DC Gearmotor (TT Motor)

What it is

The TT gearmotor is the yellow-and-blue motor at the bottom of nearly every beginner robot car. It is a small brushed DC motor bolted to a plastic reduction gearbox, with a double-D output shaft that presses straight into a matching wheel. Buy two, add a chassis and a caster, and you have a robot that can drive and turn—which is why it is the drive motor behind the first line follower or obstacle-avoider most people build.

On its own a bare DC motor spins far too fast and far too weakly to move anything. The gearbox is what makes it useful: it turns that fast, feeble spin into the slow, strong turn a wheel needs.

How it works

Two things happen inside the yellow case:

1. The motor turns electrical energy into rotation. Put voltage across its two terminals and it spins; reverse the polarity and it spins the other way. More voltage means more speed.
2. The gearbox reduces that speed. A ~1:48 gear train means the wheel turns once for roughly every 48 turns of the motor. You lose speed and gain torque in the same ratio, which is the trade you want—a wheel needs force, not a blur.

To control it you do two things at once: set direction by choosing which terminal is positive (the H-bridge does this), and set speed with PWM—switching the supply on and off fast so the motor sees an average voltage. Learn that pairing in control DC motors with PWM and an H-bridge.

When to use it

Reach for a TT motor for any light, low-speed wheeled robot: line followers, obstacle-avoiders, maze robots, a first differential-drive base. It is cheap, forgiving, and every beginner tutorial targets it.

Step up when you need more: add wheel encoders when you want to measure distance and speed for odometry, or move to metal-gear motors when the robot gets heavy or needs to climb. The plastic gears strip under abuse.

Wiring and gotchas

• Never wire it straight to a logic pin. Stall current is around 1 A. Drive it through an L298N or similar H-bridge, powered from the battery—not from the Arduino’s 5 V.
• Two motors won’t match. Identical PWM rarely drives perfectly straight; trim one motor in software, or close a speed loop with encoders.
• Mind inrush and back-EMF. Motors dip the supply when they start and kick voltage back when they stop. Keep motor power and logic power on separate rails sharing a common ground—see powering a robot.
• Match the wheel to the shaft. The double-D shaft only seats correctly in a matching double-D wheel bore; a round hole will slip.