Beyond the Horizon - School of Engineering Science
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1. 2000 http www staircraft org Beyond the Horizon Functional Specification 6 4 Output Signal Encoding The commands sent by the microprocessor need to be further processed so that they can be used as signals to enable the actuators Figure 10 illustrates the context diagram with the output signal encoding stage highlighted Signal Input Signal Actuator Acquisition Conditioning Processing Interface Figure 10 StairCraft Signal Processing Output Signal Encoding The output signal encoding stage shall contain the following features e Perform digital or any logic encoding to convert microprocessor output commands to digital input signal for the actuators e Perform digital to analog conversion for the actuator input signals Figure 11 shows the block diagram for the output signal encoding stage i To Signal From Signal Actuator Signal D A Interface P rocessing E Encoding Stage L VV Figure 11 Block Diagram for the Output Signal Encoding Stage Copyright 2000 http www staircraft org 9 Beyond the Horizon Functional Specification 10 6 5 Actuator Interface Figure 12 illustrates the context diagram with the actuator interface stage highlighted Signal Input Signal Signal Output Signal Acquisition Conditionin Processing Encoding Figure 12 StairCraft Signal Processing Actuator Interface As shown in Figure 12 this is the final destination of the whole signal processing p2. 0 5 Full Scale minimum Sensitivity 0 05 0 15mV V 0 001inch at outer sensing range 0 8 1 0 feet However in our project the sensing targets must meet the following criteria for the sensors to operate properly e Angle of impact for the sensor signal 90 with 1 of tolerance e The sensor target shall have a smooth surface so the signal will not be deflected e The steps of the staircase must have solid vertical front walls Figure 5 illustrates the block diagram for the signal acquisition stage Signal From Stair Steps To Input Signal Impulse Switch Conditioning Sensor P Figure 5 Block Diagram for the Signal Acquisition Stage Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 7 6 2 Input Signal Conditioning After the input signal is acquired the signal will go through the input signal conditioning stage Figure 6 illustrates the context diagram with the input signal conditioning stage highlighted Signal Signal Output Signal Actuator Acquisition Processing Encoding Interface Figure 6 StairCraft Signal Processing Input Signal Conditioning Within the input signal conditioning stage there are sub building blocks to convert the raw input data to something the microprocessor can understand The input signal conditioning stage shall have the following functionalities e Filter out the noise from the input signal e Amplify Rectify the input signal Pe
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4. School of Engineering Science Beyond the Horizon Burnaby BC V5A 186 staircraft 340 Q sfu ca http www staircraft org October 16 2000 Dr Andrew Rawicz School of Engineering Science Simon Fraser University Burnaby British Columbia V5A 1S6 Re ENSC 340 Functional Specification for StairCraft a Stair Climbing Mechanism Dear Dr Rawicz The attached document StairCraft Functional Specification outlines the functional requirements for our project for ENSC 340 Engineering Science Project Our goal is to design and implement a stair traveling device that can carry heavy loads and can be applied to wheelchairs or cargo loading devices to move up and down stairs smoothly and reliably The attached document lists the functional requirements of the system as well as the specifications for the components of the system The system components include the mechanical structure and framework user interface signal acquisition unit input output signal conditioning unit micro controller and actuator unit Beyond the Horizon consists of six talented innovative and enthusiastic fourth year systems engineering students Wayne Chen Kenneth Cheng Jeff Hsu Andy Ma Michael Tam and Gordon Yip If you have any questions or concerns about our document please feel free to contact any of us by emails at staircraft 340 sfu ca or contact me by phone at 604 926 6600 or by e mails at kchengc G sfu ca Sincerely Kenneth Cheng Team Manag
