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Week 30 (May 8, 2019): Prototype Evaluation Day, Final Circuit, Incorporating 3D printed parts, Final Presentation, Posters, & Maker Faire

Today, we held Prototype Evaluation Day. Like the rest of the senior project classes, the advisor walks around the classroom, evaluating the senior project apparatuses, asking the student teams to demonstrate their devices, and explain their design, though processes, and results. Dr. Furman and Ron examined and inspected the Full-Scale model, then the Half-Scale model, and lastly, us, the Small-Scale Team. We had completed our circuit to power one pod car and one of the two induction charging stations prior to Evaluation Day, so we were able to successfully demonstrate the pod car driving around the track as well as the induction charging. While we were still troubleshooting issues with the tablet’s Raspberry Pi communicating with the Arduino, the Arduino is still capable of operating on its own, so we could at least demonstrate the motor driving the pod car around the track and through the offline stations. Depicted below is our final circuit that powers the pod car: Dep...
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Week 29 (May 1, 2019): CAD of Induction Charger Hub & Podcar Door, then 3D Printing

This week, while David worked on the Raspberry Pi and the Arduino code, Patrick completed the CAD (computer-aided-design) models. We had to create 3D solid modeling of two parts: the induction charging hub to hold the induction transmitter coil and the pod car door to hold the induction receiver coil. Over the weeks, the CAD models underwent several revisions. The induction hub saw two revisions, with the third design being the final version. Because the 3D printer available to us in the shop, the Prusa Mark3 i2, had a bed length of 10 inches, we had to restrict the length of the charging hub to a safe 9.5 inches. Version 1 simply entailed us placing the hub on the side of the bracket and then screwing it into place on the bracket’s side via the two holes at the top: For version 2, in addition to placing the hub on the side of the bracket and then screwing it into place on the bracket’s side via the two holes at the top, the bracket would wrap around the two bracket...
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Week 28 (Apr. 24, 2019): Final motor selection – Mini-Stepper Motor

Since last week, we have been trying to run the new brushless DC motor; however, it is still difficult to control, let alone its speed. Therefore, we had to pursue our alternative motor, the mini-stepper motor that runs at 5V. Found in Arduino starter kits, this mini-stepper motor is accompanied by its dedicated motor driver board, the ULN2003, which is a chip containing a series of Darlington pair transistors. An image of the stepper motor and the ULN2003 board is shown below:   Sources: https://www.adafruit.com/product/858 https://www.amazon.com/gp/product/B01CP18J4A/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1   We were able to successfully run the new mini-stepper motor with the sample code included with the Arduino starter kit. One benefit to using the sample code is that it utilizes the Stepper library’s functions. One use function is the setSpeed( ) function, which allows the user to set the RPM speed of the stepper motor. We found that the ma...
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Week 27 (Apr. 17, 2019): ME 195B - Presentation #2 (Prototyping Stage Continuation) Reflection

Today, we completed Presentation 2, which is our 5 th  presentation overall, throughout the entire length of senior project, since last semester. Please refer to our Presentation #2 slides, embedded below. Covering the continuation of our prototyping efforts, we discussed progress on hardware acquisition, integration of components into a working circuit, and programming. Regarding programming, we were still working on the communication between the Raspberry Pi and the Arduino. And while the circuit is also coming together, there was one piece that gave us problems yesterday: the gimbal motor broke and so we had to order another motor that is not a gimbal but is still a brushless DC motor. An image of the new motor is found in our presentation slides below. While this was disheartening at first, we found that the gimbal is not intended for continuous rotation, but instead for precise movement, as they are used for cameras on drones. However, this was still a setback...
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Week 26 (Apr. 10, 2019): Programming – Python and Arduino Communication

The Python code and the Arduino code are able to run successfully on their respective boards, i.e. the Raspberry Pi in the tablet and the Arduino in the pod car. However, the Raspberry Pi is having issues sending data to the Arduino via the XBee RF (radio-frequency) module, specifically the user-input data. Whenever the user inputs the pickup station, destination, and selects a pod car, the Serial Monitor on the Arduino IDE does not show any of the data. Investigating further, we plugged the XBee module into one of our laptops, then opened the XCTU software’s (the software which deals with RF modules) Serial port as well. Now, whenever the user inputs the stations, we can see on the XCTU Serial Monitor that the receiving XBee does get the pickup station, destination, and pod car number, but the three inputs are all found between jumbles of random characters. As displayed in the screenshot of the XCTU software below, if the user inputs pickup station 2, destination station 5, and sele...
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Week 25 (Apr. 3, 2019): Current Amplification Solved via Buck Converter

