stationary,stationary and revolve ,moving and revolve;Cross-section of boom and column is calculated scientifically. *According ... HCJ)*stucture:stationary , stationary and revolve, moving and revolve*Cross-section of boom and column is calculated scientifically. drooping of ... of ratchet6 structure, safe and reliable.*Boom end has cross-slides,which can be controlled thru manual pendant*control roller ...