By my friend's description, the chopper control on W8 class is very difficult to handle smoothly. There is a delay of about 1.5 second in response time and if you make power adjustment within that time, the first commands are ignored. If you gradually increase power as you would on a rheostat W class, on W8 class it would surge to the acceleration of about the third notch from standstill. If Restaurant cars have to be based on W8 class, that will be a great challenge for the drivers.
They just need to get the developer of the chopper controller to do a day or two riding as an observer on a tram to see how it's really operated and then some tuning parameters adjusted.
Sounds similar to an issue with the chopper conversions to the Adelaide H where an interlock between the brakes and the chopper would not engage power till the brake cylinder pressure was zero. This resulted in a very slow take off as power didn't apply till the brake air had fully bled off and then the car lurched when power was finally applied.
It probably doesn't help that human nature appears to be if it doesn't work in 1st notch, just apply more power
. By the time the brake interlock releases the controller is 2nd or 3rd notch already, so the system goes straight to that level of power from a standing start.
Some years ago I was in Paris and was wondering by the older TFS trams were shuddering on take off much of the time. So I made my way to the front and watched the drivers. They were driving the DC chopper control TFS trams the same way I've seen them driving Citadis - 'binary'. Off, full power, full brake. On the Citadis the computer moderates the driver inputs and if the driver just pushes the handle full forward, the computer just steps the power as required for a smooth take-off. Do that on the older TFS trams and the tram actually goes straight to full power and wheel spins for a moment till the wheel spin control kicks in, but there was no 'averaging like on the Citadis, so there was shuddering as the wheel spin intervened, stopped the spin, released, wheel started to spin again, so then kicked in again. Standing on the side of the road and watching one, I could actually see this happening (the start, spin, stop, start. spin) till the tram picked up some speed and got some grip.