Vex Cortex/ROBOTC Notes



Decided to use RobotC for initial installation and setup.  Downloaded the beta version ROBOTC 2.16 and followed instructions using the tether mode.

Installed the prolific serial driver from the RobotC web site.

Tried to download firmware and ran into this message:

Bootload failed: Controller failed to respond to autobaud sequence“,  repeatedly.  Could not solve it and gave up.


I decided to get the Cortex running using the EasyC 4 Cortex trial CD that came with the cortex.  I reinstalled the Prolific drivers from the Vex website (should be the same) and updated the firmware from the  Easy C 4 START menu  ( “C:\Documents and Settings\All Users\Application Data\Intelitek\IFI VEXnet Firmware Upgrade\usbhidio.exe) per instructions  for both to the controller and the Vex game pad using the tether USB connected to the PC.

I hooked a two wire motor up and enabled the OnLineWindow and finally got it to work.  The motor seemed to run uneven and the max speed was noticibly slower going in reverse than forward.  The deadzone appeared to be +_8 pwm units when driven with a two wire port and around +_10 pwm units when driven from a regular motor port with the motor adapter. The high pitched whine was about two octaves above middle C so I’m guessing about 1 khz hbridge pwm frequency unless it was a harmonic. Check with a scope someday.


I now could download programs ok and not sure what cured the problem.   I updated the firmware again per instructions and tried the operator controller.   With the 75mhz legacy controller, got the expected results.   The game joysticks did not work, except for channel 3.  Channel 2 gave a continuous -127 cmd.   Have yet to figure out the game joystick drivers

6/17/2010  ROBOTC VexNet Joystick Bug

Fixed the Joystick problem.  There is a known bug with RobotC only.

has my posted code fix.


No Auto Save

ROBOTC has no autosave after compile even if checked.  Also a known bug.

RoundUp Mentor Bot:

Built  a prototype High hanging robot that tries to do it all.  Has 38 inch reach with a dual bobcat type linear slides.  It has a plunger and a pincher which allow it to quickly pick up and deposit tubes and also take a few tubes off a goal if need be.  Uses 4 big motors (2 wire) on the lifter , 2 servos, and only 2 direct drive motors.  Might add two motors and increase speed.  Takes about 6 seconds to lift once the initial grip is established.


Arrrrrgh! @#%$^&* Fried the new cortex today.  Did nothing unusual.  The processor works ok,  the discretes are working…but all the pwm drives are toast.   I think the big motor current transients were too much for it.  This may be a design problem.  Will talk to Vex support and see what can be done to repair.

Update: 6/30  Talked with Vex support and there is a problem with ROBOTC beta 2.16 that can cause excessive currents to blow the PWM due to a pass through on startup.   So download the next ROBOTC  beta version and should fix the problem.   Vex will RMA and fix CORTEX under warranty(whew).

Update: 7/12/2010

Got the CORTEX back from Vex and loaded the new ROBOTC 2.20.1 that fixes the H-bridge problem that smoked it.   This new software also fixes the Vexnet Joystick bias problems.

Hooked up a quad encoder and ROBOTC routines output 360 counts per revolution rather than the usual 90 cnts per revolution we are used to with MPLAB.

Wrote a motor test routine that gives you the capability to select a motor port and generate a constant command by using the Vexnet Joystick buttons.   It also computes the speed if an encoder is hooked up.    This is used to check the static and dynamic friction commands and determine the adjustments necessary to balance motor speeds.    Kind of like a mini EasyC On-line window that uses the Vexnet joystick buttons.

Although the debugger works good , I still miss the printf function capability.  Still working on getting something similar.


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