Science / Rocket Acceleration Report
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Autor: anton 05 December 2010
Words: 4071 | Pages: 17
Introduction, Background and Research
1. The purpose of this project is to consolidate the theory of the Petty Officer Engineering Course within a practical environment. The aims of the project are listed below.
a. To assess your ability to investigate problems, analyse them and generate and evaluate solutions.
b. To assess your ability to plan and organize effort as an individual and team member
c. To assess your working and communication skills.
d. To assess your sense of responsibility and self assurance at the same time as broadening your outlook.
2. One of the other aims of the period is to introduce some of the business management techniques and terminology used in industry.
3. The class was divided up randomly into five groups. Each group has software and hardware developers. The following are a list of (Group 3) members:
a. C******** - Software Development.
b. ********* - Hardware Design.
Statement of the Problem
4. The initial project brief to the class was based around a Hydro Explorer water Rocket, pictured on the front cover. The entire classes projects where add-ons to the original design, where alterations could be made to the rocket the fundamental principle of propulsion must stay the same.
5. Design and manufacture the electronics payload to fit into a rocket nose cone with the following criteria:
a. Record height at apogee (farthest or highest point).
b. The data is to be down-loadable to PC/Laptop
c. The data is to be in NMEA format.
6. During the initial design phase an abundance of information was obtained from all the sources available, some through discussion with the staff, but mainly information was discovered from the internet.
7. The rocket project that the group had been given has a large amateur following, with a plethora of ways of solving all the problems each group is faced with. Picking out which path was the best to investigate was a task within itself. Many of the amateur web pages described different ways to achieve the same aim with recommendations on what components to use. The general idea tended to be an accelerometer to determine apogee with a pressure sensor to determine the height at that point. At that point a parachute would be deployed to prevent damage to the payload.
8. Other ideas included Radar, Wire spool, GPS and Magnetic detectors. Each had its own merits and advantages, but due to time constraints and the technical abilities of the group the simplest form was determined to be the best avenue to achieve successful results.
9. The method of downloading to a PC/Laptop was considered and again many routes opened themselves up to investigation, the ones that where considered where USB, SD Memory card and serial data cable. Each again had advantages but where eliminated due to the complexity of the supporting software programming, with the exception of the Serial data cable. This had the advantage of being simple and compact with the supporting software already embedded on the PIC Microprocessor.
10. The data had to be in the National Marine Electronics Association (NMEA) format which is defined as the specification that is the recognized interface between various pieces of marine electronic equipment. The standard permits marine electronics to send information to computers and to other marine equipment.
11. After much discussion and research the following brainstorm was developed:
12. From a vast amount of research conducted by the group a number of designs ideas were produced. It was decided that all of the designs would need to consider the following:
a. Durability. The components and design of the equipment would need to be resilient to withstand a high degree of impact.
b. Size. A major consideration was the size of the equipment used, due to the constraints of the payload area.
c. Weight. Due to the minimal amount of thrust available from the launch system, the weight would have to be kept as low as possible.
d. Processing. Due to the nature and time constraints of the project, the least amount of mathematical processing, that was done in real time, would be kept to a minimum. With the short duration of the flight the sampling rate and accuracy of the readings would be paramount.
e. Memory. With the possibility of loss of power on impact the system would need some sort of memory to retrieve information after impact.
f. Connectivity. To retrieve the data from the equipment and to reduce the components required the need for a data link would be required.
g. Power. Due to the nature of the equipment, the power supply would have to be self contained and durable.
h. Cost. As with any project the constraint of cost would be an issue, therefore the cost would have to be kept within budget.
13. Encompassing the design features given above four designs were produced, each with there own additional design features, for the first customer meeting.
14. Research conducted online Ð²Ð‚?Goggle is your friendÐ²Ð‚â„¢ by the group; found that there are hundreds of similar amateur rocket enthusiasts with various ideas of how to achieve the height at apogee problem.
