Miscellaneous Projects

University Projects - Solar-Powered Evaporative Cooler For ProduceAn investigation was undertaken into the potential of evaporative cooling using forced convection for the short-term storage of fruits and vegetables on a scale which was manually transportable by a single person and used a self-contained photovoltaic system. Previous research and existing products have primarily focused on the use of evaporative cooling with natural convection and there has been minimal evaluation of the possible improvements in performance realized with forced convection. Furthermore, food insecurity in developing countries is extensive with many cases of severe undernourishment due to the spoilage of the available food, where an affordable solution under €45 to control wastage through preservation could be transformative in promoting healthier societies. With the aim of achieving a cooling effect with a temperature decrease of at least 11°C and relative humidity increase of at least 35%, a prototype of 6.62kg and 585mm by 405mm by 360mm was designed through analytical calculations and numerical simulations using a radial fan for optimal operation at ambient temperatures above 32°C and ambient relative humidities below 50%. Under practical experimentation in Johannesburg, South Africa, with a solar panel of 6.0W, the prototype was able to achieve the desired performance in 81.9% of the relevant periods using cotton ring spun and polyester for the cooling pad. This was complemented with an increase in shelf life by 88.3% on average for a sample of fruits and vegetables stored within the internal volume of 45L compared to an identical sample stored externally. For further optimization, a thermoelectric module was incorporated with an additional solar panel of 7.0W. This enhancement resulted in an improved performance minimizing the temperature fluctuations to 1°C for each 3.5°C fluctuation in ambient temperature on average, compared to the previous results of 1°C for each 2.4°C fluctuation in ambient temperature on average, at the expense of an unsatisfactory increase in costs of 83.8%. Overall, the performance was successfully promising and it is recommended for further practical experimentation under more extreme environmental conditions.
University Projects - Quadrotor Visual Servoing For Moving Target TrackingAn investigation into position-based visual servoing through end-point open-loop control was conducted for estimation of the three-dimensional position and yaw orientation of a moving target using a single camera, where a Bitcraze Crazyflie 2.1 quadrotor then tracked this position and yaw orientation autonomously. Moreover, inexpensive and low-end hardware with marginal computational effort was used in the form of a Raspberry Pi Zero W 1.1 and Raspberry Pi Camera Module 2.1 for image processing with OpenCV to utilize computer vision techniques. Comparing greyscale and colour processing for initial target detection, it was evident that greyscale processing allowed for an increased frame rate compared to colour processing by an average percentage difference of 23.2% while also eliminating more background noise for a better interpretation of the target. During the implementation, it was found that the most satisfactory resolution was 160px by 120px for lightweight processing, where the capability to generate setpoints for the quadrotor was at a frequency of 30.1Hz. The pinhole camera model was also validated and successfully implemented at a resolution of 160px by 120px which resulted in a focal length of 113.5px found through experimental calibration. This allowed for the pinhole camera model to be used to develop a control script to reconstruct the state of the target relative to the camera with the centroid of the target providing latitude and longitude coordinates, area of the target providing the altitude of the camera, and rotation providing the yaw orientation when using a disproportioned marker. With this information, the quadrotor was able to successfully mirror the translational and rotational motion of the target while maintaining the altitude of the camera. Over eight independent tests, the real-time effectiveness was captured by a Qualisys motion capture system and exhibited an average lag of 0.732s, average position deviations of 83.4mm, minimum yaw orientation deviation of -9.54°, and maximum yaw orientation deviation of 9.87°. However, if the average lag is compensated in each test, the average position deviation reduces to only 54.0mm, while the minimum and maximum yaw orientation deviations reduce to only -4.76° and 4.46° respectively. An altitude could also be maintained effectively, where the quadrotor only drifted by an average of 3.75% downwards or 3.98% upwards before returning to the correct altitude.