5. tasse e tasse seta sese eeas 12 9 1 ACCURACY eeraa raea cese rre ERE E MR E SE E R EEEE 12 9 2 STABI TIY cerren Sper eee IE EEEE EE EEEE E dugu EERE EEEE E 13 9 3 Bio cB ud m 13 10 STANDARDS iro EREPADEREKATEDERID EFE RIEPRUEFEE DI DK pL DRE FE S aiaiai 14 11 TESTING MICTHO Dis isponmnio volts ade ERPEUREE REEF EE IP ER en EC RUNE 14 11 1 SENSORY COMPONENT TESTING 0 ccccssssceeceeseeeeessseececeseaceeeesaaeeceesnaeeesenaeeeeees 14 11 2 PROCESSING COMPONENT TESTING iic E rta eiie vU ELMAR REM fu kate Ra gin 14 Copyright O 2000 ili http www staircraft org Beyond the Horizon Functional Specification ACTUATOR COMPONENT TESTING EE 15 11 4 MECHANICAL COMPONENT TESTING esee nennen nennen en nnnnetn enne 15 12 ERP TING sc bon HPO EROR EDU DRER EUER PERUL AFER EREREEE ERROR UM ERRARE ROM PR 15 13 USER MENU 552 4 brain EORR KE DURER CERDO RARE EC URU ERRARE RUIN 15 14 COMPATIBILITY WITH OTHER SYSTEMS eere esee eee ee eee een sese tnaon 16 15 POTENTIAL SYSTEM LIMITATION eee ee eee eren teen no ne tena sesta ta sos etnos 16 16 CONCLUSION Leu Gud HER CE HRS EE CR ELO REDE acount 16 Copyright O 2000 iv http www staircraft org Beyond the Horizon Functional Specification List of Figures FIGURE 1 SYSTEM OVERVIEW cccccccccecesccscssesssceeusecceeeessceceeusecessueecescueecessceeecesseueessseeuesess 2 FIGURE 2 DATA FLOW BLOCK DIAGRAM OF STAIRCRAFT ccccceseeesccc
6. LE 6 SUMMARY OF THE COMPONENT ACCURACY OF STAIRCRAPT sscccceceeeeeeeaeesees 12 Copyright 2000 V http www staircraft org Beyond the Horizon Functional Specification 1 1 Introduction Injured handicapped and elderly people traveling with their wheelchairs all face a common problem they cannot go to their desired destinations as convenient as the rest of the population Not all buildings provide ramps elevators escalators or other assistive devices that transport wheelchairs to higher or lower altitudes In addition lifting heavy objects up and down stairs has resulted in numerous injuries Thus Beyond the Horizon aims to address all these problems by creating a device that can travel along staircases smoothly reliably and most importantly safely We are dedicated to create StairCraft that brings enhanced mobility to wheelchairs in such a way that stairs or steps are no longer obstacles for the wheelchairs Injured handicapped and elderly people retain their freedom to travel on routes that they have once tried to avoid Our proposed device can also be applied to and combined with cargo transporters as well as other machines such as robots that may desire to travel up and down the stairs automatically The purpose of this document is to describe the environmental physical electrical safety and other functional requirements that we intend to incorporate into our system by December 2000 The design engineers o
7. ability to increase their mobility with the use of wheelchairs Unfortunately as the wheelchair users encounter situations such as staircases or higher lower steps while traveling they often need to find elevators or ramps in order to arrive at their destination levels In some situations where elevators and ramps are not available or too far away it is more convenient to have wheelchairs capable of bypassing the heights At Beyond The Horizon we feel that there is a real need to improve and add a stair climbing feature to the current wheelchair design especially as the baby boomers are getting old Our short term goal in the coming few months is to create a bare bone device or mechanism StairCraft that is capable of climbing up down stairs and carrying cargos Eventually we will further develop StairCraft to be integrated into wheelchairs so that it can help people on wheelchairs to go to places where they would have trouble reaching in the past This document introduces and discusses the main functional blocks of the electrical requirements as well as the physical mechanical environmental and safety performance specifications of the system Copyright 2000 ii http www staircraft org Beyond the Horizon Functional Specification Table of Contents EXECUTIVE SUMMARY siisssccsasssosctesscasssivensavpvavseaevavsesssavvucexstupnvaswspanvuatectavnuseisoanenasecsant I 1 INTRODUCTION vicnicuncanencmunnatancsiumaaeiwanawnmnrannncas 1 2
8. ding stage to convert these commands to something the motors and other actuators understand Finally the actuators react based on the processor commands Figure 3 illustrates how StairCraft processes the signals from the input sensors to the output actuators Sensor Signals Signal Actuator uu Actuator Figure 3 Signal Processing from the Input Sensors to the Output Actuators Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 6 6 1 Signal Acquisition In this stage StairCraft makes use of a proximity sensor to capture the input data Figure 4 illustrates the context diagram with the signal acquisition stage highlighted Input Signal Signal Output Signal Actuator Conditioning Processing Encoding Interface Figure 4 StairCraft Signal Processing Signal Acquisition Since StarCraft needs to be able to see the staircase well before it hits it the sensors of StairCraft shall have a superior sensing range In addition because StairCraft may be operated under various temperature and humidity conditions the sensors shall be able to work under these conditions as well Overall the sensors shall meet the following specifications Sensing Range up to 1 feet 30 5cm Operating Temperature 20 C 50 C Operating Humidity up to 10 100 Operating Frequency 10kHz 40kHz Supply Voltage 10V 20V Supply Current up to 30mA Response Time 0 8ms ON 0 8ms OFF Resolution
