West Coast Drive is Illegal?

According to R2:

“The ROBOT must have a FRAME PERIMETER, contained within the BUMPER ZONE, that is
comprised of fixed, non-articulated structural elements of the ROBOT. Minor protrusions no greater
than ¼ in. such as bolt heads, fastener ends, and rivets are not considered part of the FRAME
PERIMETER.”

I would interpret wheels as articulated elements, therefore WCD designs are illegal this year. Or am I missing something? :confused:

Please read the blue box of the rule:

To determine the FRAME PERIMETER, wrap a piece of string around the ROBOT at the BUMPER ZONE described in R22. The string describes this polygon.

The frame perimeter is composed by non articulating structural elements but is defined by wrapping a string around the robot at the bumper zone. As such, a west coast drive that is under the max frame perimeter while determined by this method would be legal.

Articulation implies a flexible joint. West coat drive wheels are on a fixed frame and do not move with respect to the frame.

In any case, the restriction is regarding the frame, and not parts.

Bumper rules are much like 2014. West coast drives then as now need structure outside the wheels to define the frame perimeter and support the bumpers. The west coast drive “frame” is well inside the frame perimeter for a legal robot

All this said though you can still make an illegal west coast drive

You can. You can also make a legal one.

The relevant requirement is R26.

R26 BUMPERS must be supported by the structure/frame of the ROBOT (see Figure 4-9). To be
considered supported, a minimum of ½ in. at each end of the BUMPER must be backed by the
FRAME PERMIETER. Additionally, any gap between the backing material and the frame:
A. must not be greater than ¼” deep, or
B. not more than 8 in. wide

A west coast drive with protrusions at the corners that stick out past the wheels will provide a nonarticulated structural element. So long as bumpers are supported in accordance with the rules (likely requiring multiple protrusions no more than 8" apart) then it will be legal. Note that R21G is also relevant to this situation:

G. must attach to the FRAME PERIMETER of the ROBOT with a rigid fastening system to form
a tight, robust connection to the main structure/frame (e.g. not attached with hook-and-loop,
tape, or tie-wraps). The attachment system must be designed to withstand vigorous game
play. All removable fasteners (e.g. bolts, locking pins, pip-pins, etc.) will be considered part of
the BUMPERS.

A robot inspector will be looking for a robust support structure that meets the requirements and is capable of withstanding the impacts of the game environment. So long as I can run a string at the bumper zone (between 4in and 12 in above the floor) and only touch nonarticulated structural elements then it should be legal.

Here are two examples of frame perimeters of a west coast style frame. The not legal one has a wheel defining the frame perimeter. The wheel moves relative to the frame so is not legal. To be legal the bumper would have to be attached to and be supported by the wheel. Not useful. On the legal frame, the upper frame defines the frame perimeter because it is in the bumper zone. If was not there the robot would still be legal because the front rail would define the frame perimeter, not the wheel. Bumper support rules would still have to be met.

While probably not as heavy defense year as beach ball bot, Good practice says you want to keep the bumpers from being driven into the wheels.







What if you are using 8" wheels? You can no longer satisfy R26 which states that you must have perimeter frame support for bumpers with gaps not exceeding 8 inches. do you have to have an outer frame member that covers the wheels from end-to-end?

You can have 11-1/4" wheels and still have a 3/4" wide continuous frame support/member fully supporting the bumpers with no gaps… :wink:

You could do what 118 did in 2014. Take a look at post 27 on this thread.
http://www.chiefdelphi.com/forums/showthread.php?postid=1515197

  • Everett

Hmmmm… not the kind of engineering I want to teach my team. I get how one can circumvent rules to remain ‘legal’ however that doesn’t necessarily make it sound engineering. I was hoping for both a legal way AND a way that follows the spirit of the rule which, I believe, is for the frame perimeter to support the plywood bumper base sufficiently so that it doesn’t crack during collisions.

If your frame meets the specifications of the end customer, there’s no circumvention. Whether that’s enough for your bumpers to have a safe home is a separate topic, but WCD with bumpers is a solved problem (generally, by adding a bar across the sides in some compliant manner to define the frame perimeter and provide the bumpers a good home).

What data do you have that it will necessarily crack during collisions? That it isnt sound engineering?
We have built them similarly to 118 in the past, drive the heck out of our robot, collisions and all, with no cracks in our plywood bumpers ever.
I’d say it was pretty sound.

To each its own.

Also, the rule (R21) says, “plywood or solid, robust wood”. If you’re worried about breaking the wood backing you could use something like, oh say, solid ash. The “structural element” supporting the bumpers doesn’t need to be nearly as robust if you manifest that strength and stiffness in the bumpers. Many teams actually rely on the bumpers to enhance the strength of their overall robot, because there is effectively free weight to be had in the bumpers which could be and has been played off as “attachment features”

It does make me wonder how many teams will pursue a ‘west coast drive’ this year. I know cantilevered wheels and the rougher defenses make me nervous, but I’ve never been terribly bold.

So, who’s going for it?

So far, we are.

The best evidence we have that it will survive is our Aerial Assist (Assault?) robot. Many photos taken of it while shooting show it a couple inches off the floor. When it landed it did so on Colson wheels a lot harder than what we’re using this year. The drive train held up fine for 3 districts, the district championship, world champs, and 3 off-season events.

The front frame rail, on the other hand … thanks 558 :slight_smile:

319 is. Pneumatic wheels will certainly help with impacts on the defenses.

When AndyMark feels good about essentially this, I’m feeling good about this.

I’d hope that most teams who have considered it an option have a WCD frame in their back pocket that they could slap together in a week parallel with field elements and see what happens. I wouldn’t consider the drivetrain a system you want to cross your fingers on.