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PL. FIND ATTACHED COPY FOR HOW YOU CAN DESIGN TWO WHEEL ROBOT
AJ HASAN
MOBILE ROBOT DESIGN
3.1 Design Objective
The objective of this project is to present design details of a self-balancing mobile robotic platform that can transport a rider while navigating in confined spaces and traversing in low clearance areas and uneven surfaces. This chapter discusses all mechanical designs issues of the robotic platform and provides a detailed description of mechanical components of the prototype model. Furthermore, Electric design issues are addressed and electrical circuitry of the robotic platform is discussed in details.
3.2 Design Requirements
The design of the self-balancing two-wheel mobile robot involves mechanical, electrical, and computer system requirements. These requirements are specified below:
1. The size must not exceed 20 inches front to back and 34 inches side to side (the latter in order to clear standard doorway widths)
2. The robot must carry a person with a weight of up to three hundred pounds.
3. The weight of the electronics (including sensors, batteries, etc.) must be no more than 80 pounds.
4. The robot must be able to support adjustable handles of between three to five feet in height and be easily adaptable for future projects.
5. Input controls must be able to be supplied by a remote control device.
6. The frame must be light weight so that the total weight of the platform including the four batteries not exceed 140 pounds, yet strong, rigid, and relative easy to assemble.
3.3 Design Specifications
The robotic transportation platform, consisting of the frame and base housing compartments, stands sixteen inches in height. The weight of the platform is concentrated below the axle in order to keep the center of gravity below the drive wheels. The robotic platform is powered by battery. The batteries supply power to the motors, control system, and other electronic parts.
3.3.1 Individual Components
Several design alternatives were developed using CAD/CAM software (Solid-Works). Design constraints were weight, cost of materials, rigidity, and ease of assembly.
The top and bottom platforms and the structural frame are the critical components of the design because they host all the other components. Its rectangular shape provides the robot with some aesthetic appeal.
The upper and lower platforms and structural supporting frame are made of aluminum that reduces weight and provide sufficient strength, and rigidity. Much of the metal used was “scrap” donated to the trade school shop where the robot was constructed. Figure 3.1 illustrates the main structural components that house the motors and drive units of the robotic platform. The design provides a total usable area of 864 square inches (both platforms taken together) and a usable volume (between the Platforms) of 1714 cubic inches.
a. 3D Frame with Center Line
b. 3D Solid Frame
Figure 3.1: View the Shape of Structural Frame
Figure 3.2: The Dimension View of the Structural Frame.
The strength and rigidity of the platform was further enhanced by designing a structural frame mounted on the lower platform of the base support as shown in Figure 3.2. Figure 3.3 shows the placement arrangement of the support bars on the upper platform plate.
a. Top View with Out Top Plate
b. Base, upper and lower platforms.
c. Front View
Figure 3.3 Illustrates a General Perspective of Base, Middle Bars and the Platform plates.
a. Dimension of the Upper Half Plate
b. Two Half Upper Plate c. Lower Plate
d. Dimension of the Lower Plate
Figure 3.4 Upper and Lower Platform Plates Details
a. Plate Holds Motor and Bearing
b. Middle Plate c. Plate Support the Wheel
d. Dimension of the Plate Holds Motor and Bearing
e. Dimension of the Plate Support the Wheel
f. Dimension of the Base Plate
Figure 3.5 Detailed drawings of the structural frame
3.3.2 Base Housing Compartment
The motors in the base wheel housing compartment are as shown in figure 3.6. The rider stands on the plate that forms the top of the housing compartment. All items included in this compartment are enclosed for safety and security. The motors are placed at the bottom of the housing compartment and the batteries are stationed in front and behind them. The batteries are secured by L-shaped brackets fixed to the bottom plate. The base housing compartment has space for two fans to cool the servo-motors.
Figure 3.6 Battery Distributions on the Bottom Plate.
