GRAVL- Autonomous Tractor (2018-2020)

GRAVL was an undergraduate research team in the robotics lab at Olin College of Engineering that focused on making an autonomous tractor. GRAVL's goal was for the tractor to run autonomous navigation, obstacle avoidance, and other specific tasks. I mainly worked on mechanical engineering projects on the tractor. Some of my projects included integrating a hydraulic system, a method of engaging the reverse and velocity pedal in autonomous mode and adding encoders to the wheels.

We are working on a research project on ground leveling. We will have the tractor go over a path and scan the bumps in the ground. The tractor will then use a box blade to level the ground out. We worked on a smaller platform first in order to increase time efficiency when we moved to working with the actual tractor. I learned more about conducting research experiments through this project.

Velocity/ Reverse Pedal Actuator

The tractor's forward velocity and reverse velocity are controlled with two pedals that are connected and pivot around an axle in between the two. The previous design was only able to control the forward velocity and was simply a pulley cable connected to a linear actuator and the velocity pedal. Since, it was a cable, it could only pull the pedal, but not push. This meant we could not actuate the reverse pedal.

I used a chain and sprocket design that would connect to both pedals and be controlled by a DC motor and potentiometer. When the sprocket would rotate in one direction, one pedal would be pulled down and the other side of the chain would follow the other pedal up.

I added a linear spring in the middle of the chain because the radii that the pedals traveled along were so different, the torsion spring on the sprocket didn't have enough give. This allowed the chain to be in tension in the direction it was being pulled.

I made the custom parts using a mill, lathe, TIG welder, and 3D printer.

Mini Platform

We spent a semester building up the smaller platform. The smaller platform works nearly identical to the real tractor. The same code is able to work on both the tractor and the smaller platform. I worked on making the structure for the platform and designing the blade. I created a three point hitch, blade frame and blade. After completing research about the controls a road grader uses to grade the roads, I concluded that control of the z and pitch of the blade were the most important. I designed the three point hitch to be similar to that on the tractor with the addition of a servo attaching to the blade frame moving the whole blade frame up and down in the z direction. The blade frame design is nearly the same as the real blade frame used on the tractor, with the addition of two servos controlling the pitch of the blade.