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General Robot FAQ/Support

Here you can find general robot building questions. Click on the questions or topics to get more information.


General Building Questions:

• How do I connect the VEX 2-wire motors to the VEX PIC (Ports 1 – 8) or VEX Cortex (Ports 2 – 9)?

Robot Behavior

• After adding the Battery Expander pack, nothing is running autonomously, what do I do?


General Questions


How do I connect the VEX 2-wire motors to the VEX PIC (Ports 1 – 8) or VEX Cortex (Ports 2 – 9)?

Description of issue:

I have a VEX kit with 2-wire motors. Some of the building instructions show 3-wire motors being plugged directly into the micro-controller. Can I plug the 2-wire motors directly into the micro-controller?

Solution:

The 2-wire VEX motors cannot be plugged directly into any of the 3-wire motor ports, on the VEX PIC or the VEX Cortex. The 2-wire motors can be plugged into motor ports 1 and 10 on the VEX Cortex, which are 2-wire ports. For all other motor ports, you must use a VEX Motor Controller 29 to connect your micro-controller to the 2-wire motors.

vex_motorController29


ROBOTC Behaviors


After adding the Battery Expander pack, nothing is running autonomously, what do I do?

Description of issue:

We just received & tried the battery expander pack.  However when we tried to run the robot using the debugger competition switch & also the black $20 competition switch, nothing runs in autonomous.  It twitches when you hit autonomous twice on the debugger switch & when you flip the black competition switch to enable.  We even lifted the robot to make sure the wheels weren’t caught but our autonomous code doesn’t run.  Yet when we flip the black competition switch to user control everything runs as it should. Any idea what could be wrong?  We’re going to try to reconnect the motors directly to the prcessor tomorrow to see if it runs again to make sure it is not our code but it was running okay earlier.

Solution:

The most common problem with using the VEX Power Expander creeps in when people use the non-keyed PWM extension cables.  That lets them get the PWM cable black and white wires reversed.  The picture showing the interconnect wiring on the wiki site: http://www.vexforum.com/wiki/index.php/Power_Expander adds to the confusion.  Hopefully the picture will be fixed by the time you get to class.  For now, you can use the attached sketch, doc073.pdf, as a starting point.  The main point to remember is “When using Non-Keyed PWM Cables on the VEX Power Expander, the Gnd/Blk wire should be closest to the key slot on the STATUS and IN Ports, and it should be the furthest from the key slot on the OUT ports”.  Also connect the Power Expander IN ports to the VEX Microcontroller MOTOR ports and connect the Power Expander OUT ports to the new motors.


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