1. VEX Troubleshooting

2. The Troubleshooting Process
Describe the problem:
What did you expect the robot to do?
What is the robot doing differently?

3. Potential Problem Areas
Power (Joystick & Robot Batteries)
Communication (VEXnet Connections)
Robot (Software/Hardware)

4. Check the Lights (on the robot & the joystick)
(red)
Main Battery = Dead (<5.5v) or CORTEX Off
(yellow)
Main Battery = Low (<6.5v)
(green)
Main Battery = Good
Solid
All Good: Both Joysticks connected
Solid + 1 Blink
All Good: Tx1 Joystick connected
Fast (red) [3]
Fault: Low Backup Battery (0v-8v)
(only works on the joystick when linked)
(no backup battery is only indicated if the competition cable is connected)
Blip (yellow)
Startup - looking for USB device
Fast (yellow)
Linking - Searching for VEXnet mate
Fast (green)
Linked
Slow (yellow)
Linked - Data quality reduced
Solid (green)
Tethered
Slow (red)
Fault: Lost Link - Searching for VEXnet mate
Robot LED only works on Joystick when Linked.
No Backup Battery only indicated if competition cable is connected.
Off
No Competition connection
Solid (green)
Driver
Fast (green)
Autonomous
Fast (yellow)
Disabled

5. Power Checklist
Check the joystick light
Check the robot light

6. Check the Joystick Light
Symptom: the joystick light is red
Solution: put fresh AA batteries in the joystick

7. (red)
Main Battery = Dead (<5.5v) or CORTEX Off
(yellow)
Main Battery = Low (<6.5v)
(green)
Main Battery = Good
Solid
All Good: Both Joysticks connected
Solid + 1 Blink
All Good: Tx1 Joystick connected
Fast (red) [3]
Fault: Low Backup Battery (0v-8v)
Check the Robot Light
Symptom: the robot light is red (solid or slow blink)
Solution: put a fresh main battery on the robot
Symptom: the robot light is red (fast blink)
Solution: change the backup battery

8. Connections Symptom: the VEXnet light stays red
Blip (yellow)
Startup - looking for USB device
Fast (yellow)
Linking - Searching for VEXnet mate
Fast (green)
Linked
Slow (yellow)
Linked - Data quality reduced
Solid (green)
Tethered
Slow (red)
Fault: Lost Link - Searching for VEXnet mate
Symptom: the VEXnet light stays red
Test: Connect with the USB A-A cable
Solutions: Try other VEXnet keys

9. Hardware & Software Check the wiring.
Use the online window to determine if you have a hardware or a software problem.

10. Check the Wiring Are the wires plugged in the correct ports?
Open the Project menu → Select the Controller Configuration
Are the wires plugged in the correct ports?

11. Drag the sliders to adjust motor speeds and servo positions.
Use the USB A-A cable to connect your robot to the computer.
Open the Tools menu → Select the On-Line Window → Click the Enable button
Test Hardware with Online Control If motors or servos don’t work properly it’s a hardware problem else it’s software.
Drag the sliders to adjust motor speeds and servo positions.
J. M. Gabrielse

12. If you can figure out the problem, you can fix it.
Hardware Checklist
lights
wiring
axles
screws
motors
If you can figure out the problem, you can fix it.

13. Check Axles Is a motor turning, but the axle isn’t?
Push the axle all the way in.
Replace clutches (if in use) if the axle still won’t turn.

14. Tighten Loose Screws Loose screws can cause friction (rubbing).
This can make the robot drive funny.
If they aren’t causing a problem now, they will later.

15. Motors & Servos Look Similar (Check to make sure they aren’t switched)
Servos won’t go all the way around. Motors will.
They are labeled on the back.

16. Check Motor Temperature (Are they warm/hot to the touch)
Solutions:
Add power by adding motors to help the overheating motors.
Reduce power consumption by making the robot lighter, balancing loads (use counterweights or rubber bands), or avoiding stalls while driving (don’t get into pushing matches).
The new two-wire motors have thermal breakers so they shut down when overheated. They don’t burn up, they just stop working for a little while.

17. If you can figure out the problem, you can fix it.
Software Checklist
check lights
check wiring
reload firmware
default program
your program
If you can figure out the problem, you can fix it.

18. Check Game Light Off No Competition connection Solid (green) Driver
Fast (green)
Autonomous
Fast (yellow)
Disabled

19. Reload Firmware Unplug the VEXnet key from the robot or joystick.
Use the USB-A to USB-A cable to connect directly to the computer.
Open the IFI VEXnet Firmware Upgrade utility, located in the easyC v4 for Cortex folder of the Start menu.
Click SEARCH
If that doesn’t work click BootLoad and then try again.
Click DOWNLOAD.
Repeat for both the robot and the joystick.

20. Reload the Program
After reloading the firmware the program needs to be reloaded.

21. Test Software with the Default Code
If the default code works fine then the problem is your program.
Check for endless loops.
If you have an endless loop in your autonomous function, you will never get to operator control.
Check to make sure you set everything the way you set it up in the controller configuration.

22. Resources
Cortex Joystick LED Codes (
VEXnet Troubleshooting Tips (
Vex Inventor’s Guide: ?·? - ?·?
Vex Forum (
search previous posts, someone else might have already
post your own question if someone hasn’t already asked it

23. Notes:
I figured out a way to rescue a Cortex controller that wouldn't connect to the firmware upgrade utility (it still doesn't work on my Windows 7 laptop).  I've only done three so far, and I had to try some of the steps multiple times.  However, this is what I think is going on. The problem: "USB Device Not Recognized" message from the computer, all red lights and then none on the Cortex The solution: Use the battery to power on the Cortex while holding in the config button. Then leave it on and then connect the USB A-A cable to the computer.    If I tried to do the config button trick with power from the USB cable, but the device wasn't in the right state when I connected it, so the computer couldn't recognize it. Notes: I also had a hard time downloading code onto the  rescued Cortex controllers.  It took several attempts before I was able to successfully load the code.  I certainly don't trust these controllers anymore.  Suggestions: Please continue to test your firmware upgrade utility with Windows 7.  It worked a couple times on my Windows 7 (Home Premium x64) laptop  and then stopped. I suspect USB driver issues.  However, EasyC works fine.  Also, I found that many teachers were confused by the firmware upgrade utility:  After pressing "Search" and they received a message telling them to press "Download" but it was grayed out.  Instead they had to first press "Bootload" and then press "Download".  Also, it would be nice if the firmware upgrade didn't say to contact Vex when the access ID number is lost. A message suggesting that pairing the cortex and the joystick would be more helpful.  If you really want to be contacted, put the phone number in the message. Another weird issue that I discovered is that sometimes you can't pair the joystick and cortex until some code is loaded (not always, just sometimes).  I don't know why.