Ballbot History

OVERVIEW OF SINGLE-WHEELED ROBOT

Abdullah Adel Firihy, Hassan Magdy Mokhtar

Faculty of Engineering

Cairo University

Giza, Egypt

Fig. 1. Dynamically-stable Ballbot and Statically stable mobile robots.

Abstract---A ballbot is based on a simple concept, which is a robot balances on a ball. This ball gives the robot an important feature which allows the robot to move in any direction, unlike the traditional robots which depend on low center of gravity and multiple wheels to maintain upright. This allows the evolution of producing human sized robot, especially w.r.t stability.

This report aims to present the ballbot history and its developers trails, structural dimensions, its components and their functions, driving mechanism, simplified

Havasi presented the first one in 2005 and named it ERROSphere, but ERROSphere wasn’t sized like the size of human, especially in height. other two robots match this criteria. The designation, construction and examination of the second one was by Carnegie Mellon University (CMU) in 2005, and its documentation was by Lauwers et al. (2005). This robot is named by Ballbot. The third one is the development of ballbot, and it is done at Tohoku Gakuin University (TGU) in 2008, and its documentation was by Kumagai and Ochiai (2008). Yamamoto (2009) produced the NXT Ballbot recently.

BALLBOT SYSTEM

Ballbot was designed to achieve two goals. The first one its dimensions approximately equal the human being dimensions, and the second to create a platform that easily can be reconfigured for the variety of present and future researches.

The cylindric body is 1.5 m in height and 0.4m in diameter.

Its weight is almost 45 kg, the ball diameter is 0.2 m. the circular disks keep holding the three aluminum channels, the lower level of these channels involves other three legs used to sustain the structure in the power off mode. Oher components are positioned on the desks, which permit the variety of positions along the structure axis that these components can be placed

5. TGU’s driving mechanism

The three stepper motors which used to drive the ball are mounted rotationally at 120 degrees, this mechanism allows rolling freely of the ball along the wheel axis, but provides travelling in the direction of wheel rotation. This mechanism involves precise control, and there is no need for encoder which is essential in CMU’s system. The nonorthogonal position of the wheels doesn’t transfer the all energy from the motors to the ball. This driving mechanism is capable of yaw control, unlike the CMU’s driving mechanism which cannot achieve this approach without adding further actuators.

The ball which TGU uses in their ballbot is a bowling ball, and in order to increase the grip the ball is covered in rubber.

• Sensors:

To maintain dynamic stability, sensors are used especially in measuring the tilt angle of the ballots’ axis. Due to the inherent sensor limitations there are errors exist in the measurements. So that Gyroscopes and accelerometers are uses to avoid these errors. Gyroscopes are used for angular velocity measurements, and accelerometers are for angle measurements by determining the direction of the acceleration w.r.t the gravity direction. Assumptions were assumed to measure the angle by the accelerometer, which are there is no anther acceleration exist and no vibrations occur within the travelling of the