EEE25: Building your own satellite 101 - CanSat
Part I: Introduction
Introduction to CanSat What is a CanSat? ● ● Simulation of a real satellite integrated within the volume of a soft drink can. How does a CanSat function? ● ● Contains sensors, microcontrollers, and a radio module that allows it to gather and transmit scientific data to a ground station. What are CanSat’s usually used for? ● ● Various uses, most are used to conduct a scientific investigation.
Introduction to our project What do we hope to achieve with our CanSat? ● ● To determine the optimal time for prolonged outdoor activity over the day according to UV radiation levels, TVOC levels and Humidex values. (From 8:00 am to 6:00 pm) How can we achieve our objectives? ● ● Drop tests conducted every hour from 8:00 am to 6:00 pm to gather data, which is sent to a ground station and plotted graphs. Data is analyzed and conclusions are drawn.
Chosen factors, metrics and guidelines Ultraviolet (UV) radiation levels ● ● Prolonged exposure to high levels of UVR can increase risk of melanoma and damage to skin. Total volatile organic compound (TVOC) levels ● ● Many VOCs are carcinogenic in nature and irritate the respiratory tract. Humidex ● ● Prolonged outdoor activity during periods of high humidex values can result in heatstroke and other heat related illnesses. 𝑈 5 9 𝑓 × (6.112 × 10 7.5× ● Calculated using: 𝐼𝑣𝑛𝑗𝑒𝑓𝑦 = 𝐵𝑗𝑠 𝑢𝑓𝑛𝑞𝑓𝑠𝑏𝑢𝑣𝑠𝑓 + 237.7+𝑈 × 𝐼 100 − 10 ） ● Takes into account both temperature and humidity to give a more accurate assessment of the perceived temperature.
Chosen factors, metrics and guidelines Chemical Recommended UV Index Risk and recommendations levels (safe/optimal) 0-2 1.Low risk of harm from (Optimal) unprotected exposure to Sun Benzene No 2.Optimal amount of UVR for recommended outdoor activities healthy levels 3-5 (Safe) 1.Moderate risk of harm from Formaldehyde < 81.4 ppb unprotected exposure to Sun Polyaromatic < 11.0 ppb 6-7 1.High risk of harm from rocarbons (Unsafe) unprotected exposure to Sun 2.Reduce time spent in the Chloroethylenes <100 ppb Sun (Tri- and Per-) 8-10 1.Very high risk of harm from (Dangerou unprotected exposure to Sun Estimated total <300 ppb s) 2.Minimize time spent in the based on above Sun data and considering 11+ 1.Extreme risk of harm from other VOCs (Dangerou unprotected exposure to Sun s) 2.Avoid spending time in the Sun
Part II: Design
Material and structural design - Basic components Considerations when using components: ● ● Size: Small enough to fit in a can ● Mass: Light enough to ensure CanSat falls at a reasonable rate ● Capabilities: Able to perform functions as required to List ● Arduino UNO microcontroller ○ XBee Shield radio module ○
Material and structural design - Sensors Considerations when selecting sensors ● ● Mass: Light to ensure that CanSat falls at a reasonable rate without the need for an excessively large parachute ● Size: Small enough to ensure all components of the CanSat fit within a can. ● Capabilities: Must be suited to the limitations of the other components, such as the battery and processing power of the microcontroller. (Hence no reliance on sensors that produce images/videos.) Sensor list ● ● SI1145 UV Radiation Sensor ● CCS811 TVOC level Sensor ● BME280
Material and structural design - Sensors
Material and structural design – Internal structure Structural features: ● ● SI1145 UVR sensor exposed at the top of the CanSat and stabilized with a metal plate, allowing for better data collection whilst being stable. ● 2 sided design to maximize the space available.
Material and structural design - Parachute Calculations and considerations ● ● Upon weighing, CanSat is found to weigh 0.180 kg. Size of parachute required 1 calculated using the equation: 𝑛 = 2 𝜍𝑤 2 𝑇𝐷 𝑒 ● Where: 𝑛 = 𝑢𝑝𝑢𝑏𝑚 𝑛𝑏𝑡𝑡 (𝑙) = 𝑏𝑑𝑑𝑓𝑚𝑓𝑠𝑏𝑢𝑗𝑝𝑜, 9.81 𝑛𝑡 −2 𝑇 = 𝑡𝑣𝑠𝑔𝑏𝑑𝑓 𝑏𝑠𝑓𝑏 𝑝𝑔 𝑢ℎ𝑓 𝑞𝑏𝑠𝑏𝑑ℎ𝑣𝑢𝑓 (𝑛 2 ) 𝜍 = 𝑏𝑗𝑠 𝑒𝑓𝑜𝑡𝑗𝑢𝑧, 1.275 𝑙𝑛 −3 𝐷 𝑒 = 𝑒𝑠𝑏 𝑑𝑝𝑓𝑔𝑔𝑗𝑑𝑗𝑓𝑜𝑢, 0.75 ● Design: Circular hole of radius 0.090 m cut at the center of parachute to increase stability during descent and to allow for sunlight to pass through to improve UVR data collection. Octagon chosen to allow for convenient calculation of the area and attachment of washers while providing a reasonable amount of drag.
