Encoders in Auto Mode

[mikets]

No, you must call SetDistancePerPulse for all four encoders after they are instantiated (as part of the encoder initialization). The parameter to SetDistancePerPulse must be calculated or experimented. Basically, one revolution of the encoder will give you x pulses (I forgot what the KOP encoder is, probably 1440 pulses per revolution), then you have to multiply with the gear ratio if the encoders are mounted on the motor side instead of the wheel side.

Do this in your encoder intiialization:
distancePerPulse = (wheel_diameter*PI/pulses_per_revolution)*gear_ratio;
leftfrontEncoder->SetDistancePerPulse(distancePerPulse);
leftrearEncoder->SetDistancePerPulse(distancePerPulse);
rightfrontEncoder->SetDistancePerPulse(distancePerPulse);
rightrearEncoder->SetDistancePerPulse(distnacePerPulse);
 
Then do this in your autonomous loop:
double distanceTraveled = (leftfrontEncoder->GetDistance() +
                                     rightFrontEncoder->GetDistance() +
                                     leftRearEncoder->GetDistance() +
                                     rightRearEncoder->GetDistance())/4.0;
if (distanceTraveled < 60.0)
{
    MecaumDrive_Polar(forwardPower, 0.0, 0.0);
}
else
{
   MecaumDrive_Polar(0.0, 0.0, 0.0);
}

[mikets]

Originally Posted by Ether

You might the discussion of forward kinematics on Pages 7,8,&9 of this paper of interest.

Thanks Ether, I will read it.

[tomy]

Originally Posted by mikets

No, you must call SetDistancePerPulse for all four encoders after they are instantiated (as part of the encoder initialization). The parameter to SetDistancePerPulse must be calculated or experimented. Basically, one revolution of the encoder will give you x pulses (I forgot what the KOP encoder is, probably 1440 pulses per revolution), then you have to multiply with the gear ratio if the encoders are mounted on the motor side instead of the wheel side.

Do this in your encoder intiialization:
distancePerPulse = (wheel_diameter*PI/pulses_per_revolution)*gear_ratio;
leftfrontEncoder->SetDistancePerPulse(distancePerPulse);
leftrearEncoder->SetDistancePerPulse(distancePerPulse);
rightfrontEncoder->SetDistancePerPulse(distancePerPulse);
rightrearEncoder->SetDistancePerPulse(distnacePerPulse);
 
Then do this in your autonomous loop:
double distanceTraveled = (leftfrontEncoder->GetDistance() +
                                     rightFrontEncoder->GetDistance() +
                                     leftRearEncoder->GetDistance() +
                                     rightRearEncoder->GetDistance())/4.0;
if (distanceTraveled < 60.0)
{
    MecaumDrive_Polar(forwardPower, 0.0, 0.0);
}
else
{
   MecaumDrive_Polar(0.0, 0.0, 0.0);
}

so this funtion will make the robot drive until it goes 60 inches.

my question is isnt there any easier way of doing it because you can fine the distance traveled by using the .getdistance in telop mode. why cant you just say something like

myrobot.drive till encoder turn so many revolutions?

[mikets]

That's basically what the code is doing: drive until the encoder->GetDistance() say it has traveled 60 inches.
You could put the code in a function like this:

void DriveDistance(float targetDistance)
{
    float distanceTraveled = (leftfrontEncoder->GetDistance() +
                                     rightFrontEncoder->GetDistance() +
                                     leftRearEncoder->GetDistance() +
                                     rightRearEncoder->GetDistance())/4.0;
 
    while (distanceTraveled < targetDistance)
    {
        MecanumDrive_Polar(forwardPower, 0.0, 0.0);
    }
    MecanumDrivePolar(0.0, 0.0, 0.0);
}

But this function is blocking. You cannot do anything else why the while loop is waiting. Not to mention this will starve your watchdog although by calling the MecanumDrive_Polar function, you probably will feed the per motor watchdog for this year's WPI library. So it's better to do what I suggested in the previous post of checking the target distance in your autonomous loop.

[tomy]

so the best and easiest way is the way you described in post 16

Do this in your encoder intiialization:
distancePerPulse = (wheel_diameter*PI/pulses_per_revolution)*gear_ratio;
leftfrontEncoder->SetDistancePerPulse(distancePerPulse);
leftrearEncoder->SetDistancePerPulse(distancePerPulse);
rightfrontEncoder->SetDistancePerPulse(distancePerPulse);
rightrearEncoder->SetDistancePerPulse(distnacePerPulse);

Then do this in your autonomous loop:
double distanceTraveled = (leftfrontEncoder->GetDistance() +
rightFrontEncoder->GetDistance() +
leftRearEncoder->GetDistance() +
rightRearEncoder->GetDistance())/4.0;
if (distanceTraveled < 60.0)
{
MecaumDrive_Polar(forwardPower, 0.0, 0.0);
}
else
{
MecaumDrive_Polar(0.0, 0.0, 0.0);
}

[mikets]

Yep, unless you have some other restriction/requirements.

[tomy]

ok i will try that thanks for the help

if i need more i will send you a message or put another post here