896 | 2016 | JUNE | SCIENCE JOURNAL 1. INTRODUCTION Wheels are statistically most commonly used in chassis design of mobile robots as a means that provides ground surface contact and implements energy transfer required for the movement. The difference in wheeled mobile robots chassis primarily lies in the requirement on their function and type of the environment where they are used. A special type is an omnidirectional wheel. Their use brings other possibilities of chassis movement, where the tyre gave way to rolling elements freely rotatable along their axis. The elements are evenly placed along the whole wheel perimeter. Currently, there are two wheel constructions according to the position of the rolling elements axis – either perpendicular to the disk axis (type Stanford), or diagonal (type Mecanum). When using wheel mobile robots chassis for indoor movement, the ability to overcome obstacles (mainly staircase) is limited by construction requirements. The radius must be bigger than the height of one stair. The research at the Department of Robotics analysed special shaped wheels for use in indoor environments. Finding a suitable shape was done by synthesising the reference curve in the form of a logarithmic (exponential) spiral. When overcoming stairs, the resulting movements significantly eliminate centre of gravity oscillations compared with other wheel chassis. The logarithmic wheels cannot be used for movement on flat surfaces, because the non-circular shape causes extreme unwanted oscillation. Combining the characteristics of omnidirectional and logarithmic wheels resulted in creation of a concept of a combined system [Krys 2014, Eich 2008]. 2. CONCEPT OF A COMBINED LOCOMOTIVE SYSTEM Based on this fact, concepts that can combine advantages of using logarithmic wheels to climb stairs and omnidirectional wheels to drive on flat surfaces were suggested. Omnidirectional (Mecanum-type) wheels were chosen due to limited space in the chassis. Based on a raw 3D concept made in Creo Parametric 2.0 and preliminary calculations THE MECHANICAL DESIGN AND REALIZATION OF THE OMNIDIRECTIONAL MOBILE ROBOT ODIN MATEJ GALA, VACLAV KRYS, TOMAS KOT VSB – Technical University of Ostrava Faculty of Mechanical Engineering, Department of Robotics, Ostrava-Poruba, Czech Republic DOI: 10.17973/MMSJ.2016_06_201542 e-mail: matej.gala@vsb.cz KEYWORDS mobile, omnidirectional, robot, wheel, trajectory, testing, Odin This article describes the process of mechanical designing for an omnidirectional mobile robot Odin. It provides an explanation of the relation between a mobile robotic stair climbing system with shaped wheels and omnidirectional wheels, which are used together in a combined locomotive system. Only a conception study of the whole system is presented. Testing of mechanical parameters and driving abilities of the omnidirectional wheels was performed on a constructed simplified chassis. There was created an experimental calculation for a flange with a clamp connection linking a 3D model. This simplified chassis was the basis of a mobile robot named Odin, which was further improved by mounting a modular manipulator Schunk on its top. The article concludes with an evaluation of the achieved progress and indicates ways of further possible development for the omnidirectional mobile robot Odin. of drives, a solution was proposed, using low-velocity rotary hydraulic drives for actuation of the logarithmic wheels. These drives are able to develop high torques at low speeds and are economically more profitable than electric drives. The required speed for this application is about 30 rpm, which is a critically low value for the control of these drives. Laboratory tests to determine characteristic behaviour in low revolutions on a test stand confirmed the concerns. The complexity of the solution of the combined system resulted in its division into two separate research areas. The first area deals with the development of omnidirectional chassis for testing mechanical parameters and drive accuracy depending on the load and the position of the center of gravity. The second area covers research of rotary hydraulic drives on a laboratory stand, primarily for independent control of several drives in low revolutions. The functioning of the combine system is divided into two drive modes. Omnidirectional wheels are ejected for movement on a flat surface (Fig. 1). Having approached stairs, all omnidirectional wheels are retracted and only logarithmic wheels are used (Fig. 2) [Krys2014, Herbert 2008]. 3. SIMPLIFIED CHASSIS WITH OMNIDIRECTIONAL WHEELS A simplified chassis with omnidirectional wheels has been designed based on the requirements and specifications of its use [Doroftei 2007]. The basic requirement is its easy and assemblable frame construction, use of off-the-shelf omnidirectional wheels, and indoor application. Specifically, it concerns Mecanum wheels sized 10" produced by Andy Mark. Other mechanical chassis components, such as bearing housings, shafts and drive holders, were designed and produced in a school workshop. Based on the determined limit chassis weight and speed requirement, 4 different drive modes were used to perform a drive design calculation. Figure 1. Drive mode on a flat surface Figure 2. Drive mode on a staircase