SPECIFICATIONS

For the last several years Team #1799 has documented our robot design with CAD models, drawings, and written specifications.  As decisions are made about the design of this year’s robot, details were added to the specifications document.  Beginning with the frame size and chassis design and continuing through the programming.  This document is not used to make the robot, but could be used to understand what we wanted the robot to be and how it was meant to work.  

1.0 Introduction

This document provides a record of many of the parts this year’s robot used along with how they are arranged and their function. This record also provides how our controls will function, what software we used, and our I/O chart. This year’s game is Charged Up, which is a power network themed competition. The field elements all have power grid inspired names (Substation, Charging Station, Grid).

2.0 Frame

The structure of the robot is made of two major components, the KOP chassis frame of the AM14U5 Drive Base Kit and a super-structure made of aluminum and polycarbonate sheets. The chassis will provide all of the structure for the bumpers, battery, wheels and motors. The super-structure will support the Crate and Intake device and provide protection to the electronic boards.

The Kit-Of-Parts Frame will be cut down to a 18 inch by 33 inch long and narrow chassis. The chassis is secured using 10-32 x .325” SH bolts with nylon lock nuts on the inside of the frame. The top of the frame is 5” above the floor.

The superstructure consists of two .25” thick Aluminum plates that run front to back on the robot.  They are mounted vertically 13.5” apart and are attached by four triangular aluminum brackets that are bolted to the front and back channel of the frame.  The plates are CNC cut to shape with a series of .25” holes and two 1.125” diameter holes for the bearings that hold the mechanisms.  There are also holes and slots in the plates to allow wires and tubes for the mechanisms to pass through safely.  A churro connected to the top of both plates supports and stabilizes them.  The churro is also used to hold the two solenoids valves for the pneumatics system.  A 1.5” L bracket is bolted to the inside surface of each to provide stiffening and is used to support the electronics board.  A 1” L bracket is bolted to the inside surface, flush with the top slant to support and hold the .125” polycarbonate top cover.

3.0 Bumpers

Team 1799 is using a one piece complete perimeter bumper system that is firmly attached to the frame with 8+ bolts. This will provide maximum protection to our robot to assure its safety and that of others. The bottom of the bumpers will be mounted at 1” above the floor to be low enough to minimize the chance of driving over a game piece. Solid ¾ inch thick and 4.5 inch tall plywood backing will be bolted together with metal L-brackets connecting the outside corners. Behind this will be metal brackets on the inside of the plywood. On the outside will be two rows of cylindrical buoyant polyethylene foam (pool noodles), secured periodically with cable ties. This foam is wrapped around the corners. Dense fabric is then cut into the proper dimensions and is stretched over the foam and wood frame. White numbers will be ironed on the outside of the fabric for high contrast identification of our robot. A second piece fabric of the opposite color will be velcroed in order to change colors at the competition.

4.0 Drivetrain 

Our drivetrain is a 6 wheel chassis with 6 inches in diameter wheels and 0.140 inch drop-center. We used 6 NEO motors, with 3 on each side connected to the Toughbox Mini Gearbox with the ThriftyBot 3 Motor Drive Plate attached to the inner rails of the frame. A ½ inch hex output shaft that is 6 inches long holds and spins the traction wheel with two sprockets, both on the inside of the wheel. The other wheels are then belt-driven with the belts that come with the KOP, providing a 1:1 transfer of motion. This means the three wheels on one side will all spin at the same time and the same speed, acting as a tank drive. To go forward, both sides spin forward. To turn in place, one side spins forward and the other side spins backwards. When turning like this, a normal six traction wheel robot would experience excessive sideways friction on the corner wheels. This would cause the robot to jump/bounce irregularly when turning. Our drive train avoids this because the middle wheels are 0.140 inches lower than the corner (drop-center), so that, when turning in place, the robot will be balanced on the middle wheels only (no contact between the floor and corner wheels). 

The design of the drivetrain was integral to the overall design of the robot.  It is only because of the small size of the NEO brushless motors that we were able to achieve our narrow 18” wide robot.  The CIM motors would have added 4 to 6 more inches to the width.  The decision to add two motors to the standard design was to increase the speed of the robot so that we can cross the field quickly.  We used the standard drop center to avoid needing omni wheels to allow for turning.  We specifically want high traction so that our extra power doesn’t result in us spinning our wheels.  Because of our desire for high speeds we have worked to keep our center of gravity low and our wheelbase wide.  This is why we have moved all six wheels as close to the outside rails as possible.  This required changing the arrangement of the pulleys.  All wheels were bolted to a pair of pulleys, bringing both belts to the inside of the wheels. 

