Broken Shaft Encoder

VEX V5 Technical Support UNOFFICIAL Tech Support
1

While testing our new program, we noticed that both of our robot’s quadrature shaft encoders started outputting really strange values. When connected to the wheel, the value would bounce around from what seems like random values, back and forth, and into the negatives, until the shaft encoder finally went past its tick goal. When disconnected from the wheel and turned manually, the value didn’t even change, bouncing in values between -1 and 1. We tried changing the shaft encoder, but the same thing would happen.

Does anyone know what might be happening? :frowning:

2

We had a similar issue where I thought a bunch of encoders had gone bad. It turns out that it was a programming problem. The program was resetting the encoder to zero

3

Our program resets the encoder too, but it’s not within the loop, so I don’t think that’s a problem.

Here are the functions allowing our robot to move;


void driveForward (int dist, int pwr)
{
	SensorValue[rightEncoder] = 0;
	SensorValue[dgtl8] = 0;
	int tickGoal = ((42 * dist) / 10) / 1.6;


	while(abs(SensorValue[rightEncoder]) < tickGoal)
	{
		pwrDrive (pwr, pwr);
	}
	stopChassis();
}

void pwrDrive(int pwrL, int pwrR)
{
	motor[frontRight] = pwrR;
	motor[backRight] = -pwrR;
	motor[frontLeft] =  pwrL;
	motor[backLeft] =  -pwrL;
}

task(main)
{
	driveForward(72, 60);
}
4

What happens in stopChassis?

5

If you drive without calling that function what happens? (just push the robot around)

6 

void stopChassis()
{
        motor[frontRight] = 0;
	motor[backRight] = 0;
	motor[frontLeft] =  0;
	motor[backLeft] =  0;
}

The shaft encoder value still does not change

7

Look through your whole program and make sure that you are not resetting the encoder somewhere.

Another troubleshooting idea: create a program for just that encoder and see what it does. Get rid of all of your other code. Isolate the issue.

8

The problem might just be the low QC on encoders. Just try the encoder on the side not connected to your chassis and see if it really is code or the encoders. The gyroscopes I remeber has big degree gaps in sensing.

9

@FrozenInTime Make sure your robot is running off of a 7.2V battery (one is plugged into the Cortex and the Cortex switch is set to ‘On’). Many sensors don’t work correctly when powered through USB.

To expand on what @Gear Geeks said:
Create a new, very basic program that is nothing more than the


#pragma

statements necessary for the shaft encoder and the typical infinite


while()

loop.

10

I’ve had luck cleaning quadrature encoders. Once I had one that didn’t work and I took the whole thing apart, wiped everything with a wet paper towel, and put it back together again. I even cleaned the IR LED and receiver. It might be worth a try. That encoder had had its cap off for a while, though. I think that’s why it had dust in it.

11

@FrozenInTime What ports are you using? Please post your #pragma statements.

12

I tried that, and the shaft encoder is still only returning values between -1 and 1…

#pragma config(Sensor, in1,    Pot,            sensorPotentiometer)
#pragma config(Sensor, in2,    selectorPot,    sensorPotentiometer)
#pragma config(Sensor, in3,    gyro,           sensorGyro)
#pragma config(Sensor, dgtl5,  leftEncoder,    sensorQuadEncoder)
#pragma config(Sensor, dgtl7,  rightEncoder,   sensorQuadEncoder)
#pragma config(Sensor, dgtl9,  cubeLeft,       sensorTouch)
#pragma config(Sensor, dgtl10, cubeRight,      sensorTouch)
#pragma config(Sensor, dgtl11, rightSolenoid,  sensorDigitalOut)
#pragma config(Sensor, dgtl12, leftSolenoid,   sensorDigitalOut)
#pragma config(Motor,  port2,           leftBottomLift, tmotorVex393HighSpeed_MC29, openLoop)
#pragma config(Motor,  port3,           middleLiftLeft, tmotorVex393HighSpeed_MC29, openLoop)
#pragma config(Motor,  port4,           rightTopLift,  tmotorVex393HighSpeed_MC29, openLoop)
#pragma config(Motor,  port5,           leftTopLift,   tmotorVex393HighSpeed_MC29, openLoop)
#pragma config(Motor,  port6,           backLeft,      tmotorVex393HighSpeed_MC29, openLoop, reversed, driveLeft, encoderPort, dgtl5)
#pragma config(Motor,  port7,           backRight,     tmotorVex393HighSpeed_MC29, openLoop, driveRight, encoderPort, dgtl7)
#pragma config(Motor,  port8,           frontRight,    tmotorVex393HighSpeed_MC29, openLoop, reversed)
#pragma config(Motor,  port9,           frontLeft,     tmotorVex393HighSpeed_MC29, openLoop)

Digital ports 9 and 10 are jumper clips.

13

Ok, those ports are fine. Swap the encoders and see if the problem is tied to an encoder or a port.

14

Haha… it was the port.

But… only those two ports work for the encoder. Is there any way to fix the ports, or do we have to swap out the cortex?

15

Surely another port works for the encoders. Try moving one from the problem port to ports 1&2.