Let's Make Robots!

Speed control with continuous rotation servo?

Hi everyone, I have a quick question regarding servos.

I've seen many similar posts around the internet but remain a bit confused. I have 2 standard, unmodified Hitec servos. I am using a Picaxe 28x1 to control these servos. I plan on using these servos as the motors that turn the wheels on my robot, and plan on modifying them for continuous rotation the most non-destructive way, without removing any circuitry. After modifications, I plan on simply sticking wheels to the servo horns and connecting my servos, coupled with appropriate resistors, to the digital output pins on my Picaxe.

The question however, is: Pretend I successfully modify and calibrate my servos, and after connecting them, if I write a line such as SERVO 2, 175, instead of turning to that position, it will instead start to spin in a certain direction at a certain speed. And then if I were to put SERVO 2, 160, will it continue to spin in the same direction but at a slightly slower speed? And then with a SERVO 2, 125, it will spin in the opposite direction at a speed faster than if I put SERVO 2, 140? So can I speed up and slow down my individual servos by simply changing the degrees of rotation? My final goal is to make the robot smoothly turn using the speed of the wheels, instead of turning them opposite directions to rotate my robot.

Sorry if my theory's way off, but don't worry about terminology and such. This isn't my first bot, just the first with this little twist... 

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You have got it right. For Picaxe 150 is theoretically the signal you send to make the servo stop. In practise you will have to experiment a bit. Also temperature can affect the servo control circuit so if you add a temperature sensor then you can compensate for temperature in your code.