Abstract
A rimless wheel or a wheel without a rim, is the simplest example of a legged robot and is an ideal testbed to understand the mechanics of locomotion. This paper presents the design, modeling, and control of a differential drive rimless wheel robot that achieves straight-line movement and turning. The robot design comprises a central axis with two 10-spoked springy rimless wheels on either side and a central body that houses the electronics, motors, transmission, computers, and batteries. To move straight, both motors are commanded to constant pitch control of the central body. To turn while maintaining constant pitch, a differential current is added and subtracted from currents on either motor. In separate tests, the robot achieved the maximum speed of 4.3 m per sec (9.66 miles per hour), the lowest total cost of transport (power per unit weight per unit velocity) of 0.13, and a smallest turning radius of 0.5 m. A kinematics-based model for steering and a dynamics-based sagittal (fore-aft) plane model for forward movement is presented. Finally, parameters studies that influence the speed, torque, power, and energetics of locomotion are performed. A rimless wheel that can move straight and turn can potentially be used to navigate in constrained spaces such as homes and offices.
Highlights
One way of understanding the mechanics of locomotion is by recreating it
A rimless wheel robot when constructed properly does not have any issues of stability and provides an appropriate system for studying the effect of morphology on gait mechanics
The computer model has two parts: (a) a steering model based on kinematics adapted from differential drive mobile systems [21], and (b) a sagittal plane model based on the dynamics [11]
Summary
One way of understanding the mechanics of locomotion is by recreating it. Legged systems with one-, two-, and four-legs have been built, modeled, and controlled. The paper presents the design of a relatively simple rimless wheel that can move and turn. We follow this by detailed modeling, simulation, and parameter studies. The rimless wheel moved straight using a single motor on its central axle and turned using another motor that rocks a wobbling mass in the lateral plane. One robot they built called the Outrunner was 0.6 m tall (2 feet) and achieved a top speed of 8.9 m/s (20 mph) and another called.
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