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Mechanical

1. List of Requirements

1.1 Functional Requirements

  • The system shall store regolith, Mars powder, and rock/probe samples in 2–3 separate compartments, keeping sample types isolated from collection through storage.
  • The robotic arm shall use a scoop tool to collect sample material from the surface and deposit it onto the container's weighing platform.
  • Once loaded, the container shall weigh the total collected sample mass.
  • If the measured mass meets or exceeds the minimum threshold (100 g), the lid shall open via the motor, and the material shall be deposited into the appropriate compartment; the lid shall then close and lock automatically via magnetic caps mounted on the lid and container base.
  • If the measured mass falls below the threshold (100 g), the motor shall actuate to open the container and reject the sample rather than store it.

1.2 Technical Requirements

  • Compartment and lid actuation shall be motor-driven.
  • The full assembly shall fit within the housing dimensions defined for the system.
  • The lid shall open to a maximum of 90 degrees.
  • Probe mounting shall follow the dimensions specified in the Mars Rover Competition manual.
  • A piezoelectric sensor shall be integrated for mass measurement, mounted directly to the chassis.
  • The system shall be fully 3D-printed to satisfy overall weight limitations.
  • The weighing platform shall be constrained to a single degree of freedom in Z-translation, ensuring the platform remains stationary during measurement for accurate readings.

1.3 Performance Requirements

  • The locking mechanism shall maintain a secure seal under vibration and transport loads.
  • Each sampling operation shall require a minimum viable sample mass of 100 g.
  • If the measured mass is below 100 g, the system shall reject the sample automatically by opening the container rather than storing the material.

2. Detailed description of the system and its subsystems

2.1 Sensing Subsystem — Weighing & Mass Detection

A piezoelectric sensor is used for mass measurement, mounted directly to the chassis beneath the weighing platform. Piezoelectric sensors were chosen for their compact form factor relative to the sensitivity required, fitting within the limited internal space of the container assembly. The weighing platform itself is constrained to a single degree of freedom in Z-translation, keeping the platform stationary in all other axes during measurement to ensure accurate, repeatable readings.

2.2 Actuation Subsystem — Motor and Gearbox Selection

Torque requirement calculation:
The torque required to open the lid was calculated at approximately 1.3 Nm. Applying a safety factor to account for friction, material tolerances, and dynamic loading during operation, the design torque requirement was set at 1.6 Nm.

Motor selection reasoning:
Motor research indicated a clear trade-off between torque output and motor weight — higher-torque motors carry proportionally more weight, which conflicts with the system's overall weight constraints. To resolve this, a lower-torque, lower-weight motor was selected, with the torque deficit compensated by a gearbox rather than oversizing the motor.

  • Motor chosen: NEMA 17 servo motor, rated torque of 0.4 Nm
  • Gearbox ratio: 1:4, giving an effective output torque of 1.6 Nm, matching the design requirement including safety factor

This approach kept the actuation subsystem lightweight while still meeting torque demand — prioritizing a compact, low-mass solution over a single oversized motor.

2.3 Mechanical Transmission — Linkage and Hinge Mechanism

Power from the motor is transmitted through the gearbox to a shaft, which drives the linkage mechanism connected to the lid hinge. The motion sequence is as follows:

  1. The output shaft transmits torque to the linkage.
  2. The linkage first drives a Z-axis translation of the connecting arm.
  3. This translation is converted into rotation via the hinge, which is connected on both sides through shafts that transmit torque from the linkage to the hinge mechanism.
  4. A slotted connection at the hinge accommodates the transition between translational and rotational motion, allowing the lid to lift and rotate open up to 90 degrees.

2.4 Compartment Subsystem

The container houses 2–3 separate compartments, each dedicated to a distinct sample type (regolith, Mars powder, rock/probe samples) to prevent cross-contamination between materials from collection through storage. Compartment access is coordinated with lid actuation, so material is only deposited once the corresponding compartment is aligned and the lid is open.

2.5 Locking Subsystem

Once a sample is deposited and the lid closes, the container locks automatically via magnetic caps mounted on the top of the lid and the base of the container. This passive locking mechanism (locked by default) ensures the seal is maintained under vibration and transport loads without requiring continuous motor engagement, reducing power consumption during transit.


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