Building the My First Robot Chassis

Introducing the RBB-BOT

You'll begin your journey with My First Robot project by constructing the RBB-Bot. RBB stands for Robot Builder's Bonanza, or Really Beginner Bot, or anything else you like! -- it's the hardware that matters. The first phase of the bot is controlled with switches. In future phases, you'll learn how to replace the switches for electronic control, starting first with a simple circuit, then moving up to several different types of microcontrollers, which are small computers on a single chip.

The base of the RBB-Bot measures six inches across, and like many robots of its type, uses a pair of motors and wheels for mobility. The two wheels are on opposite sides of the robot base. These wheels can be mounted center-line in the base, or offset to the front or back.

For the RBB-Bot, the wheels are mounted center-line. That provides a bit more flexibility.

The size of the wheels greatly influences the travel speed of the robot. Larger wheels (for a given motor RPM) make the robot go faster. The wheels on RBB-Bot measure about 2" in diameter.

This means that for every revolution of the wheels, the robot travels approximately 6.3" (2 x pi, or 2 x 3.14). With the motors specified, the RBB-Bot moves at about one foot per second.

A typical problem with constructing wheeled robots is connecting the wheels to the motors. The job is made easier when selecting wheels that are engineered to fit specific types of motors or motor shafts. That's the case with the RBB-Bot, which uses commonly available Tamiya parts for both the wheels and the motors. The motors come as a kit; construction time is under 15 minutes per motor, and requires only a small screwdriver and pair of needle nose pliers.

The arrangement of two drive wheels on each side of the robot is commonly termed differential steering. The name comes from how the robot is steered by changing the speed and direction ("difference") between the two wheels. One of the key benefits of differential steering is that the robot can spin in place by reversing one wheel relative to the other.

A feature of most differentially-steered robots is that they use one or two casters or skids, placed in the front and/or back, to provide support for the base.

This first version of the RBB-Bot uses a simple static skid, which is nothing more than the head of a metal machine screw. This works because the RBB-Bot isn't very heavy, so there's not much weight placed on the skid. The robot glides over the skid, with its rounded shape providing only modest friction.

In a more enhanced version of the RBB-Bot, described in a later installment of this series, you'll see how to flip over the robot's base, and attach a metal or plastic ball caster.

RBB-Bot Phase 1 Parts List

These are the parts you'll need to construct this phase of the RBB-Bot:

1 6" x 6" piece of 1/4" thick aircraft-grade plywood or 1/4" (6mm) expanded PVC plastic
1 6-1/2" x 4-1/2" piece of 1/8" thick aircraft-grade plywood, acrylic plastic, or picture frame mat board
2 Tamiya #70093 3-speed crank axle gearbox motor kit (via Amazon)
1 (pair)

Tamiya #70096 off-road tires (via Amazon)
4 4-40 x 7/16" pan or flat head machine screws
4 4-40 nuts
3 6-32 x 1/2" pan head machine screws
4 6-32 x 1" pan head machine screws
8 6-32 nuts
4 6-32 acorn nuts
2 1/4" cable management clips
2 DPDT center off momentary bat handle miniature toggle switches
Mini (via Amazon)
Screw Terminals (via Amazon)
Mini (via MCM Electronics)
Not Momentary (via Jameco)
1 3-cell (4.5 volt) AA battery holder
Pack of 2, int'l shipper (via Amazon)
Wires (via Jamaco)
Snap terminals (via MCM)
Misc Snap terminals for battery holder, as needed (via MCM)
24 or 26 gauge stranded hookup wire, 8 or 10 foot length of 4-conductor modular telephone extension wire

Next: Cutting Things to Size