Simple (I hope) motor speed control.

I'm making an electronics project that requires using the outputs of an asynchronous 2x D-type flip flop binary counter to power a small (toy size) motor but it is not going so well. I planned to use two asynchronous flip flops to control the motors using a very simple digital-analogue converter where progressive clock pulses on the Q output of each flip flop would both be fed into a summing amplifier to give zero power, third, two thirds and full power (00,01,10,11).

From this I was going to use an inverting op-amp to further amplify the output to drive a DC motor. Is such a motor (even a small one) able to run directly from the output of the second amplifier? The input to each flip flop is about 2.3V and after amplification from the inverting amp tagged onto the end of the summing amplifier i get approximately 0V, 3V, 6V and 9V (simulated only). In practice it does not work.

I've tried using LM324s because I learnt in a lecture that they did not require a dual supply (only +ve and gnd) but that has not worked (I've got a pretty good idea that this is the case because I'm pretty sure a summing amplifier needs a negative supply because of the inverting nature but when I do supply it with a negative supply and ground it doesn't like it).

I've also tried with a 741 with limited success. Is it possible?

Many thanks for any answers and I hope I have provided enough information.