14.4 Implementation
3D Cam and Follower:
For our final iteration for the 3D Cam and Follower, we realized our follower was too wide and would often hit the side of the follower base and be unable to follow the cam spiral. Therefore, we slimmed down the width of the follower to reach the end of the cam when it reached the end of the shaft without impeding the rotation of the 3D cam. We also swapped out the Cam supports with a detachable top to allow for easy access to the 3D Cam shaft instead of having to tap out the shaft from the linear bearings each time.
Steering Mechanism:
Our steering mechanism is a simple slider crank in which the crank is actually the X-axis movement of the follower base. As the follower follows the program, it moves the follower base up and down the X axis, which is the slider portion of the slider crank of our steering mechanism. So as the slider moves up and down, it pushes the coupler, which rotates our pivot point, enabling our steering column to turn left and right. Our follower was 3D printed, and used linear bearings and shafts for the Y-axis movement of the wheel in the program. For straight movement, our follower has a constant X-axis height, which prevents the follower base, aka the slider, from moving and turning our coupler. The steering column and pivot itself, as well as the linkages, were built with laser-cut pieces and a flat plate bearing for rotation. The steering column was assembled through the top part of the flat plate bearing connecting to the baseplate of the car, while the wheel base column was connected to the bottom half of the bearing. The wheel base column was connected to the bottom half of the bearing through a base plate, where the side columns that support the wheel shaft were connected to the base plate through press-fitting joints to keep it stable.
Drivetrain and Electronics:
The drivetrain is powered by a singular Traxxas 20-turn motor, which in turn is powered by a 3A RC car battery and controlled with a motor controller and RC car controller. We did not use any steering function for the RC car controller and only used it for setting the speed of our motor. Our drivetrain was driven by a 19T gear attached to the motor, which drove a 54T gear connected to a series of 5 belts and pulleys at a 4:1 ratio, powering both our steering and cam rotation. We attached the drivetrain to the side walls of the Da Vinci car, with slots running along the Y and Z axes to allow for adjustable placement of the pulleys and gears. This is because we were unable to get the correct gears in time for cutting out accurate shaft positions on the side wall, only receiving belts and pulleys, and unable to measure the center-to-center distance with the belts around the pulleys. The wall itself was secured to the baseplate of the Da Vinci Car through L-brackets at the top of the sidewall and edges of the baseplate.
We secured each shaft in place with shaft supports that enabled the shaft to slide along the middle slot until they reached their proper place, and then secured them in place through the top and bottom slots with M4 screws. The motor would also attach directly into the slots as it fit perfectly into the upper and lower slots with screw holes already embedded into the motor itself, allowing for an easy attachment.
Manufacturing
The base of the Da Vinci Car was primarily made of 6mm acrylic sheets that were laser cut, except for the steering mechanism. We faced a multitude of problems with the acrylic parts as they tended to crack under the torsion from our slider crank, since we used joinery instead of screw holes for the steering column. Therefore, we had to fillet any sharp edges to prevent as much crack propagation as we could, which was largely successful. However, the disadvantage of using acrylic for complex parts with no screw holes is that everything has to be extremely precise and accurate to have strong press fits and requires lots of tolerancing with various hole sizes to account for kerf.
Manufacturing the baseplate and sidewalls, however, was extremely straightforward as we only needed to have the screw hole placement for all of our parts and ensure they were dimensionally accurate. We also made sure to have an empty cutout where our 3D Cam would be to ensure that it would not hit the baseplate as it rotated along the shaft.
The rest of our parts and mechanisms were manufactured through FDM printers or 3D printers. We did not use the TIW printers as they were always booked and not of the highest quality, and as such, we used our own. This allowed us to have access to 24/7 printing, not compromise on print quality, and iterate quickly since we were able to adjust a wrong screw hole size or bearing hole immediately.
Assembly:
The most complex part of the assembly was adjusting the drivetrain shaft placement, as due to the shafts not running through the entire width of the car, the shafts were cantilevered and were often pulled out of position due to the tension of the belts. Shafts were also tricky to fix in place as they could be slightly bent, which we could not control, and would jostle out of place in their slots.
For the overall assembly, it was extremely straightforward as we ensured our parts were either press fit or secured by M3 screws and nuts that were already laser cut into the acrylic baseplate.