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Old 06-04-2018, 08:14 PM   #21
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Is there an ideal length to the wood blocks or does it require experimentation? I took some links out of the main springs which helps with the extra weight of my K9 rack and solar panel but that first initial push is tough getting it up.
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Old 06-04-2018, 08:16 PM   #22
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Gas strut in place of the helper spring is interesting idea!

Similarly I wonder about fabbing an arrangement that would put some sort of high-torque linear actuator in place behind each helper spring. (Thus you could, at any time, adjust/vary the amount of "effective shim" behind each spring.)

I've also wondered about simply finding a slightly-longer spring of the same diameter/coil spec -- and swapping that in. (To create the same total effective length of shim+spring, but without any shim needed.) Longer spring could store more total compressed "boost" energy over a longer effective impulse stroke, might be felt as more effective assist.

EDIT: OR....what about sleeving a second smaller-diameter spring **inside** the helper spring....? Having to compress two springs together seems like it would certainly increase the total compressed force energy available....?
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Old 06-04-2018, 08:19 PM   #23
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So many problems that could be solved with one big piece of fiberglass.....

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Old 06-04-2018, 08:26 PM   #24
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Originally Posted by 86Scotty View Post
So many problems that could be solved with one big piece of fiberglass.....

LOL!!!
Winning thread comment of the month.


Seriously.....haha....
Duuuuuuuude....yep. You win with that one, lol....

(But....but....endlessly attempting to solve these simple-yet-complicated problems is what keeps so many of us off the streets/out of trouble, lol....)
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Old 06-04-2018, 09:15 PM   #25
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On another note, has anyone ever replaced the main or helper springs? Our SMB is 20years old, I wonder if the springs wear out, will it make a difference replacing them with new springs.

Currently I have around 150lbs up there and use a cargo bar to lift it.
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Old 06-05-2018, 07:21 AM   #26
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Originally Posted by MountainBikeRoamer View Post
Similarly I wonder about fabbing an arrangement that would put some sort of high-torque linear actuator in place behind each helper spring. (Thus you could, at any time, adjust/vary the amount of "effective shim" behind each spring.)

That's what an SMB powered top essentially is......they use linak brand linear actuators in place of the helper springs. I took a few pics of that setup when visiting Bmerritts roof install; I'll post them if I can find them.

BTW an automotive shock absorber would likely drop right in place of the helper springs, but the rebound damping is a problem. They are gas filled and can provide a long life with lots of force....perhaps a rebuildable shock...just remove the rebound shims (revalve).


Quote:
Originally Posted by MountainBikeRoamer View Post
I've also wondered about simply finding a slightly-longer spring of the same diameter/coil spec -- and swapping that in. (To create the same total effective length of shim+spring, but without any shim needed.) Longer spring could store more total compressed "boost" energy over a longer effective impulse stroke, might be felt as more effective assist.

I've thought about this too....not clear where to get the springs. The helpers in my van have clearly been cut down with a grinder, so they are likely long springs commonly used somewhere. The extension springs look very much like extension style garage door springs from a 70's vintage California garage door.


Increasing the spring length while keeping the same outer diameter and wire diameter will lower the spring rate, so the force will increase less per inch of travel.


This may or may not be desirable; I think preloading the helper springs against the lift mech is the way to go, but the plate that keeps them in the tray area needs to be beefed up (don't ask me how I know this.. ) since the compression force of the spring will be higher when the top is down.


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EDIT: OR....what about sleeving a second smaller-diameter spring **inside** the helper spring....? Having to compress two springs together seems like it would certainly increase the total compressed force energy available....?

This would certainly work....just add the two spring rates together...again that little plate holding the spring in is the weak link. Coincidentally, I've been playing with beefing up that hold-down arrangement on my van very recently.


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On another note, has anyone ever replaced the main or helper springs? Our SMB is 20years old, I wonder if the springs wear out, will it make a difference replacing them with new springs.

Properly designed springs may take a little set after a some use, but don't wear out/degrade much over time. They are designed operate in their "elastic" deformation region not "plastic" deformation region all the way to being fully compressed.



If they did, there would be a huge business of putting new springs in high mileage autos, or off road motorcycles. *of course lots of people here need springs but it's typically from adding a few thousand pounds of weight to their vans.
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Old 06-05-2018, 09:30 AM   #27
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Originally Posted by boywonder View Post
That's what an SMB powered top essentially is......they use linak brand linear actuators in place of the helper springs. I took a few pics of that setup when visiting Bmerritts roof install; I'll post them if I can find them.
Interesting! Had no idea that a pair of linear actuators was hidden out of sight in those locations for the power tops.

So I'll admit I'm curious now....what the heck is the vertical "shock-absorber-looking" ram cylinder that is visible on SMB power tops (and looks to act directly on the intersection of the two x-braces on each side)?

I always assumed that THAT was the power top lifting mechanism. It seems now that it probably is, also....? Yet another pair of linear actuators....to push the top fully up, once the horizontal linear actuators have done the initial lift that would be done by helper springs on a manual top? Whoa. How would those two sets of linear actuators get sync'd to act/function at the right moments in the penthouse roof's lifting path?

Yeah, as 86Scotty implied.....complicated solutions......dang....
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Old 06-05-2018, 10:22 AM   #28
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On another note, has anyone ever replaced the main or helper springs? Our SMB is 20years old, I wonder if the springs wear out, will it make a difference replacing them with new springs.

Currently I have around 150lbs up there and use a cargo bar to lift it.
NO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Old 06-05-2018, 11:12 AM   #29
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So I'll admit I'm curious now....what the heck is the vertical "shock-absorber-looking" ram cylinder that is visible on SMB power tops (and looks to act directly on the intersection of the two x-braces on each side)?

I think they are some sort of air damper support stiffener.....haven't looked at those too close..


Here is a pic of the electric actuators from Bmerritt's van..they replace the helper springs.


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Old 06-05-2018, 01:40 PM   #30
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Is there an ideal length to the wood blocks or does it require experimentation? I took some links out of the main springs which helps with the extra weight of my K9 rack and solar panel but that first initial push is tough getting it up.



I've found that after 3 links on the chains it gets sketchy for the main springs....for the helper springs...slide the helpers forward until they touch the crossbar and make some blocks to take up the space...in my van around 3" but it depends on the vintage of the springs and spring retaining plate.


You can make blocks longer so that the helpers are always compressed a little even with the top up, but at some point those retaining plates won't hold the compressed spring in place with the top down.
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