Please say pull when you mean pull, all this talk of _push_ing is really confusing. Nothing is pushing anything.
You have an RC car that is pulling a rope (at upto 150N), you wish to resist the motion of the RC car by
controlling the pull back on that same rope from some device.
If the car is always moving away (or stationary), no motor is needed. However controlling
a varying torque accurately is not easy - using a servomotor in torque mode is actually one
of the most straightforward approachs to doing this.
However I wonder if the real problem is not to control pull, but really to control position?
Thanks to everyone for all the answers. Sorry for not using the correct terms. The car is pulling, and the variable that i want to control is the position of the car (it moves at a fixed speed). I also thought about using a servomotor, but dont know how the actual configuration would be. By the way, the situation where the engine is fit for keeping the vehicle in a similar spot it isnt essential.
Again, thank you very much