Motion Profile for Generic Robot Drive Systems

A Java Implementation of Motion Profiles 💯 🔥

Implemented June 2017

Imagine a car at rest that needs to move to point A from your current position. Now think about what it does when the driver steps on the gas pedal and letting it coast with constant velocity for a couple minutes then steps on the breaks until it goes to a halt. Can you tell me how far it travelled at 1s? 5s? 2000s? How about its velocity? Can you generate a graph of its movement?

Purpose:

• Generate a motion profile (sequence of positions and velocities from point A to point B) with a few constraints:
  • velocity may not exceed a specified maximum
  • acceleration may not exceed a specified maximum and must be constant from accelerating to decelerating mode
  • the path must be a continuous function
  • integrating velocity must yield position
  • profile must yield a distance approximate to the distance inputted by the user
  • start and end velocities are integrated, meaning a profile is not stuck to just starting and ending at rest
• This repository contains motion profile drive controller formulae to be ported to an FRC robot
• This will mostly be used for autonomous movements
• Team 973 The Greybots first implemented this for the 2017 season to be used in the 15-second autonomous movements
• This can lowkey be used for physics problems

How does it work? (Methodology)

• To construct a motion profile, the following values must be taken as parameters: max velocity, acceleration, distance, start and end velocities.
• From simple kinematics equations and geometry/calculus, we would be able to construct a motion profile, trapezoidal or triangular, that we can use for a simple robot drive subsystems.
• A singular motion profile will have anaccelerating mode which will be the first thing the robot will do from start velocity to ramp up to the max velocity, then a coast mode is simply for 0 acceleration and robot is at max velocity which is only exclusive for trapezoidal profiled, and finally a decelerating mode which will mark the end of the profile and the object must decelerate until it reaches end velocity.
• There will be two kinds of motion profiles: trapezoidal and triangular. In order to distinguish between them, a formula was developed to determine whether the distance travelled by reaching the max velocity from start velocity then decelerating to end_velocity (minimum distance travelled) is just enough for the distance inputted by the user. If it not enough, then it is a trapezoidal profile. If it does not need to reach max velocity, then it is a triangular profile.

How to use this?

git clone git@github.com:KyleD973/MotionProfile.git
cd MotionProfile

Install Netbeans or Eclipse or any IDE softwares that can compile in Java Open the repo in the installed software and compile, run project Now you can play with motion profiles!

If you are porting: Just make sure that you are transposing the right variable names and such so that no bugs will be a detriment to your robot program development.

Scopes and Limitations

• This project was done specifically for FRC robots and done by imagining a moving object in a perfect "physics" world (not accounting for friction and air resistance, etc.)
• This can probably do rotational motion but I have to check on that cause it might be a different formula but same concept
• Graphical representation of the Profile object is not yet supported but not needed for the basic purpose

Acknowledgements

This was heavily inspired from our 973 College Student Mentor Andrew Nelson. Reference: Trap Profile