3.4 Motors and Gear Head
The robotic platform is driven by two servo-motors. One servo-motor drives each wheel and is independent of the other. The motors are Smart Motor 2337 DT-PLS version 4.76 with a 100:1 gear head. By controlling the direction of rotation and rate of speed of each motor, the platform can be made to move forward and backward or turn left or right at any desired radius of curvature. For a zero radius turning, the speed of motors is the same in magnitude but opposite in direction. For any other turning radius, the magnitude of the speeds of the motors will differ from each other. The dimensions of the motors are as follow: 4.47” x 2.25” x 2.25”. Each weighs 2.27 pounds.
Figure 3.7 – Smart Motor 2337 DT-PLS [27]
The self-balancing nature of the platform is due to the concentration of weight below axle height. This is important because it insures the platform remains level when on inclined terrain or when accelerating and decelerating. With a rider standing on the top platform, the center of gravity of the platform/rider system as a whole is, of course, above the axles, just as in the case of a bicycle/rider system. Some balancing action on the part of the rider is needed to keep the system upright, but the cart has been designed so as to make riding on it a reasonably easily acquired skill for most people. Some experimentation has been done on various configurations of handholds attached to levers extending either vertically upward from the platform to mid-thigh, or angled forward to elbow height. Both configurations proved workable as assists to keeping one’s balance. Future experiments will be aimed at selecting the optimal design for handholds/controllers, but it objective was out of scope of this research work.
3.5 Wheels
The platform rides on two commercial rubber wheels. The smoothness of the ride depends on the type of tire that is used. Having the correct type of wheels is very important for this project. The robotic platform requires a certain diameter of wheel to work with the motors, and to meet the design requirements. Rubber tires were chosen because rubber can absorb vibrations and provide a smooth ride. Furthermore, the wheels can be used in all terrains likely to be encountered. The size of the wheels must match the size of the platform. They must be strong enough to support the weight of the entire platform. Taking all this into consideration, the wheels chosen are manufactured by Kings Tire Company with a diameter of 16 in. Figure 3.8 shows dimension of the wheel.
Figure 3.8 Shows Dimension of the Wheel
3.6 Batteries
Batteries power the platform. Three 12V-18A batteries power the two smart motors and the fourth powers the other electronics on-board. The weight of each battery is approximately 15 pounds. The dimensions of each battery are 3” x 7” x 7” (see Figure 3.9)
Figure 3.9 Rechargeable Batteries Four Numbers Use
3 .7 Pulleys and Timing Belt
Each servo-motor is connected to the drive axles by means of a timing belt. The belt passes over timing pulleys and provide minimum backlash for the motor drive shafts and. Figure 3.10 illustrates the set of pulleys and timing belt used in design of the robotic platform.
Figure 3.10 Pulleys and Timing
3.8 Sizing of the Power Unit
The robotic platform operates at 36 volts. The motor performance shown below is based on a commutating 75 voltage power to the motor. As it has been indicated on the chart below Figure 3.11, each motor is the expected peak rated torque of 225 oz-in with a continuous rated torque of 75 oz-in. Considering the gear ratio of the gear head on each motor has 100:1 ratio with 85 percent efficiency, this indicates that each servo-motor car provide a peak rated torque of 22500*0.85/16= 1195.3125 lb-in and a continuous rated torque of 7500*0.85/16= 3984.375 lb-in. For two servo-motor running parallel, that gives about (22500*2)*0.85/16= 2390.625 lb-in peak toque and (7500*2)*0.85/16= 796.875 lb-in .Continuous driving torque, which is sufficient for carrying out the specified payload. Two servo-motors, running parallel, produce double that torque, more that sufficient to power the platform given the expected payloads and the angles of inclination in the expected terrains for which the platform was designed.
