During the development of robots, one of the most critical considerations is the selection of the robot platform, as the chassis often serves as the foundational element determining the overall performance and application scenarios of the robot. Currently, common chassis types on the market are classified by drive configuration, including 2-wheel drive, 4-wheel drive, Ackermann chassis, 4WD-4WS robot platform, and tracked chassis. Different chassis types offer distinct advantages in terms of performance, load capacity, obstacle-crossing capability, turning radius, control load capacity, and cost. Selecting the appropriate robot chassis is crucial during the initial stages of a robotics project, as it directly impacts the project’s overall cost and commercialization outcomes. This article will introduce various common robot chassis types and guide readers in selecting the most suitable option for their specific project through comparative analysis.
Quick Overview of Mobile Robot Platform Classification Based on Different Drive Types
| Chassis model | Drive type | Use cases |
| Dual wheel differential | Two-wheel drive | Indoor AGV |
| Four-wheel differential | Four-wheel independent drive | Unmanned vehicle for complex terrain |
| Ackermann model | Front-wheel steering + rear-wheel drive | Outdoor unmanned vehicle |
| McNaughton wheel | Four-wheel omnidirectional drive | Low-speed, short-distance omnidirectional robot |
| Four omnidirectional wheels | Four-wheel omnidirectional drive | Warehouse logistics vehicle, follow-up wheel |
| Three omnidirectional wheels | Three-wheel omnidirectional drive | Warehouse logistics vehicle, follow-up wheel |
| Four steering wheels | Four-wheel independent drive + independent steering | Excellent passability and off-road capability |
| Dual steering wheels | Two-wheel independent drive + steering | Medium-load AGV |
| Single steering wheel | Single steering wheel | Tractor, forklift |
| Tracked | Two-wheel drive | Off-road vehicle |
Two-Wheel Differential Robot Platform
Working principle of dual-wheel differential:
The two-wheel drive robot chassis (abbreviated as 2WD) features a two-wheel differential chassis with two drive wheels located on either side of the chassis. Each wheel is independently controlled for speed, enabling chassis steering control by setting different speeds for each wheel. Typically, the chassis is equipped with one or two auxiliary support casters. When both drive wheels move at the same speed, the robot moves in a straight line. When the speeds of the two wheels differ, the robot rotates around a central point, thereby achieving steering. Thus, the 2WD robot chassis achieves various curves and steering maneuvers by controlling the speed difference between the two drive wheels.
Advantages and disadvantages of dual-wheel differential robots:
| Advantages | Disadvantages |
| Cost advantage, relatively inexpensive compared to other chassis | Limited obstacle crossing ability, not suitable for complex outdoor terrain |
| Low maintenance costs due to fewer parts and easy installation and maintenance | Limited load capacity, suitable for lightweight robots |
| Mature technology, mature drive solution, low manufacturing costs | Limited movement direction, unable to move in all directions |
| Flexible steering, capable of rotating on the spot, suitable for complex indoor terrain | Poor stability, poor performance in high-speed applications |
Applications of dual-wheel differential:
| Scenario | Description |
| Education and scientific research | Various laboratories and universities purchase dual-wheel differential drive systems as research and educational platforms because dual-wheel chassis are low-cost and easy to integrate with sensors for navigation and path planning research. |
| Cleaning robots | Home and commercial vacuuming robots also use dual-wheel drive chassis, relying on on-the-spot turning and flexible movement to cover more cleaning areas. |
| Service robots | Shopping mall guidance robots and restaurant delivery robots are all manufactured with differential drive chassis, allowing them to move flexibly among crowds and tables. |
| Indoor delivery robots | In schools, hospitals, and offices, most package delivery robots are manufactured using dual-wheel drive chassis. |
Four-Wheel Differential Robot Chassis
Four-wheel differential working principle:
Four-wheel drive robot chassis (abbreviated as 4WD), four-wheel drive chassis typically have four independent motors, with each wheel capable of independent control. The steering power source is generated by the left-right difference of the motors. After power is output from the motors, it passes through a reducer and is finally transmitted to the front and rear axles on the left and right sides before reaching the wheels. When all four wheels are driven synchronously, all wheels maintain the same steering angle, and the chassis maintains straight-line travel. When the speeds of the left and right sides of the vehicle differ, steering is achieved through the speed difference between the two sides.
