My M416 - Yes, another one

[Kiddmen57]

Working on the spring design to support the lid and tent. This website explained the required force the easiest in my mind.
http://www.gecea.com/hatchlifters/gas-springs


Also, All gas spring sites mention keeping the piston pointed down for proper lubrication.

 

[Kiddmen57]

As I am going through this design, I am also learning a lot. The gas spring thing is a tough component to properly design. The way most of us have them set up means that the springs do not provide a constant force as lift for the lid. I found this website that tells you how to determine the force in each direction from your spring.

http://dev.physicslab.org/Document.aspx?doctype=3&filename=Dynamics_ForcesActingAngle.xml

Basically, My lid at 36 degrees open the way I have the spring mounted will result in an angle of the shock at 57.5*. Taking the sin (57.5*)x200(lbs force on the shock) nets you 168.67 lbs of lift for each spring (200lb spings). This results in 168.7x2= 335.34 lbs of lift. My lid weights 200lbs with the RTT, so I have an extra 135 lbs to overcome to shut the lid.

On the closed side of things, I have a net resultant angle of 18.6 degrees. Using the same calculation sin(18.6)x200 = 63.8 lbs of lift each. 63.8 x 2 = 127.6 lbs of lift. This means I have to lift up ~72.4 lbs to raise the lid. This is why a lot of lids are difficult to open at first, because the angle of the spring when closed pushed all the force laterally, not vertically. If I go to a 175lb spring, then I have less force to overcome pulling the lid closed, but I have even more weight to lift at opening. Also, because of this, at one angle through the opening range of the lid, it will become neutral (force of springs equals the weight of the lid etc).

Ideally the spring would travel equally on either side of vertical through its range. This requires pretty long stroke shocks, which have a compressed length of nearly 20". My trailer tub is not that tall.

Essentially, having the spring as close to vertical as possible is the best for minimizing the variances in lift force.

This design was my initial, but I will be changing it to locate the spring more vertical in the closed position.

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[Kiddmen57]

Here is the re-designed location. Centered on lid, and centered on tub. Theoretically, this should allow me to use my load/2 (200lbs/2 = 100lb) springs. I will likely choose just over this as hardware, weld beads, sleeping gear, etc are not factored in. I may use a 150lb strut on the taller side of the tent and a 100lb spring on the shorter side. That will provide just about the right load. I may also go with 2 150lb springs (unfortunately 125lb is not an option). The heavier springs will mean i have load to overcome closing the lid, but over time, the struts will lose some force.

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[VDBAZFJ]

Nice posts Klayton. This past weekend has me re-thinking my lid and I was thinking the shocks I have mounted in the wrong place. In my mind I was thinking I would be better off with the shocks mounted nearly vertical and now you post this and confirms what I was thinking. The way I have it works, but there is weight to overcome both up and down. Which probably isn't a bad thing but not as much as I have now.
Another guys had an off road trailer that has me also rethinking my rack for my RTT. I am gonna build something like he has. And I'm also going to redo the lid in aluminum for weight savings.
Another fail I had this weekend is both my latches that keep the lid closed...failed. Need to find a better solution.

 

[Kiddmen57]

Nice posts Klayton. This past weekend has me re-thinking my lid and I was thinking the shocks I have mounted in the wrong place. In my mind I was thinking I would be better off with the shocks mounted nearly vertical and now you post this and confirms what I was thinking. The way I have it works, but there is weight to overcome both up and down. Which probably isn't a bad thing but not as much as I have now.
Another guys had an off road trailer that has me also rethinking my rack for my RTT. I am gonna build something like he has. And I'm also going to redo the lid in aluminum for weight savings.
Another fail I had this weekend is both my latches that keep the lid closed...failed. Need to find a better solution.

Aaron,
I'm re-considering this approach. At the end of their stoke i need a spring force just over the final weight of the lid and all attachments. But if I have over that load rating in spring force at the closed position, then the lid will want to self open, which I don't see as desirable. Now I have to determine the correct angle to have a 150LB spring (300lbs total) equate to about 10-15 lbs less than load weight at close, and ~30 lbs over the load at open.

Sheesh. This is going to be interesting.


Which latches did you use, just so I don't source a similar design.

 

[Kiddmen57]

While I wait for my lid to be fabricated I started collecting other bits that I will need to finalize it.
I drew up some brackets that I will weld onto barrel hinges for the lid. I also designed a weld in bracket that matches the lip of the tub and the 45* bend. This will support the lower part of the hinge and on the opposite side the latches.

 

[armygreen]

Nice build! What RTT did you go with?

 

[Kiddmen57]

Thanks. I picked up a CVT Mt St Helens. Will direct mount it to the lid.

 

[armygreen]

Very nice. I have one waiting for me as well. CVT is making a lid for my trailer as well. Possibly picking them both up next week.
Did you get a refurbished one? Any issues offhand? Was it all you expected it to be? More pics of it would be nice!

 

[Kiddmen57]

Are you going steel or aluminum?

I was going to buy through the group buy at a decent price, but couldnt make the funds work out. After talking to Bobby he mentioned the refurb units. I set my expectations that I would get the equivalent of a used tent, with e 6month warranty, and for a great price. Thats pretty much what I got. Its not like some companies that completely refinish to new condition. They repaired it and sold it. Looks like mine had one of the pivot brackets at the roof break free. The headliner is cut away around one. I also lucked out and got a black one, so you may have better luck with the more common white ones. There are a few little things that bug me, nut for the price I got a good tent.

Overall I have a few comments. The shel is very thin, dont try to push it around by pulling on the edge, nor lean on the shell when closed, it flexes. The material side material is heavy and doesnt let in light. I usually get up at first light and watch the sunrise when camping, I slept til 8am my first and so far only night in this tent. It was comfortable enough for me. One thing i noticed was that the connection to the lift drive acme screw is plastic. Mine has slipped a couple times while operating, so i may need to replace those eventually. If I help it up the first 6 inches it seems to do a lot better. There is a lot of force on the lower pivot at 99-95% closed.

 

[armygreen]

PM Sent~

 

[AA1PR]

nice trailer

excellent improvements

 

[Kiddmen57]

I finally gave the OK to a fabricator to get my aluminum lid going. In the meantime I have to get a lot of things ready for it. I ordered my struts and other components from McMaster-Carr, made up some brackets and welded my barrel hinges to the custom brackets. I also decided to pull at the "bedliner" that was in the trailer. Luckily, the person who lined it didn't do a very good job and it came out in sheets. A couple more hours with the scraper and all of it will be gone.

I also ordered a sample pack of peel-n-stick weather strip from Steele rubber to determine which type would be best for the lid.

Hoping to have the lid and get it installed before the OJ open house at the end of the month. The fabricator didn't follow my prints the first time and ended up short overall. Now they are under pressure to get it finished in time for me to install it. Hoping it all works out.

Cutting some aluminum on the horizontal band saw. My buddies laser can't handle 1/2" aluminum.

De-lining

These will be the lower strut mount

They fit perfectly inside the handle/reflector dimensions

Lift off hinges welded to their brackets.

Samples!

 

[Kiddmen57]

I like this one best.

 

[Delmarva]

Very cool... when I get mine going, I'm coming over so you can help me with mine...