9. er Beyond the Horizon Enclosure Functional Specification for StairCraft a Stair Climbing Mechanism ony Beyond the Horizon presents SpA ORA V a Stair Climbing Mechanism Functional Specification Prepared by Submitted to Kenneth Cheng Steve Whitmore Wayne Chen Andrew Rawicz Jeff Hsu Jason Rothe Andy Ma James Balfour Michael Tam Gordon Yip Date October 16 2000 Contact e mail staircraft 340 sfu ca http www staircraft org Beyond the Horizon Functional Specification Executive Summary Everyone should share equal rights even physically challenged people However due to their physical constraints it may be very difficult for them to go to wherever they want The invention of wheelchairs improves the mobility of injured handicapped or elderly people Nevertheless wheelchairs have their limitations including traveling staircases and steps Therefore our objective is to develop a new mechanism allowing wheelchairs to bypass the stairs and travel Beyond The Horizon Many assistive devices have been invented to help physically disabled people These people are confronted with many challenges that result from their disabilities and mobility is the most significant challenge they have to face Assistive devices such as wheelchairs and prosthetics are developed to improve mobility In terms of mobility the invention of wheelchairs allows injured handicapped or elderly people with declined mobility or permanent dis
10. er developed such that it will be compatible with other wheelchair designs 15 Potential System Limitation StairCraft may be limited by the following factors e The load capacity will be limited by the prototype support and elevation mechanisms some heavy users objects may not occupy the system Traveling speed is at a constant and relatively slow speed i e 32 cm s maximum e Users may not toggle between modes while the system travels upstairs downstairs e StairCraft may not be able to bypass some obscure stairs or steps 16 Conclusion We have discussed in this document about the environmental physical electrical safety and other functional requirements that we intend to incorporate into StairCraft by December 2000 Based on these functional specifications Beyond the Horizon is hoping to design a reliable mechanism that is cheap to manufacture It is our goal at Beyond the Horizon to make this world a better place especially for those who need extra care We determine to develop a stair climbing mechanism that will be quick smooth safe and cheap so physically challenged people can acquire StairCraft without paying an arm and a leg Hopefully by December 2000 we will be able to develop a successful prototype that can be translated into the final product easily Only then will we have truly contributed to the building of a better world Copyright 2000 http www staircraft org
11. essessceessescceeuseesseuueecess 2 FIGURE 3 SIGNAL PROCESSING FROM THE INPUT SENSORS TO THE OUTPUT ACTUATORS 5 FIGURE 4 STAIRCRAFT SIGNAL PROCESSING SIGNAL ACQUISITION ccce 6 FIGURE 5 BLOCK DIAGRAM FOR THE SIGNAL ACQUISITION STAGE eee 6 FIGURE 6 STAIRCRAFT SIGNAL PROCESSING INPUT SIGNAL CONDITIONING nee 7 FIGURE 7 BLOCK DIAGRAM FOR THE INPUT SIGNAL CONDITIONING STAGE cene 7 FIGURE 8 STAIRCRAFT SIGNAL PROCESSING SIGNAL PROCESSING eene 8 FIGURE 9 BLOCK DIAGRAM FOR THE SIGNAL PROCESSING STAGE eene 8 FIGURE 10 STAIRCRAFT SIGNAL PROCESSING OUTPUT SIGNAL ENCODING eee 9 FIGURE 11 BLOCK DIAGRAM FOR THE OUTPUT SIGNAL ENCODING STAGE eee 9 FIGURE 12 STAIRCRAFT SIGNAL PROCESSING ACTUATOR INTERFACE ce 10 FIGURE 13 STABILITY REQUIREMENTS OF STAIRCRAFT ssssssececcceeeceseesssseceeseeeesssaaenenes 13 List of Tables TABLE 1 STAIRCRAFT ENVIRONMENT REQUIREMENTS ssssssssseeeeceeeecseeeeseseceeceeessaaaaeesseeees 3 TABLE 2 STAIRCRAFT PHYSICAL REQUIREMENTS ccccccccsssessseeeeeceesecsseesseseeeeseeeesuaaenssseeees 3 TABLE 3 PHYSICAL REQUIREMENTS OF STAIRS FOR TRAVELING eere 3 TABLE 4 HIGHLIGHTS OF REQUIRED PHYSICAL ACCESSORIES ccccccccessseesssseeeeceeeecuaaeesseees 4 TABLE 5 SUMMARY OF THE ELECTRICAL REQUIREMENTS OF STAIRCRAFT eene 11 TAB
