Year: 2015

Game: Recycle Rush

Source code

Strategy

The key to scoring points in Recycle Rush is to create stacks of totes with Recycle Containers on top of each stack. A stack of totes without an RC on top scores only 13 the points of a stack with an RC.

We decided to load from the landfill because the landfill is a preset size and arrangement of totes that will not change from match to match, whereas the human player station has to deal with human speed, getting lined up perfectly, falling totes, etc. By loading from the landfill, you also are able to clear the field for easier driving.

We also realized that in eliminations, robots will be able to work together on an alliance, and that no robot will need to do everything on its own in order to be successful. That was the leading factor in our decision to specialize in tote stacking from the landfill.

Because during qualifications you do not know who you will be paired with, however, you must assume that none of the robots can do anything, and thus you must be able to do everything on your own. This was the leading factor in our decision to build a rear elevator separate from the main elevator, specifically designed to deal with RCs.

Once we made the decisions regarding our strategy for match play, we began the process of prototyping ways to accomplish the set strategy.

Prototyping

Prototyping began very early on during week 1 of build season with both vague CAD modeling, and physical prototypes. Our proof-of-concept prototype models are designed to show us that an idea will work, but not necessarily that the exact design prototyped should be the final version. We look at the flaws in the prototypes and find ways to fix them.

The collector/intake system was designed originally with two long arms that could clamp down around a tote to then pull it up our lexan surface ramp and onto the inner platform of the robot. We found after testing, that the arms got in the way more than they helped, especially when loading from the landfill, and so we changed the design to be two simple spinning wheels at the top of the ramp to center and pull the totes in, in addition to a different ramp with powered rollers to go under the totes and pull them up into the robot.

The main elevator for totes was prototyped first with 4 individual bars that bearings rode on, as well as a large carriage between them, but we found that led to jamming and more friction that we wanted. We redesigned the carriage to ride on a single vertical shaft, much like many elevators do, and then found it to be far smoother.

We also designed 5 generations of tabs that lifted and held the totes on the main elevator carriages. In the end, the final design we went with is identical to the first design, but is slightly wider. Sometimes when you prototype, the design comes back to the original idea.

The rear carriage designed changed to version 3, which is currently on the robot and accommodates RCs far better, and allows for pickup of any game piece easier. It also allows us to build stacks of 4, and then top them with 2 totes and an RC to achieve the maximum stack of 6 totes with an RC on top.

By prototyping parts of the robot before we build the final version, we save both time and money, and allow us to confirm that parts and designs will in fact work on the final robot. This leads us to CAD, where we finalize dimensions, locations, and how everything will fit together.

CAD

Once we have the strategy down, we begin building our prototypes of elements of the robot in both CAD and physical parts. The CAD designs let us try things that may take longer to actually build, or see if the part will actually fit where we want it, or to give us an idea of how to space parts. Because of this, we end up with a fully designed robot in CAD before the actual robot is complete.

After we had decided on general strategy and a vague way of accomplishing that strategy, we created a very basic level CAD model in Autodesk Inventor of what could be the robot design. There was little detail involved, and it merely showed a proof of concept design, but it was enough to provide insight into the next steps.

Because Autodesk provided teams with a fully generated FRC field in CAD, we were able to put our robot on the field to see how it would fit in different situations before making it to a competition. This allowed us to see more about size restrictions, driving room, and how cluttered the field could become – and how we could deal with it.

After we had decided on the final robot design, we made the final decisions in CAD. This meant packaging the electronics, determining bolt hole locations, final sizing of parts, supports, and more. We were then able to build the final robot confident that the robot would go together as expected.

Intake

The intake design on our 2015 robot, Dent, is designed to quickly scoop under totes in the landfill and pull them up and into the robot for stacking. The ramp makes use of two powered rollers connected both with Gates belts and polycord to pull the totes in and onto a platform within the robot, with another powered roller.

Two 8inch pneumatic wheels on compress the sides of the tote as it comes up the ramp and into the robot, centering the tote. They also allow us to come at a tote from an angle, or even perpendicular to a tote, and still pull it into the robot.

An ultrasonic sensor on the back lexan wall of the robot looks forward and automatically slows the collector as the tote is pulled farther into the robot. The sonar is also used in autonomous to detect whether a tote has been collected fully or not.

All of these elements come together to form a reliable and fast intake system for the landfill totes.

Main Carriage

The main carriage of our elevator is what lifts and stacks the totes internally in our robot. It is designed to be able to stack a full 6 totes, but after strategic analysis we determined that the best stack to aim for is a stack of 3-4 totes for our robot.

Each carriage rides on 12 bearings that glide along 1” angle pieces of aluminum that act as the elevator shaft. The carriages then bolt to the #35 chain lift with a custom made chain tensioner to ensure the chain never slips.

Lexan tabs snap down around the lips of the totes that are pulled in, and then lift the stack back up. Using this passive system allows us to stack quickly while not spending unnecessary weight on a part that could break – and potentially ruin a match.

Along the vertical frame structure by the main elevator, there are 3 custom made hall-effect sensors. The sensors recognize a magnet embedded within the elevator carriage and allow the driver to raise or lower the carriage to a predetermined height every time.

Rear Carriage

The rear carriage was designed specifically around being able to put a Recycle Container on top of a stack of totes. During testing, we found that the container is likely to be laying down during a match, and rather than spending time trying to right it, we could just pick it up as it lay down.

We then tested using just an elevator where we went under the RC and then picked it up, but found that that often resulted in us pushing the RC, not sliding under it as we hoped. This led us to v3 where we can still slide under the RC if we want, but we can also lower the carriage arms around the RC and they passively lock back in place on the underside.

This design also works with totes, allowing us to top stacks of totes with either RCs or totes and an RC. We are able to put an RC on top of stacks of 4 totes, or put an RC on a stack of 2 totes, and then lift that stack of 2 onto another stack of 4 to achieve the stack of 6 totes with RC.

Two lexan tabs stick up vertically to keep the RC from rolling off the carriage side. Lexan tabs on each side pivot and lock in place in the horizontal position to pick up RCs. Two lexan hooks, one per side, also allow us to use the carriage to pull RCs off of the step in teleop, making them accessible to our alliance to score more points.

Electronics Packaging

Designing a robot is a challenge, but getting the electronics to fit within the robot – including the wiring – can often be even more challenging. CAD allows us to layout the electronics and see how everything will fit together in 3D space, rather than just 2D as with cardboard cutouts.

This year, we faced the challenge of fitting all of the electronics within the chassis frame, underneath a platform. This meant the platform needed to be easily removable for access to the battery.

We made use of the brand new Talon SRXs on the robot, and have 10 of them powering the motors onboard. One AndyMark PG71 Gearmotor powers each elevator, 4CIMs work together to drive the 6” mecanum drivetrain, and 4BAG motors make use of VersaPlanetary gearboxes from VexPro to run the collector and intake.

Scoring Ability

We designed our 2015 robot with the goal of stacking totes internally from the landfill onto the scoring platform quickly. The rear elevator allows us to top our own stacks if necessary, but also can be folded up out of the way during matches that it is not needed for. We can score 3-4 stacks of 3-4 totes per match, or slightly fewer stacks if we have to then top our own stacks during a match. We also have 4 different autonomous sequences that can be run depending on the match.