15. Two sensors where considered, to solve the problem, these where an accelerometer and a pressure sensor. The way in which the sensors would be utilized have been considered and discussed below:
a. The initial thought was to use the acceleration and time taken to first 0 Ð²Ð‚?GÐ²Ð‚â„¢ from the launch pad, therefore the distance from the launch pad could be calculated. The problem with this first idea is if the trajectory is not exactly perpendicular to the local terrain then the distance will not correlate with the height above the earth.
b. The next idea was to use a barometric pressure sensor that would give a differential pressure proportional to height. This would only give a rough altitude reading due to the non linear relationship between pressure and temperature and altitude. The other problem with this idea is that there would be a local pressure variation and a daily pressure variation; this would have to be considered at each launch.
c. Using both types of sensor, the pressure sensor and accelerometer together to achieve the aim was considered. This could achieve an accurate reading as when the apogee was reached the accelerometer would have a 0g reading and only one sample would need to be taken from the pressure sensor. This form of reading would be required if a parachute or drone was going to be used to reduce the decent rate, although the idea of a parachute was not required as the altitude of the flight was not sufficient to justify this. Also this would increase the components required increasing weight and cost.
d. The final solution was to use the decent time from apogee to landing, this would eliminate the problem of non-orthogonal launch/flight. This uses only an accelerometer and that gravity is constant at 9.8 m/s/s. So by sampling time from the second 0g (apogee), to the next 0g (landing), this time is then integrated with the acceleration of gravity, this is used to calculate distance.
16. Due to the short duration and for an accurate result all of the sensors considered would require a high sampling rate due to the short duration and high acceleration rates that would be experienced during the flight.
First Customer Design Meeting
17. Research was conducted and a preliminary design idea was compiled. A customer meeting was conducted and after much deliberation and consultation a design idea was accepted. The design and its features are shown below.
a. Memory recall (Max/min acceleration, inbuilt in PIC microprocessor).
b. On indication (flashing LED, confidence test).
c. Battery powered (separate power supply during data transfer).
d. Serial connection. (Possible TTL conversion inline).
e. Accelerometer design using decent time to calculate height.
f. Shock mounted with surface mount components
g. Record raw data only, (post processing in XL spreadsheet).
h. Reset function (possible to earth pin one to reset by probe).
Final Customer Design Meeting
18. During the second customer briefing the design was accepted and the go ahead was given to commence the design stage. A consideration had to be given to the recording of flight time to enable the calculations required to be processed.
Analysis of My Work
1. The following section is a overview of the work carried out to design the software for the rocket accelerometer to determine height.
2. The initial task was to identify a simple flow diagrammatic view of what the circuit was to achieve. Taking into account the project requirements and the design features agreed upon, the following was produced:
3. Due to the circuit requirement it was clear that the PIC (Programmable Interface Controller) was required to be surface mount due the size of the board required and the durability of the component. The amount and type of inputs and outputs was the next consideration of which the following table shows the requirements:
Hardware Input/Output Ports
Accelerometer 1 I/P
Data Dump Switch 1 I/P
LED indicator 1 I/P
Serial Data Output 1 O/P
+VREF 1 I/P
-VREF 1 I/P
Oscillator 1 and 2 2 I/P
Master Clear 1 I/P
4. The number of input/output pins required had now been ascertained, the PIC could be chosen. This was 16F873. The main reason for this selection was that it was surface mount with the added advantage of low power consumption, less than 0.6mA typical @ 4 MHz.
5. The next consideration was the oscillator selection and the clock speed of the PIC. There was a requirement for an accurate clock, with a sufficient operating frequency that would allow the maximum accelerometer input for increased accuracy due to the short duration of flight time, also the communication USART communication link had to be considered. Therefore a 3.6864 Mhz, providing a clock speed of (t=1/f) 1.085Ð’Âµs.
7. The flow diagram provides a brief description of the operation of the accelerometer circuit:
Insert flow chart software operation
Each of the stages of the software development has been broken down into individual blocks in order to provide additional information about the software program.
Set Up Procedure
8. At the beginning of the program it is necessary to predetermine many of the file locations that are use repeatedly, this is a independent operator selection, whereas each person writing the code will have words that make sense to them. This enables the coder to write useful text instead of writing hexadecimal or binary.
9. Also in this section memory locations can be predefined to enable them also to have common names, such as (count or save), instead of 25H or 00100101.
10. Upon start up, the microprocessor configures all of the inputs and outputs required and all of the special registries that require bits to be set, the following is a list of the inputs and outputs and also the effected registers:
a. TRISA0 - input, B0 - output, C1 Ð²Ð‚â€œ input and C6 Ð²Ð‚â€œ output.
b. ADCON0 for a 8 tosc, channel 0 and the ADON bit set.
c. ADCON1 for left justified, with AN0 as analog input Vref+ - on RA3,2.
d. Baud rate set to 9600.
e. TXSTA set to enable transmitter.
f. RCSTA set to enable serial ports.
