Ultra-Light External Frame Pack

[D G]

Bill,

You might check out this site:

http://www.sheldonbrown.com/rinard/

In the upper left corner look at the
“Carbon Q&A” article and the “How I made a Carbon Fiber Frame in my Garage” articles.

There is some good general info there about how to layup the carbon fiber. The application is bicycles, but of course the concepts are applicable to lots of other projects.

You pack frame project is very interesting. I myself have been experimenting with framed packs (even for light loads under 15 lbs) after using frameless packs and I think they are a valid option with benefits even for light loads.

Cheers
Dan

[archeopteryx .]

For making something like the plywood pack frame you could use cut and fold construction with prefabricated sandwich panels. This would eliminate the need for a mold. To get the weight down to BPL standards you’d probably have to cut a lot of holes though. Here’s a pdf that explains the procedure on page 10 of 16. Rather than just gluing the joint as they show in the diagram you can also reinforce it with some glue soaked cloth. If you find a machine shop that cuts these they might be able to give you some scraps for experimentation.

[BPL Subscriber]

If anyone feels the need for a private group please speak up and we’ll see what we can do.

Wow, Bill, this is great. It’s wonderful that you’ve set off in this direction. I think improving the external frame backpack may be the “lowest-hanging fruit” of longer-distance hiking equipment development.

I’d suggest thinking “triangulation” in developing a frame instead of “ladder”. It’s easier to get strength with less materials with triangulation and molded materials allow the pieces to be arched back out of the way of physiological elements that they might interfere with if they were straight tubes. Also, it might make sense once due to the same capability for producing arched structures to bring the vertical side pieces of the frame at least somewhat around towards the front of the body, at least in spots, and then blending way forward into the wings…think of it more as molding a sheet around the back of your torso, then removing the parts that aren’t triangulated…of course in the actual layup, there’s no need to waste materials by actually cutting the holes.

As to the points of contact, with a better fit from molding than other methods allow, less padding may be needed. Bill has some experience with this with his thermoplastic webbing so will probably have some important input on that. I wonder if padding might be done away with entirely, in fact.

But for the sake of other people being able to carry the pack, and for fewer molding steps at least in an early attempt, it might be sensible to develop a universal mounting setup that could allow either padded fabric or harder but more shapely body contact points to be hung from the frame. This universality might come at some cost in closeness to the body, though.

The closest way, with the least arm-swing interference, might be to bring the frame wings very close to where they need to be for the individual the pack is tailored to at the hips, with molded contact pads with whatever the optimal pad thickness might be. Of course, the closer one gets to hard contact points, the more the pack will move with the body, and it might be desirable to build motion back in somewhere to allow for fluid movement.

That designed in flex would be an interesting project of some size in itself but it may be productive to imagine you’re replacing the flexibility of the spinal column and hips in connecting the top and bottom body-connection points of the pack.

[Dale Wambaugh]

Interesting stuff, but I’m thinking of a shaped CF sheet that is 1/16″-1/8″ thick with a couple large holes– as I said, a squared off 8 with the sides curved around to make a space for the back bands to stretch across and mount the wings near the bottom for the waist belt to swing from. The top, center and bottom cross-bars of the 8 might need some arched half-tube girders to stiffen them up a bit as most of the stress would be the back bands trying to collapse the frame– rolling it up so to speak. The pack load should be pulling backwards from the top and hopefully, pushing down towards the waist band, vectoring towards your hips. This carbon fiber pack board would be a broad shallow C shape with the legs of the C being 3″-4″ deep. Additional strength could be added by arching the broad section of the back panel, creating some resistance against the stress of the back bands.

This is the low tech version. With more carbon fiber construction technology, a ladder frame could be made with the tubes being elliptical in cross section, just like the bike frame I saw. The bottom ends of the tubes would be like a cuved L or J to form the waist band supports. The cross bars could be slightly arched. This would allow conventional shoulder strap and pack bag mounting methods to be used. Torso adjustment could be the usual pin-and-stacked-spacer arrangement. It would look very high tech and be easiliy marketed with a decent silnylon pack bag and simple, Spartan shoulder straps and waist band. I would aim for 2 pounds all up.

[BPL Subscriber]

I’m not sure where the arched half-tube girders you mention would run, but I agree that a lot of the forces try to flex the pack front to back. This might be dealt with in part by running longitudinal raised ribs from top to bottom near the left and right edges of the frame, placed so as not to interfere much with the packbag or body. This would add a lot of stiffness to a plate-like frame. The more arch there is in the frame, to a point, the more this flex issue tends to take care of itself, but there are obvious limits. Also, the fact of the wings extending forward can be used, by bracing them somewhat up along the pack (think triangular wing with the narrow point towards the belt buckle) to increase the longitudinal stiffness of the frame in the front-back dimension.

