Can anyone offer any advice on how I can manually control my bipolar stepper motor with an absolute encoder? Ive built a circuit using a L293D for an incremental encoder and it works great but the stepper loses its position very easily ie if you turn the encoder shaft rapidly, force the stepper to move or once powered down. Im thinking perhaps an absolute encoder on the stepper shaft for feedback and another for control (unless theres an easier way)? the turn ratio would be one turn encoder = one turn stepper, any advice would be much appreciated.
If your stepper is losing position, then you really need to rethink your requirements (speed of positioning) and the mechanical design (torque requirements). A properly designed stepper motor configuration won’t lose position and needs to have only its zero position calibrated. That can be done automatically upon power on and/or system initialization by driving the motor into a limit switch (a switch that signals the end of one range). You can also use a worm gear on the stepper, so that it won’t slip during power down.
If you have an encoder, you might as well use a DC motor to drive the shaft. It’ll be cheaper and stronger.
A stepper is useful when you want to avoid the cost and complexity of an encoder, and just run an open loop system. As Jim says, you want to make the stepper big enough that you don’t need to worry about slippage and stall, in that case.
I believe my setup would benefit more from a stepper than a dc motor…typical actuation range would be -20 to +20 degrees of stepper rotary movment. For simplicity and weight, the design does not use any gearing, basically the stepper turns a shaft ratio one to one This should not be too hard to achieve, basically turn a knob, stepper follows…knob to the 1 oclock postion=stepper to the 1 oclock position, power off then on, stepper positions itself exactly where knob is. An incremental encoders setup is not foolproof, if any exterior force bumps stepper one step then my setup fails, if power off then encoder moved = stepper does not take encoder knob position when powered back up.