Harold,
I'm not a scientist so whatever theory you heard from me is probably half-baked so you don't have to take me too seriously. I know I don't! :) I'm just an experimenter whenever I have too much time on my hands. Of course you can try anything. Just don't forget to have fun!
Few requirements necessary for dual-platter experiment: First, your active platter (DD table) must have speed adjustment or pitch control and the platter outside rim must be straight vertically, no sloped platters, in order for the tape or thread to ride on. Grooved platter is okay for thread or floss drive. If you have a sloped platter, like Technics, then you have to add a layer of platter or round disk thick enough for the tape to ride on and clamp it down. VHS is half inch tape so might be too tall so you can use you quarter inch tape from cassette or reel2reeel. If you do not have a DD table with speed adjustment, then your passive platter's diameter must match the active platter or vice versa so it's one to one ratio.
I tried different DD turntables as driver. They include Technics SL1200Mk2 (because of sloped platter must add flat platter on top). Suspened tables with suspensions defeated SL-1300Mk2, SL-1400Mk2, SL-1500M2 and the unsuspended SL-150Mk2, SP-15, SP25. I regret not able to try SP10Mk2 even though I had two at the time. Technics without extra platter on top: SL-M2, SL-M3 and they are excellent. Also JVC QL-F6, Pioneer PL-570, PL-550. All of them have speed or pitch control. Obviously the intrinsic sound quality of the DD table will transfer into the passive platter. Compare to the DD table itself, the tape drive always sounds slightly smoother. I guess the decoupling adds a layer of filtering or damping to the rotation. Also make sure the tables are not on soft footers. Make sure the active table is seated solidly so there's no movement to affect speed stability. NO suspended tables. My favorites are JVC QL-F6 with coreless motor, super smooth and the Technics SL-M2, essentially an SL1200Mk2 with heavier platter, muscular sound. If you can find or machine a flat platter (preferably same diameter as your passive platter) to add on top for the SP-15 with a narrow plinth, it is the most versatile as it can also play 78rpm and have pitch control and doesn't take up much space. Of course I'm sure there are many other models out that I haven't tried. I know the Luxman PD-277 allows for speed adjustment but I never owned one.
I also used two identical platters and motors gutted from two Pioneer PL-L1000 tables tape driving each other and also tried using idler wheel in between which made it an idler drive system. I should have tried wrapping one platter with a rubber band to rim drive each other! This experiment is the greatest revelation to me in terms of understanding drive system in influencing the sound. My own finding is that if all things are equal, the stylus does NOT care what is moving the platter, it can only "feel" the Torque, Compliance of the interface (belt, idler wheel, magnetism), and Motor behavior (cogging, smoothness, etc..). If those three elements are similar in different drive systems, their sound will be similar. Most tables vary so differently from each other in those 3 things that no wonder they all sound so different, not to mention dozens other sound changing things. That's why I say all three drive systems capable of making good sound so the execution and implementation are what matters.
I splice the VHS tape diagonally, much like magnetic tape splicing, to avoid bumps. I tape them down with scotch tape first on emulsion side just to hope them, and then use super glue to glue another piece of VHS or scotch tape on the shiny side. When done, peel off the tape on the emulsion side. And the scissor off the extra on the edges. Just have to experiment few times to get to optimum result. Remember to cut diagonally. Emulsion side or magnetic side is to face the platter, shiny side for adhesive facing out of the platter. VHS tape is designed to wrapped around a round metal drum anyway, just like a turntable platter so they work well. Other mylar tape will work too I am sure, just look online on those early Teres projects. Tension on the tape is important too but you have to play around with it to get the best result.
Happy experimenting!
