pic: Drivetrain Concept

[s_forbes]

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[=Martin=Taylor=]

Some of the combat robots at Robogames tried out those new Banebots wheels.

They wear down incredibly fast. And the floor at robogames is only plate steel.

The treads are deceptivley thin, they will wear down much faster than you may think (especially the Shore A variety).

They will also turn black and lose that awesome orange color...

If you want to use cheap plastic wheels, the colsons are the way to go. For FIRST or for combat.

[s_forbes]

Hmm, that's interesting about the tread wear, thanks for sharing! We were attracted to the wheels by their extremely low cost, but it looks like tread wear may be more of an issue than we expected.

The banebots wheels go up to 50 shore A, it'd be cool if someone could test them out on a first bot before the coming season to see how quickly they wear down on carpet.

[R.C.]

You could epoxy roughtop tread to the outside of it. We attached roughtop tread to a first kop wheel and it worked fine.

[gorrilla]

why not just go with the andy mark kit wheels?

[Tom Line]

Originally Posted by s_forbes

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I would be a little concerned about frame-torsion. Your design looks like you intend to screw into the wood, and over time the twisting of the frame may well loosen it up, especially since you're screwing into end-grain. I'd consider L-brackets with through-bolts to avoid that.

Also, unless there is a pressing reason for 8 wheels - I would avoid it. Unless you drop the middle 2 sets, you'll have trouble turning, and making 8 wheels the correct heights is really difficult. There's a reason stools have 3 legs rather than 4 (wood warps and twists over time). You can avoid that in part by using plywood, but that has problems all it's own if you plan on screwing into the end of it.

[Andy Baker]

Originally Posted by Tom Line

Also, unless there is a pressing reason for 8 wheels - I would avoid it. Unless you drop the middle 2 sets, you'll have trouble turning, and making 8 wheels the correct heights is really difficult.

I love the simplicity of this design. I too would suggest that the wood be made from plywood.

Another suggestion... if you make the 4 interior wheels have a slightly bigger diameter, that will work too. What I would do is put treads on the 4 interior wheels so that they have a diameter that is 0.2" larger than the outside wheels. This may be easier than varying axle heights.

Andy B.

[JesseK]

Originally Posted by Andy Baker

Another suggestion... if you make the 4 interior wheels have a slightly bigger diameter, that will work too. What I would do is put treads on the 4 interior wheels so that they have a diameter that is 0.2" larger than the outside wheels. This may be easier than varying axle heights.

Andy B.

If all 8 wheels are driven, wouldn't that cause the outer wheels to fight the inner wheels since their smaller circumferences cause slower linear translation than the middle wheels? Is it too minor to worry about?

[AndyB]

Originally Posted by JesseK

If all 8 wheels are driven, wouldn't that cause the outer wheels to fight the inner wheels since their smaller circumferences cause slower linear translation than the middle wheels? Is it too minor to worry about?

Yeah, the difference is too minor to worry about. I've seen teams use this method successfully.

[sdcantrell56]

I like it in general. It looks very similar to my design I posted. I too would switch to plywood, particularly a good 1088 meranti or baltic birch plywood as it is much stronger and more stable than a solid chunk of wood. Also u should look into epoxying the wood to the fiberglass plus screwing. If you do that you will have an indestructible joint.

[Alan Anderson]

Originally Posted by JesseK

If all 8 wheels are driven, wouldn't that cause the outer wheels to fight the inner wheels since their smaller circumferences cause slower linear translation than the middle wheels? Is it too minor to worry about?

Even if it weren't too small of a difference to actually make a difference, there is a wee bit of theoretical benefit to a minor mismatch in speed. If the corner wheels are any less grippy than the specially-treaded middle ones, they'll be slipping slightly. The way friction works, they'll thus slide sideways more easily than if they were in solid lock-step with the rest of the wheels.

But it's not an issue. Andy Baker's suggestion is a proven one. The TechnoKats 2008 robot uses six-wheel drive with in-line axles and extra tread on the center wheels, and it drives great.

[gorrilla]

does anyone use the kit wheels anymore? they work great for all kinds of stuff not just as drive wheels

at TNT i only saw 4 teams that used tham

[M. Mellott]

Originally Posted by Tom Line

Also, unless there is a pressing reason for 8 wheels - I would avoid it. Unless you drop the middle 2 sets, you'll have trouble turning, and making 8 wheels the correct heights is really difficult.

Another option is to use omnis on the 4 corners--that way, all eight wheels can contact the ground for stability, but still be able to turn smoothly...and I second the idea of adding L-brackets or some additional support to the 4 primary corner joints.

Question for anyone on the aluminum belly pan: what is the minimum sheet thickness one would use on such an application?

[gorrilla]

yes use L-brackets the dont add to too much weight for all there worth

and if the ends are fiberglass why not just glass it all its not very hard and that way you would have all the great performance of wood and the added strength of the fibergalss but it would still be able to give a little allowing for a smoother ride then a metal frame


the only problem with fiberglass is its kinda messy to work with and if it gets on a tool or something you might have to throw it away


and I second what andy said about the inner wheels

[s_forbes]

Originally Posted by Tom Line

I would be a little concerned about frame-torsion. Your design looks like you intend to screw into the wood, and over time the twisting of the frame may well loosen it up, especially since you're screwing into end-grain. I'd consider L-brackets with through-bolts to avoid that.

Also, unless there is a pressing reason for 8 wheels - I would avoid it. Unless you drop the middle 2 sets, you'll have trouble turning, and making 8 wheels the correct heights is really difficult. There's a reason stools have 3 legs rather than 4 (wood warps and twists over time). You can avoid that in part by using plywood, but that has problems all it's own if you plan on screwing into the end of it.

Good points, I forgot to cad in the top corner brackets that would reinforce those joints. It could be constructed in a very similar way to our 2008 drivetrain which was able to go through three competitions with no problems. I am not sure whether wood screws would be enough or if through bolts would be needed, that's something that may need to be tested.

Oh, and the middle four wheels are all dropped 1/8" on this model.

Originally Posted by M. Mellott

Question for anyone on the aluminum belly pan: what is the minimum sheet thickness one would use on such an application?

Last year we used a .050 or .060 sheet, I believe... not sure on the actual thickness (squirrel might know?). It held up great and provided a solid mounting surface for all of the 'guts'. Adds about five pounds to the weight, but it compensates for additional bracing and a sturdy electronics board.

Originally Posted by gorrilla

yes use L-brackets the dont add to too much weight for all there worth

and if the ends are fiberglass why not just glass it all its not very hard and that way you would have all the great performance of wood and the added strength of the fibergalss but it would still be able to give a little allowing for a smoother ride then a metal frame


the only problem with fiberglass is its kinda messy to work with and if it gets on a tool or something you might have to throw it away

We're a little hesitant to take on a project like that... like I said this particular model was designed with manufacturing taken into consideration. That means that we cut a length of wood, drill some holes, and we have a side rail. The fiberglass ends come as a pultruded channel already, so we just hack off the correct length and bolt it on. (We have this problem of being lazy and trying to avoid too much labor )

Some of you also mentioned using plywood, and I'm curious as to how it would best be implemented. One team member suggested laminating several sheets of plywood together to make the siderails...


One more thing I forgot to mention before (and why I like this design so much): Since it is constructed with siderails that require just a proper sized hole for a wheel module to fit, we could really stick wheels wherever we want. So, if it turned out that we didn't want an eight wheel drive robot after all, we could just drill another hole in the center of each side and we'd have a functioning six wheel drive robot. The difference between a 6wd and an 8wd bot with this frame is just two extra wheels and chains.