12. f Beyond the Horizon prepare this document for internal reference and for external distribution to Andrew Rawicz Steve Whitmore Jason Rothe James Balfour and other external design consultants Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 2 2 System Overview The StairCraft stair traveler transports users or other goods up down stairs Based on user inputs and statuses of the sensors the central processing unit analyzes the input signals and StairCraft reacts by driving its motors Figure 1 illustrates the relationship between the users StarCraft and the stairs User fl 9 User Command Cart Motion Q Distance to Stair Steps StairCraft Stair Traveler Figure 1 System Overview Figure 2 illustrates the block diagram of how input data is processed through each component within StairCraft ae Wheel driving Motors Data Acquisition Lifting Motors User Input Cart Direction Platform Level Steering System Start Stop Power Braking System Figure 2 Data Flow Block Diagram of StairCraft Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 3 3 Environment Requirements StairCraft shall meet the following environmental requirements listed in Table 1 Table 1 StairCraft Environment Requirements Operating Temperature 20 C 60 C Storage Temperature 20 C 70 C Humidity Full ra
13. iency test measures the energy that is needed for every lifting cycle If the energy is increasing significantly which suggest that the StairCraft is not mechanically efficient Fine turn of all the support joints will be performed after the efficiency test to improve mechanical efficiency Finally for the stability test the StairCraft has to maintain stability at any time We will test the maximum torque load that we can apply to the cart before it flips over This procedure will also be testing in various lifting height The most critical part is at the maximum lifting height The above testing will also apply to individual mechanical component first and then to the whole system 12 Training The training required for StairCraft should be minimal The only training required is the training for the user to get used to controlling the craft s motion using the control pad 13 User Menu A short user manual describing StairCraft system will be included such as teaching the user to operate StairCraft Also the manual will tell the user how to do regular maintenance change the battery and solve some simple system problems Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 16 14 Compatibility with Other Systems The StairCraft prototype will not be compatible with other electrical or regular hand powered wheelchairs However when there is more time and funding in the future StairCraft can be furth
14. ing code with a simulator and debugger The second stage is done by downloading the code into the processing unit to test the electronic components independently before they are assembled onto the mechanical parts The last stage is the final testing that tests the whole system in real time and real life Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 15 11 3 Actuator Component Testing To test the actuator component of StairCraft the tester will first check the power supplied to the actuators e g voltage and current to see if they are within the tolerable ranges of the actuators If the power check passes the tester will send an enabling signal through an external voltage source and monitor the reaction of the actuators The actuators must respond based on their specifications torque rpm Each of the actuators will be first tested separately and then the same test will be run when all actuators are powered and active 11 4 Mechanical Component Testing The testing process of the StairCraft includes loading test efficiency test and stability test Each test will be recorded for references purpose for the StairCraft mechanical limitation The loading test involves the testing of loading capacity on each individual support and the whole frame structure The StairCraft should be able to support loading up to the limit that we specify and also have some tolerance after the maximum point The effic
15. ll comply with UL CSA IEEE and ISO TC 188 Small Craft Standards 11 Testing Method The following sections specify the testing methods for the sensory processing actuator and mechanical components of StairCraft An error log sheet will be kept for future reference in similar trouble shooting situations 11 1 Sensory Component Testing To test the sensory circuitry the tester first checks the power and the fuse conditions of the circuit board After that the tester sets up a vertical stationary wall in front of the sensors to simulate the steps encountered by StairCraft The stationary wall will be set at various distance and the sensory circuit should respond according to specification To test the sensory circuit response there are various test points at each stage of the circuitry and the tester will use testing instrument such as scopes or digital multi meters to check if the inputs and outputs for each circuitry stage are correct Circuit schematic diagrams will be provided to aid the tester in the testing trouble shooting processes Any defective components found will be replaced after all other necessary modifications of the circuit board are made Each sensor circuitry will first be tested separately and then the same test will be run when all sensors are powered and active 11 2 Processing Component Testing The testing for the processing component includes three stages The first stage is testing and debugging the controll
