CCV Medium Height Top - Page 3

mgmetalworks · 06-23-2015, 12:47 PM

Thanks for the feedback and pictures guys! I appreciate you taking the time to respond.

I'm not going to lie...it isn't my favorite design now that I see things a little better. I understand the reason to do it this way.... you get a wider bed if you don't have the lift arms in the way. Who wouldn't want more room, right? But that doesn't mean that there aren't some rather important considerations to keep in mind.

Even with a proper, equal-length-member scissor lift, the forces at the joints, especially at shallow angles are quite high. For example, to lift a 450lbs weight with a scissor lift with the members starting at 10 degrees from horizontal, it takes in the neighborhood of 2600lbs of actuator force (acting horizontally) to get started. It is almost double that at 5 deg...and more than double that at 2 deg... The point is, when the lift is starting out, there are some serious forces in play. SMB uses some massive springs to help counteract those forces. No matter what though, math is math, physics is physics... You can't defy gravity or rewrite physics so you just have to do what you can to mitigate risks.

And that's my criticism of this mechanism. In my opinion, you're introducing more risks with this design than you are mitigating anything. The welded joints and hardware being my main points of concern. I think the forces in the members and joints could be reduced, or at least more evenly distributed, with a different design (thus increasing your margin of safety). I also think the lift could be more efficient (less actuator travel for the same amount of lift...which translates to shorter deployment times). But you'd have to sacrifice the wider bed...

that's my 2 cents.

boywonder · 06-23-2015, 01:25 PM

I'm still not quite seeing how this works......

Are the scissor lift cross members laying on top of each other horizontally when the top is down? Are there four cross members? (2 sets of 2)?

Are there no lift assisting springs anywhere?

mgmetalworks · 06-23-2015, 01:33 PM

Quote:

Originally Posted by boywonder

I'm still not quite seeing how this works......

Are the scissor lift cross members laying on top of each other horizontally when the top is down? Are there four cross members? (2 sets of 2)?

Are there no lift assisting springs anywhere?

See post #3 for some images without the tent material in place.

http://www.expeditionportal.com/forum/t ... -VAN-MANIA

no lift assist. just actuators

1der · 06-23-2015, 06:14 PM

So looking at the design of this lift, the actuators are hard mounted to the uni-track at one end, the extending part is connected to the long strut which runs continuously to a pivoting mount where the 1 3/4" tube rotates. Where the actuator attaches to the long strut is where the lift occurs and this point is a metal roller assembly riding in the uni strut channel.

The way I see it, the force applied by the actuator is redirected at the start of lift, via a 15 degree resting deflection where the actuator is connected via a 3/8" diam. clevis pin to the 45 inch long strut. This is where the real heavy load is first applied when the lift starts - it has to get started at 15 degrees.

The high top gets a big jump on this leverage as it probably starts at 25 to 30 degrees.

I am trying to figure out what I can carry on top and what the loading is at the different points per side. Starting with an overestimated 300 pound load (the whole top by itself), being lifted from the 15 degree starting angle of leverage created by a 24 inch stroke actuator with pivot points of 32 inches and a solid strut with 45 inch pivot points, shared by the two actuators and lifting assemblies - what weight can I carry on top (assume evenly distributed) and still have the top raise up?

boywonder · 06-23-2015, 06:18 PM

Do the actuators have a load rating marked on them?

...and your 15 degree dimension in the sketch....do you mean 165 degrees??

What is the approximate vertical dimension of both the actuator and lift bar from the roof at their fixed ends?

1der · 06-23-2015, 06:27 PM

Yep, that should be 165 degrees, not 15.

CORRECTED FOR ACTUAL: As Measured from below the same plane: Far left of drawing - that pivot point is 3 inches down, and the point at the far right lower is 5 inches. The center joint is 3/4 inch down. This provides information to calculate the exact angle, right? If it helps the measurement along the horizontal is just shy of 76 inches.

The actuators are each rated at 1000 push and 800 pull.

calclimber · 06-23-2015, 06:51 PM

Looks great Ray

REF · 06-23-2015, 07:23 PM

...all I know is me push button top go up, me push other button top go down....

mgmetalworks · 06-23-2015, 08:45 PM

Quote:

Originally Posted by 1der

...what weight can I carry on top (assume evenly distributed) and still have the top raise up?

Why don't you ask the guy who designed and "engineered" it?

I mean, honestly... CCV is the only one who can answer that. He should be able to answer the question if he did his due diligence.

For reference, I work in a very safety conscious engineering environment where every design is reviewed and scrutinized by peers and factory safety teams. You HAVE to know your raw materials, hardware, fabrication methods and stresses/forces. I don't see pop-top lift mechanisms as any less important than the human-interfaced automation systems I design every day so I'm kind of going to be a stickler about the design and engineering of the system. There are pinch points, there are overhead weight hazards... You have to do your homework to keep people safe. I see the comments that his tops are great and that may be true of the fiberglass and fabric work but I just don't see greatness in the lift mechanism design, the welds, the hardware choices, etc.... That's just my opinion though.

For what its worth, I don't see greatness in SMB tops either but I'd feel more comfortable sleeping under their top vs a CCV top.

1der · 06-23-2015, 09:39 PM

Okay. You had asked for lots of details and had thrown out loads, etc.

SMB looks like a scissors lift to me with the entire roof load being run through two pivot point on each side that is hole drilled into tube walls. Then tension the whole rig with garage door springs that require a come-along to adjust. And springs under lots of tension in the top down state.

I did ask CCV, they said the mid size top has less lifting capability than the high top because of the starting geometry. Solar plus 50 lbs was what he advised. The high top has much more capacity to lift. The ultra low top has very little capacity because of the tighter geometry.

Mg- Seems from this thread, other threads here and elsewhere you have something against CCV, not sure if that is accurate or not, but it sure comes across to me that way.