Project Information

Lil' Bomber: First Tech Challenge Robot First Tech Challenge (FTC) Robot

Synopsis
The Lib' Bomber is the robot I as a highschool softmore built for this year's First Tech Challenge (FTC) World Championship in April, 2013. It was a robot designed to compete in the FTC challenge Ring It Up.
Resources
Created by RobotGuy
300 hours over 8 months
50+ pounds
18"x18"x18"
5-15 minutes
RobotC
Autonomous and Autonomous/Wireless PC master joystick hybrid mode
Powersource: NiCAD / NiMH

A single 12V, 10 cell 2000mAh rechargable battery for the 12V and 7.4V systems and a 5 Cell 9.6V 1900mAh rechargable battery for the Lego NXT.

Locomotion: Wheel Driven

6 wheeled drive powered by 4 12V DC motors linked to all six wheels via a 1:1 gear train. The top speed of the system is around 3' a second with around 1/32 of an inch of accuracy. The best part about the drive system is it is capable of pushing 100 lbs across foam mats with little dificulty, a feature I decided we needed for the FTC challenge. The hardest part was getting this entire system to fit in the 18"x18"x18" sizing cube that the robot has to start in for the competition.

Controller/CPU: Lego NXT

The main brain is a Lego NXT running RobotC. The NXT is then hooked up via a wireless Samanta module to the field control software which specifies two joysticks to the robot.

Sensors

The robot uses 2 Ultrasonic sensors (for detecting obstacles), 1 IR seeker sensor (for detecting IR beacons), 5x 1024 count quadrature encoders (for positioning the arm within .05 arc min including gear train), voltage probes for amps consumed by each motor, 1 limit switch (for reseting the arm)

Actuators

The motors and servos are 7x 12V 152RPM DC motors, 4 HS-485HB Hitec servos. There are 7 gears in the drive train on each side at a ratio of 1:1 for 6 wheels for a total of 14 gears in the drive system alone. The robot has a 1:18 double reinforced gearbox with a total of 15 gears for rotating the arm. The robot also has 7' of chain on it: 5' of chain for extending the arm 3' and 2' of chain for rotaing the wrist joint. The claw on the robot utilizes a 1:1 gear ratio hooked up to a servo to split the bucket for the rings.

Description

This robot, the Lil' Bomber, is a robot built for the First Tech Challenge (FTC) by me, a highschool softmore. (More information at: http://www.usfirst.org/roboticsprograms/ftc with the challeng specific information at: http://www.youtube.com/watch?v=BXcldN6G-H8) This is the robot that my team 4211 used at the FTC World Championship, which was held in St. Louis in April. I headed up the technical aspects of the robot as head builder, programmer and CAD designer. This robot overall was top 8 in all three categories of engineering at the World Championship and finished 15th in 128 of the best teams in the world. This was the one and only robot in the entire world that was designed and built to hang three of the scoring elements for the game during the autonomous period. (video of one of the matches here (Robot 4211):

Before actually working on building the physical robot I spent around 50 hours building the entire robot virually in SolidWorks. Virtual tests were then performed on all the joints and mechanisms to see if they would work and hold up to the abuse we expeced them to be subjected to. Once the robot was finished being designed in SolidWorks it went to the building stage.
The robot is built out of parts from the Tetrix system (the system mandated by FIRST for the challenge). The robot's drive train is one which is able to support 150 lbs, well in excess of our robots 90 lbs. The robot has a two jointed arm with a 21" linear extension between the shoulder joint and the wrist joint. The arm can move between any two points in the 5' reach of the arm (measured from the shoulder joint) in a 270 degree arc with 1/64" of accuracy in less that two seconds. The robot also is able to accurately position itself within 1/32" of accuracy on the field itself with a mapped enviroment positioning system.
The robot has a Lego NXT brain. The NXT is programmed with a total of around 18,000 lines of RobotC code which runs independent threads, each one handling a different aspect of the robot. The list for the threads are: one for getting joystick information, one for handling one of the joystick's comands, another for the other joystick's commands, one for managing all the other threads, one for handling the drive base, one for all the sensors and a final thread for handling IK and FK engines for the arm control depending on the mode.
The robot has a total of 23 autonomous programs that the robot can choose from during the autonomous period of the match. The driver controlled mode is a hybrid mode with the driver giving only high level comands via joystick and the robot decides how to interperet and implement those commands. The robot, during the drive controlled mode, is able to switch to autonomous mode and continue trying to compete the challenge if the link to the joysticks is ever lost.