I was wondering about the feasibility of turning a car/robot, basically its just a circular platform with two wheels at east and west controlled each by a stepper motor. Two caster wheels north and south.
I am interested in only rotating 90 degrees about the center of the whole frame. Is this possible with just two stepper motors rotating each a specified number of steps such that they end up turning to the east or west. Also, since I am using stepper motors, there are not much to worry about acceleration and such. Therefore, might I need any type of feedback (e.g a digital compass?).
The short answer is a limited yes. With some calibration and fiddling you can measure how many steps it requires to turn 90 degrees. However, this is load specific, so it might respond differently if you put weight on the car, or if the floor material is different. This type of control will be very specific to that exact robot, and changing anything in the motor system will quite possibly change this calibration, including battery level.
However, with feedback, using say the digital compass you suggest, you could setup a control loop to monitor your rotation and have it respond properly. This would be the proper way to do this type of thing.