In-depth Strategy Analysis for your perusal - Team 2374

[SirTasty]

Introduction
Greetings, Chief Delphi!

I wrote this paper for the benefit of my team, but I think there are some insights here that I would like to share with the rest of the CD community, so that I can get feedback and maybe help improve another team's robot. Essentially it outlines the results of our initial brainstorming process: First, it lists and supports the insights we made into the nature of the game, then examines the priorities we decided on based on our beliefs about the game will be played, and finally it explains the design decisions we have made to date and how they further our priorities.

I am a senior, and currently the systems engineering and design lead for team 2374, the CrusaderBots of Jesuit High School, in Portland, OR. This is just our fourth year in the business and we've still got a lot to learn, but I feel like, after four years of watching how the strategy works in this competition, I have a good handle on what makes a good robot. I'd like to hear from some more experienced team members (maybe some long-time mentors?)about how their experience does/does not fall in line with my points here.

Sorry for the wall of text, but there is no tl;dr here. I think reading the whole thing will be worth your time. Cheers and good luck!

Underlying Principles
Immediately after kickoff, we agreed on some basic premises around which to build our strategy:

1. Focusing on defense is an INFERIOR strategy. I’m surprised at the number of people who favor defense in the “offense vs. defense” threads on Chief Delphi. Historically, scores at Einstein are always very high, and usually winning alliances at regionals have three strong offensive robots; strong defensive robots are not often chosen, unless they bring some truly unique quality to the table-for instance, during overdrive we were selected for an alliance that went to the finals and had the ability to remove balls from the overpass, which allowed us to swing the game with some clutch late-game plays. This year, the penalties for encroachment on the alliance zone and lanes will be substantial, and the pinning rules are very strict, and defensive teams can count on being penalized for these regularly. The ranking rules this year, like last year, have also been designed to be unfriendly to defensive teams: while WL record is the primary determiner of ranking, FIRST has insisted on keeping approximately the same ranking points system to break ties. Last year we had the best defensive robot at our regional, and the more we won, the more we went down in the rankings. The rules have been tweaked, and I expect them to be a little bit less silly this year, but being good at defense will still not help a team’s ranking nearly as much as being good at offense. Lastly, defense is easy. Get in another robot’s way, push it around, pin them to walls, block them from getting into/out of lane, etc. If we fail at offense, we can still play defense and do well.

2. One minibot will not perform significantly better or worse than another. Just like every other team in the world, we had our own stored-energy minibot rocket plans until that pesky <G19> update. Now that that’s gone, we are all limited to the same components, and there’s not a lot of room left for innovation. Put on a good motor, make it as light as possible, and there’s not much else you can do to improve that bot. Because of this:

3. Teams have the greatest opportunity to affect the outcome of the match if they focus on hanging game pieces. If you can’t significantly improve your odds by focusing on your minibot, it’s obviously better to concentrate on something over which you have more influence. Notice that I didn’t say the minibots won’t decide the game; they may. However, you won’t get a lot of mileage out of focusing on them.

4. The Logo Piece game will be won or lost in the top row. Perhaps this is an overstatement, I think the middle row will also have an impact on the game, but the bottom row is not significant. The points scale majorly as the logos move to higher rows. A logo piece on the bottom row is worth only one point; an ubertube on that row only increases that score by one, for a total of two. That same configuration on the top row is worth six points – four more! Add in the fact that a completed logo doubles the value of the row, and you can see that gap widen even more. Three logos and one ubertube in the top row is worth 24 points – in the bottom row, it’s only worth eight.

5. Rapid DEPLOYMENT of the MiniBot is a critical factor in winning the minibot race. This isn’t rocket science. If everyone is the same speed, the one with the head start will win.

Priorities
1. Efficient game piece placement

a. Mechanically easy delivery

b. Ability to deliver reliably in the top row

c. Effective use of the sensor suite for placement

2. Efficient game piece pickup/control

a. From feeder station

b. From ground (optional)

3. Driving power/traction
4. Fast/efficient minibot deployment

a. Effective use of sensor suite to get the robot into deployment position.

b. Mechanically simple minibot delivery system

5. Speed
6. Maneuverability

a. Ability to move into position to score game pieces

b. Ability to move into position to pick up game pieces

c. Ability to move into position to deploy minibot

Efficient Game Piece placement
Mechanically easy delivery: We currently have a number of prototype manipulators being designed to deliver game pieces in the most reliable fashion possible. We are planning to choose one this week, but finals are kind of in the way <.<

Ability to deliver reliably in the top row: We currently plan to use a three-segment continuous elevator system with the manipulator mounted in front. By coincidence, our elevator interface is simple and modular, and will be able to support whatever manipulator we choose.

