Teardrops n Tiny Travel Trailers

working on it wrote: I've grown tired of using my twin hatch props (awkward to lift, assemble, vice-versa), also because the wife can't do it by herself-unaided-, and on every camp-out, I have to open/close it multiple times. I never could find a telescoping prop rod capable of handling the weight of my hatch (I thought it was only 48 lbs; I was wrong, it's more), or long enough (I open it to 105 degrees, for head clearance). I might use the linear actuator I've found,

18 Stroke 150lb Force Linear Actuator.jpg (38.7 KiB) Viewed 4583 times

to be mounted on an off-center inclined base (on the shelf), between the water jug holder-A/C drainpan and the extended-run fuel tank.

• I posted measurements, angles, and proposed mounting photos in my gallery,
• measurements
• where it will go
• but I never actually weighed the hatch at the 90 degree (horizontal) point, much less the actual "proposed" attachment location for the hatch-side clevis. Today, I weighed it at 90 degrees (couldn't do it at 105 degrees, the pole kept slipping); at the chosen attachment point (9.5" from hinge center, it exerted 120lbs of force). I had anticipated a force over 100 lbs, but wasn't surprised. That's why it's a bear to lift/then hold up, and raise 6" more/then insert prop rods in their holders. I moved the extended-run fuel tank over in its mount 1/2", and now have 2" clearance to mount an actuator and angled ramp.
• I figure that an 18" stroke/42" overall length/150 lb force actuator will get me in the ballpark. Design angles/bracket mounting spots/hatch clevis-load spreader will have to be tweaked as I go. I used a gas-spring online calculator to check the possibility of using a single gas-spring, instead, but figured it three ways from Sunday, and it showed me that any spring powerful enough to lift it, would be very difficult to compress back to it's closed position. I will also include a quick-detachable pin on the hatch-side clevis (with built-in "wiggle room", to pull the pin), just in case the actuator breaks or the power supply fails. The prop rod system will also remain, as a fail-safe backup.

• I looked at Rob's video, and Len's, and observed a fundamental difference in the hatch designs: Rob's opens about 45 degrees and Len's about 60-75 degrees from start. I'm opening mine 105 degrees. The added "degrees of difficulty" are the sticking point IMO. I've opened and closed my hatch hundreds of times, always wishing I could design a two-stage lift, the first for a normal 45-75 degree hatch opening, and the second stage for the "up and over" motion for the final push to 105 degrees. I've also opened and closed my HHR's hatch thousands of times (also noting its weakening over time, and lack of lift in cold weather!), and wished I had not made the trailer's hatch hinge sit directly over it, but rather at an offset, as is my HHR's. The final compromising part of my hatch design, is the relative lack of depth (front to rear) of the compartment, only 20". This measurement, and the fact that the shelf on which I have to mount the lift(s) is 28" from the ceiling, severely restrict my equipment choices.
• The numbers are all wrong for a gas spring. Unless I construct a curved slide-mount for the lift-side clevis, and start the lift at 40-45 degrees from horizontal. Still, the online calculator showed a "hand lift" force equivalent of 112 lbs at the breakover point. This much force would require limit straps at the apex, and to pull the hatch down, my wife would have to hang from it!(not a bad idea....). And Ctstaas's hatch with the curved bars: since my hatch is angular, I need a linear solution

  

  linear.GIF (9.58 KiB) Viewed 4429 times

  I tried to modify a "door check"

  

  door-check-lg.jpg (11.71 KiB) Viewed 4429 times

  to slide up and lock in place (I made a small model)...it would work up to almost 90 degrees, but I really need more lift. and the spring force needed to aid its lifting action would be a bear to overcome on closing. That's why I'm going to experiment with an electric actuator (I've always wanted to try one for years!). If all else fails, I'll redesign my rear section along the lines of a Grasshopper...as I initially mentioned as a design possibility, when I started my trailer. Thanks for the interest; I may find my usual inelegant solution (or not), but since I love Rube Goldberg-ish machinery,

  

  rube goldberg door.jpg (150.32 KiB) Viewed 4429 times

  that'll be just fine by me!

48Rob wrote:I wish I could explain it in engineer talk, but since I'm not, I can't...