Delay Sub Routine
11. A Generic subroutine for a 0.2msec delay was created to enable the call to be placed at any required point in the program that required a delay.
12. At this point in the program the processor would check to identify if there was an accelerometer input. This input is received via the input pin RA0 (Analogue Input). This value is then changed to a digital value and is then compared with a predetermined value stored in the W register.
The process of operation of the A/D converter is shown below:
13. The analogue output from the accelerometer charges a sample and hold capacitor within the A/D module, the output of this capacitor then becomes the input for the converter. The converter then generates a digital result of this analogue level via successive approximation. ADCON0 controls the operation of the A/D module, which also controls the speed of the A/D conversion and also what input pin the A/D converter is required to monitor. ADCON0 also provides the A/D converter on bit (ADON) and the GO/DONE bit indicating that the A/D conversion is complete. ADCON1 configures the port input pins. The A/D conversion of the analogue input signal results in a corresponding 10-bit digital number.
14. The digital number is moved into the W register and is used to compare with a previous value, to sense if acceleration has been detected.
15. In the software program the corresponding 8-bit number, as only the ADRESH register is used as the ADRESL contained only the least significant bits which could be due to noise, therefore ignored.
16. The concept of storing data in a non volatile environment, Electronically Erasable Programmable Read only Memory (EEPROM), was identified as a requirement during the design phase. This requirement was necessary due to the possibility of power loss on impact or battery failure.
17. With the quick progression on the circuit design it became apparent that software needed to be developed to a stage to enable early circuit testing. Therefore a decision was made to store the information in volatile memory during the design stage with the eventual storage in EEPROM.
18. The sub routine to store the data, switched between the two available data banks (0 and 1). This enable testing to be conducted where data was input from the potentiometer, simulating the accelerometer, then converted during the A/D conversion mentioned above. This information is then transferred to the memory positioned at 026H to 0AH, in data bank 0, and ____ to _____ in data bank 1.
19. As the software/hardware testing was successful the focus was redeployed into storing the data in EEPROM.
20. The lack of information was debilitating in the early investigation into EEPROM storage. Eventually by manipulating the test software, provided in the technical documentation, with the PIC, it was possible to increment the data address starting at 00h to FFH and store/recover the data for transmission to the PC.
21. The obvious limitation of the EEPROM is the available storage space, this limits the amount of samples that can be taken and stored over the duration of the flight. The following profile was drawn up for the duration of the flight.
21. As with the above Data storage, it was required to provide some test data transmission to the PC. The sub routine was designed to transmit the data from the volatile memory position at first, for development purposes, then from EEPROM.
22. The transmission is commenced by the depression of a Data Dump Switch which will be mounted on the remote interface box external to the rocket nose cone. This switch provided logic 1 at RC1, when this is sensed the transmission commences. When the switch is disconnected there was a danger of Ð²Ð‚?floating logicÐ²Ð‚â„¢. Therefore the switch was held at a logic zero until the switch is depressed.
23. The data dump switch can be pressed at any stage to download data. This ensured that the memory bank is clear and that on loss of power after a flight, the information could be recovered at any stage not just after the flight sequence was complete.
25. With the possibility of data becoming corruptible it was necessary that the memory could be cleared to ensure that the data being transmitted is the information from the latest flight. This was facilitated by the press and hold function from the data dump switch. As the memory was non volatile the Master clear function would only reset the software, not the EEPROM.
Sort EEPROM storage/recovery
Put data dump recovery question, at position after flight recovery and at pre flight stage to ensure data recovery/test memory storage after power loss. This also allows for transmission to PC, can keep pressing transmission button, if required.
Require flash rate to ensure data clear after data dump held for 5 sec.
Take average flight time and see how many samples can be takenÐ²Ð‚Â¦then slow down sample rate to allow deviation from average. Need measurement of how long a sample takes therefore can predict flight timeÐ²Ð‚Â¦see if can tag each sample with time..
