Programming Direct drive with Direct (car like steering)

[tuna.and.cheese]

Hi everyone. I am trying to implement direct drive where all four motors are connected directly to all four wheels. I also want these wheels to each turn like a car would to make turns. If the joystick is in the upper left position, the robot will turn left and go forward and if in the right position, the same but turn right. The drive train is already built and the electronics are on the robot, but I am yet to attempt to program this and am just in the research stage.

Would anyone know how I could go about attempting this? I could get the robot to go foward and back, but to do this while at the same time rotating motors to turn left or right is not making too much sense.

Any help will be great. Thanks. Justin.

[Bryan Herbst]

If you are using labview, you can use the WPI Robotics Library's Arcade Drive VI.
This is the default VI, so the default labview code (essentially just the framework, basic or advanced) can be built and sent to the cRIO to have this working.

If you are going to use C/C++, you are going to have to implement a relatively simple formula. The way it is *usually* done is to take the Y axis and call it velocity, then call the x axis rotation.

A simple two motor example-

wR = velocity + rotation;
wL = velocity - rotation;

[nathanww]

We did something like this on our Overdrive bot with the steering(Ackermann steering system). The biggest thing that you have to watch out for is that this will not work as an open-loop system--you HAVE to have feedback from the wheels, or positioning errors will make your robot unsteerable after a few turns. Ideally, you would use servos to handle the turning, but I don't think any of the allowed servos are quite beefy enough to handle that. What we did was hook up a worm motor to the steering system, and then had a potentiometer provide feedback, but the tricky part about this was getting oscillation out of the system.