The hips have a complex set of motions, and they run somewhat counter to the shoulders. This puts vertical loads into a pack that would, for illustration, tend to collapse a simple rectangular frame into a trapezoid. There is also a rotational moment around the vertical axis of the pack, with force translations on many vectors through those extremes. I’d think any designed-in motion around the hips and shoulders would tend to be desired not in the front-back frame flex direction but in the rotation about the vertical axis and one-hip-contralateral-shoulder-up-other-down modes.

The lowest-material way to cut the tendency of a rectangle to collapse into a trapezoid is to connect the opposite corners with a rigid element, a payoff of triangulation. Because we use something related to a flat plane for a frame in order to make room for a packbag, there are some constraints on containing the rotary forces (arches in the plane would help), but I’m thinking that triangulation from the lower corners to some central point or points along the lumbar region would be the lowest-material way. An idea of the lines of stress might be had by putting a fold-prone semi-resilient material on a torso and watching where folds tend to point when walking. My guess is you’d tend to see them running in a fan shape from the hips into the lumbar much as the muscles in that region do. Adding a rib onto a basically planar frame along those lines of force would seem to increase strength and stiffness in those areas as well…I think I’m probably talking about something similar to Dale’s girders here.

Laying up hollow ellipsoidal tubes like a balloony composite bicycle frame would garner a lot of strength from the tubular structure in a material-efficient way by enclosing more space, but seems like it would be a fair amount of extra work and it still might be desirable to flatten the tubes in certain areas, e.g., to get the pack frame closer to the back or to provide more arm clearance. Also, I don’t think we’d be twisting most of our tubes very much as those on a bicycle might be twisted, and I think offhand that that twisting force is why the bicycle frame members majorly benefit from enclosing a space with a skin. Aircraft wings, on the other hand, tend to have spars to take the levering force of the wings, rather than trying to get most of the strength in that direction out of skin strength. which would require more material. So if your forces are largest in a plane, a rib in line with the force can be the lowest-material way.

[BPL Subscriber]

Prefab panels with holes cut would be a fast and strong way I would think. Double-skinning a ribbed structure is the next step up in strength once you have ribs on a plane…put another plane parallel to the first one, and it will strengthen the ribs and the points of greatest available leverage for the thickness right in the direction you’d want to reinforce the ribs to resist folding the plane, with minimal material. The hex-cell structure picks up additional strength over the skins alone to resist deformation of the rectangular shape relative to a square cell structure running vertically and horizontally by aligning planes with the lines of force. But for a backpack, the hex panel would also be thicker than might be ideal in some regions, and not as thick as would be ideal in others, and of course doesn’t form as closely to the body or pick up the arch strength, and it has pretty uniform strength in resisting bending of the plane while backpack the big need for stiffness in a backpack frame may be to resist front to back folding of the fram, but it sure does provide a quick stiff framework to build something around.

In a more idealized structure that one might build with the extra effort after going past building around hexcore, lessons can still be learned from the hexcore: double skinning the ribs in semi-planar areas of great stress is a great way to pick up strength.

[Bill Fornshell]

Dale, I know that old Army frame. It was used or one very much like it in Vietnam to carry mortar rounds when away from a base camp.

Daniel, I looked at the “how to make bike frames site”, interesting and more or less low tech of carbon fiber working. I have used a blue foam material for molds with my Thermo Plastic material. It is easy to work with.

archeopteryx, I looked at the material you referenced. I have used some core type material. You can buy it with several types of outer material. I have some samples with a thin aluminum outer cover. It is very strong and sort of light. I used some as a frame sheet for three versions of a frame I made once. Some is planned as the “deck” material for the Titanium snowshoes I now am now building.

BobOne, I need to read and re-read your last three posts and do some drawing and try to understand visually what you are talking about. I think I need a picture of sorts to see where you are heading with the “triangulation” idea. I think it is just more of a vocabulary issue. I have some Hospital Lab tests and a chest x ray this morning and will print out the last bunch of posts and take them to mull over if I have to wait for my tests. Is there anyway you can do some simple drawings to give me a better idea where you are heading. One of my old frame may be in the ball park with some of what you describe. I am having a little trouble finding the switch to turn on the light in my old brain.
==
I think it is time to develop a common vocabulary to blend high tech ideas/words with low tech words and pictures. With a few scale models or simple line drawings or we may understand the different ideas faster.

Does this have any merit?

[Jim Colten]

a common vocabulary always has merit (unless the objective is to kill a lot of time not making progress)

[Bill Fornshell]

I have 5 to 7 days to wait for the Composite Practice Kit and a couple of books.

If some of us don’t understand what is ment by some of the words and terms being used little will take place. Also others who might want to have some imput will just not try.

I am not talking about a book. The first time I/we use a word or term that I/we think some may not understand I/we could take a moment and explaine what it means or give a reference. I am not talking about teaching a MYOG Terms 101. At this point I think the list of words would be very short.

