An electric automatic folding system uses a motor or electric actuator to drive a transmission mechanism, moving the UAV arms between their extended and folded positions. The control system manages the movement, monitors the arm positions, and checks whether the locking mechanism has engaged. The main purpose is to reduce the aircraft's storage size and make deployment and recovery more convenient.
A typical electric folding mechanism consists of a drive unit, transmission mechanism, arm hinge, position sensors, locking structure, and control circuit. The actual design depends on the arm dimensions, aircraft weight, folding angle, and loads expected during flight.
Drive System
Electric folding systems commonly use miniature DC motors, servo motors, or other electric actuators. The drive unit is selected according to the required output torque, operating speed, positioning accuracy, and available installation space.
For mechanisms that require higher output torque, a reduction mechanism can be installed behind the motor. Options include planetary gearboxes and other gear transmission systems. A reduction mechanism lowers output speed and increases torque, but a planetary gearbox is not required in every folding design.
Some designs use an electric linear actuator or motorized push rod. It converts electrical energy into linear motion, which is then transferred through a linkage to rotate the arm. Other designs use a servo motor combined with gears or linkages to extend and retract the arms.
Transmission and Actuation Mechanism
The arm is usually connected to the UAV body through a hinge or pivot shaft. During folding, it rotates around this connection. The motor's rotary output or the linear motion of an actuator must be transferred to the arm through a suitable transmission mechanism.
Common transmission options include:
Gear transmission: A driving gear transfers motion to a driven gear. The gear ratio can be selected to adjust output speed and torque.
Linkage mechanisms: Crank-rocker or parallel four-bar linkages convert motor or actuator movement into arm rotation. A four-bar linkage can also control the arm's movement path according to the design requirements.
Lead screws and electric linear actuators: These convert motor rotation into linear thrust. A connecting component then transfers the force to the arm, causing it to rotate around the hinge.
Timing belts or wire ropes: Flexible transmission elements can be used in some lightweight designs. Their tension, wear, backlash, and long-term reliability need to be considered.
The choice of mechanism depends on the required folding angle, available movement space, structural stiffness, transmission efficiency, and total aircraft weight.
Control and Position Detection System
The automatic folding system requires a controller to coordinate the drive unit and determine the current position of each arm. Common position-detection devices include Hall sensors, rotary encoders, limit switches, and microswitches.
The controller can start the folding sequence according to a preset program or operator command. It stops the drive unit when the arm reaches the specified position. For systems that require accurate angle control, an encoder or another position-feedback device can be used to form a closed-loop control system.
Some designs also monitor motor current or actuator load changes to detect obstruction, mechanical jamming, or abnormal loads. However, current variation is only one source of fault information. It cannot replace reliable mechanical stops and locking structures.
When an arm reaches its extended position, it must be secured by a mechanical latch, locking pin, or another locking device. The locking structure must withstand vibration, inertial forces, and aerodynamic loads during flight. Position sensors and limit switches can report the locking status, but they do not replace the load-bearing function of the mechanical lock.
Power Supply and Safety Design
The electric folding mechanism can be powered by the UAV's main battery, a separate power source, or a dedicated power management circuit. The power supply design depends on motor power, starting current, operating frequency, and the aircraft's electrical system.
Common safety provisions include:
Overcurrent and stall protection: The drive circuit monitors current and stops the motor when an overload or mechanical obstruction occurs. This helps reduce the risk of damage to the motor and transmission components.
Arm deployment confirmation: Before takeoff, all arms should be fully extended and securely locked. If the required condition is not met, the control system should prevent motor startup or issue a fault warning.
Mechanical locking: The extended arms must be secured by a reliable mechanical structure to prevent accidental folding due to flight vibration or external loads.
Protection against unintended operation: Operation confirmation, status interlocks, and transport locks can help prevent unintended folding during transport, maintenance, or flight.
Abnormal operating conditions: If sensor signals are abnormal, the motor stalls, or the mechanism becomes obstructed, the controller should stop the movement and prompt an inspection rather than continue forcing the mechanism.
Arm folding and deployment should normally take place while the UAV is in a safe ground state. Unintended arm movement during flight can change the aircraft's aerodynamic configuration, center of gravity, and flight-control characteristics. Forced folding should therefore not be treated as a normal emergency procedure.
Main Parameters Affecting Electric Folding Performance
UAVs differ in arm structure and operating loads. There are no universal values for motor torque, folding time, or repeatability across all electric folding systems. The following parameters should be evaluated during design:
Output torque or thrust: The drive unit must overcome arm weight, hinge friction, transmission resistance, and inertial loads during movement.
Folding angle and travel range: These determine the required movement from the extended position to the folded position.
Operating time: The folding speed should meet deployment requirements without causing excessive impact at the end of travel.
Repeatability: This affects the consistency of arm positioning after each deployment. The extended position must align correctly with the locking mechanism.
Structural stiffness and locking strength: Once extended, the arms must withstand flight vibration, dynamic loads generated by the propellers, and external aerodynamic forces.
Service life: Repeated folding and deployment tests should be used to assess wear on hinges, gears, linkages, cables, and locking components.
Motor and gearbox selection should not be based on rated torque alone. Starting peak torque, transmission efficiency, duty cycle, temperature rise, and stall conditions also need to be considered. The structural strength and locking reliability of the deployed arms should be verified through engineering calculations and physical tests.
Custom Precision Machining for UAV Components
Electric folding arms involve components such as pivot shafts, hinge brackets, connecting supports, gears, and actuator mounting parts. These components often require custom machining based on the arm structure, assembly dimensions, and load requirements. Hansheng Automation provides CNC precision machining based on customer drawings, supporting both prototype parts and small-batch production for UAV structures and other automation equipment components.
