project specification

RT Mover

A four-wheel robot concept with a simple mechanism and high mobility for all-terrain usage. The robot has four drivable wheels and two leg-like axles. Each wheel is mounted on one side of the leg-like axles at the front and rear of the body. RT-Mover has four active wheels and only other five active shafts, therefor the robot can move on discontinuous rough terrain whilst keeping a sheet part of the robot horizontally. It can move like a wheeled robot and also walk over a step like a legged robot.

Specifications

Length800 mm
Width450 mm
Height134 mm
Wheel size100 mm radius
30 mm width
Weight 21.5 kg
Motor (DC Servo)23 W (Steering: 2; Sheet’s pitch: 1)
40 W (Wheel: 4; Sheet’s roll: 2 (front and rear))
Gear ratio 40 (Sheet’s pitch: 1 (warm gear)
100 (Wheel: 4; Sheet’s roll: 2 (harmonic gear)
400 (Steering: 2; (Harmonic gear: 100; Belt drive: 4)
Sensor Posture angle sensor
Encoder and current sensor (each motor)
Power supply24 V Battery

Overview

The robot has four drivable wheels and two leg-like axles. Each wheel is mounted on one side of the leg-like axles at the front and rear of the body.

RT-Mover has four active wheels and only other five active shafts, therefor the robot can move on discontinuous rough terrain whilst keeping a sheet part of the robot horizontally. It can move like a wheeled robot and also walk over a step like a legged robot.

The robot has four contact points on the ground, the minimum number to maintain stability when  it raises one leg with supporting its body with the other three legs. Each wheel is attached to the tip of a leg, because in many cases, there is not enough space available to set the leg and wheel separately on the body of the robot. When the robot  moves on a slope, the user and the load are maintained in a horizontal position.

The robot uses the Ackermann steering mechanism for direction control. Each wheel is driven and controlled independently.

Control system

The RT-MOver is equipped with two SH4 boards, one for control-ling the robot and the other for processing the posture angle sensor data. An I/O board is connected to the SH4 board for controlling the robot, and all data are inputted or outputted through the I/O board. The two SH4 boards are linked by socket communication. The robot is controlled in real time using ART-Linux.

References

Describes the technology, related work, the mechanical design, steering, and the function of the legs. Describes its moving strategy for rough terrain, and the simulations. Goes into the system configurations, and experimental results.

Shuro Nakajim. 2009

The mechanical design concept for RT-Mover is discussed, and strategies for moving on rough terrain are proposed. The kinematics, stability, and control of the robot are also described in detail. The performance of the proposed locomotion is evaluated through simulations and experiments

Shuro NakajimaPublished. - I. J. Robotics Res. 2011 (Paywall)

Wevolver 2022