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General Idea of T.I.G.E.R
| T.I.G.E.R. stands for Transponding Internet Guided Electric Rover. Its is a senior design project for students in the Auburn University Electrical and Computer Engineering Department. Below are some drawings and specifications of the Rover. |  |  |  | | Weight | 250lb |
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| Power | 36V (3 x 12V) |
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| Motor Power | 2 x 1/4 HP |
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Chassis Team Technical Information
| The power train of the robot consists of 3 deep cycle marine batteries and two 36 VDC field winding motors. The three batteries are connected in series to provide the 36 VDC needed for the armature of the motors. A DC to AC power inverter is connected to 12 VDC from one of the batteries. The inverter supplies 120 VAC to a computer type power supply which provides the different voltages needed by the electronics. This setup provides for sufficient filtering from motor noise which could possibly damage the sensitive electronics. The field windings of the motors are also connected to 12 VDC. The motors have a worm drive gearhead attached providing gear reduction.
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Electronics Team Technical Information
| The original design of the rover included motor drivers, obstacle sensors, local control, a charging system, and a central disable system (panic button). Using the motor specifications, a 20-Amp H-bridge was found sufficient to drive the motors. The H-bridge was chosen due to its versatility. The particular H-bridge chosen can be operated in four different modes. The two modes researched are the Pulse Width Modulated (PWM) mode and the Analog mode. The operational mode is determined by the position of four DIP switches. For example, with the number one and number four switches set to the on position and the number two and number three switches set to the off position, the H-bridge will operate in the PWM mode. During original implementation of the H-bridge, PWM mode was chosen to operate the motors. After further experimentation it was observed that the motors were operating at slightly different speeds. In order to correct this and enable the operator to more effectively control the rover, it has been determined to operate in analog mode and make a couple of other modifications. First, there are two different analog modes available on the H-bridge. The chosen mode was the 0volt-5volt mode as opposed to the 0-lower voltage mode. This allowed for more flexibility. The software group is controlling the frequency passed to the H-bridge through a Javelin Stamp microcontroller. A low pass filter is being designed in order to better control the frequency. In an offline experiment, software is being used to send a reduced frequency which will then be passed through a low pass filter delivered to the H-bridge. The H-bridge will in turn control the motor speed. Another specification established was the need to sense obstacles. This circuit would need to disable the rover provided an obstacle enters the rover's path. After researching the different types of sensors, we decided to use an ultrasonic sensor. The Devantech SRF04 Ranger is the sensor of choice. The sensor was chosen based on its ability to sense objects with in a wide angle range and its distance was variable depending on the user's need. At this time, the motor drivers and the charging systems are in place. The remaining systems are being researched and designed and will be implemented in the near future.
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Software Team Technical Information
| The software has two tasks: to allow communication wirelessly with the robot and to send a pulse-width modulated signal to the motor drivers to control the motors. The software team programmed a Javelin Stamp microcontroller module from Parallax, which enabled us to quickly code the signals we needed. We programmed the Stamp to output two separate PWM signals as well as two separate control line signals (forward and reverse). By modulating these signals we are able to control the rover's motion. For example, to turn left while going forward, we simply decrease the PWM signal to the left motor and increase the right motor. The software is also written to make sure that the rover would not be able to increase or decrease speed "instantaneously". We wanted to make sure that power spikes do not occur from switching speeds on the motor too quickly. Some fail-safe logic was, therefore, encoded into the software. The communication between the laptop and the Javelin Stamp is via a serial connection. The laptop was required to communicate wirelessly through the Virtual Private Network (VPN) in Broun Hall. The initial working prototype was scheduled to be rolled out for Engineering Open House, just four weeks after the inception of the project. To achieve wireless communication to the rover under this time contraint, a simple Remote Login was done. While this connection was slow, it was the quickest way to communicate with the rover before the deadline.
There are many new software features currently being added. The software team is writting code for the collision detection sensors that are going to go on the rover. This will make sure the rover does not run into anything, or anybody. The software team is also working on a better means of communications with the rover. We are currently implementing a User Datagram Protocol (UDP) server to run on the rover to receive commands from the base station. Finally, the software teams is adding a better user interface for the driver. These new features include a speedometer, a joystick interface, as well as an easier method of startup.
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