Triggering vehicle motors

I'm trying to get my vehicle's angular motor to respond to something other than keystroke input.

From a standstill this works:

control(key id, integer level, integer edge) {
    if(level & (CONTROL_LEFT|CONTROL_ROT_LEFT)) {
        llSetVehicleVectorParam(VEHICLE_ANGULAR_MOTOR_DIRECTION,<PI*4,0.0,PI*4>);
    }   
}

As does this:

touch(integer total_number) {
    llSetVehicleVectorParam(VEHICLE_ANGULAR_MOTOR_DIRECTION,<PI*4,0.0,PI*4>);
}

However, this does not:

listen(integer channel, string name, key id, string message) {        

    if(message == "LEFT") {
        llSetVehicleVectorParam(VEHICLE_ANGULAR_MOTOR_DIRECTION,<PI*4,0.0,PI*4>);
    }
}

Nor does this:

timer() {
    llSetVehicleVectorParam(VEHICLE_ANGULAR_MOTOR_DIRECTION,<PI*4,0.0,PI*4>);
}

The last two examples *do* work if the vehicle is already moving, but the first two examples work from a standstill as well. Does anyone have any insight into this? Thanks so much

Certain events cause a slight movement in an object/avatar for no real reason. This can let things like the motors overcome friction. Solution, a slight bump up with llApplyImpulse, very small, just enough to make it twitch, which emulates that same small movement. it's a hack, but it's SL.

The first two events are called repeatedly while the key or mouse button is pressed, the third one (listen) is called only once, and the timer depends on the rate. Sounds like the last two are not frequent enough to overcome friction, so check your friction/efficiency numbers.
~Boss

Thanks guys! I'll give it a go.

Boss, I thought about that too - the touch and control events buffer multiple "hits". I tried this to emulate that:

listen(integer channel, string name, key id, string message) {

    if(message == "LEFT") { 

        integer i;

        while (i < 10) {
            llSetVehicleVectorParam(VEHICLE_ANGULAR_MOTOR_DIRE  CTION,<PI*4,0.0,PI*4>);
            i += 1;
        } 
    } 
} 

But that seemed to make no difference - no movement. As Aaron suggested, it looks like the object must have *some* small bit of movement already before the motors respond to certain programmatic stimulus.