Thanks espeefan for the wonderful answer!!
I've recently bought the geared motor with 5rpm output speed on ebay (I didn't pay attention for the rpm output speed, my fault) It's very powerful but way too slow! :-( I'm planning to buy another one but unsure about the proper rpm output speed, that's why I asked for a suggestion? If u take a look the pics of my dump truck "construction equipment- rc adt dump truck" and let me know what rpm should I go for?
Thanks again!
Leon