Autonomous Speed Control Vehicle RIT Computer Engineering Senior Design Project Fall 2006 Designed by: Laura Celentano, Glenn Ramsey, and Michael Szalkowski User Interface The user interface consists of two switches two lights, and two seven-segment displays. The seven-segment displays show the speed of the vehicle in ft/s. One switch/light pair corresponds to power, the other to operations. The details of the operation are in the tables below. SwitchUpDown PowerPower is offPower is on OperationalSystem is haltedSystem is running LightFunctionDescription RedPowerOn when the power is on GreenOperationOn when the system is running Track Following Front Left Front Middle Front Right Back Left Back Right Turn Off Center Off OnRight Hard Off OnOffLeft Hard Off On Right Hard Off OnOff Right Hard Off OnOffOnRight Hard Off On OffRight Hard Off On Right Hard OffOnOff Center OffOnOff OnCenter OffOnOffOnOffCenter OffOnOffOn Center OffOn Off Right Soft OffOn OffOnRight Soft OffOn OffRight Soft OffOn Right Hard OnOff Left Hard OnOff OnLeft Hard OnOff OnOffLeft Hard OnOff On Left Hard OnOffOnOff Center OnOffOnOffOnCenter OnOffOn OffCenter OnOffOn Center On Off Left Soft On Off OnLeft Soft On OffOnOffLeft Soft On OffOn Left Hard On Off Center On OffOnLeft Hard On OffRight Hard On Center The track following algorithm utilizes five optoreflector sensors mounted on the underside of the vehicle. Three sensors are mounted at the front of the vehicle and two are mounted at the rear. When the vehicle is properly following the track, all five sensors should detect the track. The sensor values are polled by the microcontroller. The implemented algorithm can be seen in the flow chart below. The algorithm utilizes a look-up table to determine how the vehicle should turn to stay on the track depending on the sensor values. This look-up table can be seen below. Speed Limit Detection Speed Control Project Costs PowerOperation Off On Off On The speed control consists of both measuring and adjusting the speed of the vehicle. Measuring the speed is accomplished by a shaft encoder mounted on the rear axle. An opto- interrupter is mounted in such a way as to generate a square wave as the vehicle moves. The frequency of the wave is directly proportional to the speed of the vehicle. Controlling the speed is done through the use of an H-Bridge. The speed duty cycle is adjusted up and down according to the desired speed until it matches. Additionally, the turning amount must be taken into account in the speed control. This is because the friction increases when the vehicle goes into a turn and decreases when it comes out of a turn. This is taken into account by detecting turn changes and adding or subtracting empirically determined constants from the speed duty cycle. ItemOur CostActual Cost HCS12 Microcontroller$0$130 Vehicle$40 Direction Control Hardware$0$10 Speed Control Hardware$15 Speed Limit Detection Hardware$10 Track Following Hardware$15 Track and Overpass Construction$20$50 User Interface Hardware$12 Power Subsystem Hardware$30 Total:$142$312 The objective of this project was to create an autonomously speed controlled vehicle. The vehicle follows an oval reflective track through the use of infrared sensors mounted on the underside of the vehicle. Infrared sensors mounted on the roof of the vehicle detect reflective patterns on the underside of overpasses. These patterns correspond to different speeds. The vehicle’s speed is controlled to match the last recognized pattern. Overview From Left-to-Right Laura Celentano Responsiblity: Track-Following Glenn Ramsey Responsibility: Speed Control Michael Szalkowski: Responsibility: Speed Limit Detection In order to detect the speed limit, it was important that the correct bit pattern be interpreted. In order to alleviate this problem, a comparator algorithm was used, and can be seen in Figure 1. By comparing the patterns stored in memory at the current time to some previous time, one can decipher the bit pattern under the underpass. The sensor input will automatically shift the bit pattern into memory serially. If they differ, it will update the previous bit pattern variable with the current one. Once a bit pattern has been found not to change (like right after the vehicle exits the underpass), it will set the new desired speed based on the bit pattern. The threshold time that was found to work best after testing was 1 second.