Inverse Kinematics

This project was part of the University of Pittsburgh's Robotics and Automation Society (Pitt RAS). They had created a 3-axis robot arm using 3 servos motors and an Arduino Uno. It was able to be driven by a joystick, but did not track its position.My task was to take the existing robot arm and develop a program that would let the user input two coordinates (x and z) to drive the robot to an intended point in space. This is called inverse kinematics, as it deriving robot arm orientation from a know position, rather than having the orientation drive the final position in space.

Demo

The following video describes and showcases the program I wrote to drive the robot arm. The subsequent sections will detail the steps taken to get ot this point.

Mathematical Modeling

Before I could start on program development, I had to first figure out how to determine where the robot arm was in space using only the servo arm angles. Dusting off my knowledge of trigonometry, as well as using some online resources, I was able to create a mathematical model on paper that could derive the x and z coordinates input by the user into servo angles.

Following the mathematical derivation, I wanted to confirm my model was correct before driving the servos. I did not want to risk damaging any of the hardware on the robot arm due to a math error. I drew up a model in Autodesk Inventor that let me check the servo angles using given x and z coordinates. I was able to produce this model by using the defined arm link lengths, letting the software do the rest of the math for me. 

I checked these angles against a software program I wrote that spit out the servo angles without actually driving the arms. The results agreed and I was able to move onto interfacing with the arm.

Software Integration

Now that my model was accurate, I uploaded it to the Arduino and checked the servo angle produced. These angles agreed with the mathematical assumptions, meaning the robot arm was complete. 

Reflection

This project taught me a lot about programing and inverse kinematics. I had minimal experience with Arduino up to this point, and zero experience with driving servo motors. Despite this, I was able to reference a previous member's program and utilize the mentorship of the robot arm team to learn and successfully drive servo motors. Furthermore, my success in the creation of an inverse kinematic model will help future students on the team go even further with the robot arm now that it can move to known positions. I look forward to seeing where the team takes this project!