This will give me the excuse to upgrade, I would still go the JRK’s (unless anyone can advise of better alternative) they really are easy to set up.
But
Would go to 12v worm drive motors (Motiondave knows the next best alternates).
Back to the build, I will snap some shots of my DIY Tactile Transducer; there is a tone of info on moding a subwoofer into a buttkicker style unit. I have to say it has added a whole new dimension to the rig. I will include the steps I used to complete, I used a cheap (Dicksmith) 100w active sub, I also modded the sub enclosure, looks like a sub but doubles hold my keyboard and soon will house my power supply (also the amp is still in place that drives the transducer).
Here is a shot, you can just see the transducer mounted to bottom of frame (I have since lowered the new 32’’ TV)