Advantages and disadvantages of four-wheel differential robots chassis:
| Advantages | Disadvantages |
| Strong load capacity: Four drive wheels share the weight, supporting a greater load compared to two-wheel drive. | High energy efficiency: Four-motor drive requires high battery life. |
| Good passability: Suitable for indoor and relatively flat outdoor surfaces, such as slopes and low doors. | Insufficient steering flexibility: High friction when turning on the spot, less flexible than dual-wheel differential. |
| Good stability: Four-point support reduces tilting caused by uneven ground, and is less prone to rollovers and drifting compared to two-wheel drive, especially in rainy weather. | Complex structure: Compared to dual-wheel drive chassis, the structure is relatively complex. |
| Uniform power: Reliable performance in transportation and industrial settings. | Severe tire wear: When turning on the spot, the friction between the tires and the ground is high, resulting in severe tire wear. |
Common applications of four-wheel differential drives robot platform:
| Scenario | Description |
| Transportation robot | Used for material handling in workshops or warehouses, indoor scenarios with load requirements |
| Industrial inspection robot | Substations, factories, warehouse inspections |
| Park security robot | Campus patrols, park patrols, etc. Most use four-wheel drive |
| Research platform | Scientific research for algorithm research and complex environment research |
The Ackman Robot Platform Model
Ackermann Robot Chassis Operating Principle:
The Ackermann robot platform structure is similar to that of a real car chassis. It achieves stable turning by utilizing the difference in turning angles between the inner and outer wheels caused by the disparity in turning radii of the left and right wheels during front-wheel steering. This is used to control the direction of the vehicle’s movement, while the rear two-wheel drive system is used to control speed. The Ackermann chassis has two combination modes: front-wheel steering + rear-wheel drive or front-wheel steering + four-wheel independent drive. The four-wheel independent drive configuration is more expensive. The advantage of the four-wheel drive Ackermann chassis over the two-wheel drive Ackermann chassis is that it provides more stable performance in rainy or snowy conditions, as each wheel has its own driving force, resulting in better traction and stability.
Advantages and disadvantages of the Ackermann platform
| Advantages | Disadvantages |
| Realistic vehicle simulation: Widely used in intelligent driving and autonomous driving research. | Large turning radius: Not suitable for driving on narrow roads. |
| Good high-speed stability: More stable than differential gears at high speeds. | Complex structure: The steering structure and system increase manufacturing and maintenance costs. |
| High energy efficiency: Reduces lateral tire slippage, effectively lowering energy consumption and wheel wear. | Lack of flexibility: Compared with two-wheel drive and four-wheel drive, the Ackermann chassis has a large turning radius, cannot turn on the spot, and cannot make U-turns on narrow roads. |
Ackermann chassis application scenarios
| Scenarios | Description |
| Autonomous vehicle platforms | Widely used in autonomous test vehicles for path planning, perception, and control algorithm verification |
| Agricultural scenarios | Most robots used for spraying crops in farmlands and transporting fruits in orchards are based on the Ackermann chassis structure |
| Security and inspection robots | Large industrial parks, ports, and highways require rapid long-distance inspection environments |
McNaughton Wheel Robot Platform
Working principle
The McNaughton wheel is a special type of wheel consisting of a hub and rollers: the hub serves as the main structural support for the entire wheel, while the rollers are small passive wheels mounted on the hub. In the market, the angle between the hub’s axis and the roller’s rotation axis is generally categorized into three types: 30 degrees, 45 degrees, and 60 degrees. The chassis requires parallel alignment or paired installation for use. When the four wheels are driven in different speeds and directions, the robot can achieve movement in any direction.
| Movement direction | Implementation principle | Movement diagram |
| lateral movement | The wheels on the left and right sides turn in opposite directions, while the front and rear wheels turn in the same direction.
Note: “The same front and rear” here does not mean that the direction of wheel rotation looks exactly the same to the naked eye, but rather that the combination relationship of the front two wheels is the same as the combination relationship of the rear two wheels. See the left diagram for understanding: Front row: one forward + one backward Rear row: also one forward + one backward The “pattern” of the front and rear rows is the same, just opposite left and right. |
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| Move diagonally | By coordinating the four wheels at a certain speed difference, diagonal movement in any direction and angle can be achieved. | |
| Rotate in place | By turning the left and right wheels in opposite directions and the front and rear wheels in opposite directions, rotation in place can be achieved. | |
| Move forward or backward | By turning the four wheels at the same speed and in the same direction, forward or backward movement can be achieved. |
Advantages and disadvantages of McNaught wheels
| Advantages | Disadvantages |
| Omnidirectional movement: Can move forward, backward, sideways, diagonally, and turn around in place without changing the direction of the vehicle, enabling complex movements. Suitable for working in narrow spaces (such as material handling between production lines in factories). | Limited load capacity: Prolonged operation under high loads can accelerate wheel wear, thereby affecting wheel lifespan |
| High Flexibility: Can quickly respond to commands and adapt to dynamic and complex environments, adjusting paths flexibly during obstacle avoidance. | High cost: The manufacturing process is highly complex, involving multiple motors and control systems, which increases overall costs |
| Good Stability: When transporting valuable or stability-sensitive items, it reduces cargo movement, ensuring transportation safety. | High road condition requirements: Operation requires a smooth surface with moderate friction; otherwise, it may affect movement precision and stability |
| No Traditional Steering Structure: Steering is achieved through independent wheel drive and angle adjustment, simplifying mechanical structure and reducing maintenance costs. | High energy loss: Interaction between wheels can result in energy waste, leading to relatively low efficiency and potentially limited range |
McNaughton Wheel Application Scenarios
| Scenarios | Description |
| Specialized Operations | Military reconnaissance: Perform reconnaissance missions in complex terrain, enhancing stealth and mobility through omnidirectional mobility capabilities |
| Education | Emergency rescue: Rapidly enter narrow spaces at disaster sites for search and rescue operations; its flexibility aids in navigating complex terrain and obstacles |
| Service Robotics | As an educational platform, it helps students understand robot motion principles and control technologies |
| Industrial Logistics | Medical robotics: Used in hospital environments for medication delivery, its omnidirectional mobility makes it easier to adapt to narrow spaces such as hospital corridors and patient rooms |
Summary: Thanks to its omnidirectional movement and flexibility, the McNaughton wheel chassis is widely used in industrial logistics, service robots, special operations, and other fields, especially in scenarios where space is limited and high precision movement is required.
