Differential drive with steppers.

[Handmixer.com]

I am currently in the circuit design phase of building a differential drive motor that uses a NE555, a CMOS 4070 and a CMOS 4027, The latter two are conjugated to form a stepper translator circuit which recieves its order from the 555 in its astable mode, changing frequency with varying light on the LDR that is in place in the circuit. It will have two of these setups and will be a photovore/photophobe. Does anybody have any ideas to improve this setup?