Task 3: GIMBall; Further development of ball locomotion


Ball locomotion is based on a ball-shaped cover and an unbalanced rotating mass inside the ball. Propulsion can also be generated by an external force, such as wind or gravitation. Aalto has already been researching locomotion for several years. Previous applications have been the Rollo home robot (diameters from 30-40 cm) and the tumbleweed locomotion mechanics (diameter 1.5 m) for ESTEC. A camera and other optical perception and communication devices have been mounted under the transparent cover. In applications such as guarding and gas sensing the cover can be hermetically sealed.

Further development includes gaining a better understanding of ball kinematics and dynamics when using conventional pendulum drive and steering as well as utilizing more advanced gyros and momentum wheels. Simulated ball models will be completed with controllers to be also implemented and tested with the real ball robot hardware.

Expected results

Expected results include simulation of two different ball models and their controllers, and implementation and testing of the controllers with real ball locomotion hardware.

State of the art

State of the art –study on spherical robots was conducted in several phases during years 2003-2005. The results have been published in book chapter “Ball-shaped Robots” in ‘Climbing & Walking Robots, Towards New Applications’. Since then some new advances has been done around the world and some additional research needs to be done to complement the State of the art -study.

A quick search of the U.S. Patent office database immediately reveals more than 50 patents related to the autonomous mobility of a ball-shaped object. These patents date from 1897 to 2003 and all comprise a motorized counterweight that is used to generate ball motion. Obviously, the number of related patents in the USA and worldwide is much larger than found by this quick search. The number of similar one-wheeled and two-wheeled counterweight-based vehicles is even larger. The first vehicles were small spring-powered toys with one fixed axis of rotation. The patents concentrate on methods of storing and converting spring energy with different mechanical solutions. Adding steering capability to the toys has been a challenge from early times. In 1906, B. Shorthouse patented a design that offered the possibility of manually adjusting the position of the internal counterweight in order to make the ball roll along a desired curved trajectory instead of a straight path (U.S. Patent 819,609). Ever since, mechanisms have been patented to produce more or less irregular rolling paths for self-propelled balls.

The counterweight was usually constructed with a lever rotating around the ball's axis. Mobility was provided by generating torque directly to the lever. The amount of torque needed from the power system was directly proportional to the mass of the counterweight and length of the lever arm. In 1918, A.D. McFaul patented a "hamster-ball" design (a derivative of a hamster running wheel), where the counterweight was moved by friction between the ball's inner surface and traction wheels mounted on the counterweight. In this construction, the length of lever arm does not any more affect the required power system torque, and similar mobility can be achieved with less internal torque. Obviously this is of great benefit to spring-driven toys, at least if they have a large diameter. A mechanical spring as a power source was displaced by a battery and an electric motor in a patented design by J.M. Easterling in 1957 (U.S. Patent 2,949,696). Consequently, electric motors were introduced with several different mechanical solutions that were already at least partly familiar from earlier spring-driven inventions. Further development introduced shock and attitude sensing with mercury switches that would control motor operation and rolling direction, as well as adding light and sound effects. An active second freedom for a motorized ball was introduced by McKeehan in 1974. In addition to reversible rolling motion, upon impact against an obstacle, the ball would also change its axis of rotation with the aid of additional motors. This opened the way towards radio-controlled (introduced in 1985 in U.S. Patent 4,541,814) and, finally, computer controlled, ball-robots. As (radio-controlled) toy-cars became more common following 1984, they were frequently inserted inside the ball to provide a fully steerable 2-dof. rolling toy (U.S. Patent 4,438,588).

Spherical vehicles to carry people were first developed for marine applications, like the one of W. Henry in 1889. This vehicle, with its passenger floating in the water, was balanced by a ballast mass and the weight of the passenger. The vehicle would move in a manner very similar to the toys described above with balanced mass inside and with their outer surface rolling. Steering would be achieved by tilting the axis of rotation by moving the passenger mass inside the vehicle. In 1941, J.E. Reilley patented a ball-shaped car and later different types of chairs were inserted inside the spherical vehicle. In some cases, a person would enter a ball and operate it directly without any additional means, like a hamster inside his running wheel.

The most recent inventions introduce new novel solutions to alter the position of the ball's centre-of-gravity. One example is the Spherical Mobile Robot by R. Mukherjee, patented in 2001, that uses several separate weights that are moved with the aid of linear feed systems (U.S. Patent 6,289,263). In addition to the robots presented, there are several other similar devices, mostly intended for demonstration or simply for toys. The 1.5-metre-diameter scale models of the Tumbleweed Rover (Matthews, 2003) and Windball (Heimendahl et al., 2004) are intended for Mars exploration. Both of them are purely wind-driven, the only mobility-related actuation being re-shaping the structure by inflation/deflation (Tumbleweed) or with the aid of shape memory alloys (Windball). On Mars, 6-metre versions of these models would be used to carry out scientific tasks such as surface mapping and atmospheric measurements. The 15-cm Roball (Michaud & Caron, 2001) performed an important role in a study of interaction between the robot and small babies. It is anticipated that the 15-cm Cyclops (Chemel et al., 1999) and 50-cm Rotundus will be used to inspect and guard industrial plants (Knight, 2005). The Sphericle is used as an educational tool for learning the dynamics and control of a ball-shaped robot (Bicchi et al., 1997).

