If your trolley is sitting and spinning, you probably need to thoroughly oil the bearings and clean the wheels:
Note the axle oiling points.
Wheels before cleaning.
Note the thin shiny lines. This is where dirt has packed into the wheel surface, making a slippery "anti-traction tire".
See how much crud came off of just one wheel?
With all four wheels and the pickup rollers clean, your car should run like new! I used a polishing wheel to drive the unpowered axle for cleaning.
This applies, of course, to most powered locos, trolleys et cetera.
Hope this helps!
Mitch
