Hello,

I was driving our FTC Robot today when i realized that the joystick controls were kind of funky. When I was driving the robot and the joysticks were pointed full forward, the robot went forward, but when i immediately moved the joysticks full backwards, the robot kept on going forward. When I let the joystick return to the center, the robot stops and then I am able to change directions.
Can someone please explain what could be going on.

Also, there is a function to make the robot not coast after the joystick value is at zero. It seems that our robot continues to coast. Could it be that
1. We're doing something wrong
2. The robot will still coast a little bit even though coasting is disabled?

Thankx.

Hi Sunny:
I've seen this happen as well on my bot and based on what I learned from the webinars, it's a simple fix (at least in my case). If you not installed motor encoders on your bot, make sure that you uncheck PIDControl on the motor setup page. PID control is making it continue to drive straight even though you've slammed it in reverse and it takes a while to catch up. However, if there aren't any encoders feeding back to the NXT then the motors know enough to stay in synch and it takes awhile to sync.

As for the other question, I think you want to look at the bFloatDuringInactiveMotorPWM variable in the Motors help (turn on expert mode). I'm not sure about this one, but take a look at it because it talks about coast vs brake.

Mannie

Was the problem that the motors never started going in reverse? Or was the problem that the motors seemed unresponsive and there was a noticeable delay before they started moving in reverse?

I have never seen the first problem, except with programming errors in user code. I'm not saying this is the cause in your case. Just that it might be.

The 12V motors are not as responsive as some other systems with smaller motors. You can notice a delay from when you've moved a joystick to when the motor has responded to the joystick command.

See the comment posted elsewehre about the "float during inactive PWM" variable. It controls whether power level of zero is "coast" or "brake".

1. Well, in our debugger window, we can actually see the joystick values *changing* so I'm guessing it must be something with the code. We'll double check everything to make sure.

2. I was not able to find other posts about float during inactive pmw, could someone provide a link?

We've got the same problem with out bot - we were using the 2 Joystick Drive sample program on our 'bot to do an initial testing of the controls and wiring to make sure we didn't blow anything up , and for some reason after we let off the controls the motors started to twitch in either direction and just move by themselves. I do know we've got the PWM enabled and our encoders are properly connected to our controllers.

I made sure I wasn't hitting either stick when the robot was twitching around, and the Y1/Y2 values in the Debug screen stayed at -0 as they normally do.

What would it be in that case?

I wrote the following sample program to demonstrate the poor performance of the motors.

I have the motors set up with encoders disabled.

The program will beep the NXT each second and attempt to change the motor speed at that
same moment. One motor attempts a complete reversal (100 to -100) while the other motor
simply stops (100 to 0).

When you run the program, there is a short lag between the time the beep is heard and the time
that the first motor actually changes direction. However, the second motor stops and starts at the
same time as the beep (no lag).

So it appears to be something with the motor controller having to change directions without stopping first. I find this quite frustrating and expect that this will make autonomous and operator-control much more difficult. Any suggestions?

#pragma config(Hubs, S1, HTMotor, HTServo, none, none)
#pragma config(Motor, mtr_S1_C1_1, motorD, tmotorNormal, openLoop)
#pragma config(Motor, mtr_S1_C1_2, motorE, tmotorNormal, openLoop)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

#include "JoystickDriver.c"

task main()
{
while (true)
{
PlaySound(soundShortBlip);
motor[motorD] = 100; // this motor should reverse direction after beep
motor[motorE] = 100; // this motor should start after beep
wait10Msec(100);
PlaySound(soundShortBlip);
motor[motorD] = -100; // this motor should reverse direction after beep
motor[motorE] = 0; // this motor should stop after beep
wait10Msec(100);
}
}

David Burnette
Tigard High School Robotics