[Dale Wambaugh]

Your raised ribs idea makes a lot of sense. The molds would be a little more complex, but the weight would drop and the whole frame could be laid up in one step. I’m thinking 1/2″ to 3/4″ high and smoothly transitioned to the main pack frame surface over a 1″ to 1-1/2″ distance– like waves. Once you go there, it would be easy to make horizontal and diagonal waves to stiffen the frame. The smoother the transition, the easier it would be to squeegee into the bottom and work the epoxy out. Same advantage with the mold making— sanding and smoothing the mold itself.

Bill talked about motion and shoulder/hip stresses. I was thinking about a frame made in two peices, both roughly pentagon shaped and one point of each would overlap and have a single bolt with a bushing. My guess is the top unit could be longer than the bottom, with the joint near the lumbar area. That, with the wings, would allow the hips to rotate front to back (like an abdominal crunch)and swing side to side– like your leg taking a step up on a trail– a gimballed pack frame :) This would remove a chunk of material from each side too. Take a couple envelopes and open them up and put the tips of the flaps point-to-point to see what I mean.

[Bill Fornshell]

Dale, Take a look at these frames. They are what Mountain Hardwear is using on their EXODUS Backpack series.

Cruiser Frame:

Motive Frame:

These Packs are on a “Sales Hold” for a hip belt problem I have been told. I have had a real close look at both and have had them both on. But now they are gone. I would like to have one of each to play with.

[BPL Subscriber]

I agree about the terms being difficult to work out. I was struggling most to describe the forces and flex directions. If there’s some other term in particular that’s troublesome in my posts, please just point it out and I’ll try to clarify. I hope the sheer length of these posts won’t be offputting…I’m trying to give you a lot to go on now to help you avoid problems and get the best results fastest, so the project gets the most it can out of my limited available time. I know it’s an awful lot of text for just now. I’ll also keep editing to try to make the reading easy and keep hoping it’s not overwhelming.

Let me just hit a few things and see if that’s helped enough to reduce any confusion over what I said enough to make remaining bits more approachable. If something’s impenetrable, please ask for clarification.

The “wings” I think we’ve been using consistently. Someone has previously noted that Bill has made his sheet metal ones strongest in the dimension they need to be strongest by using the sheet material, the main strength of which is aligned vertically when carrying the pack…and as gravity pushes the pack downwards, the mounts on the hips resist towards the forward extremity of the wings, where the greatest leverage would be had in bending them upwards if they were too weak; that force can be called a “bending moment”. These wings can also effectively form a type of “rib” relative to the plane of the main backpack frame, which is trying to fold under weight, and additional, lower ribs running along the vertical sides of the pack frame and facing front to back like the wings are can add stiffness to the packframe; these ribs can be on either front or back of the frame depending on what clearances require, but it the ribs can be placed so that the largest forces compress rather than stretch them they will provide the needed strength with the least material.

Note how on the Stephenson frame the wings tilt upwards; this is partly to exploit the compressive strength of the tubes and joints, avoiding putting all the force into flexing the joint as would tend to occur if the tubes met the frame at 90 degrees…these parts are stronger in compression than in flexion.. So if the base of the wings (the edge where they attach to the frame) is lengthened, they form a longer rib on the frame, strengthening it more in the main direction we’re worried about the frame flexing (for which we should probably come up with a short discriptive name, I think). And if the base of the wings is mounted higher on the backpack frame, at a greater angle up to the point where the wings are most purely compressed, less material will be required to make wings strong enough to hold up to the forces from carrying the pack. This tilting of the wings is a move from cantilevering towards triangulation.

The strongest structure in resisting a simple bending moment is typically called the “I-beam”…it’s shaped like the most common of building girders, or a letter “I” if cut in cross-section. This I-beam form is a useful basis considering alternative structures, and mechanical engineers often consider how some 3-dimensional form approximates an I-beam when trying to estimate its strength. Imagine a simplified version of hexcore, with two skins around cores that are just a bunch of parallel strips. In terms of resistence to a bending moment along the length of those strips, the planar core board can be considered to be a bunch of I-beams, or nearly ideal for resisting that bending moment with minimum materials if the type and amount of materials and their attachment is ideal.

The resistence to bending moments of an ordinary round tube can be considered as a bunch of partial approximations of an I-beam; the tube’s advantage over the I-beam for some applications is partly in resistance to twisting, but especially in resistance to bending in more directions….but it’s not nearly as strong as an I-beam in the direction that the I-beam is strongest.

Now the “raised ribs” “like waves” that Dale just refered to are something we often see in molded products as stiffeners due to their being relatively easy to mold in and approximating I-beam reasonably well along their length while adding additional stiffness in a few other directions due to their curved forms…it would indeed be hard to characterize those other directions in simple language, and it’s not easy to calculate either, which is one of the reasons structural engineers tend to use old familiar forms, and when they build something out of composites to proceed empirically, that is, by building and breaking things to test them. So we could call those “wave-like ribs”? Seems descriptive. They are also somewhat like like half-tubes.

