AutoCAD Inventor :: Scissor Jack Assembly Design 3

I am working on a design at the moment using Inventor 2012.It is a Scissor Jack. It has been designed to specific dimensions.Although I am making up the majority of them as I go along.Dim's spec's of which I must design to are as follows,

Max Height @ Open position = 250mm. (must be kept)
Min Height @ Closed position = 70mm. (must be kept)
Max width = 75mm. (must be kept)

The rest I have been taking from other designs of which I saw during my investigation.I have been modelling in such a way trying to adapt the open & closed position limitations with the use of constraints as my maximum & minimum limits. In doing so I have set a Drive Constraint so I can show the jack in its mechanical motion. I don't mind making any changes that will work to achieve completing it to act as it should. I believe there is still some tweaking to be done to it, but I feel the actual engineering design to be almost sound. There is an issue with the base via support arms. I cannot have the support arms moving past the floor level.

I will need to place location pins through the saddle & base connecting the arms. Finally If possible alter the gear teeth so that they interlink & coincide with each other. My screw rod also needs to work properly & turn also the nut needs to be localised in the correct position fixed on the screw rod at the end of the Side sleeve.