. Elsewhere Helen asked if I'd fitted the struts yet.
Gas Struts. What I think I now know
So have you got your gas struts on the designer now Kevin, we may consider doing ours eventually.
No. I'm still looking for information, or I was until this afternoon.
The information has been like pulling teeth. See next installment of gas struts saga.
Just needing a little more info then negotiating price.
What I want is an idiot proof kit. All brackets and spacers included, no self made bracketry.
I want to price up looking at normal and stainless struts because the units are outside.
Then I want to test fit, because I presume if I can get a large enough bulk buy discount lots of members might be interested.
Hence I want to test fit because I want to fault find first.
I'm going to re post this on the gas strut thread because I think it helps explain my thoughts.
Why we look to mount the struts at lesser angle than 450
N.B. I'm trying to say this with a minimum of maths but it is the nature of the beast.
The strut is not there to open the bed up from folded and unfolded. Indeed we want the bed inert at rest when folded or unfolded.
Otherwise we have to lock the bed down during transit and onto the bed support when extended.
If you think of a car you often have to start the "hatch" off to open or close. The strut assists through the rest of the arc of movement.
The strut pushes open in the direction in which it is aligned.
If you draw an imaginary circle about the hinge. Then think of the bed describing (Travelling) its arc of motion.
At any point through the beds semi circle of travel the most effective force is one applied at a tangent to the circle at that point.
If the strut is mounted at 45% i.e the spacing of the mountings are equidistant from the hinge then the force upwards is
Rover 25 strut=350Newton(N)=35Kg(force)2(No of struts) X 0.71 (Tan450
= 49.7Kg so that is an almost 50Kg upward force.
The angle derived from the drawing on the Dandy Owners Yahoo Group is about 260
but it's unclear as the measurements are the distances stepped off on the trailer and bed frame. Not from strut pivot centre to centre.
I have been told we might look down to as little as 150
Upward force on open or closed bed at 450 50Kg
It can be seen that the sharper the angle the less need we have to tie down the beds.
As we open or close the bed lots of factors start to vary.
The force is quoted as 350N but at is only at its instant of opening as it opens the pressure decreases in the strut.
So the moment the strut starts to open the pressure reduces reducing the force. At the same time the strut points increasingly vertical thus increasing the force pushing upwards.
Also as the bed rises the point of the centre of mass of the bed moves towards the hinge. This reduces. the effective mass of the bed.
The bed doesn't feel as heavy at vertical as when open or closed.
By raising the mounting point of the strut on the body the force from the strut outwards (In the horizontal plane) is always greater but the force upwards is always less.
To allow for this it was suggested to use a variable pressure 650N strut. Starting off at 650N and reducing the pressure gradually.
As I'm given to believe the original option of 350N worked then I might not bother with a variable pressure strut and just use the original strut.
So I've now found out the nature of the compromises or at least some of them. I'm not sure about reducing the angle further and increasing the pressure. To quote John:
Having given more thought to this, what is needed is a new approach. A cam action that holds the bed down when closed and down when opened, at the moment the bed tends to lift from the thrust of the strut, a simple cam action would solve this similar to what a car uses , there is a point in travel that holds the boot shut and a little lift from the user and it lifts open, that is the answer. It may prove a can of worms owning to the hinge not being engineered to suit the force that will be placed on it, or indeed the weld on the bed frames, but hey why not give it a go, mine works at the moment do I need to progress this to a higher level, in theory at least I will have a go, but I do not think a dandy in it present state could handle the forces generated without costly changes to the hinge and re-enforced welds to the bed sections, it may prove a bridge too far
To top it all I've just found a gas strut supplier about 5 miles down the road