16. n stairs Consequently the centre of mass shall remain approximately at the centre of the platform 8 2 Electrical Isolation The exterior surface of StairCraft shall ensure electrical isolation from the internal circuitry All sensory inputs will contain output protection circuitry to eliminate risks to the users All electronic devices on the system will be shielded and protected from external static voltage sources Copyright 2000 http www staircraft org Beyond the Horizon 9 Reliability Requirements 9 1 Accuracy Functional Specification 12 Table 6 summarizes the accuracy of each of the building components as well as the response time of StairCraft Table 6 Summary of the Component Accuracy of StairCraft Category Minimum Accuracy Motor Supply Voltage 5 of specified value Motor Revolutionary Speed 10 of specified value Motor Torque 10 of specified value Sensor Supply Voltage 5 of specified value Sensor Accuracy 0 5 Electrical Component Tolerance 1 5 of specified value User Input Response Time 2 seconds Sensor Input Response Time 1 5 seconds Wheel Braking Time time needed to stop 1 second Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 13 9 2 Stability Stability is the most important requirement while StairCraft is in operation The prototype design is aimed to provide a platform capable of climbing up do
17. nge of ATM humidity Heat Dissipation Minimal Altitude Maximum 6000m above sea level 4 Physical Requirements The overall enclosure of the prototype shall approximately match the dimension of an existing wheelchair which is about the space spanned by the user with a sitting posture The prototype shall be rigid and stable statically and dynamically The physical requirements of StairCraft are highlighted in Table 2 Table 2 StairCraft Physical Requirements Height 10 inches minimum normal traveling mode 315 ft maximum when fully extended Length 3 ft maximum Width 2 ft maximum Weight Less than 100 Ibs Traveling Speed 0 to 30 cm s Load Capacity 200 Ibs minimum StairCraft is designed to bypass standard staircases without any obscure surfaces The physical requirements of stairs are shown in Table 3 Table 3 Physical Requirements of Stairs For Traveling Type of Stairs Standardized solid straight and even edged Height 4 inches to 6 inches Depth 9 inches minimum Width 2 ft minimum Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 4 StairCraft requires an elegant mechanical solution to travel up down stairs smoothly Table 4 lists the accessories that are required to implement the proposed stair climbing mechanism Table 4 Highlights of Required Physical Accessories Type of Accessories Number of Parts Casters 8 mi
18. nimum Motors 9 minimum Modified Car Jacks 4 minimum Platform 1 Seat 0 1 5 User Interface The user interface of StairCraft will be a wired control pad of the size that can be held by the user with one hand and operate the control buttons with another The controls on the control pad shall consist of A power on off switch A large emergency stop button Four buttons for forward backward left and right motions Three buttons for controlling normal upstairs and downstairs modes Two LED s indicating if the system is going up or down An error indicating LED A simple LED display showing battery status Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 5 6 Sensory Input Processor and Actuator Output StairCraft will make use of a sensory input system to detect the presence of the staircase steps being approached After the sensors receive signals indicating that a stair step is encountered the input signals will be buffered and conditioned Signal conditioning includes all the filtering amplifying rectifying and analog to digital converting sub processes and these are necessary for the micro controller to understand the input signals After signal conditioning the microprocessor reads the sampled inputs determines how far away the step is and how long StairCraft will reach the step and then decides on the motor action The processor commands will go through another signal enco
19. rform analog to digital conversion Figure 7 illustrates the block diagram for the input signal conditioning stage Signal From Signal Acquisiti Amplification To Signal cquisition PT Filter Stage E Sine AAA Figure 7 Block Diagram for the Input Signal Conditioning Stage Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 8 6 3 Signal Processing A microprocessor is used in the signal processing stage Figure 8 illustrates the context diagram with the signal processing stage highlighted Input Signal Output Signal Actuator Acquisition Conditioning Encoding Interface Figure 8 StairCraft Signal Processing Signal Processing The microprocessor shall perform the following duties e Based on the strength of the input signal calculate the distance to the stair step encountered Keep track of the current status of StairCraft Deduce the current position on the staircase in order to decide on which motor to turn Process the user commands sent from the user interface Command all wheel driving steering and braking actuators motors solenoids etc The microprocessor must be able to operate under the same condition as the sensors specified in section 6 1 Figure 9 illustrates the block diagram for the signal processing stage Signal From To Output Input Signal Signal Pn Signal Output Figure 9 Block Diagram for the Signal Processing Stage Copyright
