These PWM are inexpensive on the bay: http://www.ebay.com/itm/6V-90V...?hash=item41b7e6a8ef and they can be mounted in a project box. I'm using one for light dimming. Works great.
I have five bump & go trolleys running and am well a where of the need to trim the voltage for each trolley to attain the best speed and reduce the "smack". Two of the trolleys are trimmed off separate PW ZW channels. The other three are trimmed via separate variable TIU channels fed by a Z1000. My trolley runs are short. Two are each about 10 feet, one with dual reversing loops. The other three are really short, about 4 feet. Unfortunately, I can't use MTH trolleys (better low speed control) on the really short runs since the trolleys are too long.
