Yeah going to use a bit of pythag but it gets more complicated because in order for the ram to be able to start the lift its going to need to be sat in a bit so its not hanging vertically down parallel to the hatch. Although even that distance isn't clear, do think larger is better so its not got such a big leverage but that also needs accomodating in the frame. Then need to know how high in the frame the whole assembly needs to sit. Hatch itself is massive so those rams may not even be up to the job, just what I had on the shelf. In fact based on my poor maths they'd be mounted 540mm from the hinge which still leaves loads of hatch unsupported. Not sure. On the phone just now I'll follow up the suggestions on a proper computer cheers.

Have RS still got the handy Ram/strut calculator on their website? Used to use it regularly for speccing struts for boat hatches. We always had multi positionable brackets top and bottom though to be sure.

How 'long' is the hatch?

I'd just fix it to the hatch and have a play

I was thinking about it and initial thought Pythagoras too, but because the ram itself will pivot I don't think it's that simple.

Wouldn't you use Pythagoras Theorem for this? The strut shouldn't ever be perpendicular to the hatch for it to work - however, whenever I've done stuff like this I've cheated and used CAD :0

Got a ram 410mm closed, 700mm open.

Need it to lift a hatch from zero to 90 degrees.

What is the method to calculate the placement of the ram?