Now, “triangulation”, which I’ve used as shorthand for “triangulation in space frame structures” or some such term. The single word “triangulation” would make it hard to do a simple Google search since the term is used in so many other ways in geometry, surveying, politics, and so forth. The main idea of triangulation in structures is to exploit the better strength of structural members (such as tubes) in compression as opposed to flexion. Think of tubing racecar frames: here’s an early example: http://www.utahlotusmuseum.com/id267.htm. Notice how in some of the frames’ rectangles, tubes are added that break the rectangular shapes into triangles. This is the “triangulation” of which I speak. A rectangle easily collapses when pushed on a corner, as when dropping an underbuilt loaded external frame pack on its corner when lowering it to the ground. The lowest-material way to stop that collapse and keep the rectangular shape (which may be valuable for other reasons) is to brace the corner of the rectangle that you plan to drop it on to the opposite corner of the rectangle, thereby using the materials in their strongest, compressive dimension.

Why, you might ask, didn’t the external frame designers of old do it this way? Why did they make ladder frames instead of triangulating? There are probably several reasons:
1) they weren’t mechanical engineers and there weren’t as many space frames around to notice when tubular backpacks got going;
2) they weren’t hyper-concerned about getting the lightest possible structure;
3) the difficulty of getting or making non-90-degree tubing fittings was too much, as was fishmouthing tubes at other than 90 degrees,
4), with a simple tubing structure, it’s hard to get the tubes out of the way of the back with simple bends if you run them in an X-pattern across the back;
5) a simple ladder structure gives you a very simple place to mount straps and such; and
6) potential buyers didn’t have superior alternatives.
In fact, later designs did increase triangulation in certain areas. The angling of the Stephenson wings is in fact an example of triangulation of a sort, and it appears in parts of other frames too. Using a frame sheet is also triangulation; it just wastes some material since certain parts of the sheet take more force but the sheet used is typically all the same thickness; you could cut holes or thin the sheet in some particular areas without losing any strength.

Now we have CF layups, which give us more design latitude than do tubing structures. We can put the material pretty much where it needs to be to get maximum strength where it is needed, and not make it stronger than it needs to be where it doesn’t need to be strong, just within the constraints of keeping molding simple and not interfering with the spaces dedicated to such items as arms and packbags. We can also align the the fibers so the structure is strongest against the forces it commonly encounters.

The Mountain Hardware (MH) frames depart from the rectangular ladder structure typical of most older backpack frames. There are some disadvantages to that departure, but also advantages. Let me note a couple of disadvantages, so that if we move away from the rectangle we can be more reminded to compensate for those weaknesses.
1) When you set a rectangular frame down, you can use the bottom corners of the frame to take the abuse and save your packbag.
2) The “square” bottom of the frame can help balance the pack when it’s standing on the ground, and this can fairly readily be exploited to approximate a chair.
3) There are obvious points on rectangles to mount the gear that attaches packframe to human body. Likewise for packbag mounting.
4) More strength may need to be built into the waistband assembly than with a rectangular frame since attaching the waistband to the corner of a triangle at one point creates a longer lever arm between the juncture of frame and waistband assembly. Long lever arms in cantilevered structures like this require more materials to retain strength and adequate stiffness levels.

Advantages:
1)Despite disadvantage #4 above, mounting the waistband assembly to the bottom corner of a frame triangle shifts pack structural weight to a place where the body can probably most easily handle it: around the waist.
2) Again, despite disadvantage #4 above, this mounting arrangement puts a joint right about where I think we’d want if if we need to build some mobility into the joint in order to replicate biomechanics…right around the upper lumbar region. We’d probably want to make this joint stiffer than biology in the fore-aft flexion/extension motion (Dale’s “crunch”), but perhaps leave the top and bottom parts of the pack free to rotate relative to one another in two other dimensions: a) around the vertical axis; b) so the left hip can move up and right hip down (and vice-versa) while the upper pack frame floats along without going up and down on with the hips…similar to the independence of our hips and upper bodies. This can be relatively easily accomplished with two axles. I think this is aligned with Dale’s 05/18/2006 13:26:15 MDT post but I’m not too clear about the pentagons he mentioned and I’ve also been trying to get to some rotation on the vertical axis. I’m seeing triangles because I see the forces that way but pentagons and such might give a better perimeter for packbag mounting than a triangle. But pentagons don’t self-brace to the extent triangles do.
3) The MH structure seems to follow the triangulation I was speaking of with hip motions relative to shoulder motions…it’s basically an “X” shape connecting hips to shoulders.

Compensations for disadvantages:
1) If need be, projections from the frame could be added to absorb forces when the pack is set down roughly, and lighter-duty projections to the ground could be added (or deployed when needed) to make a chair.
2) Careful design can take care of the mounting points for the gear that attaches a non-rectangular packframe to the human body. Likewise for packbag mounting, one would hope.