Omnidirectional Wheel Chassis (Four Wheels)
Advantages and disadvantages of omnidirectional wheel chassis:
Omnidirectional Wheel Chassis advantages and disadvantage
| Advantages | Disadvantages |
| Omnidirectional mobility: Capable of moving in any direction on a flat surface, offering high flexibility and suitability for narrow spaces and complex environments | Limited applicability: In scenarios requiring high-speed driving or navigation on rugged terrain, omnidirectional chassis are not the optimal choice. |
| Lower cost: Compared to other types of omnidirectional mobile platforms, such as Mecanum wheel platforms, omnidirectional platforms have a relatively simple structure and typically do not require complex steering mechanisms or multiple motors, resulting in lower costs | Complex control: Due to its complex movement patterns, precise control of each wheel’s steering and direction is required to achieve accurate movement trajectories. |
| Reduced tire wear: Due to the unique contact method between the tires and the ground during rolling, the friction on the tires is relatively low, extending their service life. | Limited load-bearing capacity: Not suitable for carrying heavy loads; overloading may cause tire deformation, hub damage, or chassis instability. |
| Reduced energy consumption: The omnidirectional wheel’s movement is highly efficient, eliminating the need for additional energy to overcome significant friction or steering resistance. | Poor lateral stability: Lateral movement is prone to lateral slippage due to external forces. |
Omnidirectional wheel robot applications:
| Scenarios | Description |
| Industrial logistics sector | Warehouse logistics robot: Flexibly navigates between dense shelves to achieve precise transportation and positioning of goods, improving warehouse efficiency. |
| Humanoid robot sector | Provides guided tours and interactive services at exhibitions and events, or performs cleaning and companionship functions in home settings. |
| Special scenario applications | Security patrol robot: Flexibly patrols complex terrain or narrow passages to improve security efficiency. |
| Service robot sector | Restaurant Service Robot: Navigates between tables with obstacle avoidance capabilities, efficiently completing meal delivery and collection tasks to enhance service experience |
Omnidirectional Wheel Chassis (Three Wheels)
The three-wheeled omnidirectional mobile platform has excellent mobility and a simple structure. Its three wheels are spaced 120° apart, and each omnidirectional wheel consists of several small rollers, with the generatrices of each roller forming a complete circle. The robot can move along the tangent direction of the wheel surface or along the axis of the wheel, and the combination of these two movements enables movement in any direction within a plane. Compared to a two-wheel differential drive control system, the three-wheel omnidirectional drive solution reduces the time required for the robot to move between multiple fixed points. Two-wheel differential control requires adjusting the robot’s posture first, and the omnidirectional wheels at the rear of the two-wheel chassis can affect the robot’s posture, making chassis stability control more challenging. In contrast, three-wheel omnidirectional control does not require consideration of these factors.
