From what I gather, direct drive motors (DDM) are capable of bigger power. I suppose it's because their heavier nature allows them to withstand higher voltages and currents. They are also very quiet but they generate some drag due to the direct rotation of the rotor when the wheel wants to spins freely.
Geared motors allow the wheel to spin freely but are less powerful and noisy.
Which leaves me with no option. I don't want a direct drive motor which has all the advantages except that by choosing it, I'm adding quite a big drag. I heard someone say about his own bike: "no, you don't want to pedal this bike".
Because of the constant drag, pedalling would no longer contribute much to the range and speed and so IMO I would really classify such upgrade as basically making myself a moped, not an electric bicycle.
The problem with geared motors is the noise: I don't want everyone I pass by to notice that my bike gives out an unusual noise (like a swarm of bees) and eventually everyone would know that it's because of the motors. My goal is to create a something that only by a close look you would know.
I came up with couple of solutions which are very impractical, unless someone might help me make them a reality.
Solution 1: I want two somewhat weak direct drive motors, hoping that the drag would not be annoying as much if I decide to leave the battery at home for some short commute. They might be designed for 250W~24V, but say I would want to plug a much more powerful battery (like 48V) which would instantly give me much more power.
Problem with solution 1: I couldn't find any DD motors which on its own would have so few watts. I would like two of such, front & rear; 36 holes, disk-brakes.
Solution 2: Because I believe that the lack of freewheel on DD is just a poor design, I myself dared to sketch the design of the basic idea:
Problem with solution 2: I don't know how to get someone manufacture this for me.
If it were possible to have it built like this, I would wait and I'm sure I wouldn't be the only buyer.