T.E.S.L.A (Terrain Exoskeleton (that) Shocks Large Animals) Mark Tate

Transcription

1 T.E.S.L.A (Terrain Exoskeleton (that) Shocks Large Animals) Mark Tate April 23, 2013 University of Florida Mechanical Engineering EEL 4665C IMDL Formal Report Instructors: A. Antonio Arroyo, Eric M. Schwartz

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3 Most sentry robots are only about one thing, detection. Well this got me thinking, why not add deterrent as well? People invest in all kinds of security systems to alert them when someone is where they shouldn t but that doesn t stop them from going there in the first place! Well my robot will look for those people and give them a shocking surprise! My robot goal is to create a sentry hexapod that roams around an enclosed area and avoids all objects in the area. It will also shock all objects that appear suddenly in front of it. The objective of my project is to create an autonomous robot that will search a room for a human, and shock them when it gets near enough. This idea came from my desire to creating a fun way to keep people on their toes when at my apartment. I intend to do this with a 6-legged hexapod that will able to walk around and over obstacles to find a human (via temperature reading) and shock them when near enough. The following pages in this report will describe the function of each component of the robot and the software that connects them. Being a mechanical engineer, I understand and welcome the challenge that comes with programming a walking robot with multiple legs and sensors. The integrated system of my robot resides in the DIY Epiphany board that has an Atmel ATxmega128A1U 8/16bit Processor. The theory of operation is modeled in figure 1. As the robot is turned on and given a command to start, it will first look and see if it has any objects in front of it. If object is found, the robot will walk around the room avoiding objects with sonar. Once something appears suddenly in front of it (must be stationary after appearing) the robot will

4 try to get as near as possible. Once the robot has gotten sufficiently close to the human (or it can no longer move forward) it will flash a red led light to indicate its success and throw it s antenna forward to shock him/her. The mobile platform will be modeled similar to figure 2. The robot will subsequently be modeled in Solidworks and cut with a T-Tech. The platform can be divided into two categories, the body and the legs.

5 The body is going to be two parallel wood cutouts that are attached by standoffs. The standoffs will allow the Epiphany board to rest securely in the center of the robot for protection. Around the edge of the platform, 6 servos placed 60 apart will be attached for the legs rotation. The legs will have only 2 degrees of freedom (as opposed to 3 DoF in insect legs). All leg parts will be identical with rubber ends to provide better traction. Six more servos will be attached to the six servos on the body and legs to provide leg lift. By having six legs, the design allows three legs to move while the other three hold the platform upright. Unfortunately, two DoF legs limit leg moment compared to three DoF systems.

6 The movement the Locating Robot produces will be provided by 6 core Hitec HS-485 servos (possibly) and 6 peripheral Hitec HS-645MG servos. The core servos will rotate each leg forward or backwards and the peripheral servos will lift each leg up so it can rotate forward or backwards. The HS-645 servos are going to be in the lift position because they have more lift (200 oz in) than the 485s. Each servo will be powered by the 5V port the Epiphany board provides. One small servo will be mounted on top of the hexapod so it can rotate the sonar device and decide the best track to take around its environment. Sensors Sonar Sensor One Parallax PING))) sonar (Fig. 1) was used on the robot. The Parallax sonar has three pins, one for ground, 5V, and signal, which doubles as an I/O pin. This sensor can perform precise measurements ranging from 2 cm to 3 meters. The sonar works by sending a high value thought the signal pin to send a chirp out of the sensor and measuring the time it takes for it to return. That time difference is then sent back though the signal pin in the form of a square wave with the width corresponding to the time taken (fig. 2)

7 Fig. 1 sonar Parallax PING))) (parallax.com) Fig. 2 Sonar operation (parallax.com) Fig 3. Sonar Layout The sonar will be attached to a servo mounted on the front of the hexapod. This servo will actuate back and forth taking measurements at three positions, left, right, and forward (Fig 3). This will allow the hexapod to search for objects in its path and their relative location to the hexapod. The hexapod will turn towards to the left or right according to where the object is located. An experiment was done to characterize this sonar sensor. The sensor was connected to Port D pin 0 and tested with the DIY Epiphany board. The initial ping was sent out 5 seconds the board was reset and after timing the time it took to return, the sensor returned a high output value that was measured in micro-seconds. The result was printed and recorded along with the distance of the object to the sensor. The results seen on figure 4 show the linear relationship between the pulse length and distance and its plateau at 3 meters. The sensor was measured to be 18 cm from the ground (approximately

8 the height it will be on the hexapod). Error is most likely caused by imperfect measuring between object and sensor... Fig. 4 Parallax Test Data Infra-Red Thermometer One Melexis (MLX90614) Infra-red thermometer will be used for the robot. It needs a supply voltage of 2.6~3.6 V and is a digital device. The operating temp is between -40 to 85 C and can measure temperature between -70 to 360 C with a 0.5 C accuracy at room temperature. The schematic for wiring is shown in figure 6 and involves a 0.1 uf capacitor. Two pull-up resistors are placed between the SDA, Vcc, and SCL pin. Fig.5 IF Thermometer Fig. 6 IF therm. schematic There are two methods of output from the sensor, PWM and I2C. The I2C has a higher level of resolution (0.02 C) than the PWM which has a 0.14 C level of resolution. A chart showing the accuracy compared to ambient temperature (Ta) and measured temperature (To) can be seen in figure 7. Since these devices average all the temperatures in their field of view, the narrowest range was chosen (10 ) as opposed to the larger ones (35 ~90 ).

9 Fig. 7 Accuracy of sensor. ( Pages/ MLX90614ESF-BCF.aspx) The IF sensor will accompany the sonar sensor on top of the servo so it can read the temperature of objects to the front, left, and right sides of the hexapod. These readings will be constantly taken and alert the hexapod when it gets a reading within human body temp range. After the hexapod has investigated the source of the heat (if it moves when shocked, the sonar will alert the hexapod and the hexapod will move on) and continue this process until I think of something else for it to do. This robot will have sort of a funky gait so I wanted it s personality to match. It has a actuating head that rotates from left to right as it walks. It also will turn off or blink led lights according to where it senses an object. When something shows up ahead of it, the blue lights will turn off and the red ones will turn on to show that it s angry. TESLA will also strafe left or right according to where an object is placed far ahead of it. It will also turn sharply if something gets too close. The hexapod will also wall follow for a distance until the wall ends. I didn t get my themo sensor to work with was disappointing but I was able to code other functions into my robot. I also miscalculated the static generator s EMF production which causes my board to temporarily malfunction. But even with these setbacks, I still was able to create a walking, obstacle avoiding robot. I learned a lot about robotics and coding. This class was very entertaining and I love my robot. I wish I had done some form of video processing but I was a little afraid of it and by the end I had too many other class projects to do. I want to thank both Josh and Ryan for their help!

10 Epiphany DIY board - Parallax Sensor Product-Guide-v2.0.pdf IF sensor - Pages/ MLX90614ESF-BCF.aspx Servos= Please go to the robot website for all code and updates