Improvements over the MH frame:
1) Replacing the hipbelt assembly with a fitted CF structure might save quite a bit of weight and need for (as much) padding. A rigid structure lets us distribute the weight broadly to reduce stress on the body, and concentrate it where we might want to concentrate it a bit (because, e.g., certain parts of the pelvis are easier to get a grip on than others and/or have a preferable combination of bone near to the surface, not too many pain nerves, and so forth.) The waistband shapes they are using might be a little more cantilevered than is required by the single point of attachment to the upper frame; if in building a full-sized model around a specific human body clearances and triangulation are kept in mind it looks to me that a CF layup would allow a more efficiently triangulated hipband structure carrying forces more directly from the hipband to the joint at the upper lumbar.
2) The upper part of the MH frame looks at a glance to have been fairly carefully minimized in its major form according to ordinary structural principles. Using lighter/stronger material would certainly lighten it. Also, they may have used more material than is needed in order to simplify construction, whereas if we look for opportunities, e.g., to use ribs or double-skinned cores instead of sheets of constant thickness if they use something like that, we could save weight.

Questions:
Since the zoom function in my browser is temporaily disabled and I haven’t had time to do the necessary computer maintenance, I’m only seeing small pictures of the MH frames. Are those thin verticals along the outside edge simply straps, or are they rigid? This same zoom limitation makes it a little hard for me to understand quite where the MH parts lie on the body and how stiff they might be in certain sections.
Also, I’m not very clear on how they mount their packbags.

Time limitations are likely to keep me from sorting out drawing issues soon too. I don’t normally draw with a computer so I’d have to set something up, and I suspect that the time required would be such that we wouldn’t get the best out of me on the other issues fast enough to help set directions for projects now.

[BPL Subscriber]

Does anyone have a source for high-density thermofoam that might be used for padding? This is the stuff that molds under your body heat to distribute load better than regular foam. Sometimes called “memory foam”.

Also, racecar seats sometimes use expanding foam to custom fit seat to driver. A typical procedure (from Carroll Smith’s books as I recall) is to put the expanding foam in plastic garbage bags and quickly put the driver in the seat atop the bags till the foam sets up, then remove the bags, then trim, mount and cover the foam. This might be used for backpack pads as well: support pack at proper distance from standing body; apply foam in bags; trim, mount, and cover foam.

[Bill Fornshell]

Terms and Ideas for a New Pack Frame:

BobOne, Thanks for taking the time to address Term/Words/Ideas question. The light in my brain is now on at a much brighter level. You obviously have thought a lot about this frame subject. I have several questions about your background but will not ask them at this time.

I am a little concerned about getting all these ideas in one neat light package (model) and then being able to make it. The first few frames may be just a “mule” or test bed if I can borrow an old term once used by
“Zora Arkus Duntov” I sat in this car for a few minutes, once, many years ago.

I want to talk about a new question as I think we are ready to get started on actual designs. In my frames I first tried to second guess the Max weight I wanted to carry with the frame. In a Super Ultra Light gear load of 7 to 12 pounds or less it doesn’t take much frame to handle this weight. The frame design for me was more to try and get a space between my back and the pack bag. This window of sorts would keep my back cooler in warm weather and has a good benefit even in colder weather. There is a lot more to this idea that can be address later if necessary.

I think we need decide what our “Frame Design Goals” are at this time so we have something to focus on. They don’t need to be in any necessary order of importance’s but should be looked at as a group. Here are a few and I expect this list to grow. When we have a bunch we can decide which ones we want to focus on.

Frame Design Goals: (these are in my words and the exact wording can change)

1. A frame that pushes back from the back so it has a space (window) between the back and the pack bag. This feature was one of my main goals in the pack frames I make.

2. Frame Carry Weight: This can be several different weights and can be several versions of the frame so we can carry light loads and or heavier loads. This can be more than one frame based on the same general design ideas.

3. Frame Weight: What is the Goal weight for the frame?

4. Etc, Etc, Etc

The “triangulation” term was my big question. I thought this was what you meant and the Lotus article was all it took. I am a great Race Car and Hot Rod fan and have been since I was about 13. The old “tube” frames were a great idea.

The small pictures of the MH frames are the only ones I could find. I don’t have a way to Re-size the pictures but it could be done with something like Photoshop. I have an older Mac with PhotoShop on it but the hard-drive died. The version of Photo Shop is old and does not work on my new computer and the new Mac OS. I was going to take some pictures of the frames at my local store but they have sent them all back. The pack bag attaches at the top of the frame with a small pocket like thing sewn onto the bag and slips over a thing?? on the frame. then the pack bag has a strap at the bottom of the frame on each side that pulls down on the bag and holds it under a little pressure. The bags come off and on easy and quick.

Some random pictures of the MH Pack:

These are a few pictures of a frame I started about a year ago to carry a heavier load. It started to get a little complicated and heavier than I wanted and I stopped working on it. My idea was to replace the Aluminum parts with home made Titanium parts. You may notice a little crude attempt at “triangulation” though I didn’t know the word at that time.

[Dale Wambaugh]

That makes me feel pretty good– great minds think alike, eh?

Looks like MH is using stressed “wands” like some of the Dana packs.

