I will look into this a little more tomorrow, however, at first glance it looks like the motors you were given are standard RC servo’s so you should be able to hook up a motor controller (MC29) directly. The biggest problem you will have is that the power requirements of a VEX motor is significantly more than the parallax motor. For example, the spec for the parallax indicates a maximum of 200mA whereas a 393 uses 4.8A at stall, 24x more. So the first question is “are you allowed to use batteries other than the 9v” ?
We are allowed to use other batteries, but we have a $150 limit on the entire construction of the robot, excepting the microcontroller and a couple of basic circuit components (Power regulation components, a breadboard, a couple resistors, LEDs, and photoresistors). So, a VEX battery (for instance) would eat away significantly at our budget.
The max robot size is 8"x12"x10", so a lot smaller than a VEX robot, too.
So it looks pretty straightforward. The parallax motor is just a servo modified for continuous rotation, that’s essentially what the original VEX 3 wire motor was so you could use that directly anywhere you see the parallax motor. If you want to use a 269 than you also need the motor controller 29. The parallax motors are using 6V as the power source, you will get better performance with the vex motors using 7.2 (or 8.4) volts, perhaps 6 NimH AA batteries. The VEX 3000mAH battery can be bought from other places for about $18, look for RC car batteries. Hook up the VEX 3-wire motor or MC29 in the same way that parallax shows here. If you have any concerns then draw up a schematic and post here or send me a PM and I can take a look for you.
