FIRST Robots: Aim High

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| FIRST Robots

FOUR-

WHEELED

SHOOTING

Team 1114 began the design process with a simple

question: Do we move or stand still? The question was

not about the robot’s overall action, but about its function

during shooting. This single question guided the robot

design and helped the team, from General Motors-St.

Catherine’s Powertrain & Governor Simcoe Secondary

School in Ontario, Canada, think about possible alternatives.

The team decided to use a fixed launcher on the robot to

keep the design and controls simple. A fixed launcher

required that the entire robot base be used as the aiming

mechanism, rather than using a turret to aim at the goal.

Recognizing that the robot would need to stay in one position

to shoot multiple balls, the team designed a drive train and

control sequence to ensure this condition. High traction, tank-

style treads were selected for propulsion, with the expectation

that the high levels of friction from the treads would also

resist motion from opposing robots.

A control algorithm was written to keep the robot station-

ary while shooting. Sensors monitored the original location

of the robot before shooting commenced, and a feedback

system kept the robot in position. Referred to by the team

as “drive base lock,” this condition freed the robot operators

from worrying about maintaining position in the often

congested area in front of the goal.

By analyzing the trajectory with ball projectile formulas,

including consideration of air resistance, the team calculated

the necessary tilt angle of the shooter. With a 29-degree

shooting angle, the robot could hit every shot at the upper

goal from distances between 7 and 27 feet (2.1 to 8.2 m).

As such, there was no need to further complicate the design

with an adjustable tilt mechanism. By keeping the shooter

angle physically fixed and the robot base dynamically fixed,

the team created a simple design that was further augmented

with effective control strategies.

STILL ON

TARGET

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TEAM 1114

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Innovation in Control Award

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Early in the design process, Team 1114

investigated a four-wheel shooting system.

The system performed well.

Robot Creation

Team 1114 experimented with a

four-wheeled, wood-framed shooting

system at the beginning of the robot

design process. The design began with

an aluminum base, outfitted with four

drive motors and multiple speed trans-

missions, to provide a range of power

for different driving conditions. The

base was augmented with tread propul-

sion and a multiple-band ball pick-up

system. The shooting system, towering

over the base, was positioned at the

height needed to shoot over opposing

robots. A ball-storage hopper, con-

structed with polycarbonate panels on

a

PVC frame, completed the design.

The robot frame is constructed from

aluminum plate and bar stock, cut to length

and welded together. The design includes

foundations and supports to mount motors

and other robot systems.

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FIRST Robots

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Each aspect of the robot was mod-

eled using computer-aided design soft-

ware. Even the operator control panel

was initially planned using computer-

based design tools before it was con-

structed with real dials and switches.

The computer-aided drawings served

as a record of the design that was eval-

uated to examine functions and make

improvements.

Control Features For

On-Target Shots

Intuitive control was a guiding principle

for Team

1114. This strategy, adopted

to simplify driving, led to the creation of

four control features: drive base lock,

autonomous target check, camera aim-

ing, and curved shooting.

Drive base lock was the control algo-

rithm developed to maintain the robot’s

position and orientation at a specific

location on the field. A simple click of

the joystick trigger relinquished driver

control to the onboard microprocessor.

Using wheel encoders and a gyrocom-

pass, the microprocessor detected any

motion and automatically corrected that

motion to maintain position. In this

mode of operation, the robot would

automatically fight to stay in position,

thereby creating a stationary platform

from which to fire balls into the goal.

Autonomous target check was

applied to continually monitor the cam-

era output for the presence of the target

light. If the robot was knocked off

course and the camera lost the target,

the ball firing mechanism halted and the

robot automatically turned back in the

direction of the light until the target was

relocated. This feature ensured that

balls would only be fired when they

could be scored.

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The inside of the frame includes a tray to

support other robot systems. Dual motors on

each side of the robot, along with a gear box

capable of operating at different speeds, provide

the robot with a range of power.

Tread tracks drive the robot and keep the

center of the machine free to collect and lift balls.

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