technical question about pop-top canopy scissor lifts

Submitted: Wednesday, Sep 02, 2015 at 17:33

ThreadID: 130164 Views:7095 Replies:1 FollowUps:4

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LandCoaster

I am putting in scissor lifts on a poptop.
Problem is I dont have the original lifts and am getting conflicting measurements...

The mount bosses in the fiberglass poptop are 900mm wide, the height of the poptops sidewall is 560mm.
All the 900 wide replacement canopy lifts I have found, (Breha, Sunliner, China) have a lift of upto 685

but the 700mm wide canopy scissor lifts have a max height of upto 575

If i fit the 700x575's Ill have to build new bosses into the fiberglass poptop as the existing bosses are not long enough

If I fit the 900x865;s the apprehension of annoyance is when the canopy is fully erected it will be stressed slightly too tight and wont ever stop moving

My question is, has anyone fitted oversized canopy poptop scissor lifts and did it work out?

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Reply By: Ozhumvee - Wednesday, Sep 02, 2015 at 18:18

Wednesday, Sep 02, 2015 at 18:18

Yes and yes, basically the poptop sidewall needs to be under tension when up to keep it taut and stop it flapping in a breeze, so the 100 odd mm difference you have will be fine.
The tension is spread over the whole area of the sides and the fixings to both the top and the body of the van so it will cope ok.
The other thing to note when fitting the scissor lifts is to make sure they oppose each other on opposite sides.
I gather you have four, one on each side and one front and back.
so you need to have one side one pushing forward and the opposite side one rearwards and the front and rear the same, one in each direction.
The end ones also need to oppose the the side ones.
For example, if looking down from above from the rear the LH side one pushes forward, the front one pushes to the left, the RH side one pushes back and the back one pushes to the right, so that way the whole top isn't trying to be twisted and goes straight up.

AnswerID: 589897

Follow Up By: LandCoaster - Wednesday, Sep 02, 2015 at 19:54

Wednesday, Sep 02, 2015 at 19:54

hmmm, ok, so they twist... im really surprised about that but that may explain why on a lot of poptops ive seen have a very slight twist can be seen in a corner. I've often wondered why they couldnt get it spot-on.

Im really surprised about it 'cause i thought the scissor lifts where designed to lift up straight, using optimum materials to retain horizontal and vertical stoutness..

I have two scissor lifts, one for each side.

Ozhum, you mention "so that way the whole top isn't trying to be twisted and goes straight up"...
I get the directional set-up you described but i dont understand why. What's wrong with each side pushing in the same direction, they are only sliding along the rails with most of thier energy going up. Are you saying they have to be opposed because it would overstrain the sock one end

huge thanks for posting.....

FollowupID: 857888

Follow Up By: Member - Rosco from way back - Wednesday, Sep 02, 2015 at 20:43

Wednesday, Sep 02, 2015 at 20:43

If I read it correctly, you have a square/rectangle with a scissor lift in the middle of each side.

When erected most of the force will be vertical, however there will also be a horizontal force component. Unless these 4 forces are exactly equal, you could end up with a twist or diamond.

FollowupID: 857891

Follow Up By: Ozhumvee - Wednesday, Sep 02, 2015 at 21:18

Wednesday, Sep 02, 2015 at 21:18

Rosco is right, that was how it was explained to me when I built the poptop for the Oka by both the bods that made the vinyl skirt and caravans.
You can make the poptop so that it only has two scissor lifts, four and other combinations, they can also go the in same and opposing directions, all depends on weight, size and the height the top goes up.
The problem is that you have a large "flat" roof supported by the scissor lifts, the vinyl skirt is just there to keep the weather out it has virtually no structural affect other than sometimes limiting upward travel.
The scissors are not rigid as there is no precise mounting at either top or bottom and they can and do twist themselves, the spring tension is stopping a lot of the movement and that combined with the skirt remaining under tension at the point where the scissors can no longer lift due to the weight is what you want as the roof reaches its travel limit so that it doesn't move and creak due to vehicle movement or wind affect.
I've seen poptops where the are only two scissors, one on each side and they were slightly off centre to the top and each other which effectively cancelled the end/sideways push. It was also on a small very light van roof without solar and even interior lights on the roof section.
Landcoaster, from memory when I built my poptop the Breha scissors were good for just under 700mm lift and the bods that made the skirt suggested 500mm as a good height to make the skirt with those scissors.

FollowupID: 857895