4.1 Ballast System

The ballast system was added to the design when we realized the  robot would be significantly underweight. The small size led to a lower weight of our structural and mechanical systems.  Before scrimmage the robot weighed in around 80 pounds.  To increase traction and to protect sensitive equipment from damage from collisions, we considered several ways to add weight.  The chosen design involved bolting steel plates to the bottom of the robot so that the added weight also lowered our center of gravity.  We drilled holes at either end of six plates (.25 x 3 x 33.25”) so that they could be attached to the frame with 4.5” long ¼-20 flat head bolts.  The total weight of the plates was 40 pounds which would bring the total weight of the robot real close to the limit of 125 pounds.  The plates are arranged in 3 rows of two stacked plates, lowering the clearance by only one half of an inch and thus not dropping below the bottom edge of the bumpers.  By using six large plates we were able to purchase them pre-cut to our desired length and it allows us to remove individual plates to achieve optimal driving performance.s

5.0 Manipulators - Overview

Our robot has two manipulator systems designed to transport game pieces. The Crate in the back of the robot can receive game pieces from the Single SubStation and dump them into the bottom row of the Grid. The Intake Arm is designed to pick up Cubes from the floor and expel them into the bottom row of the Grid. Both systems use pneumatic pistons and the Intake Arm also uses motors to spin the rollers. Both systems start within the perimeter of the robot and can extend and retract back within the perimeter to more safely transport game pieces across the field. Our intention is to only extend them beyond the perimeter when we are in the protected areas of the SubStation and Neighborhood.

5.1 Manipulators - Dumping Crate

The primary component of this system is the milk crate with the FRC logo that was the game piece from the 2018 season “Powered Up”. It was a convenient object to prototype with and we liked the idea of reusing a former game piece. It worked well in preliminary testing so we decided to use it on the final robot. Two .5” hex hubs are bolted to the create to hold the churro axles that are supported by bearings in the vertical sides supports. The crate can rotate about these axles from a vertical position (for receiving and carrying game pieces) to a negative 110 degree position to dump the game pieces out the back of the robot. The relatively light weight of the crate and game pieces along with the axle being positioned at the bottom back of the crate, makes it possible to dump with little input force. 

The crate is actuated by a .75” x 4” double action piston that is mounted to the outside surface of the port side (driver’s side, left side) vertical side support. The piston arm actuates the edge of a .5” hex hub held by the churro axle and a .5” hex collar. Using the rear mounting bolt of the piston, it is connected to an L-bracket that can pivot on the bolt that attaches it to the robot. An Igus .25” end bearing is screwed onto the end of the piston rod and can pivot about a ¼”-20 bolt that is attached to one of the six mounting holes of the hub. When the crate is in the vertical position, the piston arm is extended and the bolt is at a 4-O’Clock position on the hub. When the crate is in the dump position, the piston arm is retracted and the bolt is at a 7-O’Clock position on the hub. When the 60 psi of compressed air is supplied to the front port of the cylinder, the piston rod is retracted, pulling the bolt on the hub, and causing it to rotate clockwise about 110 degrees. When the compressed air is supplied to the back port of the cylinder, the piston rod is extended, pushing the bolt on the hub, and causing it to rotate counterclockwise about 110 degrees. The hex hubs and axle translate the rotary motion to the crate causing it to move from the vertical position to the dumped position and back.

There are two sensors attached to this mechanism to provide feedback that can be used by the program or drivers. On the starboard side (right side) crate axle is a REV Robotics rotational sensor that will tell the RoboRio if the crate has rotated fully. The light sensor in the bottom of the crate will be able to identify the presence of a game piece. This will confirm if a game piece has been loaded into the crate and if it was successfully dumped out of the crate. This is important information to have because of the game rule that limits a robot to controlling only one game piece at a time. Since we have two manipulators that can each control a game piece, it is important that only one does so at any given time in a match. 