[Robert Miller]

Bobone,

>>racecar seats sometimes use expanding
>>foam to custom fit seat to driver. A
>>typical procedure (from Carroll
>>Smith’s books as I recall) is to put
>>the expanding foam in plastic garbage
>>bags and quickly put the driver in the
>>seat atop the bags till the foam sets
>>up, then remove the bags, then trim,
>>mount and cover the foam

I did this once and it worked well. It gets quite warm sitting there waiting for the foam to solidify. I used a two part urethane foam used by boat manufacturers for flotation.

For a small project like this I would recommend the rigid types now available in spray cans.

Robert

[BPL Subscriber]

I want to play with some of that foam again soon to see if it will help keep traffic sounds from passing through hollow-core doors here. There’s apparently both hi-expanding and low-expanding types available in spray cans, with the latter being the type you’d use on hollow-core doors so as to not blow the panels off. I haven’t used expanding foam in a really long time (last was 2-part boat foam, I think) and it would be a nice thing to have in the tool kit, I’m sure.

Wands at the sides, eh? For the mobile joint to work, they’d have to be somewhat resilient, I suppose, or would need to float. It seems like they’d help keep the packbag under control, don’t you think? I guess wands might be inserted through loops sewn into the packbag then attached top and bottom, obviating packbag straps.

I’d think the first pack to build might be one directed at very light loads…then go out and use it until it breaks under measured loads, working upwards and refining to make things stronger only where they tend to fail in use and maybe lightening some in areas where there is no problem. But it might make sense to also have a second, somewhat heavier frame that could be carried as luggage on the first so that when the first one fails the second one can get the tester home. One might work upwards this way until some tester is willing to carry 65 pound loads long enough to develop a light reliable frame for those loads…this is just because I’m not imagining I’ll ever see reason to attempt more than 65 pound loads again personally, someone else might want more. The military might be interested in providing testers around this load range?

I also like the ventilation of an external frame pack. In fact I’ve wondered about ways to use forced-air cooling here at times. There is a bit of a bellows effect just with the bag and body moving a bit relative to one another, and there’s probably some slight chimney effect as well.

Another note on joint placement. The likely best height for a single mobile joint is at the intervertebral space between the 12th thoracic and 7th lumbar vertabraes. This is the most mobile joint in the region that’s near to the lumbar which are more limited in motion in order to provide stability. Going above this point with the joint would, I think, tend to restrict motions more than we’d prefer as it would more immobilize joints that normally can move. Going much lower could tend to concentrate those motions at joints that don’t have as much freedom to move as those in the thorax, which could overburden them. You can locate this spot with your thumb in your mid-back while standing as the most prominent convex bony point.

Also, I wonder if for some future project there’s enough motion at this pack joint for a power take-off for electrical generation. If we used axles it would be relatively easy to get some of the hip up and down motion off. If we used a ball joint (limited in the crunch direction, presumably), it might be harder to extract power; it might be easier to find an off the shelf ball joint that could be adapted to simply get the desired motions, but I’m not sure.

[Dale Wambaugh]

“I want to play with some of that foam again soon to see if it will help keep traffic sounds from passing through hollow-core doors here. There’s apparently both hi-expanding and low-expanding types available in spray cans, with the latter being the type you’d use on hollow-core doors so as to not blow the panels off.”

Even the low expanding stuff could be ummmm…. interesting… with a door– there’s so much surface area to push on, vs the glue line on the door. Drill through the top first and see if the door has cardboard spacers in it. I’d buy some nice noise-cancelling headphones myself :)

Back to the pack– I was thinking of simple straps or elastic cords to limit the travel of the joint. Some Sprectra Aircore would do the trick.

The wands I was referring to were used by Dana as a frame piece. The top of the wand was fixed to a plate/crossbar at the top which was also the attachment point for the shoulder straps. The bottom of the wands ended in pockets in the corners where the waist belt was anchored. It was overbuilt but capable of bearing loads that I would laugh at now. With all the hardware and heavy fabric a 2500ci pack was well over 4 pounds.

[Bill Fornshell]

I am reposting this for input on “just” the Frame Design Goals. I really didn’t expect to get many replies to the project and thank those that took the time to join in on Design comments and Material suggestions. I even thank Jim though I think he is a bit of a joker.

I will edit this post to update ideas as they are suggested and will start with what we have to date.
===============================

Frame Design Goals: (the exact wording can change as can the number).

1. A Frame designed that pushes back from the back so it has a space (window) between the back and the pack bag for ventilation. This feature was one of my main goals in the pack frames I make. This gives a “Moisture Management” breathing space for upper body garment material to really do there thing.

Things to try:
1-a. Some ways to use forced-air cooling.

1-b. Test to see if there is some slight chimney effect as well.
(NOTE from Bill)
On my packs that do push away from my back I did get a good breeze through the open area. This was tested on several hikes here in Texas last summer when it was about 100 degrees F.

1-c. Wands at the sides, eh? For the mobile joint to work, they’d have to be somewhat resilient, I suppose, or would need to float. It seems like they’d help keep the packbag under control, don’t you think? I guess wands might be inserted through loops sewn into the packbag then attached top and bottom, obviating packbag straps.

