I Jackshaft to a 3-speed hub and love it.
These pics give you an idea of how they work.
Is your Schwinn Badlands Mountain bike new?
Does it have the front shocks, 21 speed, and Shimano STX gears?
If the derailer and rear hub are in good shape you should be fine, but you won't get 21 gears and you will have some work to do.
First you will pull off the whole pedal crank system and front derailer system and controls, that whole thing is replaced with the one in the kit so you will only have the 7 gears on the rear.
That is not a bad thing, heck, a 3-speed hub is worth it.
Then, you will want to move the rear shifter control to the left, and get Sick Bikes dual pull brake lever when you order the kit.
When it's all said and done you have the throttle and single brake lever on the right, the clutch and gear shifter on the left.
I'll be happy to give you riding tips if you go that far, and I'm sure others like Pablo will as well.
Currently I am trying to finagle a way to use the new version of the SBP Jackshaft and the new NuVinci programmable fully automatic 64-speed hub* in my next Luxury ride.
That is a whole new can of worms however as I want to take it to extreme.
The goal is to put a 66cc 2010 Grubee with an SBP X-chamber on a sturdy bike frame with a perfectly programed automatic NuVinci hub and beat the pants off a 5-speed manual 125cc dirt bike in any kind of street race or other competition like pulling power, and be able to ride it legally on the road without a drivers license, tags, insurance, bla bla bla... And not even have to manually shift it.
Expensive sure, but you can't help but ponder how cool that would be ;-}
*fully automatic 64-speed hub
Actually you program it do whatever you want up to like 256 speeds, but that would be silly on a motorized bicycle, I am thinking a dozen would be just dandy but you have to read up on that hub to understand.