Micro Controller Problem

Our Vex Robot can’t be operated as the manual says. for now, the front wheels move in the opposite way as we commanded. We’d appreciate if you would give us your advice.

We are using 4 motors for the bot. We configured the bot as the manual says, we used motor slot 2,3,7,8 and jumper slot 15 on the micro controller.

With the tank-style operation mode (#23), all motors except motor slot 7 moves to opposite direction. When we sent the signal to go forward, it went backwards.

With the arcade style operation mode (#12), front wheels in slot 2,3 moves to opposite direction, but, the back wheels in slot 7,8 works fine.

We connected the controller directly to the micro controller using the phone line, the results described above did not change, means, I guess the receiver is working correctly.

We changed the motor, but, the result did not change. We also tested the speed controller for the high strength motors, the results were the same so the speed controls working fine as well.

As a result, we are suspecting the micro controller on the bot has been broken, or there is some communication issue in the device, or programmed and need to be reset/initialized or etc…

We’d appreciate any of your advice to solve the issue, which is front wheels moves opposite direction as we commanded.

We tried to do jumper 15, but wheels 1,2, and 4 were going the opposite direction. We tried motor 4 going into slot 8, motor 1 going into slot 2, and motor 2 going into slot 3. We later tried jumper 16 and wheels 1 and 2 were still going opposite directions.


Dear DSumo,

I assume you are using the 276-2153 75 MHz Transmitter/Receiver and 276-2170 PIC Microcontroller. If the Motor is attached directly to a wheel, the wheel will spin in one direction. If there are two gears between the motor and wheel, the wheel spins in the opposite direction.

Here are three ways to fix your reversing problem.

The six channels on the Transmitter can be configured for normal or reverse operation. Refer to the Inventor’s Guide Appendix E as referenced at http://www.vexrobotics.com/wiki/index.php/VEX_75MHz_Crystal_Radios.

If you are using 2-wire motors and the 276-2193 Motor Controller, you can also independently reverse motor direction by connecting the red Controller wire to black motor wire instead of red-to-red and black-to-black.

Finally, if the PIC Microcontroller has been programmed with custom code, then how the motors respond to Joystick input may be unknown. To return the PIC back to factory code, you will need a 276-2186 Programming Hardware kit and files described at http://www.vexrobotics.com/wiki/PIC_Microcontroller_Downloads.

Thanks for your suggestions!We will surely use them for our robot. Again, thanks!