I still believe you don't fully understand the way the gas springs operate, and how the correct, and precise mounting points and angles make them work together.

The gas springs can be made to open with the door, and in the process change their angles considerably, allowing the range of motion you are after.
It can take some serious study (or ask an engineer) but it can be made to work perfectly.

On my trailer, the spring starts at one angle, and ends at another.
When open, the spring is about an inch from being fully extended.
When it is being closed, it compresses to nearly the closed position, and then through the rest of the door travel (while the door is being closed) it begins to open again.

The big stumbling block most have when trying to visualize the operation is assuming that the spring, in order to work, must be positioned like the typical broomstick hatch support, that is, from the counter out toward the hatch handle.
The springs, to work properly, are installed the other direction.

Rob

48Rob wrote:Another try...

Measure the distance that your hatch pulls away from the trailer in an arc at the bottom, where you pull the handle to open it.
If you are after 110 degrees, with a 4' hatch it should be around 7 feet.
Now, from a point about 12 inches down from the hinge, measure the arc as you open the hatch.
That number should be around 16-18 inches.

Using a gas spring to open the hatch 16-18 inches will be a lot easier than several feet.

Perhaps this picture will help too;


Rob

• You are quite correct, Rob; I seem to have missed some point in the gas spring theory & operation masterclass. I'm relying on computer help, now. I was stuck on using the mid-galley shelf as a spring/actuator/prop rod mounting location, and ignored the obvious conclusion...it was too near the hatch door for proper articulation of a gas spring, and severely restrictive of even an actuator. I agree now, that the gas spring is the way to go (no power failures!), and the "magic" of the self-opening (as Tom described) are enticing. I also thought that the straight up hatch door was a drawback, as all the other examples shown are teardrop "curved" hatches. Then I saw that marine hatches, and flaps, are often opened with gas springs.
• After entering dimensions into some online calculators, I am getting consistent and repeatable results from them. I have now used three different gas spring calculators, and made actual confirming measurements of the hatch in question (including the exercise you outlined above...my measurements matched your conjectured ones), and find that I have to use a really long gas spring (1002-1328mm, depending on the manufacturer; the example shown in the attachment is a 1028mm spring, measured from clevis eye-to-eye) to do the job. I also found that if I use the suggested spring(s) (if I can find one... the ones suggested by the calculators are sold in Europe!), I will have to create a spring-base space under the shelf to accommodate the long spring.
• Here's a snip of the computer-generated design:

  

  gas spring computer designed layout.png (87.37 KiB) Viewed 4281 times

• If you note the location designated "A", it coincidentally matches the point I chose to mount the actuator clevis, that I calculated by triangulation. Also, the online calculator shows that the hatch requires an initial force of 5.1kg to start the opening curve, then becomes self-opening 11 degrees from closed. Conversely, the initial closing requires 6.5kg force to start down, then progressively more, up to 11.9kg, until the hatch self-closes at that same 11 degrees open location. Sorry about the metrics,,,I've grown tired of converting them back and forth for several days....

• Still at it. Re-measuring everything, moving items around in the "galley" to test possible mounting spots, and so on. Wish I had been able to attend LCG instead.... If I was there, I was going to closely inspect everyone's hatch springs (those that have them), measure actual angles, distances, and browbeat everyone for hard data on weights and spring force (surely someone has data; I don't think I'm the only frustrated - no degree, darn it - backyard engineer.
• I examined the only set of gas springs I had available, on my HHR, and measured angles and looked up spring force data: they are 23.25" extended, 14.75" compressed, 89 lbs force rating; hatch opens 90.5 degrees . I would've attempted to fit them into some sort of simulacrum on my trailer, just as a thought exercise (since I have no previous experience with them), but the attaching points are ball sockets and I have no way to connect them to the trailer hatch. I'm not even sure that they would even hold up my trailer hatch, since they are losing force over the past 5 years. I guess I could detach them, and at least weigh the HHR hatch door, to see what GM views as a proper lift rating for the HHR. Then, I would have proportions and weights, so I could have a basis for a real-world comparison.
• I only have generalities on past descriptions from the forum, no specifics, and I am hesitant to buy the wrong size/force gas spring online, only to have to exchange it afterwards if possible). However, I'm going to order a set of 36" extended-20.5" retracted 150 lb force springs, and test them. And brackets (including a set of curved ones, to allow the upper mounts to pivot inside the trailer, and for adjustment purposes).

