Team 236's robot for 2017 FIRST Steamworks
The robot has 5 distinct subsystems:
- Drive
- Climber
- Garage door
- Intake
- Shooter
The drive system this year is a 6-wheel drop-center tank drive on Colson 4-inch wheels, which provides maneuverability and traction. Each side is powered by twin CIM motors connected into a WCP DS gearbox with a two-speed pneumatic gearshift which provides two distinct speeds to give greater control over the robot.
Because the robot is a tank drive, 236 is using our TickTank class which provides a variety of features including motion profiling and abstract interfaces. More information on motion profiling, turning and other autonomous behaviors is in the Autonomous section below. By default, the tank drive runs in a simple tank drive control mode on two joysticks. However, the driver is also provided with buttons to activate a more precise drive mode for alignment with the peg for gear delivery and a reversed drive mode. Because this year's robot has functions on both sides of the robot, it lacks a clearly defined "front." Giving the driver the ability to reverse the drive can make driving more intuitive.
The climber is the simplest subsystem of the robot. It consists of two 775Pro motors mechanically linked with a VersaPlanetary dual-input gearbox attached to a custom-built wheel designed to capture a knot on the rope. A racheting wrench is used to prevent the weight of the robot from causing the motor to backdrive and to hold up the robot when the match ends and the motors lose power.
The garage door is the colloquial name given to the robot's gear delivery device. It is so named because the movement of the mechanism approximates that of a garage door. The door part consists of a lexan sheet attached to delrin tracks that allow it to roll up and down and spin by 90 degrees. The raised position allows the gear to easily slide onto the door. Then, the lowered position allows the gear to be placed precisely onto the peg for delivery to the airship. The door also has a cutout designed to push up the spring so the gear can be placed without actuation.
On the front of the garage door are two small arms made of delrin that can be opened and closed. When the robot receives a gear from the loading station, it opens the flaps to guide the gear to the correct position. When the door is lowered, the flaps close to hold the gear securely while placing it on the peg.
The garage door is powered by two pneumatic pistons - one to pull the door up and another to open and close the flaps. This allows powerful control over the door while simplifying the wiring and programming.
The intake of the robot is an arm that is lowered over the bumpers to obtain fuel and move it to the hopper. The intake roller is powered by two 775Pro motors with gearboxes on opposite sides of the intake. The intake arm is lowered over the bumper by a pair of Bosch seat motors on opposite sides of the robot. Limit switches on the top and bottom of the intake prevent the seat motors from driving into the floor or the robot. Because seat motors burn out very easily, these limit switches are crucial in preventing damage to the motors over the course of the season.
The shooter is one of the most tightly tuned and controlled components of the robot. Fuel is launched by a flywheel which rotates at speeds of around 3,000 to 4,000 RPM to push fuel around a curved hood. The hood itself is a curved piece of lexan held in place by a custom-machined aluminum frame, which is raised and lowered by a linear servo.
Because the flywheel is compliant and can expand, there is a lot of pressure between the ball and flywheel at high speeds. The increased friction increases the load on the flywheel significantly, lowering its speed when the next ball enters the hood. To prevent this, we run a PI loop at 200 hz which uses a banner light sensor to count the speed of the wheel and to vary the motor speed to maintain a consistent RPM. Using this system, we are able to return to full speed after shooting a ball within hundredths of a second.
The shooter can be set to a variety of different "presets" which have an associated speed (in RPM) and a hood angle (absolute). This provides a variety of different points on the carpet to shoot from, making the robot harder to defend. In order to align the robot with the boiler, the robot has a flashlight which the drivers can see on the boiler stack, as well as a camera which can be rotated to see the boiler. Later in the season, we may add a coprocessor to run vision on the robot to aid in alignment.