Sorry, there is no simple answer to that....
There is a difference between the 12 V= and RC motors. The 12 V= is more powerful and the motor drives the two axles directly by gears. The 12 V= Playmobil locomotives can be compared with the Stainz from LGB. For the Stainz 11 2-axle cars unloaded and 13 4-axle cars with bogies unloaded is the maximum on flat terrain. Keep in mind that 2-axle cars has a higher friction in the curves. The maximum gradient with no (0, zero) cars is 18%.
In practice 5 to 6 loaded cars on a 3% gradient is a neat train. You can improve that by reducing the friction from the cars:
— Replace the axles by axles with roller bearing and independent moving wheels (quite expensive, LGB 67403).
— Replace the R1 curves by more gentle curves.
— Replace the 2-axle cars by 4-axle cars with bogies (pity, Playmobil is making only one passenger car with bogies).
— Reduce the gradient to less than 3%.
The RC motor is a different story. The old RC motor (with the blue remote control) is powered by a 6 V= motor that drives only one axle direct with gears. The second axle is powered by coupling rods on the outside. In my opinion this is a weak solution with a lot of friction.
The last RC locomotive with the gray remote control is much better (5258), this locomotive is powered by two axles each with it's own (smaller) motor.
The maximum train lenght in practice is about 5 cars, but greatly depends on:
— The batteries used in the locomotive (4x2600 mAh NiMH gives more power than 4x1100 mAh NiCd).
And the same rules as the 12V= trains:
— Replace the axles by axles with roller bearing and independent moving wheels (quite expensive, LGB 67403).
— Replace the R1 curves by more gentle curves.
— Replace the 2-axle cars by 4-axle cars with bogies (pity, Playmobil is making only one passenger car with bogies).
— Reduce the gradient to less than 3%.