20. rocess The actuator interface contains all the wiring connections to all the actuators motors and solenoids The actuators react based on the commands sent by the microprocessor The followings are the functional requirements of all actuators used in StairCraft e Steering The left and right wheel drive motors must be able to operate individually one ON the other OFF so that steering left or right can be accomplished e Steering All wheel drive motors must be able to rotate both in clockwise and counter clockwise directions so that forward or backward motions can be accomplished e Braking Each of the active wheels the ones driven by motors must have a braking mechanism which provides enough friction and is able to stop the cart within 0 5 second Wheel Drive The wheel drive motors will be located at the front set of wheels e Wheel Drive Each of the wheel drive motors shall be able to sustain 120 1501b of load 200Ib 2 sets of wheels at one time 100Ib adding 20 50 contingency factor 1201b 1501b e Wheel Drive Each of the wheel drive motors after gear ratios are taken into account shall have a rotational speed of 30 60 rpm for wheels of 4 inches in diameter the linear velocity turns out to be 4x2 54cm m 30 60 60sec 16 32 cm sec e Lifting Each of the platform lifting motors shall supply 30 40 Ibeinch of torque for a shaft diameter of about 0 50 inch 120 150Ib x 0 50 2 inch of shaft radiu
21. s 30 40 Ibeinch of torque e Lifting The platform lifting mechanism shall provide a vertical lifting speed of 10 15 cm sec Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 11 7 Electrical Requirements Table 5 summarizes the electrical requirements of StairCraft Note that appropriate conducting wires must be used for specific current ranges Table 5 Summary of the Electrical Requirements of StairCraft Category Requirements Motor Supply Voltage 10 20 VDC Motor Supply Current maximum 0 5 1A Motor Power Dissipation 5 20 Watts Circuit Board Supply Voltage 20 20 V Circuit Board Supply Current maximum 10 20 mA Circuit Board Frequency Source 10 40 kHz Total System Voltage Supply 15 20 VDC Total System Current 10 12 A 1A x 9 motors plus other components 10 12 A 8 Safety Requirements StairCraft shall meet the safety requirements outlined in Sections 8 1 and 8 2 8 1 Overall Mechanical Structure The enclosure shall have no sharp corners or edges that would pose a danger to the users The actuator or motor units shall be enclosed to reduce chances of injuries to minimal and to avoid dust or other contaminants that may damage the motors The platform of the prototype shall be statically and dynamically stable at all times Therefore the user shall be able to maintain his her sitting posture while the system travels up dow
22. wn stairs By demonstrating the success of the StairCraft mechanism application and integration with the wheelchair will be feasible The sequence of operations is shown in Figure 13 As we can see the constraint will be to maintain the platform at a horizontal position at all time and thus the weights i e handicaps or cargos are stable on the platform However due to limited budgets and prototype testing purpose StairCraft is not designed to possess a built in shock absorption system that can provide comfortable rides for the handicaps at this time StairCraft StairCratt StairCraft StairCraft Figure 13 Stability Requirements of StairCraft 9 3 Durability StairCraft is designed to operate for at least 2 years of operation without any maintenance services The entire structure shall be rigid enough to carry heavy loads up to 200 Ib on the prototype platform in daily operations Also the design shall withstand extensive vibration when the system is utilized on bumpy surfaces The battery unit will have a lifetime of approximately 2 years depending on workloads The battery can be rechargeable and it will provide sufficient power for a few hundred steps of stair climbing Finally all other mechanical parts must be durable enough for daily operations without any major maintenance services within 2 years Copyright 2000 http www staircraft org Beyond the Horizon Functional Specification 14 10 Standards StairCraft sha
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