Development of an Autonomous Cleaning Robot Based on Helical Propulsion

The figure conceptualizes the multi-dimensional interference of anthropogenic litter with the biological functions of benthic organisms. Physical Pathway: the diagram illustrates how macro-debris and micro-plastic fragments create a "physical barrier" within the sediment matrix. The chemical route shows the release of plasticizers (e.g., Phthalates). These toxins are absorbed through the respiratory surfaces of invertebrates, disrupting endocrine functions and reducing reproductive viability.Trophic Impact: the diagram connects these individual stressors to the broader ecosystem, showing how the decline in benthic health reduces the caloric availability for migratory shorebirds.

The locomotion of autonomous vehicles on uncompacted sand is fundamentally governed by the pressure-sinkage relationship. The total sinkage (z) of a conventional rigid wheel is not merely a static response to vertical load but is significantly amplified by dynamic motion. According to the slip-sinkage effect illustrated in Figure, a wheel undergoing rotational motion experiences an additional downward displacement compared to its static state  > .

This phenomenon occurs because the tangential shearing of sand particles reduces the soil's bearing capacity underneath the contact patch. In contrast, the helical blades utilized in this project generates axial thrust through lateral shearing rather than vertical soil displacement, maintaining a lower and more uniform Ground Bearing Pressure.

The locomotion core of the robot consists of a dual-screw drive system.A front-mounted active collection unit was developed and positioned at the leading edge of the chassis and is independently driven by a dedicated DC motor to ensure consistent intake velocity regardless of the robot’s travel speed.The collection roller features a specialized gear-like profile with 16 soft-textured and alternating "long-short" teeth distributed along a 60 mm circumference.

The robot adopts a hybrid structure combining an aluminum alloy frame with a 3D-printed PLA shell. This design not only provides torsional stiffness but also protects the core components from sand and salt spray by enclosing them in a sealed compartment. By installing the battery pack at the low center position of the chassis, a low center of gravity structure was achieved.

As two figures show that the elastic recovery of the teeth provides a "spring-action" effect that efficiently propels lightweight litter into the chassis while leaving the underlying benthic structures undisturbed. The interspersed short teeth provide secondary agitation, ensuring that sand is filtered through the gaps rather than being scooped into the vehicle.

The experimental design is divided into two stages: mechanism verification and vehicle comparison. Firstly, determine the influence of different parameters on the speed of the screw mechanism. Then, test the traction efficiency and slip rate under different sand compactness conditions, and explore the relationship between the motor speed and the slip. Finally, conduct a comparative test between the screw mechanism and the traditional tracked mechanism in a standardized sand trough environment.

As shown in the figure, a 45-degree helical angle is the optimal angle. As the pitch and length increase, although the theoretical speed will rise, it is more likely to slip and damage the sand layer.

Experiment 2 demonstrated that the traction efficiency has a strong positive correlation with the compactness of the sandy surface. On a hard and compact sandy surface, the efficiency reached 96% while the sliding rate was only 4.0%. Loose sand is more sensitive to changes in speed than compacted sand.

During the vehicle performance verification, the system was able to maintain an extremely high efficiency of over 84% within the low-speed range of 10-20 RPM. When the motor approached its extreme value (50 RPM, approximately 17.12 mm/s), the slip rate sharply increased to 31.5%, proving that the low-speed range is the best working interval for this system to perform cleaning tasks.

After conducting 10 garbage collection tasks at a 10-meter distance in a standardized environment, the core measurement indicators are as shown in the following figure: task success rate (whether sand blockage occurred), average traveling speed, degree of ecological damage on the sand surface (sinkage depth), and final garbage collection rate. The differences between the screw mechanism and the tracked mechanism are extremely significant. The screw system achieved a 100% task success rate at a stable and uniform speed of 4.82 mm/s, and the garbage collection rate was as high as 94.2%. In contrast, the tracked mechanism was affected by the bulldozer effect and sliding subsidence, resulting in a task success rate of only 80% (twice due to sand blockage) and a collection rate of 81.9%. The most crucial ecological damage indicator shows that the average sinkage depth of the screw mechanism was only 11.8 mm, which significantly reduced the physical damage to the sand surface by approximately 58% compared to the compacted track of the tracked mechanism, which reached a depth of 28.3 mm.

These results demonstrate the advantages of the spiral propulsion structure in coastal cleaning: it causes less damage to sandy areas than traditional tracks and has a lower failure rate. With a 100% failure-free operation rate and a 58% reduction in subsidence depth, the goal of cleaning the beach without harming bottom-dwelling organisms was achieved.

Next, I plan to bring the robot to the actual coastline for long-term testing, focusing on observing the impact of seawater's salt fog corrosion on the 3D-printed structure, as well as whether fine sand will enter the motor bearings causing jamming. Based on the feedback, I will design a more rigorous dust-proof sealing cover to enhance the robot's survival ability in the real natural environment. Additionally, the material and spacing of the collection teeth can be changed to adapt to other types of garbage.

For this project, I would like to first thank my family to support my interest on this engineering project. They spent an amount of money on some of the materials needed for the robot. I would also like to thank my school and my school science teachers. They provide a great environment for the robot building and gave me a lot of help on making the poster. My friends also contributed a lot. Some of them looked at the project and gave me some suggestions while I have no idea what to do.

(Here's a photo of one of my middle school's classmate and I having dinner together)

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