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I2C on the VEX Cortex

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The VEX Cortex is a nice platform made by VEX Robotics. It is supported in two programming environments, one of which is ROBOTC. Much to my dismay, the master firmware does not support I2C, which is why ROBOTC does not support it. I don’t really like it when someone tells me I can’t do something, so I went ahead and remedied the situation.

Mindsensor Magic Wand controlled by VEX CortexMotor MUX and Servo Controller controlled by VEX Cortex

I spent a few evenings writing and tinkering in ROBOTC to write my own bit-banged I2C implementation, which much to my surprise, worked very well.  First I tested it with the Mindsensors Magic Wand (above left) and later also with the Holit Data Systems Motor MUX and Mindsensors NXT Servo Controller (above right).  Jesse Flot from Robotics Academy was kind enough to send me some old VEX cables so I could splice two of them into an NXT cable for I2C. I will post a HOWTO for that at a later date.

As you can see in the right picture, I was already contemplating controlling the omniwheeled robot with the Motor MUX and so I did.

The robot is remote controlled via VEXnet over Wifi (which is a totally awesome feature which I wish the NXT had). The short video was taken at the RobotMC meeting of 19 March 2011, which happened to coincide with an information day for the technical university where we hold our meetings.

The coolest part about it is that my driver suite is almost completely transparently portable to the VEX Cortex platform once you switch out the NXT I2C subsystem functions for the Cortex specific ones. Some NXT dependencies do need to be removed and made more generic.  I intend to work on that in the next few weeks.  That would make a very wide range of new sensors available to the VEX Cortex platform.

Original article: [LINK]

Written by Xander Soldaat

March 19th, 2011 at 12:59 pm