Drive Train Prototype

[Henry Williams]

Just a quick update for everyone interested, since the last post we have fixed the mecanums, we had actually done this a while ago but some of the media was not up to date. We also replaced all the electronics board material with pegboard and we added a shooter so we could use it as a demo/show bot. It is still made of nearly all 80/20 so with the shooter and hopper it probably weighs about the same as a normal FRC bot now (but we haven't weighed it since so thats just an estimate).

[Aren Siekmeier]

Originally Posted by nitbaj

We put the mecanum wheels on the outside because we thought those would be the primary driving wheels, and then the traction wheels would be used in a pushing match or a similar situation. And if a robot with a relatively high center of gravity is moving quickly on mecanum and switching directions, it is much more stable to have the wheels on the outside.

Also, tank turning with the traction wheels will be easier with a shorter wheel base because you will get less tread rub.

[Tom Ore]

We used these Mecanum's this year. They do look a lot sturdier, but the bolts and rather small and can bend easily. Our Breakaway robot had a similar drive, but without the moveable wheels. We used 4 Mecanums on the inside and 4 traction wheels on the outside, raised slightly. This allowed us to cross the bump easily - the traction wheels were geared down and pulled us over the bump. We could cross the bump easily at full robot speed but when the robot came down on the other side of the bump, the bounce would bend the small Mecanum wheel bolts. The electronics guys didn't like us crossing the bump that fast anyway...

[MattC9]

Just curious how did you interface the gearboxes to the pods, do you have any CAD files we could look at? Because I was playing around with this idea (like ever one else it seems like) and could not find a good stable way to inter face the transmissions (I was just using the tough box nano in it) also what gear box are you using on it?

[greasemonkey]

how many air tanks did you need for that?

[CENTURION]

Is the mesh material you used for the eletronics board that
fiberglass-reinforced plastic that is used for catwalks and the like? Or is it just a plastic mesh?

I've been looking around for a simple plastic mesh to use for electronics boards that isnt the more expensive fiberglass stuff, but haven't had any luck.

[Lil' Lavery]

Originally Posted by compwiztobe

Also, tank turning with the traction wheels will be easier with a shorter wheel base because you will get less tread rub.

The inverse is also true, it will also be easier for you to be turned.

A longer wheel base grants more resistance to rotation, both caused by your robot, as well as caused by other robots. This is precisely why 148 and 217 opted to put their traction wheels on the outside, as they only planned to use them in pushing matches and why they were attempting to hold their position.

It all comes down to precisely what you want to accomplish with the drive system. There are reasons and rationales behind all sorts of different wheel configurations.

[Aren Siekmeier]

Originally Posted by Lil' Lavery

The inverse is also true, it will also be easier for you to be turned.

A longer wheel base grants more resistance to rotation, both caused by your robot, as well as caused by other robots.

But the robots motors will have to be back driven for this to happen... The tread rub in tank turning is sideways, but there is still traction inline with the wheels, and this doesn't go away when transverse tread rub is reduced. Rotation of the robot will still require that the wheels turn, and therefore the motors are back driven, or the treads slip. If you are powering the motors, like during a pushing match, you should be fine if the traction is enough.

[Lil' Lavery]

Originally Posted by compwiztobe

But the robots motors will have to be back driven for this to happen... The tread rub in tank turning is sideways, but there is still traction inline with the wheels, and this doesn't go away when transverse tread rub is reduced. Rotation of the robot will still require that the wheels turn, and therefore the motors are back driven, or the treads slip. If you are powering the motors, like during a pushing match, you should be fine if the traction is enough.

I bolded the key point in your statement, "or the treads slip." The treads can slip sideways when an external force is applied. Draw up some free body diagrams and think about the problem some more, and it become quite clear why a long wheel base can resist more torque before having the wheels slip.

[AdamHeard]

Originally Posted by Lil' Lavery

I bolded the key point in your statement, "or the treads slip." The treads can slip sideways when an external force is applied. Draw up some free body diagrams and think about the problem some more, and it become quite clear why a long wheel base can resist more torque before having the wheels slip.

Physics are right on this one, that's the beauty of it.

[nitbaj]

Originally Posted by CENTURION

Is the mesh material you used for the eletronics board that
fiberglass-reinforced plastic that is used for catwalks and the like? Or is it just a plastic mesh?

I've been looking around for a simple plastic mesh to use for electronics boards that isnt the more expensive fiberglass stuff, but haven't had any luck.

For the electronics we just used some plastic eggcrate (I think that's what it's called). We just got it at a local hardware store, and it's similar to this:

http://www.goodmart.com/products/1133880.htm

It isn't the sturdiest material, though and after a lot of driving and running into things, the plastic snapped in a few mounting places, so we're planning on swapping it out for something else soon. It is nice for prototyping because it is quick and easy to put on, but I wouldn't necessarily recommend it for a robot you want to be able to take some impact.

[CENTURION]

Ah, cool...
You might want to try out some of this stuff:
http://www.corrosionfluid.com/fiberg....aspx#benefits
Or something similar, apparently the FRP (fiberglass-reinforced-plastic) is pretty strong (people can stand on it) though I can't seem to find any with a mesh smaller than 1.5"x1.5", and I'm not too sure about the pricing.