Development of a Compact Robust Passive Transformable Omni-Ball for Enhanced Step-Climbing and Vibration Reduction

Abstract

This paper introduces the Passive Transformable Omni-Ball (PTOB), an advanced omnidirectional wheel engineered to enhance step-climbing performance, incorporate built-in actuators, diminish vibrations, and fortify structural integrity. By modifying the omni-ball's structure from two to three segments, we have achieved improved in-wheel actuation and a reduction in vibrational feedback. Additionally, we have implemented a sliding mechanism in the follower wheels to boost the wheel's step-climbing abilities. A prototype with a 127 mm diameter PTOB was constructed, which confirmed its functionality for omnidirectional movement and internal actuation. Compared to a traditional omni-wheel, the PTOB demonstrated a comparable level of vibration while offering superior capabilities. Extensive testing in varied settings showed that the PTOB can adeptly handle step obstacles up to 45 mm, equivalent to 35 $\%$ of the wheel's diameter, in both the forward and lateral directions. The PTOB showcased robust construction and proved to be versatile in navigating through environments with diverse obstacles.

Figures (11)

• Figure 1: Omnidirectional chassis structure with PTOB can drive even on uneven terrain.
• Figure 2: Basic structure of the PTOB: (a) Three spherical cap-shaped wheels that contact the ground and have sliding parts that move passively. (b) The spherical cap-shaped wheels have a hollow structure with a barrel-shaped roller inside, covering the singular points of the spherical cap-shaped wheels, similar to the structure of the Omni-ball. (c) The sliding motion allows the wheels to engage with steps by sliding against external forces.
• Figure 3: Relationship between sliding distance and the height of the step that can be overcome: (a) When the PTOB is positioned at a 45-degree angle to the direction of the step, the spherical cap-shaped wheels come into contact with the step and slide. (b) Whether the step is cleared or not depends on the sliding distance. Approximately 40 $\%$ or more of the radius is required for successful clearance.
• Figure 4: (a) External appearance, exploded view, and cross-sectional view of the PTOB. Each spherical cap-shaped wheel is equipped with a linear guide to achieve high strength and sliding. (b) Product characteristics of bearings and linear guides. Selected based on prioritizing strength, considering installation at the leg end. The numbers correspond to the exploded view.
• Figure 5: Overall view of the chassis structure. The wheel contact positions are arranged at 400 mm, with a central rotation axis to ensure easy contact with all four wheels even on uneven terrain. An IMU is installed in the center for evaluation purposes.