University Projects - Electrically Enhanced Personal TransportationThe assigned low-level task was to design a vehicle or device for the personal transportation of a single user with capabilities for electric, manual, or combined propulsion on asphalt, pavement, cement, gravel, or flat soil. Briefly, it was desired for a mass lower than 19kg, support for users up to 100kg, 50km electric range, and speeds of 25km/hr on a level grade and 15km/hr on slopes with gradients up to 3% with maintained performance in the presence of winds up to 10km/hr. For an initial idea, preliminary concepts were generated for the Cycle, Skateboard, Scooter, Wheelchair, and Roller Skates, where the Cycle was found to be the most promising due to its high level of accommodation for each mode of propulsion. The design development was then undertaken for the electric propulsion, manual propulsion, wheel arrangement, and frame structure through analytical calculations and finite element analyses. The electric propulsion was found to be satisfactory with a Heinzmann DirectPower PRA 180-25 brushless DC hub motor producing 250W of continuous rated power, as limited by legal regulations; and 835.2W.hr battery pack using 80 Panasonic NCR18650PF cells each rated at 2.90A.hr for a range of 50km depending on the terrain. Comparing chain, belt, and shaft drives for manual propulsion, it was decided that a chain drive with an ISO 606 081-100 roller chain would provide versatility, where a gear ratio of 1:2.15 was used between the 43-teeth driving sprocket and 20-teeth driven sprocket while receiving a pedalling input using 170mm cranks constructed from aluminium 6061-T6. For the wheel arrangement, it was concluded that two wheels would offer the best compromise between operating skill and performance with decreased drag, weight, and rolling resistances. Specifically, Challenge Gravel Grinder TLR pneumatic tyres were chosen to be fitted to the designed wheels consisting of rims with a diameter of 622mm and profile classification of 19C and 36 stainless steel spokes of 2.6mm diameter connecting the rims to the hubs on each wheel, where the front hub was designed with a 9mm steel AISI 4140 axle and SKF 609-2RSH bearings. To accommodate male and female users between the 5th and 95th percentiles, the aluminium 6061-T6 frame and front fork were sized according to a conventional medium to large diamond structure for a seat tube angle of 73o, top tube length of 585mm, and wheelbase of 1095mm. The construction of the headset, stem, and handlebars was proposed with a width of 640mm for a steering torque up to 6.4N.m. An ABS enclosure with a volume of 22.0L is also to be fitted within the frame for the controller and battery pack. Overall, the design can be seen as fairly successful, where the independent electric propulsion and manual propulsion are able to reach sustained speeds of at least 25km/hr on a level grade within 4.809s and 15km/hr on a slope with a gradient up to 3% within 1.631s while experiencing an incoming wind at 10km/hr; and the combined propulsion is able to achieve sustained speeds of at least 30km/hr on slopes up to 3% gradient and 20km/hr on slopes up to 6% gradient with wind speeds over 10km/hr. The total mass of the designed components is 17.02kg, which allows for the controller, braking system, and miscellaneous accessories to have a mass up to 1.98kg. Finally, for further development, it is recommended that the controller and braking system be designed.
University Projects - Supersonic Flow PropertiesAn investigation was conducted using a supersonic blowdown wind tunnel to determine the half-angle of an oblique shock wave for fixed cones with half-angles of 20°. The range of Mach numbers considered was between 2.5 and 3.3. The cone specimen was seen to be pitching in the test section and the upper and lower half-angles had to be considered separately. The obtained experimental data showed that, as Mach number increased from 2.5 to 3.3, the oblique shock wave half-angle decreased from 42.2° to 33.0° for the upper half-angle of 16.8°, while the oblique shock wave half-angle decreased from 45.7° to 33.7° for the cone lower half-angle of 23.2°. This experimental data was compared to the theoretical predictions from the Theta-Beta-Mach relation, in an attempt to warrant the applicability of the theoretical model and accuracy of its approximation. Subsequently, it was seen that almost all the points were satisfactorily in agreement, when considering the uncertainties present in the experiment, except for the measurements at the Mach numbers of 3.0 and 3.3 for the cone lower half-angle, which should be tested again to examine the repeatability in the values. It should be noted that the largest source of uncertainty and error was from the schlieren visualization, which led to the uncertainty of the experimental half-angles being ±1.6°. Overall, the experiment was accepted as successful given its standard.