How to Connect Motors to Your Robot or Electronic Project

Movement differentiates a robot from just another electronic device. Choosing the right size motor, based on voltage, current, efficiency, weight, size, gearing, torque, and speed makes the difference between success and failure.

A small DC (direct-current) electric motor can be easily controlled by a single transistor and diode if you simply want to start and stop it. You can even electronically control motor speed using pulse-width modulation. However, to change directions, you'll need an H-bridge or motor driver chip.

Many builders struggle with attaching the motor to the robot or connecting a wheel to a motor. In fact, I’ve probably written more articles on making motor couplers than anything else.

Thumbnail blueprint of an H-bridge schematic Bipolar Transistor H-Bridge Motor Driver
For battery-powered (low voltage, low current) motor operation, the classic discrete-transistor bipolar H-bridge beats most MOSFET and prepackaged motor driver chips for most hobbyists. But, are some of the newer transistors better in this well-known hbridge design over the common 2222, 2907, 3904, or 3906 TO-92 transistors?
Trimmer potentiometer to adjust the PWM duty cycle Pulse-Width Modulation (PWM) for Motors and LED Displays
Variable duty-cycle PWM is a great method for controlling the speed of a DC motor and the brightness of an LED display. You can make a simple PWM circuit (without a microcontroller) by using off-the-shelf electronic parts such as an inverter chip, diodes, a capacitor, and a potentiometer.
LEGO hub with solid single-piece aluminum coupler Mounting Motors and Attaching Wheels
Three different ways of connecting wheels to motors and securing motors to robot platforms. Includes drilling a pair of glued LEGO bricks, a solid UHMW coupler rod, creating motor mounts from aluminum angle stock, and a v-groove belt pulley system.
PCB motor mount thumbnail PCB Motor Mount
If you don't have a home machine shop or 3D printer, you can make a motor mounting bracket from a PCB. Printed circuit boards are strong, lightweight, precise, and are easily manufactured. The PCB bracket can then be attached to your project using screws, straight solder, right-angle headers, or dual-row headers. The video in the article shows you the process step-by-step, including how to make the board non-rectangular and how to place screw holes at angles.

Faulhaber gearmotor Faulhaber Gearmotor with Encoder and Right-Angle Shaft
A number of surplus sites are selling a compact, low-current motor that is perfect for robotics. The 6V motor includes a 141:1 gearhead, a magnetic quadrature encoder, and a 90-degree output shaft.
Toggling a switch to control motor direction. DPDT Bidirectional Motor Switch
Controlling a motor in both directions (and on/off) with a single physical switch. You can control a motor without any transistors or chips.
The TelCom TC4424A 3-amp dual MOSFET driver chip H-Bridge Motor Driver
A wiring diagram, photograph, and movie of an H-bridge dc motor driver circuit implemented with a TC4424A, TC4427A, MAX4427, or IXDN404 dual MOSFET driver IC. Very useful for running small bot gear motors.
Motor mount clamp block Motor Mount Clamp Block
Sometimes, a small electric motor will lack mounting screw holes. Other times, a robot or device needs several things tied to the motor mount. A simple slitted block with screws can securely hold a motor in ways that other mounts cannot.
An aluminum LEGO compatible hub An Aluminum LEGO Hub Made on a Mill
Because LEGO tires, gears, and axles are great for building robots, I keep coming up with new adapters to connect them to standard motors. This latest method applies to the LEGO wheels that don’t have cross-axle holes. Couplers and hubs are best made on a lathe, but this shows that you can create miniature round parts on a mill.
A pair of couplers for Lego wheels and gears Making a Lego Wheel to Gearhead Motor Coupler on a Lathe
Lego has some fantastic wheels to use on robots. But, Lego doesn’t have a wide selection of motors. Here’s how you can machine an adapter on a lathe to use Lego tires with off-the-shelf gearhead motors.
Sturdy motor coupler thumbnail Sturdy Attachment of a Lego Wheel to a Gearmotor
Nothing is more pathetic than a robot that has lost a wheel. Couplings based on the standard mating cross axle have a habit of sliding off. But, the peg holes present in larger wheels provide opportunities to securely attach the hub with screws. Using a lathe, milling machine, digital readout, magnets, PVC plastic, and a carefully-drafted layout can produce a rugged Lego coupler. Ah, an article on math and machining; what could be more universally appealing?
Tiny motors ready to spin Tiny Motors
Miniature motors are wonderful for B.E.A.M. robots or moving small loads. A plentiful source of inexpensive commercial motors are those used as vibrating alerts in pagers and cell phones. But how does one remove the metal offset weight?
Miniature shear with gearmotor added on Motorizing a Shear for Cutting PCBs
Machining a motor coupler with a round hole and a square hole. Making a motor mounting bracket adapter. Damage assessment of an over-torqued gearmotor.
Three varieties of LEGO crown gears LEGO MindStorms Crown Gears
There are at least three variations of the LEGO 24-tooth crown gears. Watch out that you don’t accidentally mismatch pairs!