# On the Unification of Legged and Aerial Robots for Planetary Exploration Missions
## 2 Landing Platforms
### Drone Landing Platform for Fixed Frame Drone  
This landing platform was designed for the Spot robot unification with a larger drone that is referred to as Shafter [14]. Its dimensions, excluding the 12-inch propellers, are \(W\times L\times H\), 513 mm \(\times\) 335 mm \(\times\) 339 mm, and the total weight is 3615 g. The landing platform design fulfills the following requirements such that the platform is able to allow take-off and landing of the drone. At the same time, the drone can be securely locked  
Figure 4: Schematics including the basic dimensions of the landing platform with the R-shafter drone. Presented in the H configuration (**a**,**b**) and locked in place (**d**). Overview of the components (**c**): 1—aluminium profile platform frame, 2—3D printed landing desk, 3—drone aligner, 4—R-Shafter body, 5—R-Shafter arm. Figure 5: The legged-aerial explorer with the Boston Dynamics autonomy package and the R-shafter landing platform. in the platform when the Spot robot is moving. The locking and unlocking sequence is controlled via the Robot Operating System (ROS) framework that is installed on the Spot onboard computer. Recommended payload areas for Spot (Figure 3) were first examined in the intended usage environment with mostly flat floors, avoiding climbing intricate obstacles and staircases. This allowed us to relax the demotions of the recommended areas a bit, as shown in Figure 6, so the landing platform is slightly interfering with the restricted zone above the rear shoulders and is expanding outside of the maximum recommended width boundaries. In extended testing procedures in the lab environment, collisions between the robot legs and the platform were not detected. The landing platform is designed with a passive drone landing alignment and an active landing gear locking. Its core component is the two rails, which have openings of 90 degrees in the \(X\) axis and 45 degrees in the \(Y\) axis. This design can compensate for a total error at landing of 80 mm along the \(Y\) axis and 31 mm along the \(X\) axis, respectively, which was experimentally verified in the lab environment. The platform is attached to the Spot robot using the payload T-slot rails in the front and custom-made rear mount plate in the back, as shown in Figure 7. The rear mount plate repurposes the rear body panel screws. This setup ensures a secure connection and at the same time provides enough clearance above the rear shoulders when the robot is moving, especially during the transition to and from the seating position. Figure 6: The dimensions of the landing platform relative to the recommended payload areas. Figure 7: The dimensions and components of the landing platform for the Shafter drone: 1—left V-rail, 2—right V-rail, 3—locking clamp, 4—door-lock-style solenoid, 5—end stop, 6—stepper motor NEMA14, 7—aluminum profile frame, 8—rear Spot mount plate, 9—front Spot T-slot mount. The active locking is represented by a pair of rotating clamps in each rail, which are controlled by the NEMA14 stepper motor. Each clamp is secured in the locked state by a door-lock-style solenoid, and by default, clamps are closed and secured with the solenoids. This state does not require any power, and it provides a fail-safe in case of power shortage when the drone is loaded. When the drone is ready to take off, the unlocking sequence is performed by retracting solenoids so clamps can move freely and rotate to the open position and thus the drone can take off. This process is controlled using an onboard Arduino computer tied to the landing platform. The schematics of the landing platform are depicted in Figure 7.  
The landing gear on the Shafter drone, shown in Figure 8, was designed while considering the design and dimensions of the landing platform. It has a ski-style landing gear with two carbon fiber tubes with diameter 15 mm and length of 330 mm in its base. The legs are 3D-printed from Nylon filament (Taulman3D PCTPE).