The three mobile robots used in this research topic are the Performance PeopleBot, Segway RMP200, and Segway RMP400. The platforms were chosen on the basis of their availability, they are mainly used for research purposes and not suited for manufacturing environment applications, which is acceptable for this research since the objective is to establish the concept of a cooperating team of heterogeneous mobile robots, irrespective of their abilities and functionality.
The subsections below discuss the functionality of each robot and outlines the technical specifications as well.
2.2.1 Performance PeopleBot
The Performance PeopleBot (shown in figure2.2[55]) is a mobile robot that was designed byActivMedia [56] for the purpose of human-robot interactive research and applications.
The robot is equipped with a reversible two-wheel differential motor drive system and a balancing caster; this ensures that the steering control can be achieved by varying the relative rate of rotation of each wheel. The Peoplebot is also installed with four
Figure 2.2: Performance PeopleBot robotic platform
sonar arrays of eight sonars in each array, bumper switches, a two degree of freedom gripper, a pan/tilt/zoom colour camera, and on-board computer with wireless ethernet and monitor.
Table 2.1 [55] lists some of the technical specifications of the PeopleBot. The robot operates on three rechargeable batteries with a typical run time of eight hours. Like its fellow family members of Pioneer mobile robots [56], the PeopleBot has a relatively small footprint, thus capable of maneuvering in small, tight spaces.
Table 2.1: Performance PeopleBot technical specifications
Parameter Specification Base robot weight 21 kg
Footprint 51.5 x 42.9 cm
Tire diameter 19.5 cm
Operating payload 8 kg
Turn radius 0 cm
Maximum speed 0.8 m/s
Rotation speed 150◦/s
Run time 8 hours (3 batteries) Battery recharge time 2.4 hours
Battery voltage 12 V Battery capacity (each) 7.2 Ah Battery chemistry SLA
2.2.2 Segway RMP200
In 2001, the Segway Personal Transporter (PT) was introduced to the market as the first self-balancing, zero emissions personal transportation vehicle [57]. The Segway PT operates on the concept of dynamic stabilisation (similar to the classic control problem, the inverted pendulum); it has two wheels which are rotated in the correct speed and torque to prevent the user from falling when leaning forwards or backwards.
A few years after the release of the Segway PT, the Robotic Mobility Platform (RMP) was developed by Segway, based on the design of the PT, for scientific and engineering research purposes. The RMP was designed for an integration into a system that has a control processor to communicate velocity and steering commands via the USB or CAN bus interface. Segway has developed balancing and non-balancing models of the RMP in a variety of 2, 3 or 4 wheel configurations [58].
The RMP200 (shown in figure 2.3 [59]) is a two-wheeled differential drive robot that is capable of maintaining its balance while carrying a heavy payload. The robot can operate in one of two modes: 1) Tractor mode causes the RMP to function in a static
stable condition with a large footprint and low payload height, whereas 2)Balance mode is a dynamic stable operation with a smaller footprint and higher payload.
Figure 2.3: Segway RMP200
Table 2.2 [59] lists the technical specifications of the RMP200. The robot operates on two rechargeable batteries with a typical run time of 8 hours. Unlike the PeopleBot, the RMP200 has a larger tire diameter and footprint but it has the ability to operate in tight spaces due to its turn radius specification of 0 cm.
Table 2.2: Segway RMP200 technical specifications
Parameter Specification
Weight 64 kg
Footprint 64 x 61 cm
Tire diameter 48 cm
Operating payload 45 kg
Turn radius 0 cm
Maximum speed 16 km/hr
Data update rate 100 Hz
Run time 8 hours (2 batteries) Battery recharge time 6 hours
Battery voltage 72 V
Battery capacity (total) 380 watt-hours Battery chemistry Ni-MH
Mechanically, the RMP200 consists of a base plate which houses the batteries, motors, drives and control box. The payload plate is supported by two side plates. Electronically, the robot has five gyroscope sensors which measure the following:
Yaw angle and yaw rate
Pitch angle and pitch rate
Roll angle and roll rate
In addition to the above itemised quantities, the RMP interface also returns left and right wheel speeds as well as a calculated odometry. The RMP200 does not contain an on-board computer so a laptop is used in this research as the control processor. The purpose of the laptop is to establish a communication interface with the robot to obtain data (yaw, pitch, roll, speed and odometry) and control its movement through speed and yaw commands.
2.2.3 Segway RMP400
The RMP400 is one of Segway’s most powerful mobile robots, it is capable of carrying loads up to 181 kg for long distances over rugged terrains. The robot operates on four independent drive motors and five rechargeable batteries. A graphic image of the RMP400 is shown in figure 2.4 [60] and its technical specifications are listed in table 2.3[60].
Figure 2.4: Segway RMP400
The RMP400 was designed for research applied in outdoor environments, therefore it does not function well in indoor, manufacturing environments. For instance, the turning radius of this robot is dependent on load conditions, operating surface type and tire fric- tion, hence tire skid and wheel slippage can be expected over smooth surfaces pertinent to manufacturing or research lab environments. Despite these realities, the objectives of this research are not compromised.
The RMP400, like the RMP200, returns measurement data such as yaw, pitch, roll, speed, and odometry and once again, a laptop is used as the control processor to control the robot’s movement through speed and yaw commands.
Table 2.3: Segway RMP400 technical specifications
Parameter Specification
Weight 109 kg
Footprint 76 x 112 cm
Tire diameter 53 cm
Operating payload 181 kg
Maximum speed 29 km/hr
Data update rate 100 Hz
Run time 8 hours (4 batteries) Battery recharge time 8 hours
Battery voltage 72 V
Battery capacity (total) 1600 watt-hours Battery chemistry Li-Ion