FIRST Robots: Aim High

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| FIRST Robots

RELIABLE,

POWERFUL,

ADAPTABLE:

ATTRIBUTES OF

STRONG DESIGN

KEEP GOOD

IDEAS AT

THE READY

Although the actual construction period for the FIRST

Robotics Competition is six weeks, teams are free to test

ideas throughout the year. Sometimes teams will use the time

between competitions to re-examine ideas that surfaced

during the previous competition season but were not imple-

mented. Progressing from an idea to a working design

sometimes just takes a bit longer than six weeks.

During the

2004 FIRST Robotics Competition season,

Team

100, from Woodside, California came up with a great

idea for a versatile propulsion system, but there was not

enough time to transform that idea into a working system.

Rather than scrap the idea, the team stored the design on the

chance they could find a use for it in a future competition. For

the 2006 FIRST Robotics Competition, the team resurrected

the stored design and converted it into a great competitive

advantage.

TEAM 100

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Driving Tomorrow’s Technology Award

|

Selecting a Drive Train

Team 100 began with a desire to build a

robot that could easily climb the ramp

and have strong defensive characteris-

tics. Other robot functions would com-

plement the drive train, so this system

was the first component designed. In

addition to the performance character-

istics, the entire mechanism had to be

simple enough that it could be built

using the limited tools and resources

available to the team.

Three different ideas were presented

for the drive system. A swerve drive

was proposed to allow omni-directional

movement, but this system was too

complex to build, given the team’s

capabilities. Also, a swerve drive sys-

tem was not ideal for the type of robot

needed for the 2006 FIRST game.

A two-speed, six-motor, six-wheel

drive propulsion system was also sug-

gested, as it would be fast and have the

power to force its way around the field.

This design was also considered to be

too sophisticated given the available

resources.

The third alternative was to build the

drive system from the material provided

in the FIRST Kit of Parts. This would be

easy to put together, but it also meant

that many other teams could be using

the same drive and there would be no

advantage gained.

The final design merged two of these

ideas. A two-speed transmission would

be combined with parts in the kit to

drive four wheels. The transmission

gearboxes would be constructed and

mounted on the kit frame. This would

create a powerful, multispeed drive

system mounted on the easy-to-

assemble frame.

The drive system called for six of the

most powerful motors supplied in the

Kit of Parts to provide a propulsion

edge over teams using a four-motor

propulsion system.

Transmissions would shift the system

into a low-speed, high-torque mode or a

high-speed, low-torque mode as

required. The high-speed mode would

be ideal when playing offense, to allow

the robot to outmaneuver other robots.

In defensive mode, the high-torque

option would provide an advantage with

a stronger ability to block opponents.

The high-torque option would also

improve the robot’s ability to climb the

ramp. Using six motors allowed for a

greater range of speeds without com-

promising the rotational torque applied

to the wheels. The concentration of

motors also created a low center of

gravity for the robot.

Custom gear boxes, combined with the kit

frame, provided Team 100 with an easy-to-build

chassis powered by a shiftable drive.

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| FIRST Robots

Six-Motor Drive: An

Evolutionary Design

The drive train on Team 100’s 2006

robot resulted from two years of tweak-

ing. The team first proposed using a

two-motor, two-speed transmission in

2004, but didn’t implement it. However,

the proposal sparked interest in a dual-

speed option that would be reliable and

advantageous. Although a shifting

mechanism presented complications to

the drive system, it was believed to be

worth the effort.

Following the

2004 FIRST

Competition season, a preliminary

version of the dual-speed drive system

was built. Though large, bulky, and

heavy, the system demonstrated relia-

bility and utility. Throughout 2005, the

team continued to fine-tune the dual-

speed transmission concept.

A second revision to the transmission

used gears cut from steel spur gear

stock. Transmission components were

upgraded to handle the high loads

placed on the system. The shifting

mechanism’s gears were heat-treated

to accommodate the forces from shift-

ing and changing direction and to pre-

vent failure.

The gearbox housing was fabricated

from a 1/4-inch (0.635 cm) -thick

aluminum plate, into which ball bear-

ings were pressed to hold the steel

drive shafts. The actual shifting mecha-

nism used a form of “dog-shifting,”

where a metal dog with protruding teeth

slid along a hexagonal shaft to mesh

into pockets that were milled into a gear

riding along the same shaft.

The second revision of the transmission was

sketched and drawn in AutoCAD. Two CIM

motors and one Fisher Price motor, coupled with

gears that were housed in an aluminum gearbox,

powered this version.

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