Today, we made the decision of going with the 12V, 600mA induction coil set, as they allowed for a greater distance between the transmitter and receiver, which was a maximum distance of 0.787 inches, as opposed to the 5V, 1500mA induction coil set, which had a maximum charge distance of 0.5 inches. As a reminder, we are implementing induction charging, also known as wireless charging, to charge the 3.7V Li-ion battery at designated charging stations within the track. This helps to enforce autonomy, which will further eliminate human intervention and manual maintenance of the system. Because the charge current is smaller, we tried to find a way to increase the charge current used to charge the battery. We settled upon using a buck converter, which decreases voltage with the advantage of increasing current. The buck converter would be placed after the induction receiver and before the battery charger. After some testing, we found that the buck converter could amplify the curren...
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Week 24 (Mar. 27, 2019): Revised Gimbal Motor Velocity Calculations

Today, we realized our velocity calculation was incorrect because we used the wrong radius in the circumference calculation; we erroneously used the diameter (35 mm) as the radius. Source: Carryer, J.E, et. al.  (2012)  Introduction to Mechatronic Design . Pps. 536-541, 547-548. We were expecting a velocity of around 1.0 m/s, but 0.88 m/s is good enough, with the new bogie, the new gimbal motor, the new 12V power supply from the boost converter, and a 2:1 gearing set.
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Week 23 (Mar. 20, 2019): Driving the Gimbal Motor with the ESC

Today, we finally figured out how to drive the gimbal motor with the ESC (electronic speed controller). As a reminder, the gimbal motor is a brushless DC motor, and brushless DC motors require an ESC to control them.  Source:  https://circuitdigest.com/microcontroller-projects/what-is-bldc-motor-and-arduino-bldc-motor-control We wired the motor connections according to the image below. The Arduino MEGA is connected to the ESC’s control pins, the gimbal motor is connected to the ESC’s motor pins, and the battery is connected to the boost converter, which is then connected to ESC’s battery pins. A potentiometer is also connected to one of the Arduino’s analog pins to control the speed of the brushless motor. We also found that the ESC can power the Arduino, as it contains a 5V BEC (battery eliminator circuit). As its name implies, it eliminates the need for another battery to power the Arduino, as it regulates the input voltage down to 5V. Thus, we simply hav...
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Week 22 (Mar. 13, 2019): Battery Clarification and Boost Converter

To begin today’s post, we will make a slight rectification to our earlier posts. In prior posts, we stated that we are going to use a 3.7V Lithium-polymer (LiPo) battery. However, more specifically, we are using a 3.7V Lithium-ion (Li-ion) battery. While there are some differences between the two types of batteries, since they are both lithium-based batteries, they utilize the same chemistry for the most part. Li-ion batteries are the ones that are found in most cellular phones. We found that these batteries are more favorable to use in our project than their LiPo counterparts. Whereas LiPo batteries suffer from a shorter lifespan, Li-ion batteries are more efficient and have higher power density, meaning they contain a large amount of energy in a small package. Furthermore, Li-ion batteries cost less than LiPo batteries. Even though Li-ion batteries are “potentially dangerous”, we won’t be driving heavy loads, and we will be testing in an open environment, rather than a confined ...
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Week 21 (Mar. 06, 2019): ME 195B - Presentation #1 (Prototyping Stage) Reflection

Today, we presented our first presentation of our second semester of ME 195B - Senior Design Project, making it our 4th presentation overall, throughout the entire duration of senior project, since last semester.  Please refer to our Presentation #1, embedded below.  Up to now, we have gathered all of our major components and are starting to prototype one small-scale podcar. Although, if we find that we need to buy a smaller component, we do so immediately to get ahead of the delivery time. Besides the gimbal motor and the accompanying ESC (electronic speed control), we have tested all the parts and have found that they all work individually.  Despite the fact that there's limited information on gimbal motors on the internet, we found some Arduino code to run the gimbal motor and ESC. However, regarding the connections, we have all but one connection - the connection between the ESC and the battery; all we need is an XT60 connector to connect the ESC to the...
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Week 20 (Feb. 27, 2019): Power Electronics – Battery & Amplifier

Since last week, I have been working on the current amplifier for the induction charger. We decided to abandon using the TPS53313 step down voltage regulator-current amplifier IC (rated at a maximum of 6A continuous output current) because we found that supplying +5V to a 3.7V LiPo battery was possible and safe. Additionally, charging a LiPo battery at 6A was found to be dangerous; the battery should be charged at 25% of the capacity rating (.25 x C), or .25 x mAh. In the case of the 6600mAh battery, it should be recharged at a rate of 1.65A or less. The last reason is that dealing with a surface mount device (SMT) is a bit difficult. I started out using a BJT NPN transistor (model: 2N3904), something I was most familiar with. However, its datasheet states that it has a 200 mA maximum continuous collector current rating. This is a significantly low current. Most, if not all, fast charging adapters today have a 2 A charging rate. While I don’t want to charge the LiPo batteri...
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