Effective use of sensor suite for approach and placement: Currently we are exploring the idea of “Autonomous Placement” (AP). The drivers of a robot with AP capability would be able to input some basic data parameters such as which line it is approaching and on which peg to place the game piece. Barring interference from other robots, the robot would then be able to reliably place the game piece without further driver interaction.

Interference from other robots is, of course, likely, so our placement will rarely be fully autonomous, but developing such an advanced sensor suite will be an invaluable resource for our drivers.

Efficient game piece pickup and control
From Feeder Station: Most of our manipulators involve some tricky placement by the feeder. A general theme in several of our manipulators is to place the logo piece on the prong horizontally and then let it fall into the vertical position. This can be a major problem, as some of our manipulators have very small tolerances as to the distance the robot can be from the feeder station to successfully receive a piece; a little too close or too far, and the logo simply falls off. It may be very difficult to reach that “sweet spot,” as the drivers are all the way across the field, and we aren’t certain how effectively our sensor suite can mitigate this risk. The design team should take this problem into careful consideration when choosing our manipulator.

From ground: Some of our manipulators can be adapted to pick up logo pieces from the ground, others cannot. Ground pickup is not a necessary robot feature; there are 36 logo pieces on the field, feeder stations most likely will not run out until late in the match.

Torque/traction
The reasoning behind having a lot of pushing power is that if a robot tries to block us from entering our alliance zone, we can just push them into our alliance zone instead, forcing them to GTFO our receive a penalty. In the process, they must get out of our way. This will also benefit us in the event that our manipulator flops; we will still be able to play solid defense by pushing/pinning other robots.

We opted for a six-wheel drive chassis rather than a mecanum drive because of the simplicity and power of the six-wheel drive model. Additionally, we chose to use plaction wheels on our central and rear wheels, sacrificing some turning effectiveness in favor of extra traction. While having four traction wheels on the ground at the same time will reduce our turning, we feel that the small drive base will mitigate most of the negative effects. If it is too much of a problem, we plan to put regular AndyMark traction wheels on the back instead. We will retain the traditional omni-wheels in the front. With regards to power, it is imperative that our center of gravity be as low as possible, even when lifting, so that we can push defending robots out of the way. A light manipulator is therefore most desirable with respect to this priority.

Fast/efficient minibot deployment
This is going to be majorly dependent on our sensor suite. Priorities are reliability and speed, we should be able to drive up to the tower, deliver the bot, and have it moving with 9.7 seconds remaining. We have been focusing on our logo placement for now, but this week we will give serious thought to our minibot deployment strategy, before we finalize our elevator/manipulator design.

Speed
Most of our design choices are conducive to a high-speed robot, we haven't really needed to devote a lot of attention to this category.

Maneuverability
Ability to move into position to score pieces: Our chassis has made some sacrifices in this area in order to further our progress in other areas. We gave up on a mecanum drive design because of its significant lack of torque and because it would make Zuhair’s job of implementing AP horribly complicated. We also replaced our rear omni wheels with plactions, which will slightly inhibit our turning. Maneuverability is a low priority for our robot because of our “through rather than around” drivetrain policy, but once in the alliance zone we will need to be able to maneuver to place game pieces on the pegs – ideally, AP should make this easy from a driver standpoint, but our robot still has to be maneuverable enough to actually make the play. This shouldn’t be too much of an issue – a 6WD robot can turn on a dime, and since we won’t be interfered with in our alliance zone, we can essentially go where we want once there. Overall, our mediocre maneuverability won’t hinder us from effective scoring.

Ability to move into position to pick up pieces: This shouldn’t be an issue for picking up pieces from the feeder station, but our six-wheel drive will make it difficult to get into position to lift from the ground, particularly if our manipulator’s “window” for successful pickup is small and our drivers cannot effectively use the camera.

Ability to move into position to deploy minibot: This is largely dependent on which deployment scheme we choose, but our 6WD should be adequate.

Conclusion
Because of our interpretation of this year's rules, our robot is an OFFENSIVE-minded robot that plans to go THROUGH, NOT AROUND defenders in order to score as EARLY AND OFTEN as possible, on the TOP ROW. I'm hoping to get some feedback from some people with more experience than I, particularly before we begin manufacturing our chassis. I also hope that some of you take away some lessons of your own. Thanks a lot for reading this WoT, it was five pages in OpenOffice.org, single spaced.

Here's to a great season,
Dolan “SirTasty” Murvihill
Team 2374