My purpose is to build a cheap quick-and-dirty "robot" using 2 electrical screwdrivers connected to the wheels and a smartphone to control them. I want to control each motor (forward/idle/reverse) using two phototransistors/photodiodes/photoresistor facing the smartphone screen.
My idea is to use the battery (3.6V) and motor of this electrical screwdriver http://www.ikea.com/us/en/catalog/products/60196103/ and somehow connect it to a smartphone screen to move it forward or backward or switch it off. The smartphone would show two squares on the screen each of them can be black or white. The phototransistors would be placed on the screen, detect the color and switch the motor (using other transistors or relays). For example if both squares are white the motor would go forward, if both are black backwards and if one is white and the other black the motor would be idle (without short-circuiting the battery).
I am not an electronics expert and I don't know what is a good detector for the light coming from a smartphone screen (infrared detectors won't work). I assume that the detector should be touching the screen and isolated from exterior light. I don't know which is a good switch for this kind of motor (3.6V), either a transistor or a relay.
I would like the solution to be simple and cheap, using the 3.6V battery of the motor. I want the motors to be either on or off depending on a light threshold (no linear response depending on the light).
UPDATE: This is the motor
When running without load (only the gears) the current I measured is 1.84A, but when it starts is higher (I think I saw more than 3A).
I found this specs that may be from the same motor: http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_380sh the name is nearly the same (there's an extra H) and the dimensions are the same.