Introduction: A number of sensors were presentedto us for the purpose of this assignment. These included a compass, anaccelerometer, an infrared and ultrasonic sensor, a gyroscope and an ambientlight sensor. These were all from a company named Diligent who are a nationalinstruments company. For the purpose of this assignment I was responsible forthe investigation of the accelerometer therefore the majority of this reportwill consist of information on this. The reason for the investigation of thesesensors is to integrate them onto a two wheel balancing platform or Segway toallow it to move and navigate whilst maintaining its balance and direction. Research: A two wheeled self-balancing scooteror Segway was first developed in the late 90’s and early 2000’s as an alternatemode of transport to a pedal bike or car for city goers. Its function was forthe user to stand on the platform and lean in the desired direction and anelectric motor will propel the board forwards. There have been advancementssince then however, such as increases in speed, size and length of battery lifeas well as off road versions of the product.
In theory this product is verypractical however there have been a large number of cases showing that theyhave caught fire and thus been banned on airlines and in some countries. The two wheeled self-balancingplatform we plan to make is not designed for human use but rather to use it asa platform for which the various sensors can be used and integrated. Our systemwill require an accelerometer because it is desired that we measure how quicklythe platform is accelerating or decelerating. Different accelerometers work indifferent ways such as; the piezoelectric effect which works by stress put uponcrystal structures during acceleration, which in turn causes a voltage whichgenerates the value of acceleration.
Alternatively, some detect changes incapacitance with two microstructures moved under accelerative forces and thusconverted into a voltage. The accelerometer provided is the ‘Diligent Pmod ACL3 axis accelerometer’ which provides 13 bits of acceleration data as well asthe ability to detect inclination changes of less than 1 degree and costs just$15. The accelerometer itself is only an inch long and 0.
8 inches widetherefore ideal for integrating into the platform. SensorSelection and Interfacing: In order to actually construct thisplatform a suitable controller will be needed, we are using a myRIO device. Thiscontroller allows us to link up the sensors and convert this into a set ofvalues which can be monitored and then alter the platform to adhere to ourrequirements. With respect to the sensor I am responsible for, there is an accelerometerbuilt into the myRIO controller however it is not as sensitive as the PmodAccelerometer. The myRIO is capable of an accelerative range of +/-8g, 3 axisdetection and 12bits of accelerative data compared with the Pmod accelerometer capableof +/-16g and 13 bits of accelerative data. Adding the sensor also allows themyRIO is be positioned on the platform in any orientation therefore itsinternal sensor isn’t required.
Moreover, the Pmod sensor is specificallydesigned to measure acceleration and therefore can be considered to give highervalidity of value output. The two wheeled self-balancingplatform will require all of the sensors in order to function properly. Thegyroscope will allow the platform to orientate, measure and control the correctangle whilst moving and also when an external force is applied to it.
The lightsensor can be used as a guiding system for the platform to follow. The IR andUS sensors will be used for measuring distance from objects so the system canreact and change direction to avoid it. The compass will be used as a referencepoint for the platform whilst it is moving and/or navigating around an objectfor example. The accelerometer will measure the acceleration and perform asimilar job the gyroscope as far as orientation and guidance whilst balancing.
Formy sensor, the accelerometer, it will be required that it is positioned on theplatform suitably to measure a helpful reading in order to correct any problemsthat may occur.