Figure 3.11 Smart Motor Speed-Torque Characteristic
3.9 System Wiring Diagram
The electrical wiring diagram of the robotic platform and its power distribution arrangement along with safety features and power control schemes is illustrated in
Figure 3.12 a. Electrical Circuit Diagram
Figure 3.12 .a, the robot platform uses four 12 volt batteries. One 12 volt battery has been allocated to provide 12 volt devices on board. The three other batteries are installed in series to provide up to 36 volt power to the servomotors on board. Two of these 12 volts are also placed in series to create 24 volt power source for electronics requiring 24 volt power. An emergency switch is placed on the control panel of the robot. Its purpose is to cut the power off the motor drive in case of emergency. Additional the high voltage power lines are protected by a 10- Amp fuse in case of electrical shock occurrence on the system. The robot control panel has three LED that illuminate when 12, 24, and 36 power lines are on. Further more, be changing all four batteries on board. Three charger sockets are installed on the control panel. One 12 volt socket allows charging the first isolated 12 volt battery. The other two would allow charging the other three batteries using 24 volt charger. Five switches are also installed on the robot control panel in use of operation of the robot and turning on and off on board power lines. Appropriate wire gages were selected in safe power distribution of the robot and avoiding over-heating the wiring system.
Figure 3.12.b. illustrates the method of installing the servomotors in a daisy-chain fusion using the port arrangement on board the servomotor. The smart servomotors use RS-232 serial communication protocol in communication with a PC and another smart servomotor is another serially communicating devices. A tacit should be taken in preparation of special cable required for communicating from a PC to servomotors. The diagram shown below illustrates the wiring scheme for preparation of this cable. Although the smart motors are serially connected, they rather communicate with a PC using 9600 baud rate. At 9600 baud rate the program codes can be rapidly transmitted to the servomotors for an immediate change of action. This feature is used for programming
Figure 3.12.b. Illustrates the Servomotors Daisy-Chain
of the smart-motor using an on board serial-communicating modem. Using this wireless modem, the users programs can be readily upload the servomotor memory for rapid execution by its micro-procession. As simple Man-Machine interface using FMcell software has been also developed for seamless preprogramming of the robot platform.
SORRY I TRY TO LOADED WITH DRAWINGS BUT THE SIZEOF THE FILE IS MORE THAN 9 MB REALY I DON'T KNOW HOW I LOAD BIG FILE AT THE FORUM
AJ HASAN
AJ HASAN
MOBILE ROBOT DESIGN
3.1 Design Objective
The objective of this project is to present design details of a self-balancing mobile robotic platform that can transport a rider while navigating in confined spaces and traversing in low clearance areas and uneven surfaces. This chapter discusses all mechanical designs issues of the robotic platform and provides a detailed description of mechanical components of the prototype model. Furthermore, Electric design issues are addressed and electrical circuitry of the robotic platform is discussed in details.
3.2 Design Requirements
The design of the self-balancing two-wheel mobile robot involves mechanical, electrical, and computer system requirements. These requirements are specified below:
1. The size must not exceed 20 inches front to back and 34 inches side to side (the latter in order to clear standard doorway widths)
2. The robot must carry a person with a weight of up to three hundred pounds.
3. The weight of the electronics (including sensors, batteries, etc.) must be no more than 80 pounds.
4. The robot must be able to support adjustable handles of between three to five feet in height and be easily adaptable for future projects.
5. Input controls must be able to be supplied by a remote control device.
6. The frame must be light weight so that the total weight of the platform including the four batteries not exceed 140 pounds, yet strong, rigid, and relative easy to assemble.
3.3 Design Specifications
The robotic transportation platform, consisting of the frame and base housing compartments, stands sixteen inches in height. The weight of the platform is concentrated below the axle in order to keep the center of gravity below the drive wheels. The robotic platform is powered by battery. The batteries supply power to the motors, control system, and other electronic parts.
3.3.1 Individual Components
Several design alternatives were developed using CAD/CAM software (Solid-Works). Design constraints were weight, cost of materials, rigidity, and ease of assembly.
The top and bottom platforms and the structural frame are the critical components of the design because they host all the other components. Its rectangular shape provides the robot with some aesthetic appeal.