(NOTE from Bill) Point me to something that shows what you are referring to when you say “Wands” . I think you maybe talking about the up-right tubes or cross tube on the MH frames? If this is what you are referring to I used something like the side tubes on my recent frame. The one I call my Exodus Clone.

1-d. Another note on joint placement. The likely best height for a single mobile joint is at the intervertebral space between the 12th thoracic and 7th lumbar vertabraes. This is the most mobile joint in the region that’s near to the lumbar which are more limited in motion in order to provide stability. Going above this point with the joint would, I think, tend to restrict motions more than we’d prefer as it would more immobilize joints that normally can move. Going much lower could tend to concentrate those motions at joints that don’t have as much freedom to move as those in the thorax, which could overburden them. You can locate this spot with your thumb in your mid-back while standing as the most prominent convex bony point.

2. Frame Weight and Frame Carry Weight: This can be several different weights and can be several versions of the frame so we can carry light loads and or heavier loads. This can also be more than one frame based on the same general design ideas.

2-a. SUL Version ?? Pack Load ?
2-a-1. The first pack to build might be one directed at very light loads….then go out and use it until it breaks under measured loads, working upwards and refining to make things stronger only where they tend to fail in use and maybe lightening some in areas where there is no problem.

Next it make sense to also have a second, somewhat heavier frame that could be carried as luggage on the first so that when the first one fails the second one can get the tester home. One might work upwards this way until some tester is willing to carry 65 pound loads long enough to develop a light reliable frame for those loads…this is just because I’m not imagining I’ll ever see reason to attempt more than 65 pound loads again personally, someone else might want more. The military might be interested in providing testers around this load range?

2-b. UL Version ?? Pack Load ?
2-c. Something in-between ?? Pack Load?
2-c. Heavier ?? Pack Load ?

3. I wonder if for some future project there’s enough motion at this joint for a power take-off for electrical generation. If we used axles it would be relatively easy to get some of the hip up and down motion off. If we used a ball joint (limited in the crunch direction, presumably), it might be harder to extract power; it might be easier to find an off the shelf ball joint that could be adapted to simply get the desired motions, but I’m not sure.

(NOTE from Bill)
When that pack that could generate a bit of electricity first came out I did a search for small generators that might work with the up and down motion from something built into the frame. I found several little generators that might be adapted to a frame set-up. I was looking for a way to power my “Backpackers OnStar” device. I had several ideas for a better system but it required the development of some really small hardware. There are better ways than the frame to generate some electricity from motion. I don’t think the hardware necessary has been developed or is available. The idea I have may never even been though about. How much battery power do you want? The small “off the shelf” generators didn’t put out much juice. Solar might be easier if you can depend on enough sun light.

4. Etc.

5. Etc.

6. Etc.

[BPL Subscriber]

WANDS / STRUTS / VERTICAL LATERAL ARCHES
Wands are the term Dale used, I think for the largely-verticals at the outside edges of the usual location of a rectangular packframe. I can’t see the MH pictures well enough to see if they have something like that, but it makes sense to have such verticals to give structure to the packbag once you’ve taken the primary loads into an X-shaped central structure, like what MH also does. Aircraft terminology might suggest “struts” for these items.

The simple way might be CF tubes. It might be nice to build some CF arches for this to get them to optimal strength and stiffness and exploit the strength of an arch to resist the packbag coming forward against the body, as well as to fit the “arches” (which might thus be more complex) so that they will clear the back of the body well but still let the weight carry as close as good ventilation allows. Seems like the they might be anchored at the top and float at the bottom (allowing free hip movement, if only to get noise associated with the floating arrangement away from the ears. Solid anchoring at both ends could also work if the pieces are flexible enough to allow the hip motion to still work. In a model without the mobile joint, of course, floating or flexibility would not be necessary.

POWER
How much power do I want…that’s hard to answer off the cuff (at least once we get off talking about ruling the known galaxies)…I’d need to go look at rated battery capacities and lifes for current portable computers and phones. The basic idea is to be able to walk around part of the day then use a computer, phone, GPS, and some lighting the rest of the waking hours; some partial functionality less than that would also be useful. Last time I caught up, solar didn’t have the conversion efficiency needed to collect much power by walking around with solar cells, but if I recall correctly, if there were some really solid improvements in conversion efficiency there might be enough sunlight hitting the body in some circumstances for it to work out. It would be nice to be able to kick back when you get where you’re going and still have power, which recommends solar cells.

