WCD vs Standard

[smistthegreat]

Originally Posted by LedLover96

Okay, so in the 4th link, I saw that WCD's use a live axle, vs. a Standard using a dead axle.
First off, could some elaborate on the difference between the two? I found the posts kind of confusing as to the difference (the live axle is spun by chain or gears or motor while dead axle is just sitting there, not powered?)

Next: Why would you choose a live axle over a dead axle, if the center wheel is lowered, thus making your robot rock between the front and back wheels? It seems that live axles (if I have their definition correct) would make the 6 wheeled work like a 4 wheeled when it turns, porblematic. But, when observing many WCD's, I do not see slick wheels or omniwheels to offset the traction/turning problems associated with a 4 wheeled.

All of your information is correct, but you make a couple of incorrect conclusions. Yes, live axle is when the axle itself is powered, and dead axle is when only the wheel is powered. Also, you are correct about the drop center making it turn like a 4 wheeled drive. However, this 4 wheeled drive now has a shorter wheelbase, making it easier to turn. The whole point of dropping the center wheel is to shorten the wheelbase enough to where it turns smoothly without adding slick or omniwheels

[EricH]

Originally Posted by smistthegreat

All of your information is correct, but you make a couple of incorrect conclusions. Yes, live axle is when the axle itself is powered, and dead axle is when only the wheel is powered. Also, you are correct about the drop center making it turn like a 4 wheeled drive. However, this 4 wheeled drive now has a shorter wheelbase, making it easier to turn. The whole point of dropping the center wheel is to shorten the wheelbase enough to where it turns smoothly without adding slick or omniwheels

And the other implied conclusion--dead axles don't need a drop--is also an incorrect one. A 6WD, dead or live axle, without the drop will act almost exactly like a 4WD with all traction wheels (there are exceptions, like FRC25); so will an 8WD without any drop.

[Garret]

No outer framing. Basically eliminates about 86" of outer railing (assuming a 37" long by 27" wide bot). Center wheel is direct drive, so less chain (6 chains per average 6WD, 4 for your average 6WD WCD).

How are you getting 86" I would think that you are only eliminating 74" of railing, though I have never built a WCD so I may be off. Also I have seen plenty of plain non-cantilevered 6WD robots with direct drive on the center wheels.

However I do know that with the WCD it allows for wheels to be removed much easier because the shafts do not need to be removed.

[Walter Deitzler]

Originally Posted by EricH

And the other implied conclusion--dead axles don't need a drop--is also an incorrect one. A 6WD, dead or live axle, without the drop will act almost exactly like a 4WD with all traction wheels (there are exceptions, like FRC25); so will an 8WD without any drop.

What does 25 do? why are they an exception?

[EricH]

Originally Posted by LedLover96

What does 25 do? why are they an exception?

6WD flat. I don't know how they do it, but they don't bounce when turning, even with high-traction wheels. I think it has something to do with how they groove their tread, but I'm not sure.

At least, they used to do that. I'm not sure if they still do or not.

[MichaelBick]

For weight it honestly depends: if you are running tube then WCD is a pretty good choice to save weight. If you are running sheet there is really no need to run a WCD. However wether you run sheet or tube you always should drop the center wheels and should direct drive the center wheel.

[Walter Deitzler]

And I am assuming that the standard KOP C-Channel will not work for a WCD, or, at least, that C-Channel is not a good choice? I have never heard of a C-Channel WCD.

[MichaelBick]

The KOP is not made for running a WCD. WCD is overall a better drivetrain, but for teams that don't have the capabilities to build a WCD the KOP is a find alternative. I believe they even make supershifter mounts for the KOP

[Walter Deitzler]

Originally Posted by MICHAELABICK

The KOP is not made for running a WCD. WCD is overall a better drivetrain, but for teams that don't have the capabilities to build a WCD the KOP is a find alternative. I believe they even make supershifter mounts for the KOP

Why can you not run a WCD on a KoP chassis?

[BrendanB]

Originally Posted by LedLover96

Why can you not run a WCD on a KoP chassis?

Technically you can make a WCD using the KOP but it isn't the most efficient way. The team who made it escapes me but I know there is a photo here on CD.

How they did it was they took the outer most rails in the standard KOP frame and moved them inward so they ran flush with the inside rails. This meant all they had to do was put their KOP bolts through the holes with chain and sprockets and they had a WCD. Cantilevered in all.

This method could make for a great fall project for any team that doesn't want to spend money yet still wants to work towards custom drivebases. Who knows, we might do it this fall just as a learning experience!

[MichaelBick]

The definition of WCD usually means that you are running a cantilevered, live axle, direct driven a dropped center drivetrain. While the KOP is drop center, it is not any of the other things. The C Channel of the KOP is definitely not strong enough to cantilever something off of it. because you are not cantilevering you might as well run a dead axle set up.

[Walter Deitzler]

Originally Posted by MICHAELABICK

The definition of WCD usually means that you are running a cantilevered, live axle, direct driven a dropped center drivetrain. While the KOP is drop center, it is not any of the other things. The C Channel of the KOP is definitely not strong enough to cantilever something off of it. because you are not cantilevering you might as well run a dead axle set up.

That makes sense, thanks.

[Kristian Calhoun]

Originally Posted by LedLover96

What does 25 do? why are they an exception?

Originally Posted by EricH

6WD flat. I don't know how they do it, but they don't bounce when turning, even with high-traction wheels. I think it has something to do with how they groove their tread, but I'm not sure.

At least, they used to do that. I'm not sure if they still do or not.

Jared from 341 made a really good post about our drive train about two years ago: http://www.chiefdelphi.com/forums/sh...5&postcount=31.