I went to hang my daughter's punching bag frame (meant to attach to the studs with lag screws) and the blasted studs are an infuriating 20 inches apart. The two sides of the frame are vertical, each side to be attaced with 3 lag screws. They are set 16" apart (of course).

So, one side of the frame is no problem, but what do I do with the other? I am not sure of the weight of the frame, but it will take a lot of stress as the bag is used. Will I have to devise some sort of frame that is screwed to the studs, or is it possible to use toggles on the side not screwed into the studs?

 

You may have to resort to spanning the 20" studs with 2x dimension lumber across where the manufacturer has located the attachment holes (make the spanner slightly longer than the 20" to prevent end split), then lagging the unit to the lumber. Of course it will set it out from the wall about 1 1/2", and she may require you to make the spanners "pretty", but you do need the support.

 

Or you can cut out a square of the drywall, place a spanner inside the wall (attaching it to the studs), then replace the drywall square
That would be more work but it could be made to look pretty seemless

Either way, you will need something spanning inbetween the 20" on center studs
There is no other fastening method that I can recommend for your needs