Quadcopter Landing Gear

Landing Gear Lead for PolyUAS

Overview

PolyUAS is developing two custom autonomous quadcopter platforms for the 2026 C-UASC competition. The first platform, Osiris, is optimized for peak competitive performance, leveraging proven and reliable design solutions. The second, Horus, serves as a dedicated development platform, where new innovations are designed, tested, and integrated before potential implementation into the competition vehicle.

 Figure 1. Current drone CAD

Preliminary Ideation

The landing gear was designed around a drone frame platform characterized by two aluminum plates that sandwich the remaining components. Before reaching the final design, multiple concepts were explored, constrained by this existing geometry and a one-motor-per-leg requirement.

 Figure 2. Selected Ideation CAD

Mechanical Design

Osiris’s static landing gear is primarily designed to efficiently transfer landing impact forces into the drone’s primary frame structure. The tubular legs are detachable for ease of transport and integrate at a fixed angle to ensure the feet are properly aligned upon installation.

To support the package retrieval system, Horus utilizes a retractable landing gear system actuated by a Hitec servo. The design is centered around a single-motor concept, allowing the gear to remain in the retracted position without requiring continuous servo power. 

Both platforms were designed to withstand a single-leg 5G vertical and 3G off-axis crash condition and incorporate compliant landing feet to attenuate impact forces.

 Figure 3. Landing gear design CAD

 Figure 4. Static landing gear bracket

Hardware

Both systems attach to the main frame with 6-32 bolts and clamp onto the landing carbon tubing using M2.5 × 10 mm screws. Horus’s retractable system also uses these screws with plastic heat-set inserts to support the servo, with a 1/4" shoulder bolt acting as the primary support connecting the landing leg subassembly to the frame-supported spider bracket.

 Figure 5. Retractable gear exploded view

The foot tube is attached to the flexible landing feet via epoxy while clamping bolts allow the main landing tube to detach.

 Figure 6. Foot connection methods

A 3D-printed bracket supports the landing tube and feet beneath the drone frame, enabling a more aggressive landing leg angle while providing clearance for the folding arms. The linkage geometry is designed to allow a controlled range of motion that ensures the arms remain upright when the servo is powered off. When lowered, the arms brace firmly against the bracket, preventing the landing leg from retracting during landing impact.

 Figure 7. Extended and retracted servo states 

Flexible Landing Feet

To assist with impact damping, compliant feet were 3D printed from TPU, allowing them to deflect under impact before forces are transmitted to the carbon foot tube. Mimicking airless tire design, the feet incorporate an array of internal fins that bend under load. Following six prototype iterations that addressed issues including stiffness, stability, durability, and integration with the tube, the final design was achieved, as shown below. 

 Figure 8. Final landing gear feet design

Servo Sizing

To determine the required servo torque for the landing leg mechanism, the kinematics of the linkage were first modeled by mapping the changing angular relationship between the servo horn and the landing tube throughout the full range of motion. At each position, the gravitational force acting at the system’s center of mass was calculated, and the resulting moment about the servo axis was determined. This analysis enabled evaluation of the torque required from the servo to maintain static equilibrium as a function of leg position.

 Figure 9. Holding torque vs. servo horn angle

To develop a more accurate model of the system, dynamic effects were incorporated using a multibody dynamics simulation in MSC Adams. A design requirement was established specifying a one-second transition time between the raised and lowered positions of the landing leg. Under this aggressive actuation profile, the servo torque demand was evaluated throughout the motion.

 Video 1. Adams simulation

 Figure 10. Required torque plot

With this analysis complete, a Hitec MD141SH was selected for the project, capable of 97.21 oz-in of torque at an operating voltage of 7.4V. A 2s step-down from the power distribution board is used to run the servo.

Material Selection

Both platforms utilize carbon fiber–reinforced nylon (Bambu Lab PPA-CF) for primary printed structural components. This material was selected for its high strength-to-weight ratio and elevated stiffness while maintaining relatively low density.

The landing feet are manufactured from Bambu Lab ASA, providing controlled compliance under landing loads.

In finite element analysis (FEA), PPA-CF was modeled as a transversely isotropic material to account for its fiber-reinforced behavior using the material properties listed below. ASA was modeled as a linear elastic isotropic material.

Table 1. PPA CF material model properties

FEA

To simulate the drone crashing, two cases were tested. First, a 5g axial crash where the force is applied in-line with the landing tube, and second, a 3g off-axis crash where the drone lands on the edge of the foot tube, introducing a torque. Notable results are presented below, where all carbon tubing and bolts are modeled as discrete rigid bodies in Abaqus 2025.

Figure 11. Static landing gear bracket under 5g axial and 3g off-axis load cases

Figure 12. Retractable landing gear bracket under 5g axial and tube support 3g off-axis load

Testing

Supported by a bracket on each side, the landing feet were tested by applying loads from 0 to 55 lb and measuring ground clearance. Stability was also evaluated; above approximately 55 lb, the feet were unable to remain upright without assistance.

Figure 13. Manufactured landing foot assembly and testing configuration

The results showed a nonlinear response with acceptable stiffness. The static point represents the expected ground clearance of the drone under maximum payload conditions.

Figure 14. Landing gear feet testing results

This project is currently in progress. Next steps include final design manufacturing, integration and testing.