As the operating principles of different ball models are different, so the kinematic and dynamic equations describing ball behaviour are different. The possibility of rotation in all directions makes the control of the ball challenging. In addition, a hard-surfaced unbalanced ball on a smooth floor behaves like a pendulum; any change in motor torque or disturbance from its surroundings easily generates oscillation that attenuates very slowly. Oscillation around the rolling axis is controlled in Aalto’s Rollo by means of a closed-loop system that controls the drive motor torque. The control loop is equipped with attitude sensors and gyroscopes that measure the forward and backward motion of the payload mass. Controlling the sideways oscillation is a more difficult task, since we do not posses any actuators in this direction. So far, no active instrumentation has been included for this, but, in future, passive dampers or an active closed-loop controlled movable counter-weight or pendulum may be considered. The kinematics and control of the early versions of Rollo are discussed in Halme et al. (1996a). Apart from the development of Rollo at TKK, Bicchi et al. (1997) also describe the kinematics, dynamics, and motion planning of the single-wheel ball robot Sphericle. Laplante (2004) discusses the kinematics and dynamics of ball robots in great detail and develops a control scheme to steer a pendulum-driven Roball along curved paths. Regarding the same ball robot, Michaud & Caron (2001) write more about higher-level behaviours and interaction with people.


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System description

Figure 1. Gimball spherical robot

Gimball continues our tradition in development of spherical robots. It is 44 cm in diameter, clearly larger than its predecessor Rollo in its different variants. It is constructed with a 2-dof. pendulum system which provides a driving unit different from any of the previous versions of Rollo-robot. The drive system is similar to that of the large 1.3 m Mars-ball.

Aim of the Gimball is to develop an embedded control and navigation system that eventually allows the robot autonomously roll along office corridors fluently, with high speed and without stops or collisions against the walls. First version of mechanical structure was finalized in 2007. SpaceMaster student Masaki Nagai performed his Thesis research on Gimball during 2007-2008 and developed micro-controller based system to drive the motors and control steering angle and -radius. Gimball is equipped with an on-board computer (OBC), a power source, a communication system, and sensors used for closed loop control of motor velocity and steering angle of pendulum. A ground station is for processing and displaying the sensor data, and for controlling higher level functioning, such as "set speed", "brake", "turn left" or "turn right". For controlling lower level functioning such as "accelerate to the commanded speed" or "keep the orientation of the robot", the OBC uses different control methods. Currently Gimbal is remotely driven with very little autonomous functions and lacking completely navigation capabilities. These issues are to be addressed in next phases of the project. Illustration below presents system architecture.

Figure 2. Gimball system architecture

Gimaball Dynamic simulator

Dynamic simulator for Gimball was created with MSC ADAMS to be used in development of control algoritms. The dynamic model is co-simulated with Matlab Simulink as the controller is developed using Matlab. Simulation results animation of Gimball making a U-turn. (1.2M .avi) avi

See also Thistle_simulator

Planned activities and publications

Time of Acticvity

Activity & Responsible persons
Publication(s) & Journal / Conference


State of the art survey (Ylikorpi)
Ball-shaped Robots, Tomi Ylikorpi and Jussi Suomela, Helsinki University of Technology, Otaniementie 17, 02150, Espoo, Finland, Climbing & Walking Robots, Towards New Applications, ISBN 978-3-902613-16-5


Mechanical structure was designed and built ready at TKK


Basic communications and motor control (Masaki Nagai, Ylikorpi)
Master’s Thesis: Control System of a Ball-shaped Robot (Nagai)
GIMBall report 1: ’Construction and basic control techniques’, GIM Internal Report (Ylikorpi)


GIMBall modeling and simulation 2008-2009 (Ylikorpi)
Building of IDeas-3D-model and ADAMS dynamic model of the ball. Simulation of the ball using Matlab/Simulink co-controller with ADAMS. Adding gyro-wheel and/or momentum wheel in model if necessary.
GIMBall report 2: ‘Simulation of GIMBall’, GIM Internal Report (Ylikorpi)


GIMBall control system development (Nassir Oumer, Ylikorpi)
Master-level research on advanced oscillation dampening and higher-level control for trajectory following. Developing gyro/momentum wheel if necessary.
Master’s Thesis (Nassir Oumer)
GIMBall report 3: ‘Advances in GIMBall control techniques’, GIM Internal Report (Ylikorpi)


GIMBall control system development
Master-level research on higher-level control, path planning, sensors and reactive behavior. (SpaceMaster student, Ylikorpi)
Master’s Thesis (SpaceMaster student)
GIMBall report 4: ‘To Be Defined’, GIM Internal Report (Ylikorpi)


GIMBall control system development 2011 (SpaceMaster student, Ylikorpi)
Master-level research on higher-level control, path planning, sensors and SLAM.
Master’s Thesis (SpaceMaster student)
GIMBall report 5: ‘To Be Defined’, GIM Internal Report (Ylikorpi)