  

  curved bracket.jpg (22.57 KiB) Viewed 4200 times

• I have established two possible mounting locations (on top of the shelf!): 1.) next to my current hatch props (not going to remove them, a back-up never hurts), and 2.) if I find that two 150 lb springs are too much, and one will work instead, then I'll use the center mount position (where I was going to place the linear actuator). Then I'll have a spare, or find another use for it. I'll order the set today, and get them by next weekend. Then, I can actually find out from hands-on-experience, whether the data I've gathered, and plugged into calculators is accurate and feasible, or the way experienced builders on the forum accomplish it, by just fitting them to work is the best way to do it. By the way, some of the online calculators seem to disagree with each other, either by my error in data entry, or some quirk in their programming. But not by much.

• Went ahead and ordered a pair of gas springs, as I said I would. I'm still not sure if they'll be too strong as a pair or too weak used as a single, so we'll see. I have been researching all the threads on TnTTT for installation hints (there are three running currently) and posted on noseoil's build thread about my wonderment concerning the lack of data on the hatch springs they used (much like very few-proportionately- have weight and balance data to share on their trailers). I know that each home build is unique, no one even follows bought plans exactly, and each trailer (and builder) has quirks. Materials are different from varying sources, and builders have vaying abilities, so none will ever be identical. And when one builds a trailer very dissimilar to the norm, then basically, he's pioneering a new trail(er). As in my case. Of course, many trailbreakers get eaten by the bear around the bend.... Thanks to the people trying to educate me in what must seem a simple? task, attaching a hatch lift, but, as I have stated, I've been so far from the norm for so long on this trailer build of mine, I will always have a series of design quirks to complicate the matter.
• Noseoil just (kindly) posted a set of detailed instructions to determine the ideal mounting points for the hatch lift, and they are well thought out, and will work great, especially on a curved hatch design. But, I'm already committed to a plan of action, using scale models (dowels cut to length), triangulation, and always allowing for some wiggle room in my measurements (things are often not as advertised; I allow for variations). And I paid my money, I'll take my chances (as paraphrased from Twain, Huxley, et al...)

  

  basic spring layout scheme 10-26-14.jpg (115.78 KiB) Viewed 4042 times

noseoil wrote:I'm looking at your diagram & it looks good to me. The layout is clear & simple and you did your weight assessment. Like that you actually weighed the hatch at the point you will be using for the pivot, what a novel idea to get it right! It should be better than new once things are installed. Just make sure you use some hefty fasteners, which are well set with T nuts or inserts to take the loading they will have to deal with for mounting. Wood screws or sheet metal screws won't hold up over time on this one.

Curious about the weight of the hatch in the open position at the outer-most edge. If you put a scale under it with a prop resting on it and placed at the "bottom" of the hatch, what is the actual weight compared to the strut location you have selected? tim

• Everyplace that I drilled thru the 3/4" plywood (sides, roof, floor, and hatch) is sealed with PL adhesive, and I used stainless 1/4"-20 carriage bolts, except for special "security head bolts". I'll use the same on the gas spring mounts. I haven't had any problems with them pulling thru or loosening, since they are glued in place, and have acorns (glued also), nylocks, or double-nuts holding them tight.
• I don't have the mounting brackets yet, and can't tell from the photos if they will need reinforcing plates or whatever, to hold them firmly on each end. The 3/4" wood shouldn't need backing-up, but I will use some extra metal or wood to spread the force anyway.
• I never weighed the opened (at 90 degrees) hatch at the outer-most edge, because I knew that wouldn't ever figure in my calculations. But, if I remember correctly, the weight at dead-center was 40-60 lbs (not sure, I was just fabricating a hold-up rod for the accurate measurement at the proposed mtg. point, 9.5-10" from the hinge). I'll make a set of measurements/weights at distance from hinge next weekend. I'm also sure that if I had measured at 4-5" from the hinge, the force would probably double.