California Drive
 

In a California or West Coast drive system, how much lower should the middle two wheels be relative to the two in the front and the two in the back? What are the pros and cons of using California vs. Tank?

Re: California Drive
 

Never heard it called "California Drive" but considering your non-US location, it certainly makes sense as a name.

The "drop" part of a West Coast style drivetrain is actually common to most high traction tank drives, six or eight wheel. The center wheel or pair of wheels is lowered a small amount (between 3/32" and 3/16") to aid in turning while maintaining high traction.

Re: California Drive
 

Just to add onto what Chris said, drop center 6WD's and 8WD's don't always have to be 'West Coast Drives' but the numbers stay true. Drop center six and eight wheel drives are extremely common - and very effective - using about any build method.

If you do a search on West Coast Drives or drop center drive trains you'll find all the info you could ever want and then some.

Re: California Drive
 

Thanks a lot. I have been reading about it, and I am wondering what is a live axle and what is a dead axle?

Re: California Drive
 

Using standard tank drive, where all wheels are the same height, leads to trouble turning. Picture your robot from the top. Now draw two circles representing the direction you want to turn - one will hit the middle of the left side of the drive train, the other will hit the middle of the right. As the robot turns, you'll realize that the wheels have to move sideways (called scrub). This motion is high friction, and reduces your ability to turn quickly or sharply. See the attached example for details.

Now, change this to a West Coast drive train with 3 wheels and the center dropped lower than the others. If you imagine adding a center wheel to the tank example, it now rests entirely on the circle it's traveling on. That means it can travel along the circle without any scrub*. By dropping the center wheel, you can essentially pick up the outer wheels. If your center of gravity is balanced over your center wheels, you'll probably see the robot rock back and forth on it a little as it turns - that's the small amount of friction when the outer wheels hit the ground causing them to pop back up.

If your center of gravity is NOT balanced over the middle wheels, then two of your wheels (either the front or the back two) will essentially be off the ground the entire time - giving you a standard tank drive between the middle wheels and the other two outer wheels. The advantage here is the distance between those 4 wheels is much shorter - in effect, they are closer to the ideal spot for turning, giving you less scrub. Having those two wheels off the ground all the time isn't a bad thing - there are still situations where they'll be used, like when you hit another robot, or hit an uneven surface of the field (like around the towers this year).


I've seen high traction tank drive robots that couldn't turn. West Coast robots can easily spin in place, giving you a turning radius of 0. I've also seen normal tank drive robots that do just fine... but they do require more power to turn than West Coast systems, power that can often be used elsewhere on the robot.


* In an idealized example where the contact surface area between wheel and floor are points. In reality, it's more of a rectangle and you have a small amount of scrub from one side of the rectangle to the other... but it's really not worth considering.

Re: California Drive
 

A live axle has the axle rotating and used to drive the wheel. A dead axle is where any rotation of the axle is inadvertent; it's your standard chain-sprocket-wheel setup.

Re: California Drive
 

Just to add some clarification on terminology to prevent confusion:

'West Coast Drive' is a term used to describe the type of drive train pioneered by 60 and 254 in the early 2000's (2004, if memory serves me). It's distinguishing features are rectangular tube construction, live axle setup and cantilevered wheels. Almost all WCD's have a dropped center to aid in turning (only notable exception was 2009 - the lower COF between the wheels and floor negated the need for a dropped center in most applications).

That being said, a dropped center drive train isn't always a WCD. Referring to all dropped center drives as WCD may lead to some confusion.

Also, on the same line of thought, 'Tank Drive' really refers to a type of steering and not a specific type of drive train. Technically, 95% or more of the Robots in FRC are Tank Drive, meaning that they don't have any sort of active steering - the two most common types of live steering in FRC are Car Style Steering (Front and/or rear wheels mimic those on a car) and Swerve Drive style steering - so referring to a drive as a tank drive isn't really all that specific. When discussing drive trains it helps to refer to them by wheel configuration since it reflects the performance of the drive much better, for instance, 4WD Tank, is very specific and easy to understand and visualize - anyone familiar with basic drive trains should be able to predict the performance of the drive if they're also given the wheel type.

