sorry to be late on that :)
mmm... It's going to be "hard" if you want to get something working with 3 different luxeons.
- Lux III & K2 : about 3.7V for white/blue/green/cyan, 2.85V for the other redish
- Lux V : about 6.8 V
In this case, the potentiometer / trimmer / adjustable multiturn resistor is strongly advise. Well, actually, I'm using that on ALL my designs, so great to tune the feed back and adapt it to how the hilt transmits vibrations etc.
To get the required value of the potentiometer, make the calculation using the lux V, since it has the biggest forward voltage.
For instance, my motor is doing great vibrations at .9V and takes 50 mA.
Lux V : (6.8 - .9) / 0.05 = 118 ohm
If you want to get a nice trimming span, take a 220 ohm adjustable resistor, preferably a multiturn trimmer to get an accurate selection of the speed of the motor. It will also work with a 1kohm adjustable resistor, I've done it too.
And then... you'll need a hole or something to get an access to the trimmer's screw to change the speed depending on the luxeon you're using.
Hope this helps !