crain question?

[cosworth34677]

ok i want star a r/c crane. but after doing reseach i find the the boom is a little pass my skill level to make....... well at lease well so i was wondering if there is a such thing as a crawler crane with a teleoscopic boom? and are they pretty heavy? i wan to make this crane about four foot from tip to bottom. but i don't want to make something that is not scale looking .

any input ?