5.2 Manipulators - Intake System

The Intake Arm mechanism is the heavier and more complex of the two manipulators. It is based on the 2023 Everybot manipulator but has been simplified to only pick up Cubes from the floor of the game field. Pneumatic pistons with springs are used to raise and lower (retract and extend) the arm and NEO 550 motors are used to rotate the rollers. The job of the Intake Arm is to grab a Cube from the floor of the game field (primarily in the SubStation area), and hold it securely. The arm and Cube are raised/retracted within the perimeter of (above) the robot, for safe transport of the game piece across the field to the neighborhood. Once in the neighborhood, the arm is extended (lowered), and the rollers spin backward in order to drop the Cube in the bottom row of the Grid.

The intake system has a left and right arm that are connected by the backstop, rollers, and connecting rods. Each arm is made from 1”x2” aluminum tube. ½” hex hubs are bolted to the bottom of each arm. The ½” hex steel axle is supported by flange bearings, allowing the arm to pivot up and down. The pneumatic piston is attached to an aluminum plate that is bolted to the arm four inches from the pivot point. The end-effector is connected to each arm with four bolts and the sensor and electrical wires for the motors are routed through the arms.

The end-effector of the intake system is made of four ¼” polycarbonate plates that support all of the mechanical components. A pair of plates spaced 1.25” apart on each side provides the space for the belts and pulleys that transmit the force from the motors to the rollers. The NEO 550 motors with PlanetaryMax gearboxes (3:1 ratio) are bolted to the inside plates at the rear top corner of the triangular mechanism. One motor spins the front roller counterclockwise and the other spins the bottom/rear roller clockwise to pick up the cube. The direction of rotation is reversed to eject the cube. The design of the plates are made to create the correct spacing between the rollers to perfectly fit a cube. When extended to pick up cubes, the plates hold the front roller eight inches above the floor and the back roller three inches above the floor. There are also holes in the plates for attaching the backstop and several spacers that provide strength and rigidity to the mechanism.

The two rollers have  1/2" hex axles (aluminum churros) supported by  1/2" hex bearings and spun by  1/2" hex hubs within the pulleys. The outside of the roller is made of a 2” PVC pipe cut to a length of 16 inches. Each end of the roller is held by a 3D printed hub with a  1/2" hex center that press fits inside with a lip that wraps around the outside of the pipe. The pipe is spray coated with Flex Seal to give it a rubbery surface that will better grip the cube. 

The intake system is raised and lowered with a pneumatic piston attached to each arm. Each piston is a 1.125” diameter cylinder with an 8” stroke. The piston is rear mounted to the robot with an L bracket and  1/4" bolt that allows for the slight pivot required. A  1/4" bolt attaches the fork at the end of the piston rod to the arm. Behind the fork is a washer and spring that compresses when the piston is retracted. To raise the arm, 60 psi is supplied to the front port of the cylinder retracting the piston. The pneumatic pressure compresses the spring while in the up position. To extend the arm, the compressed air is vented from the front of the cylinder allowing the springs to push the piston rod out, pushing the intake system past the tipping point so that it will fall into the extended position.

6.0 Electrical System

Our main power source is a 12 volt KOP battery that stores electric energy and provides it for use by the robot. This is connected to a 120 amp KOP Thermal Breaker that protects the entire robot from damage due to a short-circuit and is used as the on/off power switch for the whole robot. The power is regulated by a Rev Robotics Power Distribution Hub that sends power to all powered functions of the robot. On the power distribution, each circuit is protected by a fuse or breaker. There are 40 amp thermal breakers to protect each of the motor circuits.. There are six Rev Robotics Spark Max motor controllers that control how much power to give each drive motor to control the speed of the robot. There are two Rev Robotics motor controllers for the two NEO 550 motors that spin the rollers of the intake mechanism. The REV Robotics Pneumatic Control Module, which is powered by a circuit with a 20 amp breaker, controls the two solenoid valves that actuate the pneumatic pistons for the intake arm and the crate.  It also powers and controls the air compressor based on the feedback of the pressure sensor.  Another circuit with a 20 amp breaker powers the RoboRio. The radio is powered by the Voltage Control Module which is on its own circuit with a 20 amp breaker.

The bill of materials used to be a required item to have during the inspections of the robot at each competition.  It was required to include all parts and materials included in the robot except for fasteners under one dollar.  There was an overall cost limit for the robot, but the cost of kit-of-parts items did not have to be added to the total.  Our bill of materials includes two columns with dollar values that add up to two different total costs.  The first is the total cost of the robot if all parts needed to be purchased.  The second column better represents how much money our team spent on parts that are included in the robot.  We have not included all of our team expenses for this year, but that is a different  document we would share with our sponsors. 

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