I got just the trail-version of Algodoo, so i cannot save scenes with more than 100 Objects, and your tank has more than 500, sorry. But I tell you how to fix the problem with the track :
You just have to select all the hinges from the track/chain of your tank -> go to "Hinges..." -> check the box "Motor" -> set the "Motor speed" to 0 -> set the "Motor strength" to +inf -> check the box "Auto-brake" !!! Problem solved !