i've been playing drums for about half a year. 3 months ago i bought a practice pad and tried doing double strokes. i dont know if im doing it correctly but when i compare it with the double stroke lessons, its the same. and i only spent fifteen minutes. i guess its just getting the rebounce and hitting it back again. its suppose to be easy. try not doing right right left left right right left left but just hitting one time and rebounce the 2nd one.
just my 0.02..
I wouldn't encourage you to depend on the rebound because you'd not be able to get much (if any!) rebound off toms that're tuned low or loose, for instance floor toms.
I don't mean to cast any doubt on your playing, but seeing how you've been practicing on a practice pad for 3 months, and have been playing for slightly more than half a year, I'd wager that you might be doing your double strokes wrongly. Double strokes and single strokes are the building blocks of your playing, so they're easy to pick up, but extremely difficult to master and to play them cleanly and smoothly
To TS, the best way to practice would be to play the double strokes at a very slow tempo, not accenting anything but keeping all the strokes even. Then slowly work up a good speed and mantain it, increasing speed slowly as you get used to the tempo. Once you can get the "feel" down, you can work on the accenting.
Thomas Lang's exercise for double strokes sound ridiculously simple, but its a biatch to pull off... simply put, accent your 2nd note. (r R l L) Dave Weckl's exercise is good if you're working with rebound and the natural movement of the stick, simply put, after your first hit, you move your wrist and hit the 2nd stroke as though you were playing with a German grip, hitting in a circular movement outwards. This allows for maximum rebound and maximum resonance from whatever drum you're hitting on.
Hope it helped
p/s: HAHA i'm not one to talk, not like i'm a double-stroke god lah.