West Coast Drive, WCD
 

Hello teams,
Can anyone shed some light on west coast drive? Our team has been reading about it and seeing these types of robot chassis/frames. what are the specifics?
I have been through cd-media, too many "this is not wcd" pics. Is there a white paper or somekind of criteria teams follow?
thanks

Re: West Coast Drive, WCD
 

A "west coast drive" is generally a term referring to a drive similar to 254's drivetrain. IMO these things need to be present for it to be a "West Coast Drive":

• Six / eight wheel drive, with the center wheel dropped
• All wheels cantilevered
• One wheel directly driven, rest chained to that wheel.

Once you have these three things, you have something resembling a "West Coast Drive".

There are many different variations of even this drive, though. Some teams, like 27 and 118, cantilever the wheels on dead axles and tie the wheels together using chain and sprockets bolted to the wheels. Other teams like 254 and 973 use live axles and run their chains on the inside of their drivetrain, cantilevered off the back of the axle.

Tensioning is another system where differences occur. Many teams use sliding bearing blocks that move each wheel in order to tension drive chain. Some teams tension in other ways.

My team's (2791) west coast drive is really different enough that I'm not sure I'd even use the name. We cantilever our wheels on live axles, but we run timing belt instead of chain. Because timing belt does not stretch, we can run systems with basic idlers instead of tensioners and never need to adjust the belting after we get it right. In addition, for added security and to save space, we run the timing belt on the inside of our drive's welded tubing. This results in a very clean and simple drivetrain that has been remarkably reliable for us.

Re: West Coast Drive, WCD
 

The West Coast Drive is the Drivetrain traditionally used by many West Coast Teams including 60, 254 968, 1323 and 1538.

In it's purest form, it's a 6 Wheel Drive with cantilevered wheels (Only supported on the inboard side) that are all driven via live axle (usually hex) from a central transmission. Most WCD's use either 4 or 6 inch wheels to keep weight down and to simplify the transmissions. If done correctly a WCD should be lighter than an equivalent "Standard" drive train.

Here's a picture of a WCD based on Team 221's Super Light Chassis System: http://www.team221.com/upload/594-te...OS_frc1429.JPG

Also here are some good examples:

http://www.chiefdelphi.com/media/photos/27537
http://www.chiefdelphi.com/media/photos/24654
http://www.chiefdelphi.com/media/photos/31597
http://www.chiefdelphi.com/media/photos/30564

Re: West Coast Drive, WCD
 

http://www.chiefdelphi.com/forums/sh...st+Coast+Drive Should help you.

Re: West Coast Drive, WCD
 

west coast drive is a drive-train where the axles are canteleverd (unsupported on one side, like a car. typically 6-8 wheels, but i have seen a team (dont know name or number) that had a 20 wheel west coast drive (roller blade wheels) the reasons for doing this are;

1)weight, there is no frame outside the wheels, so fame weight is drastically less.

2) wider stance. moving the wheels out 1.25-1.5 inches on either side allows for a wider wheelbase, which makes the robot more stable, as well as aids in turning.

3)ease of repair. it is easier to repair a WCD quickly. because the wheels can be taken off without moving the axles. changing tread, or replacing an axle, takes much less time.

Re: West Coast Drive, WCD
 

Thanks guys, this helps a bit.
One thought though, if the wheels are cantilevered and there is no plate on the outer perimeter of the robot would there just be some sort of pegs or standoffs to mount bumpers too? I thought bumpers had to be rigidly mounted to frame/chassis with minimal "openings" or voids behind the plywood.

Thanks again.

Re: West Coast Drive, WCD
 

This year's rule allow for up to 8 inches between "openings". To rectify this on modern robots, it's pretty simple to add brackets to mount bumpers with.

Here's 2791's "west coast" chassis showing our simple bumper mounts.

For what it's worth, I've never been more satisfied with a drive base than this one. Other than the axles, which were made with the wrong aluminium alloy, I've never been more satisfied with a drive base.

Re: West Coast Drive, WCD
 

Here's an early shot of FRC27, Team RUSH, using our Super Light Chassis kit.

FRC 27 on Super Light Chassis

You can clearly see the cantilevered wheels and the bumper standoffs.

Re: West Coast Drive, WCD
 

I think everyone has said it right. ALthough two things, the middle wheel doesn't have to be directly driven, and there can be framing on the outside if desired. Our team uses belts and is not directly driving the middle wheel, and we have a sheet metal plate on the inside and outside of the wheel. This is still west coast I believe right? Unless our drive train isn't considered west coast...

Re: West Coast Drive, WCD
 

For it to be a "True" West Coast Drive, one of the wheels should be direct driven, and the wheels should be cantilevered.

If your drive isn't cantilevered - if it has supports on the outside basically - then it's probably not a WCD. (Unless the support is superficial or for bumper mounting)

Re: West Coast Drive, WCD
 

Not every single six wheel drop center drivetrain is "West Coast".