Re: California Drive
 

I want to say that it was even earlier. I remember seeing it before the '04 season; I believe it was the '03 SCRRF Fall Workshops. 60 used 4WD in '03; not sure if 254 used 4WD or 6WD.

Competition debut was in 2004, when the aforementioned teams built identical robots.

Re: California Drive
 

Team 60 used the cantilevered output shaft/wheel design for many years prior to the 254/60 collaboration. I would argue that those designs were the foundation of today's “West Coast Drive." The addition of six/eight wheels and a lowered center wheel/wheels was the next obvious iteration. The elegance and simplicity of the design, however, was something that had been done by team 60 for many years before the prototype 6WD drive train that was used at Cal Games in the Fall of 2003 and the collaboration between 254 and 60 that occured in 2004 and brought about the now well known 6WD West Coast Drive..

Re: California Drive
 

To elaborate.

Live axle is where the axle is suspended in bearings and the sprocket and wheel are rigidly attached to it (direct drive is also a live axle design using the gearbox shaft as an axle)

Dead axle is where the axle is any rod (in some cases just a standard bolt from a hardware store) and the wheel is on bearings with a sprocket bolted to it.

Another note, 6WD is often much better than 4WD especially in a drop center configuration because it takes an incredible amount of torque to rotate a 4WD system due to the long wheel base, whereas 6WD with a drop center configuration has an effectively shorter wheelbase.

Re: California Drive
 

A force calculator (and, for those interested in the physics, a complete explanation with the equations) can be found here.

Re: California Drive
 

Just by seeing the name of this thread, I want to create a parody of Katy Perry's California Girls. Just imagine it: Cal-i-fornia drive, it's so incredible! No outer frame, live axel setup.

DSK, if you're listening, and have a female vocalist, PLEASE make this song!

Re: California Drive
 

I'd rather have it go along to Tupac's *California Love....



*-(real music)

Re: California Drive
 

I will never be able to view West Coast Drive the same way ever again.

Re: California Drive
 

Nicely done!

Re: California Drive
 

Currently my team builds robots with a 6 wheel drivetrain (pneumatic or AM rubber wheels + omnis), and we just completed our 3rd season. This past season we built our own chassis (as opposed to a kitbot) and housed the wheels in 1" x 3" tubing on one side, and 1/8"plate on the other, and drove 8" pneumatic wheels using sprockets and chain. But, with our side plates taken off, our robot was stanced, and all the wheels were angled. We have accurately drill pressed all our holes, and house the shafts of the wheels through both faces of the tube. Is there a different means to go about constructing a West Coast Drive? How would you prevent your wheels from angling under load?

Thanks in advance,
Xifilzer:cool:

Re: California Drive
 

Might be a dumb question, but are there bearings in BOTH faces of the box tubing? How much space is between the outside of the the box tubing and the wheel?

Re: California Drive
 

How did you drill the holes? A drill press does not have the same ability to drill straight like a mill. I would suggest drilling the first wall, then use a transfer punch to get the second wall in the same location. For anything over 1/4" diameter, start with the hole in the first wall being the largest size transfer punch available, transfer it, then drill the larger hole.

Re: California Drive
 

Do photos of the original still exist?

Re: California Drive
 

Sorry a correction to my original post, we used pillow blocks mounted to the underside of 1x3 tubing instead of running the shaft through the tube.

http://www.mcmaster.com/#5913k61/=1285fnp


Looking from an aerial perspective, going from the outer side of the robot inward, this was our setup:

shaft collar, flange bearing in a 1/8"side plate, two 1/8" thrust washers, 8"pneumatic wheel bolted to a keyhub, a sprocket for 25 chain, two thrust washers, pillow block, shaft collar (for spacing), a sprocket for 35 chain, shaft collar.

This sums up to around 3.25" between the pillow block and sideplate, and 1.5" from the pillow block to the tip of the shaft on the inside. I'll try and take a picture tomorrow.

Thinking about it more, i think the pillow block may have been the source of our problems, since it allowed the shaft to pivot, instead of binding in place had we simply gone straight through the tube (with bearings XD).