Divide by 0 Exception - Unofficial reply

[jpearman]

You asked the following question in the ROBOTC tech forum. Most forum users cannot answer there, so I’m quoting the question here so others can help

@9364F

I am making an x-drive and some wheels were running faster then they were supposed to so I wrote out some code to fix it. My Genius friend helped me write it and he said it is the same problem he had (the faster motor problem) and he told me exactly how to write it. Here is the code

#pragma config(I2C_Usage, I2C1, i2cSensors)
#pragma config(Sensor, I2C_1, , sensorQuadEncoderOnI2CPort, , AutoAssign)
#pragma config(Sensor, I2C_2, , sensorQuadEncoderOnI2CPort, , AutoAssign)
#pragma config(Sensor, I2C_3, , sensorQuadEncoderOnI2CPort, , AutoAssign)
#pragma config(Sensor, I2C_4, , sensorQuadEncoderOnI2CPort, , AutoAssign)
#pragma config(Motor, port1, FR, tmotorVex393_HBridge, openLoop, reversed, encoderPort, I2C_1)
#pragma config(Motor, port2, BL, tmotorVex393_MC29, openLoop, encoderPort, I2C_2)
#pragma config(Motor, port3, BR, tmotorVex393_MC29, openLoop, encoderPort, I2C_3)
#pragma config(Motor, port10, FL, tmotorVex393_HBridge, openLoop, encoderPort, I2C_4)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

void fixThis (){
float rlRatio = 1.0* motor[FR] / motor[BL]; //finding out the ratio of the motor's power
float lrRatio = 1.0* motor[FL] / motor[BR];

float rlEncoderRatio = 1.0*SensorValue[I2C_1] / SensorValue[I2C_2]; // findig out the same motor encoder value ratio
float lrEncoderRatio = 1.0*SensorValue[I2C_4] / SensorValue[I2C_3];

float rlDifference = rlEncoderRatio - rlRatio; // Finding the difference of both to see how off th motors power is than it is supposed to be
float lrDifference = lrEncoderRatio - lrRatio;

float lrConstant = 1.4; //The Constant will be used to correct the motor's power later
float rlConstant = 1.4;

if (lrDifference < 0) {
motor[BR] -= lrDifference * lrConstant;
}
if (lrDifference > 0) {
motor[FL] -= lrDifference * lrConstant;
}
if (rlDifference > 0){
motor[BL] -= rlDifference * rlConstant;

}
if (rlDifference < 0) {
motor[FR] -= rlDifference * rlConstant;
}
}

task main()
{
SensorValue[I2C_1] = 1;
SensorValue[I2C_2] = 1;
SensorValue[I2C_3] = 1;
SensorValue[I2C_4] = 1;

while (true) {



motor[FR] = vexRT[Ch3] - vexRT[Ch4] - vexRT[Ch1];
motor[BR] = vexRT[Ch3] - -vexRT[Ch4] + -vexRT[Ch1];
motor[FL] = vexRT[Ch3] + vexRT[Ch4] + vexRT[Ch1];
motor[BL]= vexRT[Ch3] + -vexRT[Ch4] - -vexRT[Ch1];

fixThis ();

}
}

and when I run it on my robot i get this error

Exception Error in User Program:

Exception Type: ‘Divide by zero(91)’

Program Slot: 0, Task ID: main[0]
Error at PC: fixThis+0x0074
TaskState: ‘Exception’

The program allows me to press start but When I do that the robot has no response (the robot had response when the wheels were moving faster than the other wheels) And I checked the local variables in debugging and it said this

rlRatio = 1
lrRatio = 1
rlEncoderRatio = -1.#QO (That is not a mistake in typing)
lrEncoderRatio = 0
rlDifference = 0
lrDifference = 0
lrConstant = 0
rlConstant = 0

I have tried so many things but yet nothing seems to work

please give me some instructions on what I need to do to fix this problem

The simple answer to your question is that the cortex does not know how to divide by 0, that’s why you get the exception, the following lines will all potentially cause this to happen.

float rlRatio = 1.0* motor[FR] / motor[BL]; //finding out the ratio of the motor's power
float lrRatio = 1.0* motor[FL] / motor[BR];

float rlEncoderRatio = 1.0*SensorValue[I2C_1] / SensorValue[I2C_2]; // findig out the same motor encoder value ratio
float lrEncoderRatio = 1.0*SensorValue[I2C_4] / SensorValue[I2C_3];

motor[BL], motor[BR], SensorValue[I2C_2] and SensorValue[I2C_3] can all potentially have the value 0.

One way to handle this is with some conditional statements as follows.

float rlRatio;
if( motor[BL] != 0 )
    rlRatio = 1.0* motor[FR] / motor[BL];
else
    rlRatio = 1; // or whatever makes sense 

Even if you fix the exceptions I’m not sure how well the code will work, the code may be unpredictable under acceleration and deceleration. You also set motor values in more than one place, not a good thing to do (see this bad programming habits post #4).

[97934U]

Thanks so much for the help you have no idea how much this mean to me