What is the difference between a four-wheel steering robot chassis and a differential chassis?

Selecting the appropriate chassis design is crucial for determining a robot's performance, maneuverability, and application scenarios. As the two most common mobile platforms—four-wheel steering with four-wheel drive (4WS-4WD) robot chassis and differential drive robot chassis—they exhibit significant differences in structure, control complexity, and applicability. These differences directly impact cost, maintenance, and project efficiency. This article analyzes their differences to help you better understand and select the solution best suited to your needs, thereby achieving superior cost-effectiveness in practical applications.

The four-wheel drive robot chassis essentially refers to a chassis architecture featuring “four independently driven wheels + four independently steered wheels.”By leveraging the capability of each wheel to independently control both direction and power, it achieves omnidirectional mobility including on-the-spot turning, lateral movement, and diagonal travel. This makes it highly suitable for specialized robots and high-end AGV/AMR applications demanding superior space utilization, positioning accuracy, and adaptability to complex environments.

Four-Wheel Steering (4WS):

Refers to all four wheels having independent steering capability.

Each wheel can rotate independently around its vertical axis (or near-vertical axis) to alter its direction of travel.

Four-Wheel Drive (4WD):

Refers to all four wheels having independent drive capability.

Each wheel is powered by an independent motor (or via a transmission mechanism), enabling precise control over the speed and torque of each wheel.

By precisely coordinating the steering angles and drive speeds of all four wheels, the chassis can achieve multiple motion modes that conventional chassis cannot accomplish:

Zero-Turn / Pivot Turn: All four wheels are adjusted to turn tangentially, while the drive wheels rotate in unison, enabling the robot to rotate in place around its own center point.

Crab Steering / Sideways Motion: The steering angles of all four wheels are adjusted to be perpendicular to the robot's longitudinal axis. Simultaneously, the drive wheels rotate in the same direction, enabling the entire robot to move sideways to the left or right.

Diagonal Movement: By adjusting the steering angle of the wheels to any diagonal direction, the robot can move in a straight line along any path.

Tight Turns: Achieved by applying different steering angles and speed differentials to the inner and outer wheels, enabling turns with an extremely small radius.

High-Precision Path Tracking: Independent control of each wheel enables highly accurate path tracking and positioning.

Omnidirectional Mobility: Combining lateral movement, diagonal travel, and on-the-spot turning, the robot can move in any direction and adjust orientation at any angle within a plane. Unlike differential drive or steering wheel chassis, it eliminates the need to turn before moving forward. This makes it ideal for narrow, complex environments requiring precise positioning, such as warehouse aisles, factory workshops, and disaster relief sites.

High Traction and Stability: Four-wheel independent drive delivers superior traction and stability on uneven or low-friction surfaces (e.g., sand, snow, slippery terrain) with optimized power distribution.

Slip-Free Steering: By precisely coordinating steering angles and wheel speeds, pure rolling steering is theoretically achievable, reducing tire wear and energy loss (especially on smooth, hard surfaces).

Differential robot chassis (i.e., two-wheel differential drive chassis) is a wheeled mobility solution that achieves steering through the speed difference between two independently driven wheels: the left and right drive wheels are controlled by separate motors, supported by one or more unpowered caster wheels, eliminating the need for physical steering mechanisms.

Drive Structure:

Two drive wheels: One on each side, each powered by an independent motor (typically DC motors + encoders).

One/two idler wheels: Usually one caster wheel or two fixed casters (e.g., in a three-wheel configuration), serving solely for support without power or steering control.

The primary differences between four-wheel steering and four-wheel drive robot chassis and four-wheel differential chassis lie in steering methods, maneuverability, and application scenarios: Differential chassis rely on speed differences between left and right wheels to achieve slip steering—a simple yet tire-wearing approach. In contrast, four-wheel steering and four-wheel drive (typically referring to independently steered wheels) enable complex maneuvers like turning on the spot, lateral movement, and crab steering. These systems offer smoother, more precise operation, making them suitable for high-precision tasks and complex environments, though they feature more intricate structures and control systems.