If you saw the video in the previous post you'll have seen the segment where the old AHM trolley and trailer got stuck in the Neville Park Loop. The curves have a 7" radius - which is ok for single-car operations with the fleet - but cause a problem when the trolley is pulling a trailer. I think the problem is with the coupler - which is just a short metal bar that pivots on posts moulded on each trolley. The bar isn't right for such tight radius track. I need to replace it with something that has more free-play so the trucks aren't forced into odd angles against the rail during turns. An interesting problem.