Advantages/Disadvantages of West Coast Drive

[jfox100]

Hello Mentors/Teams/Students. I'm hoping to learn more about the advantages and pitfalls for a West Coast Drive type of chassis/drive train compared to the traditional drive train. Which of you have recently transitioned from traditional drive train to WCD? Please share your experience.. the good, the bad and the ugly!

What are unique design challenges? Maintenance issues? Challenges with buying WCD parts during the rush of build season? Cost? Reliability? Since we dont yet know what the 2017 game: is WCD drive better for certain playing field surfaces but perhaps not-so-good for other surfaces? Discuss some of the varoius versions of WCD.

Anxious to hear your thoughts!

Thanks

Jim

[Isonine]

What would be your definition of a traditional drivetrain? I thought that WCD was the traditional drivetrain...

[SenorZ]

Originally Posted by Isonine

What would be your definition of a traditional drivetrain? I thought that WCD was the traditional drivetrain...

Maybe 6-wheel drop-center KoP drive is traditional?

[D.Allred]

Originally Posted by jfox100

Hello Mentors/Teams/Students. I'm hoping to learn more about the advantages and pitfalls for a West Coast Drive type of chassis/drive train compared to the traditional drive train. Which of you have recently transitioned from traditional drive train to WCD? Please share your experience.. the good, the bad and the ugly!

What are unique design challenges? Maintenance issues? Challenges with buying WCD parts during the rush of build season? Cost? Reliability? Since we dont yet know what the 2017 game: is WCD drive better for certain playing field surfaces but perhaps not-so-good for other surfaces? Discuss some of the varoius versions of WCD.

Anxious to hear your thoughts!

Thanks

Jim

First and foremost for me, WCD is a tube and gusset construction technique that is handy for making the full frame. VersaFrame as a system makes it simple without needing complex tooling.

Making bearing blocks used to be the toughest part for us. Again VersaFrame COTS parts have fixed that.

Mounting the gearboxes is the next challenge. There are COTS solutions for some of the drive train gearboxes. We have a milling machine to make custom mounting plates for any gearbox we use.

Design challenges: You can quickly design your base frame shape to fit the scoring section configuration. Cut and rivet the tubes... (to borrow a phrase) Boom. Done.

Maintenance: Wheels are easy to change if your tread wears out.

Buying parts: We commit to WCD style before seeing the game and buy tubing, gussets, and bearing mounts before the season starts. We've pondered swerve drive but haven't yet committed the resources to develop one.

Surface: I usually consider WCD a 6 or 8 wheel skid steer system. There are several variations on this theme. However, the wheels don't care which construction technique you use. Skid steer driving performance comes down to designing for scrub / traction forces, good construction, good control, and good weight distribution.

David

[connor.worley]

Pros:

1. Reliability. If you have a 6-wheel WCD, you drive the center wheels directly off the output shafts of your transmissions. Even if every chain to the outer wheels fail, you should still be able to drive your center wheels.
2. Maintainability. Because the wheels in a WCD are cantilevered, removing a wheel is as easy as removing a snap ring. No need to take apart your frame to get at a wheel.
3. Simplicity. No outlandish parts or software required to use.
4. Drivability. Driving a good 6-wheel WCD is incredibly smooth, thanks to the dropped center wheel.

[mman1506]

I've found a good WCD to be far more rigid than other drivetrains. This gives it better, more consistent driving characteristics and allows you to run less drop.

[GeeTwo]

While my team has never built what I would consider a true WC drive train, we have incorporated at least one element of WCD in all but our rookie year. First of all, my understanding of the definition of WC vs traditional skid steer:

Common elements:

• Both traditional and WC normally have 6 simple (non-roller) wheels with a drop center, though variants of each with additional wheels and/or omni on the corners exist.
• There is no notable difference in software required; you have two banks of motors, one on either side. Either may have one, two, three, (or occasionally more) motors per side.
• Either can be used with a single speed or shifting gearbox.
• [Edit]Any articulated drive train does not properly fit either category, though an articulated gearbox may be extended from either design.

Distinctions:

• West coast drives feature cantilevered drive shafts; traditional has a bearing on either side of the wheel.
• West coast drives provide direct drive to at least one wheel on either side, usually (if not always) the one closest to the center of gravity of the robot; traditional usually had chain or belt to all wheels, though direct drive is now common in non-WC drive trains, including the 2014-2016 KoP chassis.
• WCD usually employs tube (though occasionally channel with the opening on top or bottom) in order to support the cantilever; traditional usually employs channel with the opening inboard or outboard, or vertical plate, most commonly bent inboard or outboard at the top and/or bottom.

Note that there are also drives which incorporate these features mix-and-match. The common example which comes to mind first is the (recently discontinued?) Andy Mark nano tube chassis. It has direct drive on four cantilevered axles, but these are the two corners, NOT the one usually nearest the CoG. Our second and third year drive trains also featured direct-drive wheels on cantilevered axes, but for similar reasons were clearly not WC drive trains [Edit: Our 2013 robot only had two driven wheels and two idle omnis, whereas our 2014 robot had mecanum drive; we learned a lot from these mistakes].