Advantages and disadvantages of three-wheel omnidirectional wheels
| Advantages | Disadvantages |
| Omnidirectional mobility: Enables translation and rotation in any direction on a plane without the need to adjust the direction before moving | High control precision requirements: Precise control of the speed and direction of each wheel is required to achieve smooth omnidirectional movement, placing high demands on sensors and control algorithms |
| Low cost: Compared to four-wheel omnidirectional wheels or Mecanum wheel chassis, three-wheel omnidirectional chassis reduce the number of motors and drive mechanisms, thereby lowering hardware costs | Low power efficiency: The rolling direction of omnidirectional wheels is perpendicular to the direction of hub movement, causing some power to be diverted laterally, resulting in relatively low driving force for straight-line travel |
| Simple structure: No complex steering mechanisms are required, and the algorithms are relatively simple, making precise motion control easier to achieve | Limited load-bearing capacity: The three-wheel structure has a relatively dispersed load distribution, resulting in overall load-bearing capacity inferior to that of a four-wheel chassis, thereby limiting load capacity. |
| Lower energy efficiency: Omnidirectional wheels have relatively low friction, and tire wear is relatively uniform, reducing energy loss | Insufficient lateral stability: Omnidirectional wheels are prone to slipping under lateral forces, leading to poor chassis stability and making them unsuitable for operation on rugged or uneven terrain. |
Three-wheel omnidirectional chassis application scenarios
The three-wheeled omnidirectional chassis, with its flexible mobility and adaptability, is used in scenarios that require high space utilization efficiency, movement precision, and flexibility. It has significant advantages in industries such as industrial, emergency response, scientific research, and service.
| Application Scenarios | Description |
| Emergency Rescue | Disaster Site Reconnaissance: In disaster sites such as earthquakes and fires, it can quickly navigate narrow spaces, flexibly adjust its posture through omnidirectional mobility, transmit on-site images and data, and provide support for rescue operations. |
| Security Field | In complex terrains or enclosed spaces, such as underground parking lots and warehouses, it can perform 360° patrols, promptly detect situations, and issue alarms. |
| Service Robot Field | Medical Assistance: In hospital wards or operating rooms, it can carry medical equipment or medications, providing healthcare personnel with convenient mobile support. |
| Industrial Automation Field | Logistics Handling and Material Loading/Unloading: In factory workshops, the three-wheeled omnidirectional chassis can maneuver flexibly in narrow spaces, enabling precise logistics handling and rapid material loading/unloading of equipment. |
4WD-4WS Robot Platform
The AGV achieves straight-line movement, lateral movement, turning, and obstacle avoidance through the angle and speed of the four steering wheels. Motor power is directly converted into driving power, while the steering mechanism is controlled by a separate motor, resulting in a simple and compact structure. AGVs with a four-wheel steering chassis structure can simultaneously meet the flexibility requirements of narrow working spaces and the applicability requirements of complex workshop road conditions.
There are three types of wheels commonly found on four-wheel drive chassis on the market. The following table provides a quick comparison of their advantages and disadvantages.
| Type | Picture | Steering method | Working Principle | Advantages | Disadvantages | Use cases |
| Differential wheel four-wheel drive |  |
Left-right wheel differential steering | The left and right wheels have different speeds, and both the front and rear wheels can be driven. | 1. Simple structure
2. Easy maintenance 3. Low cost 4. Low energy consumption |
1. Unable to rotate or move sideways in place
2. Dependent on control algorithms 3. Slow steering response |
Industrial handling, light load inspection, open areas |
| Horizontal steering wheel four-wheel drive |  |
Horizontal servo steering | The front and rear wheels are equipped with horizontal servos, enabling them to rotate in place and move sideways. | 1. High mobility
2. Rotates in place, moves sideways 3. Suitable for narrow spaces |
1. High cost
2. Complex structure 3. High maintenance cost |
High-precision logistics handling, garden mowers, special inspection |
| Vertical steering wheel four-wheel drive |  |
Vertical servo steering | The front and rear wheels are equipped with vertical servos, suitable for small and flexible designs, with some capable of lateral movement. | 1. Compact structure
2. Suitable for small robots 3. Good expandability |
1. Complex control algorithms
2. Limited load capacity 3. Lower maneuverability than horizontal rudders |
Small inspection robot, portable lawn mowing robot, light-duty work platform |
Dual Steering Wheels Robot Platform
The chassis consists of two drive wheels and one or more trailing wheels, and is typically used in medium-load AGVs. The dual-steering wheel chassis structure design enables 360° rotation and omnidirectional lateral movement, offering high flexibility and precise operating accuracy.
Single Rudder Wheel Robot Chassis
The single steering wheel drive structure consists of 1 steering wheel and 2 directional wheels, and is widely used in forklifts. This structure can directly adapt to various ground conditions, ensuring that the drive steering wheel remains in contact with the ground at all times. Depending on the distribution of the vehicle’s center of gravity, the steering wheel typically bears approximately 50% of the vehicle’s self-weight, resulting in strong traction. The single steering wheel structure is simple and cost-effective. Since it is a single-wheel drive system, there is no need to consider motor compatibility issues, making it suitable for a wide range of environments and applications.
Tracked Chassis
Track chassis are divided into two major product categories: steel track chassis and rubber track chassis. Steel chassis have a load capacity ranging from 2 tons to 120 tons, while rubber chassis have a load capacity ranging from 0.5 tons to 12 tons.
