WCD vs Standard

[Walter Deitzler]

I tried finding them, but only found WCD vs. Swerve and many pictures of a WCD.

Some things I've found on my way asking the same questions you do:
http://www.chiefdelphi.com/forums/sh...&highlight=WCD
http://www.chiefdelphi.com/forums/sh...&highlight=WCD
http://www.chiefdelphi.com/forums/sh...&highlight=WCD
http://www.chiefdelphi.com/forums/sh...&highlight=WCD
http://www.chiefdelphi.com/forums/sh...&highlight=WCD
http://www.chiefdelphi.com/forums/sh...&highlight=WCD
http://www.chiefdelphi.com/forums/sh...&highlight=WCD

All in all, WCDs are lighter, allow for direct drive (more efficient), and the wheels a bit farther out for better turning. 6WD vs. 8WD is mainly based off of whether or not the robot has to traverse an object (climbing over the bumps in '12 and '10). 8WD also allows a smaller wheelbase, so that a robot can be more maneuverable, but the turning difference is often nothing a 6WD can't do, and the extra weight isn't worth the little bit of turning help on a flat field.

[Walter Deitzler]

Thank for that Andrew, some of those links will be helpful, but as for the 6 vs 8 wd, I phrased the question poorly, that is not what I am looking for. The standard vs. WCD ones are useful though!

Thanks!

[avanboekel]

SuperNerd's last link is probably what you are looking for (If I am reading your question right, you want to know the pros and cons of a WCD vs a non WC 6WD, not 6wd vs 8wd).

http://www.chiefdelphi.com/forums/sh...&highlight=WCD

[Walter Deitzler]

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.

[JosephC]

To my understanding, A live axle is one that supports part of the weight of a robot and drives the wheel(s) connected to it. A dead axle is one that carries part of the weight of a robot but does not drive the wheel(s). The wheel(s) rotate on the end of the dead axle.

[jspatz1]

Originally Posted by JosephC

To my understanding, A live axle is one that supports part of the weight of a robot and drives the wheel(s) connected to it. A dead axle is one that carries part of the weight of a robot but does not drive the wheel(s). The wheel(s) rotate on the end of the dead axle.

Live axle = Axle turns, wheel is keyed to the axle.
Dead axle = Axle is fixed, wheel turns on the axle.

[Walter Deitzler]

So, doing more research on CD, I have come across bearing mounts called "Sliding Bearing Mounts". What are these exactly. It seems as if they are used for chain tightening, but I have no details about how they do this.

[Aren Siekmeier]

Originally Posted by LedLover96

So, doing more research on CD, I have come across bearing mounts called "Sliding Bearing Mounts". What are these exactly. It seems as if they are used for chain tightening, but I have no details about how they do this.

Many teams build bearing blocks for their drive train which hold the bearing and axle. This bearing block can slide forward and backward in the frame (moving the wheel with it) in order to adjust chain or belt tension.

Unfortunately, 254's website is under construction, so I can't pull up any of the great pics I know they had there. I'm sure someone else here can dig up some instructive photos.

[BJC]

It's interesting to hear so many people say that canilevered, direct driven systems are the lightest and best when some of the most successful teams in the world do neither of those things (most notably 67 and 1114).

I know Jim Z has done annalysis on 254, 1114, and 67's frames. I *think* 1114's frame was lighter than 254's by about two pounds.

We used .06 sheet metal this year and will probably go down to .05 sheet metal next year. I am pretty sure that our frame weight beats out 254's by a pound or two. What get's 254's weight so far down is there use of tiny wheels which takes weight out of both their gearboxes (which are custom and very light) and wheels (also custom and very light). Direct diving helps too I'm sure.

Perhaps, some 254 people could chime in and correct me here if I'm wrong on any of these points?

In any case, I'm just stirring the pot.
Regards, Bryan

[AlecMataloni]

I will side with the live axle cantilevered drivetrain not on the grounds that it "weighs less", but by the fact that maintaining one can be easier. When the wheel is supported by live axles on both sides by the frame, working on the drivetrain becomes easily more painful and irritating when frame members are in the way. With the average west coast drive, replacing components like wheels, axles, and chain is a snap because there's only one frame member to deal with.

[Adrian Clark]

Originally Posted by compwiztobe

Many teams build bearing blocks for their drive train which hold the bearing and axle. This bearing block can slide forward and backward in the frame (moving the wheel with it) in order to adjust chain or belt tension.

Unfortunately, 254's website is under construction, so I can't pull up any of the great pics I know they had there. I'm sure someone else here can dig up some instructive photos.

For the best example of a well executed sliding bearing block I would strongly suggest downloading some of 973's CAD models.

[Pat Fairbank]

Originally Posted by compwiztobe

Unfortunately, 254's website is under construction, so I can't pull up any of the great pics I know they had there. I'm sure someone else here can dig up some instructive photos.

I can't find a good picture of the bearing blocks themselves, but here's a shot of the rectangular holes in the frame where they go. You might get a better idea from browsing the rest of the 2012 build season album. Basically, there are two halves that come in from either side of the rail and fit inside each other, each having a bearing pressed into it. Long bolts through the rail are used to hold the two halves together, and there's a cam mounted to the rail that is torqued once the chain is installed to push the block which tensions the chain.

Originally Posted by BJC

It's interesting to hear so many people say that canilevered, direct driven systems are the lightest and best when some of the most successful teams in the world do neither of those things (most notably 67 and 1114).

I wouldn't say that weight is the top factor in 254's choice of using a cantilevered drive year after year. It probably only comes in fourth after ease of maintenance, robustness, and aesthetics (you wouldn't believe how many design decisions come down to aesthetics).

[Adam Freeman]

Originally Posted by Pat Fairbank

I wouldn't say that weight is the top factor in 254's choice of using a cantilevered drive year after year. It probably only comes in fourth after ease of maintenance, robustness, and aesthetics (you wouldn't believe how many design decisions come down to aesthetics).

I can't say for sure, but my notes say that I weighed our competition chassis (0.06" sheet AL) at 8lbs, before we started assembling any of the components on to it.

Weight is a factor in our decision to use this type of drivetrain...but, it's probably #3 on the list. #1 would be resources available (in-shop waterjet) and ease of construction (no welding) and #2 would be robustness.

Our design is a nightmare for ease of maintenance. Changing wheels or drivetrain components is not something we could do easily/quickly.

[Chris is me]

I think the main reason anyone does any type of drivetrain the way they do is because they have access to resources that make their design optimal. A sheet metal chassis can be done excellently. So can a welded tube chassis. Rather than sketch an exact copy of the best, drive design should play to the resources your team has. What use is a drive that's 5 pounds lighter of it takes you 2 weeks longer to build it?

We use a Poof inspired but *highly* derivative drivetrain that plays into our resources and goes together relatively quickly. It's light enough. It's definitely strong enough. Probably overbuilt. And it works because it uses what we have and what we were able to get in an offseason.

The way the Poofs do it, when you get down to the details of their bearing blocks, custom wheels, etc. takes a lot of resources that not a lot of teams have as readily available as 254 has worked hard to have. Play to your strengths.