• Andrew Lawrence

F4 CADathon Spring 2021

Today marks the beginning of the F4 CADathon. F4 is a group within the FIRST Robotics community that does.....well I'm actually not quite sure what they do anymore, but I do know that over the past few years they've held CADathons, which are basically "hackathons" for CAD, usually in this context based around FRC robot design. I used to run CADathons too, but that's a story for a different day.

The F4 Spring 2021 CADathon began today, and ends a week from now on Sunday, April 25th, so that's ~7 days to design this robot and get all the extra documents made. Really I've got Monday, Tuesday, Wednesday, and a bit of Thursday to design the robot because the rest of today (Sunday night) is gonna be mostly strategy and maybe some sketching, and Thursday evening I'm leaving and probably not gonna have a decent CAD computer with me until I'm back home the following Monday, so it's about 3.5 days of CAD for me. Most people create small teams for the CADathon but I'm gonna run this project solo because I can't think of too many people who have the time / interest in working on this project over the next few days on sudden notice.

Back to the CADathon - the game was released at this link: . If you care to follow along in this blog, it's probably a good idea to read through some of the supplemental information they have there, since I'm probably not gonna go too far in-depth on explaining the game or how it works.

The game itself is pretty interesting, and I think I like it. Still figuring that last part out, but it seems pretty solid so far. The game is called Barrier Breakers, and involves robots collecting and scoring soccer balls one at a time and scoring them into goals at the end of large ramps. The ramps themselves have some interesting features, such as little holes in them where robots can place these game pieces called "Barriers" that look like the baton from the relay races we did in high school PE class with some extra bits hanging down below. I'll put a picture under this to show you what it looks like in the field CAD.

At the center of the ramp is a big polycarb circle that can sense the weight of whatever is put on it. You need two robots on the circle to "activate" it, and when it's activated the soccer balls are worth more points. At the end of the match there are some bars for the robots to lift themselves up on called "pull-up bars" that definitely offer a different kind of lifting challenge than the ones we've previously done in FRC. There are only two bars and they don't seem wide enough to easily fit multiple robots on them each so I think the game creators intended for some partner climb shenanigans.

There's no auto mode so that's all there really is to this game. I'm gonna go read the rules again and sort through how I wanna approach this game and then get back to writing. For now I'll end this here, and start after the page break when I get back.

The best part about Hero Quest...I mean Barrier Breakers is the Barriers, because I do not care about them. I'll get to why in a bit, but here are my initial impressions:

  1. Cycling balls quickly will be important

  2. Being able to shoot the balls from the polycarb circle is important, and also doesn't seem to require much in the way of aiming and precision

  3. Scoring balls when the polycarb circle is "activated" is so much better than scoring when it's not "activated", to the point where waiting a couple seconds for a partner is probably worth the increased cycle time

  4. I feel like a dominant strategy for quals is gonna be having the stronger 2 teams on an alliance bully the weaker team on the alliance into either just sitting on the polycarb circle the whole match so that the other teams can boost points easier without waiting or to limit their travel to the bottom of the ramp and some of the flat part of the middle of the field so that they can speed over to the polycarb circle at a moment's notice when one of the better teams needs them. Not sure how I feel about this but it's something to consider when designing these kinds of games

  5. Barriers are 100000x easier to remove than they are to place. I don't see any point in trying to collect, keep clocked to the right angle, and score a barrier when a small polycarb sheet can just yoink them from the ground once the 10 seconds passes by sliding under them with a little bit of kinetic energy. The hardest part is gonna be figuring out if a barrier has been placed for 10 seconds or longer but that's a detail I don't really care much about right now, which is a shame, since they're kinda half the name of the game and a contributor to a ranking point, but I'd be willing to bet my last donut that if this game were played in real life there's be little to no alliances earning that ranking point since it requires an alliance to score all of their barriers and just descoring one ruins it

  6. Climbing is 100% necessary, and definitely will see partner climbs at higher levels. Unsure if I wanna tackle that, though. Will probably put it as a "nice to have" and revisit it if at some point I find myself done and bored with lots of time left (unlikely). Climb is also second order ranking after RP, and also earns an RP if you get at least 2 bots climbed and 1 parked, so with that barrier RP being nearly impossible I think most of the top half of the bracket of teams is gonna be averaging 2.5 - 3 RP, in which case those tie-breakers are gonna be real important. Gotta #climbeverytime.