Need flight diagram to show sample rate and time blocks
Analysis of Group Members Work
Business Management Technique
BUSINESS MANAGEMENT TECHNIQUES
1. Any engineering business is liable to incur a variety of costs. These will typically include:
a. Rent for premises.
c. Energy costs (heating/lighting).
d. Purchase and maintenance of production equipment.
e. Salaries and National Insurance.
f. Transport costs.
g. Postage and telephone.
h. Insurance premiums.
2. Given the wide range of costs, it is customary to classify them under various headings, including fixed and variable costs, overhead and direct costs, average and marginal costs. In order to be able to control costs, it is vital that all the costs are known. The consequences of not being fully aware of the costs of a business operation can be dire. The prime objective of costing techniques is that of informing commercial decisions such as:
a. How many units have to be produced in order to make a profit?
b. Is it cheaper to make or buy an item?
c. What happens to our profits if the cost of production changes?
d. What happens to our profits if the cost of parts changes?
3. As the project is to be undertaken as a business venture all modern methods of business enterprise skills should be used. An effective costing system is needed to take into account the real cost of manufacturing the product or delivering the service that it provides. Without such a system in place it is impossible to control costs and determine the overall profitability of the business operation.
4. Cost accounting is necessary for a company to be able to exercise control over the actual costs incurred compared with planned expenditure. A costing system should be able to identify any costs that are running out of control and provide a means of determining the action that is required to correct it.
TYPES OF COSTING METHODS
5. It is a simple method which usually applies to a unique operation such as fitting a part or carrying out a modification. It has three associated elements: direct materials costs, direct labor costs (wages, inclusive of overheads like National Insurance) and direct expenses. Usually a fixed price is agreed prior to commencement of work.
6. It is conceptually the same as job costing but usually relates to larger jobs which are longer in duration. It is used for things such as civil engineering or ship building.
7. It is a straight forward method which is simply a question of determining the cost of the physical parts and components used in the engineered product. It is common place to group the individual component parts under groupings of similar items. The reason for this being, such groupings tend to be subject to the same fluctuation in cost. It can be quickly determined the effect of such fluctuations by examining the effect of changes on particular groups of parts.
8. This method takes into account the cost of continuous manufacturing process and apportions part of the cost of each process to an individual product. E.g.: machining parts, soldering of printed circuit boards, heat treatment of metal parts, paint spraying and finishing. In order to carry out process costing it is necessary to show how the flow of products is costed at each stage of the process; Process1:2:3 and so on until the finished product.
9. Another way to determine the total cost of a given product is that of adding the costs of overheads to the direct costs by a process of Ð²Ð‚?allocation, apportionment and absorptionÐ²Ð‚â„¢. Since overheads (indirect costs) can be allocated as whole items to production departments, it is possible to arrive at a notional amount that must be added to the cost of each product in order to cover the production overheads.
Mark up = total fixed and variable costs attributable to the product
Total number of units produced
10. It allows the observation of the interaction between costs, volumes and profits. The marginal cost of a product is equal to the cost of producing one more unit of output. Marginal costing avoids the problems associated with overhead apportionment and recovery. Where several products are being made, marginal costing can show which products are making contribution and which are failing to cover their variable costs.
Activity based costing
11. This method is an attempt to assess the true cost of providing a product or service. It focuses on indirect costs (overheads). In effect it traces costs and overhead expenses to an individual cost object.
Steps required to carry out activity based costing are:
a. Identify the activities
b. Determine the cost of each activity
c. Determine the factors that drive costs
d. Collect the activity data/calculate the product cost
Costing method used for Project
12. The obvious choice for the projects was the JOB COSTING method. This is due to the projects being a Ð²Ð‚?one offÐ²Ð‚â„¢ task. Also it is the simplest form of costing to ensure accurate estimate and final costing for the project.
a. Direct costs of parts and labour.
b. Daily rates of pay for manpower were at a fixed daily rate.
c. Overheads were set at a daily fixed rate.
d. Consultant fees daily rate set at a fixed rate.
