pic: my version of a wooden chassis

[MrForbes]

Originally Posted by gorrilla

oh and interestingly, i think the bottom panel added a lot of stiffness, before i had it on, it would kinda flex out a litle bit

When we made ours, we did not attach the ends to the sides at all. We glued/stapled the sides to the bottom, then glued/stapled the corner gussets on the top. With 3/4" sides, and 7/32" (slightly thinner than 1/4") bottom and gussets, it is very stiff and strong, and only weighs 13 lbs. The 7/32" bottom can flex a bit in the middle, but should have no problem supporting the electronics, as well as heavier stuff near the edges.

If you can get some 1/4" and 3/4" plywood, I strongly suggest you build one similar to ours and see how you like it...you might be surprised how strong and light it is.

[gorrilla]

Originally Posted by squirrel

When we made ours, we did not attach the ends to the sides at all. We glued/stapled the sides to the bottom, then glued/stapled the corner gussets on the top. With 3/4" sides, and 7/32" (slightly thinner than 1/4") bottom and gussets, it is very stiff and strong, and only weighs 13 lbs. The 7/32" bottom can flex a bit in the middle, but should have no problem supporting the electronics, as well as heavier stuff near the edges.

If you can get some 1/4" and 3/4" plywood, I strongly suggest you build one similar to ours and see how you like it...you might be surprised how strong and light it is.

why dident you?

ill see what I can get....
im not very good with small objects and I tend to break things easily(which is why they call me gorrilla)

i was thinking about the dead axles when i made the decision to use 2x6's that way they could be supported better without putting to much stress on the wood

i think i could combine the two designs, like keep the 2x6's for the sides, but have the plwood for the ends and bottom, I like those steel L-brackets, they added lots of lateral stiffness

[MrForbes]

There is no need at all for the steel corner brackets if you use the triangle gusset plates on the top. All they do is add weight.

The 2x6 sides are way overkill, if you think you need some more strength at the axle attachment points, you could double the plywood at that area, but it really isn't needed. The cantilevered axles are short, and if they are made of 1/2" bolts then they are very strong, and the nuts and washers used to attach them spread the load out over a large area of wood. Also birch plywood is harder and stronger (because it's laminated from plies that go different directions) than a fir 2x6.

There is a lot of engineering thought behind the design we came up with....

[gorrilla]

Originally Posted by squirrel

There is no need at all for the steel corner brackets if you use the triangle gusset plates on the top. All they do is add weight.

The 2x6 sides are way overkill, if you think you need some more strength at the axle attachment points, you could double the plywood at that area, but it really isn't needed. The cantilevered axles are short, and if they are made of 1/2" bolts then they are very strong, and the nuts and washers used to attach them spread the load out over a large area of wood. Also birch plywood is harder and stronger (because it's laminated from plies that go different directions) than a fir 2x6.

There is a lot of engineering thought behind the design we came up with....

the L-brackets are small, only two inches long and 1/2inch wide......

If we were gonig to use it for competition I would use your design but intstead of dead axles, i would use directly driven wheels so there ould be as little pressure on the shaft as possible,

i also think that its way overkill for just a demo-bot, but if we had to use wood next year, i know that it would be a very long decision on which way to do it,(probobly would end up a mixture of both)

could you list what you think are the pros and cons of both?

[MrForbes]

Originally Posted by gorrilla

If we were gonig to use it for competition I would use your design but intstead of dead axles, i would use directly driven wheels so there ould be as little pressure on the shaft as possible,

There is no need to have as little pressure on the shaft as possible, if you make the axle shaft strong and well supported. If the shaft is short and large diameter and well supported, it can take a lot of load!

could you list what you think are the pros and cons of both?

The neat thing about the wood chassis concept, is that you can build a couple of them, using different designs, for not much money. Then you can see how they work.

[gorrilla]

Originally Posted by squirrel

There is no need to have as little pressure on the shaft as possible, if you make the axle shaft strong and well supported. If the shaft is short and large diameter and well supported, it can take a lot of load!

The neat thing about the wood chassis concept, is that you can build a couple of them, using different designs, for not much money. Then you can see how they work.

but wouldent having the wheels directly driven do both jobs at the same time and be stronger and lighter?


ill see if i can get back to home depot and get some more wood,

ill try building your design and see what happens

[MrForbes]

Originally Posted by gorrilla

but wouldent having the wheels directly driven do both jobs at the same time and be stronger and lighter?

Yes, it could be stronger and lighter...but you might not be able to make it have all 3 wheels on each side driven by two motors, which is something we think is kind of important.

We used a cantilevered dead axle design last year, and it was very strong and light. It's hard to compare two designs without having some drawings or pictures of them, though.

[gorrilla]

Originally Posted by squirrel

Yes, it could be stronger and lighter...but you might not be able to make it have all 3 wheels on each side driven by two motors, which is something we think is kind of important.

We used a cantilevered dead axle design last year, and it was very strong and light. It's hard to compare two designs without having some drawings or pictures of them, though.

ill see what happens in the next week or two I have off


ill put some dead axles on my current frame to see how they would work out

[Rick TYler]

Originally Posted by gorrilla

the only thing im concerned about is taking an hit on the side, and cracking the 2x6(but there will be bupers so it shouldent be that big of a problem)..

When we built "Wooden Thunder" in 2005, we were underweight, so we added 2x4s as bumpers. Not only did they not break, they made us pretty much indestructible. I wouldn't worry about that.

- Rick

[gorrilla]

is the bearing really needed fo the dead axle? couldent you just drill a half inch hole and put the bolt through it? would a simple bronze bushing work?

[MrForbes]

A dead axle does not use a bearing, the bearings are in the wheels. The axle can be bolted to the chassis.

[MrForbes]

Gary is working on the Inventor model of the chassis, adding the axles so you can see how we are planning on making them. Hopefully we'll get to our fab shop this Saturday and put on the axles and some wheels. Meanwhile here's a video of the bare chassis showing how strong it is.

http://www.youtube.com/watch?v=VhNhnrPTRMw

[gorrilla]

wow, it dident even flex at all


I just dident think with it being thin plywood, you could get a strong enough connection to the other pieces

like there wasent enough for the pieces to hold onto.....


Im thinking 1x6' s for the next one

[Rick TYler]

Most robotics kids underestimate the strength and flexibility of wood and wood composites. Here's a link to a Wikipedia article on the de Havilland Mosquito, a WWII British fighter-bomber made largely of plywood: http://en.wikipedia.org/wiki/De_Havilland_Mosquito. It could carry 1,000 pounds of bombs nearly 1,500 miles, and fly almost 400 miles an hour.

Or how about a plywood/composite boat that can go 50mph and has a hull that only weights 875 pounds?: http://www.bateau.com/studyplans/MG2....htm?prod=MG20

Nothing we do with robots is as tough as these engineering problems.