ModWheels Fall 2019
Mechanical Design
Author/s: Uzziah J. Lontok
Final Rendition of Fall 2019 ModWheels at the CSULB Japanese Garden
Introduction
The Fall 2019 version of ModWheels mechanically has drastic changes as compared to the previous versions. Other than the fact that a car shaped chassis is implemented, the different materials, moving parts, and features are clearly different from previous versions.
Previous ModWheels
Figure 2: Previous Version of ModWheels
As shown in Figure 2 above, the previous version of ModWheels was given to our team by professor Hill. The chassis and steering linkage system were 3D printed in a material that is most likely PLA. Also, a major difference seen here is the use of an Arduino as the main controller for the car. There is no holder for the electronics, just placed on hex standoffs; there is also no external cover or shell. The wheels implemented were bought and the wires are all grouped together; this is a problem that we spent trying to fix.
First Attempt
ModWheels V1 included the same chassis as the original version; the main goal was to implement the 3DoT board and have the car running using the 3DoT. There is no mechanical design required for that version, so the first discussion will be about V2. The main design change for Fall 2019’s rendition of ModWheels is to have an exterior shell on it. The customer has requested that the exterior shell will be the paper car models distributed at Ruby’s Diners. These car models are designed by KidStuff.
Figure 3: Fall 2019 Attempt at ModWheels Chassis
Figure 4: Interior for Fall 2019 ModWheels
For Fall 2019, our team wanted to get away from the inaccuracy and time consuming properties of 3D printing, so we decided to experiment with a new form of manufacturing – laser cutting. Laser cutting requires all models to be two-dimensional vector files; all models must be top down view only. Any part that requires 3 dimensions would need multiple cuts, but laser cutting a 12×12 inch job will still only take around 10 minutes with incredible precision. A cheap, yet effective material that was used in this project is a 3mm baltic birch wood – specifically made for jobs like this.
Figure 5: SolidWorks Model for ModWheels V2
A constraint for this project is that ModWheels must fit within the dimensions of the paper car models given out at Ruby’s Diner. This proved to be a challenging task, making sure every component fits inside the car, which is relatively small. The previous steering system had the servo low on the ground, and that must be fixed in the final version of ModWheels.
The SolidWorks 3D Model for ModWheels V2 is shown in Figure 5. The first step in designing a new mechanical model is knowing the measurements of the shell and making sure that the entire product will fit within the dimensions of the Ruby’s diner paper car model. Once that is set, the same goes for every important component of the project; in this case the important components are: the 2 motors, the 3DoT board, the SG-90 micro-servo, and the size of the wheels based on the car model. Once those dimensions are set into stone, the 3D modeling begins.
Figure 4 contains a black PETG 3D printed part as a holder for the 3DoT board; this was necessary due to the fact that the previous ModWheels utilized an Arduino and we could not use the previous mounting system. The design process for this is standard: find the dimensions of the 3DoT and have the necessary connectors accessible. What was done here is have the 3DoT slide into the holder, with the holder completely secured onto the middle of the car’s chassis.
The side panels are meant to have the paper shell just drop in to the car, this proved to not be ideal because tape had to be used. The steering is similar to the original version of ModWheels, but a 3D printed L bracket was used to house the wheels. This again was not ideal because the amount of friction and the unstable platform made it hard for ModWheels to maneuver. It did however fix the issue that the servo was too low to the ground, but the steering linkage system needs major improvements.
Figure 6: ModWheels V2
Figure 6 shows the final version of ModWheels V2. The main issue with this design was the size of the rear wheels and the unstable steering linkage system. The large rear wheels was due to the sheer size of the chassis encoder. The unstable steering system just needs a redesign.
Most Recent Rendition
Figure 7: ModWheels V3 SolidWorks Model
Major differences with the V2 was the addition of the speaker, ball bearings, and the replacement of the motors to the bottom side of the chassis. The reason why the motors were eventually moved to the bottom was to fix the steering problem being too low to the ground. By doing that, we were able to have more clearance on the bottom of the car. The steering linkage received a relatively major redesign: the L bracket has also been laser cut and ball bearings have been added. This helps with the overall rigidity and stability of the steering system, and eliminated any sort of friction and unnecessary movement of the wheels.
The addition of ball bearings were superb in terms of the smoothness and handling of the robot; compared to the freewheeling tires in the previous iteration. Also, Figure 7 shows the fully assembled (without the cover) 3D model of ModWheels. Shown is a fully laser cut chassis; the only 3D printed parts are the tires and wheels. The 3DoT is encased in a wooden slide in system where it is secured in place by wooden structures. This replaces the 3D printed 3DoT holder in V2. Those wooden structures have areas where the LED’s and the wiring will be routed, marginally fixing the problem experienced in the previous ModWheels. The front and rear LED panels will hold the actual LED’s and will serve as a support structure for the KidStuff paper car model.
Figure 8: Every Piece of the Laser Cut Chassis
Figure 9: V3 with Extra Components
Figure 9 shows the components necessary for assembling the full car; the speaker, motors, encoders, 3DoT, and custom PCB. All the dimensions have been accounted for, and everything fit how they were supposed to thanks to the SolidWorks assembly feature which lets the user test the sizing of each part.
Figure 10: Final Assembly
The final assembly is shown on Figure 10 above. The front and rear panels hold the LED’s and are secured using superglue. They will stay on the chassis when disassembled; the wiring can be pulled off from the 3DoT and replaced by hand. The wooden structures are seen helping route the wires and secure the 3DoT by simply sliding it in. The steering system with the redesigned laser cut L-brackets and the addition of the ball bearings are showcased. The ABS wheel and polyjet tango tires proved to be a solid alternative to buying tires; creating our own wheels enabled us to fit the tire dimensions to the paper car model.
Conclusion
ModWheels transitioned from a 3D printed, Arduino based project to a laser cut, 3DoT based project. The main issues to address with the previous ModWheels were the replacement of the Arduino, fixing the lose wires, and having an external shell for aesthetics. In the end, our team was relatively successful in transitioning the previous ModWheels into one that is driven by the 3DoT and the ArxRobot app, and switched into a mechanical design that featured laser cut baltic birch. Mechanically, we have fabricated a solid mechanical design that will serve as a basis for the next rendition of ModWheels