler or easier than a well designed base using more conventional materials.

[Tom Bottiglieri]

Originally Posted by AdamHeard

Exactly, there seems to be a frenzy of people wanting wood bases because of how "Simple" and "Easy" they are. So far, I've yet to see a design or setup that really is simpler or easier than a well designed base using more conventional materials.

The last time we built this frame, a high school student assembled it in less than one day, on their own. I think that's pretty good by anyone's standards. Lots of teams have wood shops, fewer have machining capabilities.

[GUI]

The load is mostly vertical, and the problem i can forsee is the wood being too soft/malleable to handle the load in the relatively concentrated area of the bearing. By using something like a 6061 aluminum tube, we could easily spread the load out and reduce the chance of wallering/widening the bearing holes.

We want to use hardwood because it is strong and available in boards the size/shape we need. We are looking at wood because it provides an easy way to do live axles with minimum machining. The robot in the rendering would require only basic cutting, gluing, screwing, and drilling. Not to mention it would be easier than previous chassis we have done, for a little gain in weight and simplicity.

[dtengineering]

Wood makes for some great possibilities. Our arm in 2005 ( http://www.trobotics.ca/#MAXX ) weighed only three pounds, but could support the weight of two judges bouncing on it in a three point bending test. We brought along a prototype for them to bounce on.... the rest of the robot couldn't handle the stress, but the wooden arm could... easily! I will admit to being rather surprised how strong it was, and didn't actually believe my fellow technical mentor, Gregg, that it would work until I saw him sitting on it!

The next year ( http://www.trobotics.ca/#MAXX%202 )we machined our turret on our CNC router, and pressed the bearings right into the baltic birch turret sides. Not exactly the same impact loading as on a drivetrain, but we're still shooting nerf balls from that thing. The main sprocket on the ball loader ( http://www.chiefdelphi.com/media/photos/22924 ) was mahogany, if I recall... and you'll note the Maple bearing blocks. We also machined up a Maple motor mount for the big CIM to run our intake roller mechanism.

At this point we had pretty much fallen in love with baltic birch, so we built an elevator and actuator out of it http://www.trobotics.ca/#MAXX%202007 and last year it formed pretty much the entire superstructure of our robot http://www.trobotics.ca/#MAXX%203

So we're big fans of wood. In fact we were seriously considering a wooden chassis for last year, untill we realized that we could build an aluminum frame using the KOP parts quicker, cheaper and lighter. But then again... we have access to a full metal shop, including a TIG welder, as well as students who know how to run the mill and TIG. If we had only handsaws and drills, this design might be an ideal solution. At the very least it is a cool design exercise to see how "minimalist" one can get.

Jason

Baltic Birch is good stuff, same for Maple. We build longboards out of both. If it's strong enough to support me standing on a 3/4inch plank of the stuff while going down a hill at 50+mph (no exaggeration) without breaking or cracking, or even flexing too much, then it should be plenty strong for FRC.

[MrForbes]

Originally Posted by sdcantrell56

Also, why use hardwood? Baltic birch is more than strong enough and is a lot more uniform than hardwood lumber.

We found several appropriate sizes of oak boards at our local building supply stores, but we did not find any baltic birch. If you have birch readily available where you are, then you could use it.

The bearing issue is something that needs to be tried out. I'm still waiting for a parts request from the students so I can get some materials.....