  7. Robot should weigh at least 110 lbs for the polycarb circle....shouldn't be a problem.

  8. Realistically I don't see swerve having too much of an advantage here, especially when you wanna drive over the barriers and the cutouts they go into. But also COTS modules make it ez and spinny robot go brrrr

  9. Ball mechanism gonna be taken straight outta 2010, calling it now

Reigning it back in to a more organized set of objectives, I'm gonna use the following as my "Need", "Want", and "Nice to Haves". For those unfamiliar, basically I take every robot action or robot criteria and sort it under "Need", "Want", or "Nice to Have". "Need"s are my highest priority objectives, and accomplishing them takes precedent over everything else. My "Want"s are things I would like to do once I've done all of my Needs. "Nice to Have" is the same as want but one tier lower. The items within each section are numbered but those numbers don't indicate that one is more important than another as long as they're in the same section.


  1. Drive around the field

  2. Drive up the ramp

  3. Be able to fall off ramp without breaking

  4. Collect 1 soccer ball from ground

  5. Collect 1 soccer ball from HP station

  6. Score soccer ball in any of the 3 goals from anywhere on the polycarb circle

  7. Climb on the bars


  1. Descore barriers

  2. Climb on bar taking up minimal space

  3. Score and intake on opposite sides of robot in order to grab center balls first

Nice to Have:

  1. Partner climb

There are a couple things about this game that seem kinda broken but they're slowly getting fixed. No disrespect to the game designers - designing a game is hard and unless you pass it around several groups of people who try and break it it's easy to forget certain things and rules that you mentally just assume, and even then there's always something that gets discovered on kickoff day. There was just a clarification about one of the rules stating that the ball must contact the ramp before launching it so that changes certain things up a bit but it doesn't hurt things too much. I've started my own hashtag for my primary design strategy, #TeamStopDropandGoal, basically implying I'm gonna stop on the polycarb circle (where you enable the ball bonus), drop the ball so that it's touching the ramp, and then launch the ball into the goal. Sure it's dumb but I wanna see if it catches on.

I kinda have a feel for what this robot is gonna be - prolly gonna grab the ball and pop it up into the bot and hold it there until I get to the polycarb circle thing, drop it into a column with no bottom so that it touches the ramp, and then kick it out the back a la 2010 bots, which I'm guessing is how they're imaging it. With all the motor freedom and power these days my kicker is just gonna be some position and velocity-controlled spinning arm. Will prolly have a hopper that allows human player station intake, and then the climber can be a variety of things depending on whether I'm feeling like doing a buddy climb. Tbh I'd rather just try and take up minimal space on the bar and climb next to a partner on the same bar. Less effort, will probably do that. Kinda digging the 148 2010 climb just because it shows the underside of the bot and I'm 100% putting style points on having something funny on the bottom of the bot. Yeah I think I'll go with that, buddy climb is too much effort for the time I've got.

I hate being pragmatic but I'm probably gonna have to go with a 6wd for this, just to make sure I can drive over those barriers and so that I can hop up onto the ramp from the side passageway leading to the human player station and so that if I fall off the ramp I don't break my drivetrain. Wish I could go swerve but I just don't think it's the play here.

I think that's all I'm gonna say for today. May get a bit into sketch work if I'm feeling like it. It's 10:39pm and I don't need to be up super early tomorrow so I've got some time, but also have some things I wanna do before bed tonight. Either way I'll update this later once I have more progress made.

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