I have just recently opened up some Vex robot kits and downloaded RobotC. I built a recbot to spec and am trying to run simple motor functions on it. I have updated and downloaded firmware via USB with no errors. I have no problems compiling and downloading via USB, but when I start the program, the motors jerk once and do the same afterwards. I have downloaded several sample programs and had identical results. I'm hoping this is just my lack of knowledge and training. Any ideas? Here's one of the programs I tried.

#pragma config(Motor, port2, , tmotorNormal, openLoop)
#pragma config(Motor, port3, , tmotorNormal, openLoop)[/color]



task main()
{

motor[port2] = 127;


motor[port3] = 127;
wait10Msec(2000);

motor[port2] = 0;


motor[port3] = 0;
}

The quick jerk when the VEX starts up is unavoidable. What you can do, is insert a wait at the beginning of the program to give you time to correct the placement of the robot.

Thanks! That part is comforting at least. Any idea why the programs do not produce any results?

Are you using the newer VEX Cortex? If so, what type of motors are you using? If they're the two-wire motors, you have to use them with the Motor Controller 29's (2-3 wire converter) to use them in ports 2 and 3.

port 2 and 3 are both 3 wire motors.

Hi SCarleton,

I know that this may sound a bit inane, but have you checked that all wires are in the correct ports?
Have you tried different ports (changing both your code and hardware setup)?
Are you certain that the power switch is ON? (The USB will power the board but not the motors so even though it may seem ON, it is only halfway awake.) When the switch is on, battery is charged, and motors are not broken, you should hear a faint and seemingly random beeping-like noise from the motors.

Hope that this helps you,

Tried different ports/program; checked the battery; hear the motors hum; switched on. Still nothing

Sooooo.....I decided to bypass the programming and run the bot just from joystick controls. I set up a different cortex and synchronized it with a new controller. The motors only run for a short burst in either direction. They are not impeded. Do I need to do anything with the jumpers?

Hello SCarleton,

Can you paste your code here for us to take a look? Do you think it's possible that your motors may be damaged?

Make sure you're using motor, and not servo modules. Servos will run only for a short burst in either direction, but only have a ~120 (I think...) degree range.

Just a thought did you calibrate the joystick after loading the firmware? I had a similar problem where the motor only ran in one direction but a calibration cleared it up Kb