More Tank stuff to go with Tank Track 2in and related parts to build a RC or Robotic Tank. This is the idler sprocket that goes on the free spinning end of the track from drive sprocket. Uses 1/4"x3/8"x1/8" sealed ball bearings and 1/4" shaft with lock collar/spacer or 1/4" shoulder bolt. Use #4 sheet metal screws to attach hub to sprocket. This is what started it all. An idea for a track tensioner to make a RC tank like the Howe and Howe Rip Saw Tank, that would allow the track to stay in place with long travel suspension and not flop around or loose tension when you hit bumps. If you watch the rip saw tank it just takes the bumps like they are not even there. The tank is a stable go anywhere platform for anything mobile. Made the tensioner arm and shaft out of a long 1/4" bolt and some 1/2" flat steel with an arm welded to a lock collar and spring to keep tension on the track. Lock collar allows you to adjust track tension on bolt shaft. The spring has to be a stiff one, because when the tank backs up, the spring has to overcome the all of the weight of the tank trying to move in reverse. But you also have to give the track a little flex room to digest small pebbles that get in the track and sprockets in dirt. Tensioner shaft goes through 1/8" aluminum frame with some bushings (1/4"IDx3/8"ODx1/2" long with flange) I found at True Value. 3D printed support for bolt in middle of tank with 1/4" bearings. This was my second design. I placed the shaft further forward on the frame, and angled the arms back like other swing arms so the spring and tensioner would soften the first hit of anything the track has to go over at speed. Would love to see any other ideas for ways to do a track tensioner! Have fun! Added a hub cap for the idler sprocket. Use #2 screws, drill (2) holes in sprocket to hold hub cap.The hub will need raft and support. Sprocket will print without raft or support.