Project Costing Estimate
13. At the final customer meeting a budget was set at Ð’Ðˆ6000, with a contingency of 11%, every effort, where possible, would be made to bring the project in as low a cost as reasonably practicable. The predicted costs are shown below:
DESCRIPTION SUPPLIER PRICE DAY/EA QTY
DAY/EA TOTAL %
GROUP 3 CPO Firth Ð’Ðˆ54.79 20 Ð’Ðˆ1,095.89 18%
GROUP 3 LET Nixon Ð’Ðˆ54.79 20 Ð’Ðˆ1,095.89 18%
Consultancy PEG Ð’Ðˆ82.19 10 Ð’Ðˆ821.92 14%
Purchase Ð’Ðˆ100.00 2%
Stores Ð’Ðˆ200.00 3%
Office Space PEG Ð’Ðˆ30.00 20 Ð’Ðˆ600.00 10%
CAD Computer PEG Ð’Ðˆ20.00 5 Ð’Ðˆ100.00 2%
Software Development PEG Ð’Ðˆ20.00 9 Ð’Ðˆ180.00 3%
Office Computer PEG Ð’Ðˆ15.00 3 Ð’Ðˆ45.00 1%
Workshop PEG Ð’Ðˆ80.00 10 Ð’Ðˆ800.00 13%
PEC Production PEG Ð’Ðˆ60.00 5 Ð’Ðˆ300.00 5%
Total Expenditure Ð’Ðˆ5,338.70 89%
14. To ensure maximum time and cost efficiency throughout the project it was necessary for the group to set deadlines for each individual task. The group had been divided into Software and Hardware development, these tasks where further sub divided into smaller tasks of the total project.
15. Microsoft Project was used, as shown below, in the Gannt chart view. This clearly illustrates the projected manpower allocation to each stage of the task. The chart below was updated at intermittent periods to enable the group to see shortfalls in time management.
Final Project Cost and Manpower Allocation
16. The Group had very few unplanned problems with BMT as all of the stores required were delivered on time the group had predetermined any problems, such as a late stores arrival. The charts below show the final figures for the project:
_________________Final Cost Table
Final Pie Chart
17. The manpower management strategy worked well throughout the project with the team maintaining there relevant areas of responsibility to ensure that time and indirectly cost where accounted for. The chart also ensured that it was clear at what stage each member had to be at in what time frame, this instantly showed any time management problems that needed to be dealt with.
Final Gannt Chart
18. With any project, communication and the correct planning are essential to achieve the aim. What was appreciated by the group was that to achieve, what at first appears to be an insurmountable task, can be completed on time and on budget with the correct systematic approach. This course has enlightened the group to this systematic approach, and has shown how that it can be used to achieve any future project that may be encountered.
Operating Instructions, Conclusion and Recommendations
Acceleration Recorder Procedure
1. Insert/replace battery as required.
2. Does memory require confirmation of clear?
a. Yes - Go to step 3
b. No - Go to step 8.
3. Connect serial interface connector to nose cone.
4. Connect serial interface to PC/Laptop.
5. Ensure Hyper-terminal running, correctly configured to receive data.
6. Press Data Dump Switch.
7. Observe FFH displayed at all memory locations.
8. Intentionally left blank.
9. Does memory require clearing?
a. Yes - Go to step 10.
b. No - Go to step 14.
10. Press and hold Data Dump switch for 5 seconds.
11. Observe LED flashes at 4 Khz rate for 5 seconds.
12. Does Memory require confirmation of clear?
a. Yes - Go to step 3.
b. No - Go to step 14.
14. Intentionally left blank.
15. Is an acceleration sample required?
a. Yes - Go to step 16.
b. No - Go to step 22.
16. Connect the serial interface box.
17. Press master clear button.
18. Disconnect serial interface box.
19. Observe LED flashing once per second
20. Replace nose cone, carefully.
21. Await recovery of nose cone.
22. Is Data sample recovery required?
a. Yes - Go to step 23
b. No - Go to step 1
23. Remove nose cone.
23. Connect serial interface box to nose cone and PC/Laptop.
24. Ensure Hyper-terminal ready to accept serial data.
25. Press data dump switch, less than one second.
26. Conduct Hyper-terminal acceleration/height conversion procedure.
Hyper Terminal Acceleration/Height Conversion Procedure
The engineering design and project module has reinforced the classroom theory I have learnt throughout Artificers Candidates Course over the past two years, and has allowed me to gain experience and confidence to apply these skills gained during training.
The following modifications and alterations could be made to the digital thermometer in order to improve the product:
All of the modifications and alterations are achievable with further research and development, which would provide the customer with a cheap, attractive, robust and effective digital thermometer.
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