We used wood for the prototype and made it a 30x30 square to show to ourselves the max area we can have. On our prototype, the wheels were a few inches outside of the actual frame. However, we noticed per Rule R4 that nothing can extend outside the frame perimeter at the start of the match.
I saw on another post that the wheels would constitute the edge of the frame perimeter. Is this the case?
Any part of your robot, including the wheels, affects the frame perimeter… If your frame itself is 30x30, and your wheels stick out more, then you are too big… Also keep in mind that the frame perimeter must be non-articulated, and that bumpers mount to the frame perimeter, not inside of it.
It sounds like your best bet to fix the issue is going to be to move the wheels inwards.
Yep. That’s the case. And, if those wheels are outside the frame on the prototype… looks like you need to lose a couple of inches.
Here’s how the Frame Perimeter works. I’m going to differentiate it from the Robot Frame.
Robot Frame: In this case, your 30x30 square. This is the structural material of the robot in the Bumper Zone.
Frame Perimeter: Wrap a string or stretch some surgical tubing around the Robot Frame and anything you have sticking off of it (like wheels), and pull tight. That will show the Frame Perimeter. THIS is the part that the bumpers will attach to, the inspectors will measure, and all the other stuff that goes on with the Frame Perimeter.
It’s a good thing you asked now… instead of next week.
Imagine you wrapped a string around the widest section of your robot. That is your frame perimeter. It sounds like your widest section includes the wheels, so at those points, they would define the frame perimeter.
It sounds like your actual frame perimeter now exceeds the 120" perimeter limit.
To clarify:
In starting config… robot extensions(up to 15" beyond) beyond actual frame perimeter polygon are in their starting config (within the polygon and up to 54" high)
Now with robot in starting config wrap a string around** the widest portion in bumper zone **(4"-12") and that will define the perimeter of the bot.
Rule references:
“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.”
“If a ROBOT is designed as intended and each side is pushed up
against a vertical wall (in STARTING CONFIGURATION and with
BUMPERS removed),** only the FRAME PERIMETER (or minor
protrusions) will be in contact with the wall**”
As a side note any corners defined by the polygon then need 8" bumper sides and any straight or circular sides under 8" need a bumper.
Since our team chose to use a “west coast drive system” this year, I would like to ask anyone, what advantage does it really have? The robot still has to have a outer perimeter frame structure for bumper attachments. Why not incorporate that into added support for the wheel axial instead of the cantilevered design? If the robot didn’t have to have bumpers, I could see the advantage.
At least the times my team has done WCD, we’ve been able to do it with direct drive from the gearbox, eliminating the need for chains or belts. Then again, we’re doing direct drive this year, but have both ends of the shaft supported (i imagine with the defenses anyone without both ends supported may run into issues!).
The benefit of not needing that outer support, regardless of how you power the wheels, is not needing to get everything perfectly aligned. You don’t have to worry about the holes lining up for your shaft at all - I know that was a significant focus for us our first week when we made this year’s robot.
Have you ever tried turning your robot with 3 pneumatic wheels on a side? Pneumatic wheels (and traction wheels for that matter) don’t slide well on carpet. WCD drops the center wheel a bit so the majority of normal force is pivoting on the center wheels.
As does practically every other 6-wheel drive system used in FIRST. Drop center does not equal WCD.
One observation not noted yet that you may or may not be able to address. You want to design your frame so that it is LESS than 120 inches. Things happen, parts don’t fit perfectly or aren’t cut perfectly and so on, and if you design for 30x30, you might find the real world makes it 30.5 x 30.25 and now you are 1.5 inches over the limit. This maybe is less of an issue since we’ve switched to the perimeter limit vs. the 28"x38" that was common before where you had to fit inside a sizing box, but it is still worth designing for ~118.5" max.