However, not every non - "West Coast" drive is bad, by any means. If I used sheetmetal instead of welded tube to build robots, I probably wouldn't cantilever the wheels, because it doesn't really save much material weight.

Re: West Coast Drive, WCD
 

As others have stated, West Coast Drive System was created by Glen on Team 60 and has been popularized by FRC 254/968/973/1538 etc...

But the best pics of the system:

http://team254.com/media/photos/2010-frc-build-season

254 does a great job showcasing the WCD.

-RC

Re: West Coast Drive, WCD
 

Maybe that's why my mentor had me write "Midwest Drive" on our post this year http://www.chiefdelphi.com/forums/sh...ghlight=pwnage

And we made the decision to have sheetmetal plates on the inside and outside for strength, because last year our wheels got bent, and then we made plates for IRI last year with great results. http://pwnage.foxvalleyrobotics.com/..._newrobot.html

Re: West Coast Drive, WCD
 

Nick, from what I can see, that looks like a standard drive train to me.

Re: West Coast Drive, WCD
 

That's a great looking and clean chassis! Only thing I don't totally understand is why you go dead axle instead of live with the chain on the opposite side? Not really a critique just wondering what the decision making process was.

Re: West Coast Drive, WCD
 

Hello All!
After following this thread, I was curious about what the advadntages of WCD are, and when is the optimal situations to employ such a system. I am curious because we are about to begin working on offseason training which might entail building various drive chassis and systems to get some offseason design experience. Thanks!

Re: West Coast Drive, WCD
 

The advantages that lead us to a west coast-ish style drive were:
1) ease of maintenance
2) wider track width
3) less weight
4) protected belts

We were already planning on direct driving a wheel no matter what frame style we chose and also leaning heavily towards a live axle system since for us it is easier to fabricate the components so a west coast inspired drive fit in perfectly with what we were already leaning towards.

Re: West Coast Drive, WCD
 

Some of the reasons:

-standard axles. we use chromoly tube to form the dead axles.....simply cut to length. this reduces machining.
-we use AM standard wheels. the plaction variety is cheaper than the performance wheel....so using a dead axle saves us having to add AM hex or key hubs back into the wheel, thus increasing the cost.
-we can service the wheels just as easy as any live axle setup i've seen. when the chain is tensioned properly it slides off the axle with the wheel as part of the assembly...no issues.
-dead axle blocks are slightly easier to manufacture....just ream an undersized hole for the axle. no precise bearing fit.
-chain on the outside of the frame rail doesn't interfere with any assembly on the inside....this makes life easier when we have to add something unplanned inside the perimeter
-we can adjust the rocker by swapping out different end blocks. live axle blocks don't allow this because there isn't enough material to machine away in the vertical direction.
-we used to use custom Dewalt planetary drive transmission....they wouldn't have worked well with a double sprocket on the inside of the chassis rail.

Note that the Super Light Chassis product can be used in either variety. The standard version is "dead" axle, but "live" axle blocks can be dropped into the outer wheel positions.

Re: West Coast Drive, WCD
 

WCD sounds like it has a lot of benefits, but how do you mount a standard gearbox to the rail?

Re: West Coast Drive, WCD
 

Normally if your going to all the trouble of making a custom drivetrain, you'll be making your own gearboxes as well. The only place that currently sells gearboxes integrated for a WCD is Team 221 Robotics.

But 973 Back in 08 used a shifter shifter in a WCD setup:

http://www.chiefdelphi.com/media/photos/31605
http://www.chiefdelphi.com/media/photos/31604
http://www.chiefdelphi.com/media/photos/31603

-RC

Re: West Coast Drive, WCD
 

The one neat thing I loved about our chassis this past season was how easy it was to take the wheels off. Given the fact that we never broke a wheel this season; but after last season and going through three plaction wheels, this one feature definitely caught my eye.

Re: West Coast Drive, WCD
 

48/3193 competed in the 2011 season with our first-ever WCD-style drivetrain, using modified Super Shifters (milled the transmission plates down for ground clearance, drilled mounting holes for the angle brackets that attach gearboxes to the frame). The drivetrain has proven very reliable and resilient (and will therefore now explode at IRI, since I said that). See attachments, and also http://www.chiefdelphi.com/media/photos/36507.

The white delrin cam tensioners in the attached pics proved bulletproof - I don't believe they came loose once. There is also a thin strip of white delrin sheet velcroed to the belly pan underneath each chain that adds additional tension.

Re: West Coast Drive, WCD
 

I'm not sure chain tensioners are even necessary.
In the past several years prior to this year, we slotted our frame so that we could tighten our chains via movement of the bearing blocks. However, after doing 4 tournaments plus per season, we've never had to tighten it even once.

