#ROBOTC PID CONTROL FULL#
#ROBOTC PID CONTROL SOFTWARE#
#ROBOTC PID CONTROL CODE#

In most simple cases only a P value is needed. 05 for P.Īs always, you can do these calculations to determine a starting P and I values and then adjust then to tune actual robot behavior. 05 (5%) correction power for 1 degree of error worked well, correcting the error without overshooting too much (wandering): .05 / 1 =. So we have to determine how much correction we want to apply for how much error. In the case of driving straight, the target and error are the same at the start so the error is zero. Here is the above example modified to compute the P and I values for any angle/power combination input to the rotate() function. You would have to compute new values for other angle/power combinations. They will not work as well for other angles or power levels. Note that these values are optimal for a 90 degree turn with 30% power. You can adjust I to get the turn completed accurately in a timely fashion. The I value will compensate for P not reaching the setpoint and start adding power until the robot completes the turn. To fix this, we add some I (integral) value. Often with just a P value alone, the robot may stall out before completing the turn because the PID controller reduces the power below the level which will move the robot. In the case of moving from a non-zero error to zero error, we took the maximum error value, 90, and the power level we want applied at max error. 003 for the P value on the turn PID controller. The example below takes the previous DriveAvoidImu example and uses two PIDController instances to manage straight driving and the 90 degree turn on obstacle contact.Īn obvious question is how did we arrive at. PIDController is a library or utility class, a class that does nothing by itself but is used by other classes. Because PIDController is in the same package as the examples below, Java will be able to locate it when you reference it in the examples.

#ROBOTC PID CONTROL CODE#

Create a new class called PIDController and paste that code into it. Here is the source for a class called PIDController that will perform the PID calculations. The FIRST forums on programming have extensive discussions of PID in robot applications. Here, here and here are some resources to start with to investigate PID further. There are many resources and discussions of PID online. Here the target is zero (gyro not deviating from direction we are traveling) and any change in the measured angle will result in a correction value calculated by the PID controller.Ī PID controller can take a lot of tuning to get the desired result but once you get a feel for how they work you can tune them fairly quickly and by using all three of the PID factors you can get quite fine control over motors. The PID controller can also apply a tolerance margin that indicates when the actual value is within some percentage of the target to further control robot motors.Ī similar example is to use a PID controller to compute the power correction needed to make the robot drive in a straight line. In theory this reduction in power and slowing rate of turn will eliminate the overshoot. As the turn gets closer to 90 degrees, the PID routine starts to return smaller and smaller values thus reducing the power being applied and slowing the rate of turn. As the turn progresses, the angle of turn is fed to the PID controller routine which measures error and produces a value (the turn power) at or near the starting (full) power.

#ROBOTC PID CONTROL FULL#

So in our example we start out turning away from zero towards 90 degrees at the full power we specify. The idea behind a PID controller is to take the desired state value (90 degrees in our turn example), compare that to the actual (feedback) state value (the current gyro or IMU angle) and apply factors to the difference (called the error) that produce a proportional output value. PID stands for Proportional, Integral, Derivative.

#ROBOTC PID CONTROL SOFTWARE#

To do this we will use a software routine called a PID controller. Fixing this can be tricky to do manually but there is an automated way to better control the turn. On our test robot, a 90 degree turn would end up being 110-120 degrees. When turning at a constant power setting and setting the power to zero when the target angle is reached, depending on motor configuration, gear ratio, robot weight and the turn power, the robot will most likely not stop quick enough to be on the desired angle. With the test robot used to develop this course, there is a problem with the previous examples of turning under gyro or IMU control.

Robotc pid control