paper: 4 wheel independent drive & independent steering ("swerve")

[Ether]

Originally Posted by Ether

Just added a very simple Excel spreadsheet to demonstrate the swerve wheel speed and steering angle calculations. Might be a useful teaching tool for mentors (or learning tool for students).

User inputs values into cells A1 thru A6. Spreadsheet calculates and displays wheel speed command and wheel steering angle command for each of the 4 wheels.

For students who are visual learners, I updated the spreadsheet to add a graphical display of the wheel speeds and steering angles.

Input the vehicle's wheelbase and trackwidth into cells A1 and A2.

Input the forward, strafe_right, and rotate_clockwise commands into cells A4, A5, and A6.


As a point of interest, note that if you enter FWD=1, STR=0.3, and RCW=0.384, you get Ackermann steering.


In fact, for any values of FWD_Ackerman and Turn_Ackermann, if you input

FWD=FWD_Ackermann, 
STR=Turn_Ackermann*sign(FWD)
RCW=STR*sqrt(L^2+W^2)/L

...you will get Ackermann steering. The derivation of this relationship is shown in the PDF attachment "convert Ackermann commands to holonomic".


Or you can get front-wheel Ackermann steering when going forward and rear-wheel Ackermann steering when backing up if you enter:

FWD=FWD_Ackermann
STR=Turn_Ackermann
RCW=STR*sign(FWD)*sqrt(L^2+W^2)/L

Or you can get "snake" steering (both front and rear wheel steering) if you simply set STR=0 and use:

FWD=FWD_snake
RCW=Turn_snake*sign(FWD)