Project Description
Rigatonii is the new autonomous go-kart that that the RoboRacing team is building for the EVGP competition that happens each spring. On the mechanical sub-team, I worked on the steering system to control the kart as it drives around the track. For the initial design, the steering column was driven by a timing belt that connects it to the stepper motor. The design utilized a moving idler gear that acts as a clutch so that we can disengage the steering wheel from the stepper motor so the car can be steered independent of the motor. Through many iterations and design reviews the final design was eventually decided on.
Heading into the May 2022 competition, a new steering system was designed to reduce complexity and increase steering quickness.
Project Updates
September 2022 - EVGP 2022 Competition
Although Rigatonii didn't place as well at her second competition, the improvements to the steering design were clear during testing. As planned, the steering quickness had been dropped by 80% while also reducing the complexity of the system in terms of number of parts, cost, and potential failure points. The new design was based on a more compact construction, with the steering shaft placed parallel with the ground instead of at an angle. This required the design and production of a custom steering shaft and a welded pitman which I was able to complete using a waterjet and TIG welder. This shaft was directly connected to the motor through a shaft collar so that there was no chance of slipping as what occurred with the previous design.
September 2021 - EVGP 2021 Competition
Rigatoni competed well at its first ever competition, evGrand Prix 2021 at Purdue University. Our go-kart placed 2nd out of the other competing teams. This competition was a real learning experience, we got to communicate with the other teams and we got many ideas for how to improve the kart going forward. For its second iteration, Rigatonii (a new 'i' is earned after each competition) will be getting a completely redesigned steering system. One of the main drawbacks for the kart was the lack of turning speed, especially considering the autonomous software assumed turning was done instantaneously. Additionally, the complexity of the system could be reduced in order to help minimize failure modes.
August 2021
Initial testing at the beginning of this semester revealed that the 1:3 gear ratio was still not providing enough torque for the wheels to turn when the cart was on the ground. In order to remedy this, we decided on replacing the 15:1 gearbox with a 47:1 gearbox. This greatly increased the torque (while slowing the turning speed) enough to allow the wheels to turn while on the ground. It was noticed that the car only turned one way very well since only one side of the belt was being tensioned, so an idler was added on the opposite side to add pressure from both sides. Finally, a method of tensioning the middle gear was added in the form of the four bolts that can be tightened to pull the gear closer to the center-line between the driving and the driven gear. These changes resulted in the elimination of the belt-slippage that was causing the turning issues to one side. The steering system is looking ready for the competition coming up in mid-September.
April 2021
Although the competition was moved from April 2021 to September 2021, the extra time will be much needed. While the initial design for the steering system worked while the car was in the air, as soon as the car was on the ground, the belt began to slip and the wheels wouldn't turn. As a solution to this, we plan to purchase a new gear for the steering shaft to raise the gear ratio from 1:1 to 1:3 to increase the torque output from the motor to the steering shaft.
January 2021
COVID-19 restrictions made progress more difficult in the Fall 2020 semester, but we still managed to fabricate and assemble the majority of the design. Over the course of the semester, we used the Manual Lathe to fabricate a custom shaft that interfaces with the steering column and the encoder to provide absolute position information of the steering column to the autonomous driving software. The timing pulley gears were also bored out to the correct interior diameter to fit the various size shafts that are present in the design. Heading into the spring semester, there are just a few minor things that need to be finished and then the system will be ready for testing.
April 2020
Although the planned competition for Rigatoni was canceled this year because of COVID-19, we still made great progress on the steering system before the school was shut down. We completed the main design after a series of design reviews and began manufacturing some of the main components. Using the waterjet, we fabricated the two main plates and rectified a measurement error using the CNC milling machine. Additionally, the motor clamp was 3D printed and ensured that it clamps down on the stepper motor properly. More information about the final state of the steering system after the Spring 2020 semester can be found here.