Advantages of WC:

• Easier to change wheels by removing a single lug screw, snap ring, shaft collar, or clip.
• Reliability despite failure of chain, as the axle nearest the CoG is direct driven (though this feature is now on some newer "traditional" drive trains)
• Track width can be a greater proportion of robot width, as there is no need for an outer plate/channel (other than to meet bumper support rules)

Advantages of traditional skid steer:

• You are much less likely to bend an axle. (I never saw an FRC axle with a bearing on both sides of the wheel bent until STRONGHOLD.)
• Requires less precision in machining (though this can now be mitigated with dollars by buying a COTS WC chassis kit).
• [in recent years] Available through the KoP chassis program at little or no dollar cost, as a kit which can be assembled in a remarkably small number of worker hours.

[ToddF]

Well, let me tell you all about our experiences at 2363!

Quick Build Drive Train Concept

Triple Helix West Coast Drive Trains

[RoboChair]

Here is my only question for you, has 254 ever not done a WCD?

I'd bet $100 that 254 does a WCD next year, and another $100 that that is what we settle on as well.

It is quick, easy, and robust. Most of the design drawbacks for a particular game can be designed around with WCD without much effort, this year it was wheel spacing.

[EricH]

Originally Posted by RoboChair

Here is my only question for you, has 254 ever not done a WCD?

As a matter of fact, yes, I believe they have.

BEFORE the WCD was developed (2002-2004 timeframe), of course, but seeing as 254 is one of the developers of the WCD...

The WCD was officially unleashed in late 2003/2004 season, the result of a collaboration between 254 and 60. There are photos in CD-Media from 2001 showing both teams running elements of what is now known as a WCD, though 254 for some reason ran their chains outside their frame from a central gearbox that year (either one of which would, under the traditional definition, disqualify the drive as being WCD), and neither had more than 4 wheels on the ground (also disqualifying as a WCD under the traditional definition, which requires 6 (or more, depending just how traditional you want to get)).

So, more detailed answer: yes, but it's been quite a while and they were developing WCD when they did.


And now back to your regularly-scheduled discussion of the pros and cons of the WCD.

[Andrew Schreiber]

Originally Posted by RoboChair

Here is my only question for you, has 254 ever not done a WCD?

I'd bet $100 that 254 does a WCD next year, and another $100 that that is what we settle on as well.

It is quick, easy, and robust. Most of the design drawbacks for a particular game can be designed around with WCD without much effort, this year it was wheel spacing.

Here is my only question for you, why does "254 does it" make something a good design decision for a team without 254's resources?

[dirtbikerxz]

Originally Posted by Andrew Schreiber

Here is my only question for you, why does "254 does it" make something a good design decision for a team without 254's resources?

Because it does not take many resources to do a WCD, and by 254 doing it, they are proving that it is a good solution. Which means that is a good solution for not much resources. (Man my grammar was bad in that sentence.)

We are a low resource team, like really low resource, yet we do WCD with success.

[Billfred]

Originally Posted by Andrew Schreiber

Here is my only question for you, why does "254 does it" make something a good design decision for a team without 254's resources?

Originally Posted by dirtbikerxz

Because it does not take many resources to do a WCD, and by 254 doing it, they are proving that it is a good solution. Which means that is a good solution for not much resources. (Man my grammar was bad in that sentence.)

I think our definitions of "not many resources" differ. I've been on teams where the build budget was maybe $1,000, the machining resources stopped at that of a disused wood shop, and the mentor expertise didn't really include machining. I would wager my dollars to your donuts that that situation describes More Than A Couple Teams. I would also say those teams are less likely to have an inspiring season if they reached for WCD without more of a grasp of the situation than "254 does it and does well".

[RoboChair]

Originally Posted by Billfred

I think our definitions of "not many resources" differ. I've been on teams where the build budget was maybe $1,000, the machining resources stopped at that of a disused wood shop, and the mentor expertise didn't really include machining. I would wager my dollars to your donuts that that situation describes More Than A Couple Teams. I would also say those teams are less likely to have an inspiring season if they reached for WCD without more of a grasp of the situation than "254 does it and does well".

You can make a WCD these days with a hack saw, a hand drill, and some aluminum tube. The gear box and bearing block options from Vex make producing a WCD a trivial task these days as long as you can drill some straight holes. This is how 5458 made their drivetrain this last season. You can make a 6 wheel drive for around $450 depending on your choice of gearboxes(~$150 and up) and motors.

[Andrew Schreiber]

Originally Posted by dirtbikerxz

Because it does not take many resources to do a WCD, and by 254 doing it, they are proving that it is a good solution. Which means that is a good solution for not much resources. (Man my grammar was bad in that sentence.)

Then that would have been a better argument than "254 does it".

I'd disagree with that argument since it's not a function of raw number of resources but more a function of what type of resources and the allocation of them. For teams with tight budgets and resources using the KoP or VP DIAD may be better uses of tight resources. I don't see how 254-copy describes advantages or disadvantages for the purposes of resource allocation.