A single-steering-wheel AGV typically uses a three-wheel configuration consisting of one integrated steering drive wheel and two passive support wheels. The steering drive wheel provides the traction required to move the vehicle and controls its travel direction by changing its orientation. The two rear support wheels carry part of the vehicle load and support overall movement.
Compared with AGVs using dual-wheel differential drive, a single-steering-wheel design does not rely on speed differences between two independently driven wheels to steer the vehicle. Its chassis and drive arrangement are relatively simple, making it suitable for indoor logistics and material handling applications with defined travel routes. However, its steering range and movement capabilities depend on the wheel layout and steering mechanism. A conventional configuration generally cannot rotate in place around the center of the vehicle in the same way as a differential drive AGV.
1. Basic structure of a single-steering-wheel AGV
A common configuration places one integrated steering drive wheel at the front of the AGV and two passive support wheels at the rear.
1. Front steering drive wheel
The front steering drive wheel is the vehicle's only powered wheel. It performs both traction and steering functions. Its assembly typically integrates a drive motor, travel gearbox, steering motor, steering reduction mechanism, encoders, and brake.
The drive motor generates the power required for vehicle movement. The travel gearbox transfers motor torque to the wheel, while the steering motor uses a separate reduction and gear transmission mechanism to change the wheel's horizontal orientation. This allows the AGV to follow its programmed route.
The steering drive wheel commonly uses a rubber or polyurethane tread to provide the required friction, wear resistance, and load capacity. The wheel material, diameter, and structural design should be selected according to the vehicle load, operating speed, and floor conditions.
2. Rear passive support wheels
The two rear wheels support the AGV chassis and transfer part of the vehicle load to the floor. They do not directly generate driving force and move passively as the vehicle travels.
Depending on the chassis design, the rear support wheels can be fixed follower wheels or swivel casters. Fixed follower wheels maintain a fixed rolling direction relative to the chassis, while swivel casters can rotate around their vertical axes to adjust their orientation during vehicle movement.
These two arrangements have different mounting requirements and movement characteristics. Selection should take into account the chassis dimensions, center of gravity, load distribution, and turning requirements.
A three-wheel layout provides three contact points that define a stable support plane. However, this does not mean that the load is automatically distributed evenly across all three wheels. Actual load distribution depends on the vehicle's center of gravity, wheel mounting positions, and chassis design.
2. Main components of a single-steering-wheel drive unit
Although a single-steering-wheel AGV has only one powered travel wheel, the steering drive assembly contains several mechanical, transmission, and control components. These can be divided into the following groups.
1. Drive motor
The drive motor provides the power required for forward and reverse travel. Servo motors and other motor types suitable for mobile robot drive systems are commonly used.
Motor torque passes through the travel gearbox before reaching the drive wheel. By controlling the motor speed and rotation direction, the system can adjust the AGV's travel speed and forward or reverse movement.
2. Steering motor
The steering motor changes the orientation of the drive wheel. It is one of the main components that distinguishes a steering drive unit from a conventional drive wheel.
When the AGV needs to turn, the control system sends an angle command to the steering motor. The motor drives the steering assembly through a reduction mechanism and gear transmission, rotating the wheel to the required angle.
The drive motor and steering motor control travel speed and wheel direction separately. Both systems must operate together for the AGV to follow its programmed route.
3. Gear reduction and transmission mechanisms
A single-steering-wheel drive unit generally has separate travel and steering transmission systems. Each performs a different power transmission function.
The travel gearbox connects the drive motor to the wheel output and reduces rotational speed while increasing output torque. The steering transmission system consists of a steering gearbox and associated gears. It transfers torque to the rotating assembly and turns the steering drive wheel around its vertical axis.
Some steering drive units use planetary gearboxes, worm gearboxes, or other reduction mechanisms. The selection depends on the required output torque, available installation space, and steering accuracy.
The travel gearbox and steering reduction mechanism serve different purposes. They should not be treated as interchangeable components. Their mounting positions and mechanical interfaces must also be considered in the assembly design.
4. Encoders
Encoders monitor the operating condition of the steering drive unit. A typical system includes travel speed feedback and steering angle feedback.
The travel feedback encoder detects the rotational speed and position of the drive motor or wheel. The control system uses this information to adjust motor output.
The steering feedback encoder measures the actual steering position and sends angle information to the control system. This allows the steering drive wheel to move to the commanded position.
The information available to the control system depends on the encoder mounting position. An encoder installed at the motor end generally requires the steering gearbox ratio and mechanical zero position to be considered when calculating the actual wheel angle.
5. Limit devices
Limit devices restrict the permitted steering range and prevent the wheel from turning beyond the limits of the mechanical structure or cable arrangement.
Common designs include limit switches, proximity sensors, and mechanical stops. Some steering drive units also use encoder feedback to establish electronic limits through the control program.
When the steering assembly approaches its preset angular limit, the control system can restrict or stop the steering motor based on the sensor signal. Mechanical stops provide physical restrictions in designs that use them. The specific arrangement depends on the steering angle and internal mechanical structure.
6. Brake
The brake is generally installed at the drive motor or an appropriate position in the transmission system. Its main function is to hold the AGV after stopping.
