There are 3 pairs of floorboards, and each one of them moves three times separately
 when moving backward (the load above does not move)
 At the time of forward movement all the floor boards move simultaneously
 (the load at the top moves)

・Large capacity（７０㎥）                            ・Unloading is quicker, but less beneficial 

・Can be used to unload in                                  because of the long travel time
    low ceiling areas                                           ・Unloading on unstable 
・Can be unloaded on uneven ground                  and uneven terrain is dangerous
・Easier to drive than a full trailer                  ・Impossible to unload from a low                                                                                            ceiling