This season, we didnt even bother to slot it at all. Hasn't failed yet.:rolleyes:

Re: West Coast Drive, WCD
 

I tend to agree that you could get away without tensioners on your comp bot.

That said, our practice bot saw 2 hours of practice 4-5 days a week throughout the season. We saw significant sprocket wear and as a result had to make slight chain tension adjustments routinely.

We also have a special purpose demonstration robot that sees parade duty and special event duty.....we'd be in serious trouble without the tensioners.

Having the tensioners adds a piece of mind. Not to mention the ability to quickly change wheel sizes, which has happened more than once over the years.

:yikes:

Re: West Coast Drive, WCD
 

It would seem that they aren't if you can space the axles an even number of chain links apart.

@ajlapp: How has wheel size affected your chain runs? Is there a sprocket reduction you've had to change?

Re: West Coast Drive, WCD
 

It doesn't have to affect your chain run...but a wheel diameter change often coincides with a wheelbase adjustment. Especially your outer most wheels.

This is the idea behind the tensioning system in both Universal Chassis and Super Light Chassis. The slot in the chassis rail supports 4, 6 or 8" wheels. You just need to adjust the length of the tensioning bolt.

Re: West Coast Drive, WCD
 

If we were to use sliding bearing blocks to tension the chain what kind of bearings would we use. And where would we get the blocks if we purchased them?

Re: West Coast Drive, WCD
 

We use standard 1/2" ID open ball bearings in all of our chassis products.

You can see the blocks used in our Universal Chassis here.. They support two 1/2" bearings and fit inside a 1.25" wide rail.

You can see the rest of our chassis systems at www.221robotics.com

:o

Re: West Coast Drive, WCD
 

In a live axle setup like team 254's they use a cam tensioner to slide their bearing blocks to tighten the chain.

cam tensioner-


http://team254.com/media/photos/imag...e=orig&id=3124

Can such a tensioner be purchased somewhere? or do we have to machine them ourselves?

Re: West Coast Drive, WCD
 

No off-the-shelf cam tensioners of this type exist to my knowledge....

We use bolt style tensioners on our systems.

Both designs have their individual merits.

Re: West Coast Drive, WCD
 

Is 1/16" thick enough for the aluminum frame or should 1/8" thick tubing be used? Would it be a problem to use flanged bearings in such a thin tube?

Re: West Coast Drive, WCD
 

How difficult is it to create a WCD? By the looks of it, it can be easily made from parts from the KoP.

Re: West Coast Drive, WCD
 

To make a WCD you would want to make the frame out of 2x1x1/8" Tubing. Bearing blocks can be made in house with a milling machine and a drill press. Hex shafts and hex bearing can be bought off AndyMark and you can use pretty much any Gearbox that you choose.

Anyone can add to this list.

Re: West Coast Drive, WCD
 

Revival of a long dead post yet I have one question that does not seem to be answered.

The dropped center axle. I can see how that helps with turning since the robot can rock back and forth depending on direction yet I fail to see how only have four of the six tires actually pushing is beneficial if you get in a pushing match?

Thanks in advance

Cheers

Re: West Coast Drive, WCD
 

In the big picture traction (and pushing power) is not dependent on surface area in touch with the ground.

As you add more wheels, each wheel carries less weight, and the traction from that wheel decreases. Adding a million wheels to the robot won't make it super high traction.

If you have 4 wheels, each being pushed into the ground with 30 pounds, you should have the same traction as 6 wheels each being pushed into the ground with 20 pounds.

All that said, the interaction between tread and carpet isn't doesn't work with an ideal model of friction. Increasing surface area in contact with the ground does actually increase traction, but only by a very small amount.

Re: West Coast Drive, WCD
 

The other two wheels may actually be contacting the ground. This depends largely on how much drop you've put into the system, but you may get some extra push out of them.


The other factor is that (in an ideal world) you get the same, or nearly the same force out of four wheels pushing as you would with six. The reason is that the normal force is distributed over fewer points, thus the portion of the normal force on any given point is greater, thus roughly balancing out the loss of two wheels.

Re: West Coast Drive, WCD
 

This statement should carry a huge asterisk.

While it is very true that simplifying friction as F=(mu)*m*g does mean that friction does not depend on the surface area, this is not really the case. In reality, tread digs into the surface of the carpet, so in addition to the (mu)mg friction, you're going to see some additional component that's proportional to surface area. The simple (mu)mg model was true in years like 2009, or would be true if we played on smooth surfaces or with smooth wheels, but unfortunately (or fortunately, in the case of 2009), that's not the case. There's a reason why no team plays with 1/4" wide wheels, and some teams make their wheels 2" wide or wider.

By the way, this question "does surface area effect friction?" used to be an absolutely huge topic of debate in the olden days of CD. I believe Paul Copioli (and many of the greats) have some good posts on the subject. So if you're interested in a more full story, search away.