The upper and lower platforms and structural supporting frame are made of aluminum that reduces weight and provide sufficient strength, and rigidity. Much of the metal used was “scrap” donated to the trade school shop where the robot was constructed. Figure 3.1 illustrates the main structural components that house the motors and drive units of the robotic platform. The design provides a total usable area of 864 square inches (both platforms taken together) and a usable volume (between the Platforms) of 1714 cubic inches.
a. 3D Frame with Center Line
b. 3D Solid Frame
Figure 3.1: View the Shape of Structural Frame
Figure 3.2: The Dimension View of the Structural Frame.
The strength and rigidity of the platform was further enhanced by designing a structural frame mounted on the lower platform of the base support as shown in Figure 3.2. Figure 3.3 shows the placement arrangement of the support bars on the upper platform plate.
a. Top View with Out Top Plate
b. Base, upper and lower platforms.
c. Front View
Figure 3.3 Illustrates a General Perspective of Base, Middle Bars and the Platform plates.
a. Dimension of the Upper Half Plate
b. Two Half Upper Plate c. Lower Plate
d. Dimension of the Lower Plate
Figure 3.4 Upper and Lower Platform Plates Details
a. Plate Holds Motor and Bearing
b. Middle Plate c. Plate Support the Wheel
d. Dimension of the Plate Holds Motor and Bearing
e. Dimension of the Plate Support the Wheel
f. Dimension of the Base Plate
Figure 3.5 Detailed drawings of the structural frame
3.3.2 Base Housing Compartment
The motors in the base wheel housing compartment are as shown in figure 3.6. The rider stands on the plate that forms the top of the housing compartment. All items included in this compartment are enclosed for safety and security. The motors are placed at the bottom of the housing compartment and the batteries are stationed in front and behind them. The batteries are secured by L-shaped brackets fixed to the bottom plate. The base housing compartment has space for two fans to cool the servo-motors.
Figure 3.6 Battery Distributions on the Bottom Plate.
3.4 Motors and Gear Head
The robotic platform is driven by two servo-motors. One servo-motor drives each wheel and is independent of the other. The motors are Smart Motor 2337 DT-PLS version 4.76 with a 100:1 gear head. By controlling the direction of rotation and rate of speed of each motor, the platform can be made to move forward and backward or turn left or right at any desired radius of curvature. For a zero radius turning, the speed of motors is the same in magnitude but opposite in direction. For any other turning radius, the magnitude of the speeds of the motors will differ from each other. The dimensions of the motors are as follow: 4.47” x 2.25” x 2.25”. Each weighs 2.27 pounds.
Figure 3.7 – Smart Motor 2337 DT-PLS [27]
The self-balancing nature of the platform is due to the concentration of weight below axle height. This is important because it insures the platform remains level when on inclined terrain or when accelerating and decelerating. With a rider standing on the top platform, the center of gravity of the platform/rider system as a whole is, of course, above the axles, just as in the case of a bicycle/rider system. Some balancing action on the part of the rider is needed to keep the system upright, but the cart has been designed so as to make riding on it a reasonably easily acquired skill for most people. Some experimentation has been done on various configurations of handholds attached to levers extending either vertically upward from the platform to mid-thigh, or angled forward to elbow height. Both configurations proved workable as assists to keeping one’s balance. Future experiments will be aimed at selecting the optimal design for handholds/controllers, but it objective was out of scope of this research work.
3.5 Wheels
The platform rides on two commercial rubber wheels. The smoothness of the ride depends on the type of tire that is used. Having the correct type of wheels is very important for this project. The robotic platform requires a certain diameter of wheel to work with the motors, and to meet the design requirements. Rubber tires were chosen because rubber can absorb vibrations and provide a smooth ride. Furthermore, the wheels can be used in all terrains likely to be encountered. The size of the wheels must match the size of the platform. They must be strong enough to support the weight of the entire platform. Taking all this into consideration, the wheels chosen are manufactured by Kings Tire Company with a diameter of 16 in. Figure 3.8 shows dimension of the wheel.
