My Dynabar V-7, has a FULL 12 inches of travel, (305mm).
It has a Nice Soft frame that my belly Likes !
It has a Big Hook to attach my chicken loop to.
It's got a Pulley to make the travel Really SMOO00oooth !!
And 321 kiteboarding will sell Ya the V-7 for $87.99 ---
Hardly worth the effort to make your own ; "Especially", if Ya Screw-Up
Ya Could Die !!http://www.321kiteboarding.com/Dynabar-V7.html