Material and structural design - Parachute Parachute: ● ● Final area found to be 1.13 m 2 2)𝑏 2 − 𝜌𝑐 2 ● 𝐺𝑝𝑠𝑛𝑣𝑚𝑏: 𝐵𝑠𝑓𝑏 = 2(1 + Proof of parachute working: ● ● During test drops, terminal velocity with the parachute fully deployed was shown to be around 1.1 meters per second, lower than the 2 meter per second limit.
Electrical design - Circuit Circuit interface ● ● All sensors use analogue signals and are connected to A4 and A5 pins of the analog side of the microcontroller. I2C connection used for all sensors. ● All sensors soldered onto a PCB board, with 2 loops connecting the sensors and forming the circuit.
Electrical design - Software Flowchart of data during mission: ● ● Data flows from sensors to the microcontroller, which determines the format of the data transmitted via the radio module to the ground station, which uses PLX-DAQ to plot the data into graphs in real time. Arduino software ● ● Code used first ensures each sensor functions properly, then it groups data from each individual sensors into 1 group and makes it compatible with PLX- DAQ.
Part III: Results and discussion
Initial testing Results obtained ● ● Xbee module has a maximum effective range of around 50 meters. ● CCS811, BME280 giving reliable information. Anomalies observed ● ● SI1145 giving unreliable information, with unstable UVR readings due to oscillation of CanSat during drop. Approx. Altitude (m) 80 60 40 20 0 14:32:58 14:32:59 14:33:01 14:33:02 14:33:03 14:33:05 14:33:06 14:33:07 14:33:09 14:33:11 14:33:12 14:33:13 14:33:18 14:33:30 14:33:35 14:33:44 14:33:47 14:33:48 14:33:50 14:33:51 14:33:52 14:33:54 14:33:55 14:33:56 14:33:57 14:33:58 Approx. Altitude (m)
Initial testing - troubleshooting Comparing results of ground testing vs drop testing ● ● Difference found to be an average of about 15%. Addition of code to eliminate erroneous data points ● UV Index of drop test vs ground test 10 8 6 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Drop Test Ground test
Drop tests: 22/12/18 Drop test procedure: ● ● 5 tests every hour, from 8:00 am to 6:00 pm. Then repeated across 5 days. Results are obtained from the averages of data gathered.
Drop tests: Results over 5 days
Trends observed and discussion ● UV radiation levels: Increases from 8:00 am to 1:00 pm, then decreases. UV index readings all in the “unsafe” and “dangerous” category from 10:00 am to 4:00 pm. UVR levels only relatively safe outside this 6 hour period. ● TVOC levels: Insignificant in general and no obvious trend across the day. Probably due to the lack of a distinct source of TVOCs. ● Humidex levels: Generally high and peaks at around 12:00 pm to 2:00 pm. Even the lowest readings were near “unsafe” levels and could cause “some discomfort” during prolonged outdoor activity. During most daylight hours, prolonged outdoor activity with the humidex levels obtained would cause “great discomfort” .
Conclusion Time UV Index TVOC concentration (ppb) Humidex Overall 8:00 AM Optimal (2.64) Optimal (13) Safe (37) Optimal 9:00 AM Safe (4.12) Optimal (14) Safe (38) Safe 10:00 AM Unsafe (5.87) Optimal (18) Unsafe (41) Unsafe 11:00 AM Dangerous (8.62) Optimal (17) Unsafe (42) Unsafe 12:00 PM Dangerous (9.80) Optimal (27) Unsafe (42) Unsafe 1:00 PM Dangerous (10.9) Optimal (22) Unsafe (43) Dangerous 2:00 PM Dangerous (8.68) Optimal (25) Unsafe (41) Unsafe 3:00 PM Unsafe (6.39) Optimal (12) Unsafe (40) Unsafe 4:00 PM Unsafe (6.24) Optimal (11) Unsafe (40) Unsafe 5:00 PM Safe (4.21) Optimal (16) Safe (39) Safe 6:00 PM Optimal (1.52) Optimal (13) Safe (39) Optimal
Limitations of results For individual data sets: ● ● UVR data: Represents a worst case scenario with no cloud cover in the sun. ● TVOC: Not indicative of overall air quality. (Other measurements such as CO concentration, PM2.5 levels and PSI should be taken into account as well) ● Humidex: Does not take into account wind speed, which also affects perceived temperature. Specific timing and location ● ● Timing: Data obtained during month of December, may vary throughout the year. ● Location: Most drops conducted in a small area, hence might not be representative of Singapore.
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