Figure 3.8 Shows Dimension of the Wheel
3.6 Batteries
Batteries power the platform. Three 12V-18A batteries power the two smart motors and the fourth powers the other electronics on-board. The weight of each battery is approximately 15 pounds. The dimensions of each battery are 3” x 7” x 7” (see Figure 3.9)
Figure 3.9 Rechargeable Batteries Four Numbers Use
3 .7 Pulleys and Timing Belt
Each servo-motor is connected to the drive axles by means of a timing belt. The belt passes over timing pulleys and provide minimum backlash for the motor drive shafts and. Figure 3.10 illustrates the set of pulleys and timing belt used in design of the robotic platform.
Figure 3.10 Pulleys and Timing
3.8 Sizing of the Power Unit
The robotic platform operates at 36 volts. The motor performance shown below is based on a commutating 75 voltage power to the motor. As it has been indicated on the chart below Figure 3.11, each motor is the expected peak rated torque of 225 oz-in with a continuous rated torque of 75 oz-in. Considering the gear ratio of the gear head on each motor has 100:1 ratio with 85 percent efficiency, this indicates that each servo-motor car provide a peak rated torque of 22500*0.85/16= 1195.3125 lb-in and a continuous rated torque of 7500*0.85/16= 3984.375 lb-in. For two servo-motor running parallel, that gives about (22500*2)*0.85/16= 2390.625 lb-in peak toque and (7500*2)*0.85/16= 796.875 lb-in .Continuous driving torque, which is sufficient for carrying out the specified payload. Two servo-motors, running parallel, produce double that torque, more that sufficient to power the platform given the expected payloads and the angles of inclination in the expected terrains for which the platform was designed.
Figure 3.11 Smart Motor Speed-Torque Characteristic
3.9 System Wiring Diagram
The electrical wiring diagram of the robotic platform and its power distribution arrangement along with safety features and power control schemes is illustrated in
Figure 3.12 a. Electrical Circuit Diagram
Figure 3.12 .a, the robot platform uses four 12 volt batteries. One 12 volt battery has been allocated to provide 12 volt devices on board. The three other batteries are installed in series to provide up to 36 volt power to the servomotors on board. Two of these 12 volts are also placed in series to create 24 volt power source for electronics requiring 24 volt power. An emergency switch is placed on the control panel of the robot. Its purpose is to cut the power off the motor drive in case of emergency. Additional the high voltage power lines are protected by a 10- Amp fuse in case of electrical shock occurrence on the system. The robot control panel has three LED that illuminate when 12, 24, and 36 power lines are on. Further more, be changing all four batteries on board. Three charger sockets are installed on the control panel. One 12 volt socket allows charging the first isolated 12 volt battery. The other two would allow charging the other three batteries using 24 volt charger. Five switches are also installed on the robot control panel in use of operation of the robot and turning on and off on board power lines. Appropriate wire gages were selected in safe power distribution of the robot and avoiding over-heating the wiring system.
Figure 3.12.b. illustrates the method of installing the servomotors in a daisy-chain fusion using the port arrangement on board the servomotor. The smart servomotors use RS-232 serial communication protocol in communication with a PC and another smart servomotor is another serially communicating devices. A tacit should be taken in preparation of special cable required for communicating from a PC to servomotors. The diagram shown below illustrates the wiring scheme for preparation of this cable. Although the smart motors are serially connected, they rather communicate with a PC using 9600 baud rate. At 9600 baud rate the program codes can be rapidly transmitted to the servomotors for an immediate change of action. This feature is used for programming
Figure 3.12.b. Illustrates the Servomotors Daisy-Chain
of the smart-motor using an on board serial-communicating modem. Using this wireless modem, the users programs can be readily upload the servomotor memory for rapid execution by its micro-procession. As simple Man-Machine interface using FMcell software has been also developed for seamless preprogramming of the robot platform.
SORRY I TRY TO LOADED WITH DRAWINGS BUT THE SIZEOF THE FILE IS MORE THAN 9 MB REALY I DON'T KNOW HOW I LOAD BIG FILE AT THE FORUM
AJ HASAN