Project Progress Blog

October 11, 2024

This week the group began CAD modeling the column rotation limiting device and the main assembly for the rack and pinion. The group also began drawing the electrical schematic for the input encoding and motor control. We looked into the design of each specific component and discussed how that component would be manufactured. After this discussion we made certain small changes to part designs in order to make sure they are easily manufacturable. 

October 25, 2024

The group began with finalizing the design of critical parts and beggining technical analysis. The group completed technical analysis on gear stresses, bending stress, Finite Element Analysis, and electrical analysis. The group also began working on the project website. In our meeting with our advisor, Dr. Aziz, we discussed gears and the different ways to analyze gears.

November 8, 2024

The group completed analysis on the gears used in our project and verified that they would not fail in our application. The group also analyzed the keyway used to transmit the torque from the pinion shaft to the pinion gear. The group began testing a few different 3D-printed gears for the column rotation limiting device. The gears tested included PLA spur gears, PLA helical gears, and PLA herringbone gears. The group selected the herringbone gears to move forward with since they have the advantage of having more contact area which makes them stronger. Helical gears have the same benefit, however they push each other apart naturally and make an axial force. The axial force would need to be considered when choosing bearings and axial load-rated bearings tend to cost more. Conversely, the herringbone shape gives the benefits of more contact area while also canceling out axial forces. After selecting the herringbone gears, we printed them out of PETG to test, and then we printed them again out of PETG and made them 100% solid. This is a good finding, since 3D printing gears is more cost effective than off-the-shelf gears. Originally we planned to use commercially available metal gears, but they were going to cost a total of $60.  

Electrical testing occurred relating to the speed control of the motor. MOSFET turn on transient was analyzed on an oscilloscope, using a gate driver under a variety of conditions.  Initially this testing was conducted with a 60 W resistive load at 13.8 V, and then 24 V. Data was collected about the response with different duty cycles, and at different frequencies. The testing also included the effect of adding additional capacitance to the gate driver to assist with charge pumping. The ADC on the ATmega328p and the wires connecting the motor to the battery were also analyzed as part of the technical analysis.

November 22, 2024

Our group has began the manufacturing for our alpha prototype. We began with sourcing material. Some materials were ordered and others were found as scrap material at our university. A lot of manufacturing was started. We began with the steering column rotation limiting device and associated parts. We also manufactured the shaft coupler and parts to make the case. Many different manufacturing processes needed to be done for these parts. We utilized CNC plasma cutting, CNC milling, manual milling, manual turning, and TIG welding for this portion of our manufacturing. Many hours were spent in the SAE Baja garage using the manual lathe, manual mill, welder, and CNC plasma cutter. In addition, many hours were spent in the Stevens Machine Shop using the CNC mill and the manual lathe. Our group encountered a few challenges such as the machine shop only being available for use from 7am-3pm. For our CNC parts we utilized Fusion 360's CAM (Computer Aided Machining) feature to create toolpaths to tell the machines how to make our parts. Before manufacturing the case and case parts, we needed to design fixture plates. The purpose of the fixture plate is to hold our part in the vise during different setups. Two fixture plates were designed; one to hold the case for different operations, and one to hold the case cover for different operations. These parts were machined using a Fanuc Robodrill CNC which is new at Stevens. We had to learn how to operate this new machine as well as attend a training last Wednesday hosted by a representative of Fanuc. The new Fanuc machine will be good for the manufacturing of our Aluminum case for a few reasons. The first is accuracy, the machine being more accurate than the other machines means that we will be able to create precise interference fit bores for our bearings using interpolation with an endmill rather than having to use a boring bar. This saves time as well as removes the human error of using a boring bar. The next reason is that this machine is more powerful and has more features. The machine has 5x more horsepower, 5x more spindle speed, faster rapid travel speeds, faster cutting speeds, an automatic tool changer, and powerful flood coolant. All of this will allow us to reduce our cycle time, reduce human error, and have better surface finish. For example, one of the roughing operations for the case (the case has about 8 different operations) would have taken 1.5 hours on the old Southwestern Industries machine. On the Fanuc the roughing operation for the case was less than 20 minutes. This machine has countless other benefits compared to the old CNC milling machines. These benefits will be very important for our project especially considering the tight timeline for phase 3 of the project. 

Further electrical testing was conducted to begin controlling the motor with multiple MOSFETs. A second gate driver was used to facilitate the simultaneous high-side and low-side operation. Different MOSFETs were used to study the affect of the drain current and on resistance verses the gate charge, which negatively affects turn on time. Further test with different model gate drivers, and paralleled devices to improve function. Development of the logic circuiting for the motor controller was also progressed, such as the anti shoot-through logic and the thermal protection circuitry.

December 6, 2024

The finishing operations were completed for the case. The Southwestern Industries machine was used to bore the side of the case for the linear bearings. We used a boring head with long boring bar to ensure both bores could be done in the same setup. This is critical since it ensures both bores will be perfectly concentric. This is required since any misalignment will cause friction between the rack gear and the linear bearings. After the case was completed, the group moved to manufacturing the fixture plate for the case and the case cover. The same process and machine was used as the case in the Fanuc milling machine, in order to ensure accuracy and to ensure the parts would be made efficiently. The next part that was made was the pinion shaft. The pinion shaft was turned on the lathe from 1" 4140 stock. Then it was put into a Bridgeport milling machine to mill the keyway. An 1/8" precision ground endmill was used to ensure the proper size for the keyway. The final part was the rack gear. The gear was cut down on the horizontal bandsaw then it was faced to size in the lathe. Then holes were drilled and tapped into each end to attach to the heim joints. After these parts were manufactured, the prototype was assembled and we verified everything fit and moved freely without extra friction. 

While work was still being completed on the motor control circuit, the microcontroller circuit was finalized and the PCB layout was designed. Since the board design was complete for the microcontroller, it was sent out for production. Once the team received the board back, the components were soldered and the microcontroller was tested to ensure it could be programmed on the board. For the motor control, the logic circuit to implement dead time was finalized and it was verified to be functional using the oscilloscope. The whole circuit was then prototyped on breadboard to ensure it could turn the motor. Tests to run the motor were successful, with the circuit able to run the motor in both directions and stop the motor near instantly. Since the motor controller was not yet fully integrated with the microcontroller, a small PCB consisting of several LEDs was designed to show a proof of concept for taking the steering input. The column potentiometer was connected to this board, and the microcontroller took input from the potentiometer and turned on corresponding LEDs on the board based on its position. This allows for the column to be rotated, and the team can verify the input by viewing the LEDs that are illuminated.