Some steering drive units use electromagnetic brakes with a spring-applied, electrically released design. The brake is released during operation and applies holding force when the vehicle stops or loses power, preventing unintended movement.
The brake holding capacity should be selected according to the vehicle weight, parking requirements on slopes, and transmission arrangement. Motor power alone is not sufficient for brake selection.
7. Steering support and mounting structure
The steering drive unit is connected to the AGV frame through a mounting base, support plates, bearing housings, and related connecting components.
During steering, the drive wheel and associated components rotate around a vertical steering axis. The mounting structure must therefore provide sufficient support strength and maintain the required rotational alignment.
For non-standard steering drive units, the dimensions of mounting bases, connecting shafts, bearing housings, and other metal components may need to be adjusted to match the vehicle layout. We can manufacture these metal parts through CNC precision machining according to customer-supplied engineering drawings.
3. Working principle of a single-steering-wheel AGV
A single-steering-wheel AGV controls vehicle movement through one integrated steering drive wheel. The drive motor provides traction, while the steering motor adjusts the wheel orientation. Both systems work together to achieve straight-line travel and turning.
1. Straight-line travel
When the AGV receives a straight-line travel command, the control system first sets the steering angle so that the drive wheel points in the required direction.
The drive motor then starts rotating. Its output torque passes through the travel gearbox to the wheel, moving the AGV forward or backward. The travel encoder continuously reports the motor's operating condition, allowing the control system to adjust motor output according to the target speed.
2. Turning
When the AGV needs to change direction, the control system calculates the required steering angle from the target path and sends a command to the steering motor.
The steering motor drives the wheel through the reduction and gear transmission mechanism, adjusting it to the commanded orientation. The drive motor then provides traction in accordance with the new steering angle, moving the vehicle along its new path.
The rear support wheels follow the movement of the chassis. Depending on their design, they either roll in a fixed direction or passively adjust their orientation.
Unlike a dual-wheel differential drive system, a single-steering-wheel AGV turns primarily by changing the orientation of its powered wheel rather than by creating a speed difference between two drive wheels.
4. Advantages and limitations of single-steering-wheel AGVs
Advantages
Relatively simple chassis arrangement. A single-steering-wheel configuration uses one powered wheel and two passive support wheels to form the basic three-wheel layout. Compared with systems requiring multiple powered wheels or separate steering wheels, the drive components are more concentrated and the chassis arrangement is relatively simple.
Clear division of control functions. The drive motor controls vehicle movement, while the steering motor controls wheel orientation. The two systems operate through the vehicle control system. This arrangement can meet basic path-following requirements in material handling applications with relatively defined travel routes.
Concentrated installation space. The traction and steering functions are integrated into one steering drive assembly. This simplifies the arrangement of other drive components on the chassis and can leave more space for cargo handling structures.
Suitable for standard indoor material handling. On relatively flat floors and in warehouses or production areas with sufficient aisle width, this configuration can handle straight-line travel, turning, and routine path-following operations.
Limitations
Turning space is restricted by the chassis design. The turning radius of a single-steering-wheel AGV depends on the powered wheel mounting position, steering angle, wheelbase, and overall vehicle dimensions. Unlike a conventional dual-wheel differential drive AGV, it cannot rotate in place around the midpoint of its drive axle by reversing two drive wheels. The vehicle's actual turning envelope must therefore be considered during path planning.
Limited movement modes. A conventional three-wheel single-steering-wheel configuration mainly supports forward travel, reverse travel, and curved turning. It cannot move directly sideways or rotate in place while keeping the vehicle center stationary. Applications requiring lateral movement or omnidirectional motion generally need a different wheel arrangement.
Steering geometry must account for forward and reverse travel. For AGVs that frequently move in both directions, the relationship between steering angle and vehicle movement may differ depending on the direction of travel. The control system must account for wheel position and vehicle movement direction when calculating the path.
5. Applications and selection considerations for single-steering-wheel AGVs
Single-steering-wheel AGVs are commonly used in warehouse logistics, production line material delivery, and indoor automated material handling. They are particularly suitable for applications with relatively defined routes that do not require special lateral movement or in-place rotation.
During selection, the main factors to consider include drive wheel load capacity, motor output torque, gear ratio, steering angle, tread material, and the space available for vehicle turning.
For AGVs carrying heavier loads, the actual vertical load on the steering drive wheel should be checked. The available traction must also be evaluated according to the friction conditions between the wheel and the floor. The steering mechanism must provide sufficient output torque for the vehicle weight and steering resistance.
The installation height, mounting hole positions, bearing support structure, and motor installation space should also be checked to ensure that the drive and steering mechanisms fit the chassis correctly.
For non-standard AGVs, the steering drive mounting base, bearing housings, connecting shafts, gears, and other metal components may need to be manufactured according to the actual engineering drawings. Hansheng Automation provides CNC precision machining of components based on customer-supplied drawings for automated logistics equipment.
In addition to AGV chassis components, our custom machining services cover precision yacht parts, tobacco packaging machinery components, RC racing car structural parts, and filling machinery components. We manufacture these parts according to customer drawings and assembly dimensions.
