P16221: FSAE shock dyno/public/
Team Vision for System-Level Design PhaseSummarize:
- What did your team plan to do during this phase?
- What did your team actually accomplish during this phase?
- Access Damper
- Receive from Customer
- Load Profile
- USB Stick
- Cam Selection
- Displacement Profile
- Track Data
- Made up datapoints
- Cross Beam Adjustment
- No Adjustment
- Motor Driven Ball Screws
- Pinned Mast
- Bolted Mast
- Semented Inserts
- Mounting Shock
- Regular Clevis
- Clevis with height adjustment
- Clevis with width adjustment
- Load Damper to be tested
- Mechanical ball screw
- Worm gear
- Stepper motor
- Rack and pinion
- Stand Mobility
- Fixed to floor
- Fork lift slots
- Adjustable height casters
- Hook on top
- User interface
- LCD display
- Chart recorder
- External PC
- Internal Processor
- User Protection
- Enclosure around entire system
- Stop switches
- Safety Glasses
- Movable magnetic shields
- Warning Stickers
- Safety Circuit
- Temperature Sensor
- IR Sensor
- Resistance thermal device
- Position Sensor
- Linear Potentiometer
- Rotary Potentiometer
- Force Sensor
- Load Cell
- Spring Gage
- Strain Gage
- Elapsed run time
- Cesium Clock
- CPU Ticks
- Send Data to User
- Chart Recorder
- Save Data Format
- binary file
- Stop Test
- PC Control
- Internal microprocessor control
Morphological Chart and Concept Selection
Feasibility: Prototyping, Analysis, Simulation
Memory Required to Store an Hour of Track Data
- Track data is sampled at 500 Hz (0.002 seconds between samples)
- Data is in a pair of numbers (time, displacement)
- Displacement is a signed floating point number of inches ranging from -3.5" to +3.5"
- Time is an unsigned floating point number of seconds ranging from 0.000 seconds to 3600.000 seconds
- ASCII representations of these numbers would be about 5 bytes for time and 5-6 bytes for displacement (depending on displacement resolution)
- IEEE 754 represents single precision floating point numbers in 32 bits per number (4 bytes) to 7 digits of precision
- Single precision floating point numbers have more than enough precision to store our data
- One sample in the calculations following represents 2 floating point numbers (time and displacement)
Calculations:Total number of samples = 3,600 seconds * (500 samples/sec) + 1 = 1,800,001 samples. The +1 is because we are starting at t=0.
Total number of bytes = 1,800,001 samples * (8 bytes/sample) = 14,400,008 bytes = 14,062.5 kB = 13.74 MB.
- 13.74 MB is a lot of memory to use for data. If we don't store the time data and only supply displacement data then our memory requirements would be half. However, the interface program would need to always send displacements in 0.002-second intervals and interpolation may be necessary.
- If time is sent, the micro-controller could set the actuator position at the appropriate time even if the data was captured at less than 500 Hz.
- Another idea would be to buffer 1-5 minutes of data and send chunks of data across the interface to and from the PC. 5 minutes of data would need 1.14 MB of memory for both time and position.
- A rotary cam solution wouldn't need a profile to be loaded (it is on the cam design) other than shaft speeds for the motor and would require very little memory.
RS-232 Serial Speed Analysis
- Based on required Data Size calculated above
Calculations:64 bits of data in 0.002s = 32,000 bits per second
- Typical Baud Rates:
- For 32,000 bps speed: 38400, 57600 and 115200 baud rates are feasible for the application.
Load Cell Analysis
- Capable of logging/reading at 500Hz
- Capable of 1500lbf force measurement (@ 10m/s. 1500 lbf max)
- No measurement phase lag
- Positive and negative force measurement
- Costs less than $1000
- 1500 lbf @ 500Hz is a large range of measurement to cover accurately that fast
- PCB 1403-14A/084A100 meets all requirements except price
- Measures up to 2500 lb : ~300% overload protection
- Sensitivity (± 10%) 2mV/V
- Need to confirm this is accurate enough to satisfy (another engineering spec?)
- Non-repeatability <= 0.02% RO is very good
Microprocessor Read Speed Test
- This sketch tests only the speed to read three analog inputs and store their values in a variable.
- No processing is performed on the values such as scaling them.
Sample RunProgram Output
- Mode 340 us
- Mean 339.3 us
- Median 340 us
- St Dev. 9.981303911 us
- Min 332 us
- Max 432 us
CommentsAt a maximum scan time of 432 us, we should have plenty of time left to move the actuator, send the data to the host PC and receive more track data to achieve the 125 Hz control speed requirement. Careful consideration should be taken to not perform too much as the 5 variables in the sketch took up 16% of the available stack space on the microprocessor.
Risk AssessmentRisk Management Document
Design Review Materials
Plans for next phase
- As a team, where do you want to be at your next review? What questions will you answer during the next phase?
- As an individual on the team, what are you doing to help your team achieve this vision? (Use the individual 3-week plan template for this).