I considered various mechanical conversion possibilities over the years, and several approaches have received some development. The backpack up-and-down item was the most recent news, but I’m not sure that’s a very good approach to let the pack move up and down relative to the body. But if we’re already generating a partial rotary motion with the hip rocking in the backpack’s motion joint, that might be sensibly exploited. The heel-pressure devices as far as I know never went much of anywhere, although that approach seems to at least put things out of the way except for wiring, and perhaps not interfere with normal motions. Using major muscles that are being employed in large walking movements seems like the obvious fount of more power, and I think I drew a leg-lever apparatus at one point. It doesn’t take much load to mess up gait, though, nor much pressure on leg muscles to intefere with function. Running cords from heels to backpack would exploit probably the largest available motion (making for low load per inch of movement) and wouldn’t squeeze the thighs, but could present a tripping danger. Similar approaches might be taken with arms, with maybe more fatigue problems but less danger of catastrophically hanging up on the scenery. There are probably several other mechanical approaches that I gave thought to at one time or another. I haven’t really thought about power generation in a while, though, and have just tried to keep my eyes open for what someone else might have developed. Methanol fuel cells might be of some use, but then you have to carry more fuel…but you have to feed yourself to generate power too, so the efficiencies have to be considered, and the weight of all this versus solar cells, with due account taken of the number of days one will be out, with solar becoming more sensible as more watt-hours of fuel need to be carried.

[BPL Subscriber]

This is getting pretty far off the pack development thinking, but this very nice device was just announced and gives some idea of the capabilities soon to come to fairly-light backpackers that might make power-generation more of a must-have item: http://www.mil-embedded.com/news/db/?2873

You might want to pair something like that with a (forthcoming) wireless video headset to get a larger display, a phone/3G wide-area networking device or satellite phone in more remote areas, and a wireless fold-out keyboard.

[Bill Fornshell]

Electronics and what I want. I want a PDA with a Cell Phone built in that I can connect to the internet. The PDA needs to have a replaceable battery so I can carry more than one if I want to. (Many will do this I just have to decide which one I want). It needs to use SD as that is what my Digital Camera has. I would like to have one of the “roll-up” keyboards that are about 2/3’s the size of a standard keyboard. They roll-up about the size of a coke can. As the PDA’s are coming with bigger keyboards I might forgo the “roll-up keyboard.

I want a real GPS that will work with the PDA if possible. I want to be able to plot way points when there is no snow and go back into the same area in snow and if I can’t tell where the trail is use the GPS to guide me. The GPS is only one of my land nav tools. One year soon I hope to try winter SOBO AT Thru-Hike. Start in Jan/Feb on Katahdin and go south as far as I can, snow permitting.

I just looked at the link you posted. To bad there is no picture. Satellite phones are getting cheaper everyday and I think you can also rent them. I am thinking about making one of these little gems:

[Dale Wambaugh]

Bill, if anyone every breaks into your house, they are going to go running out the door– one look in your workshop will convince them you are building torture devices for the CIA :)

As to joint stabilizing:

I was just thinking of shock cords to keep the top and bottom from flopping around and it may not be needed at all– the pack bag would keep it all together and your body should do all the stabilizing needed once you are strapped in. If the bag is full, it will sit up by itself.

I wonder if the weight will vector off to the waist belt with just the two frame sections (vertabra?) shoulder straps and waist belt. Does it need anything like the wands (flexible shafts) to pick up the weight of the bag and transfer it to the belt?

Simple is good for general design and weight saving too. More traditional ladder/H pack frames don’t flex and the weight is sent straight to the hipbelt. Once you break away from the fixed frame/backboard idea, the complexity and the weight may go exponential. I guess what I’m after is an external framesheet.

As far as pack weight, IMHO, 25 pounds would be more than enough load to aim for. There are plenty of pack frames out there for folks who want to haul half the house with them.

[BPL Subscriber]

Oh, I get the wand idea much better in that picture. The picture size and especially color contrast helps.

It’s a lot like something I tried right after seeing a hip belt on the trail for the first time…made or bought a hip belt for my shelved-aluminum-tube khaki-bagged scout pack, got the soft foam pads including slide-ons for shoulders, thought, “there must be something better than this and this was too expensive”, thought…”prop the pack on the front of the belt to form a triangle with something running under the armpit…now stiffen the belt”. Hard to get the belt stiff enough with what I had. Then I struggled with the arm clearance issues of having something from that far on the front run that high up on the frame. Nowadays, carbon tubes could be thinner but I still don’t perceive a lot of clearance for them next to my body.

The underarm prop attempt got me thinking of running a rod to a projection out front from over the shoulder and maybe have some of the weight hang less far off the back, but I didn’t have a good way to make it in the sixties so it weighed too much in the state to which I developed it, and the stuff out front was a bit in the way but it was nice step up in shoulder comfort…it all felt much lighter when it was balanced and not squeezing my shoulders any more…but I needed a better waistbelt setup. I think I was trying aluminum electrical conduit among other things for the forward tubes.

Around that time my Dad was making fiberglass boats out back of the house, and I decided there ought to be a wrap around backpiece made out of this amazing fiberglass and polyester resin goop, but didn’t develop it a great deal and got hung up on how to make a decent waistband with very limited materials and tools…and the local cub and boy scout pack and troop were pretty inactive and disorganized so I wasn’t getting to use the gear enough.

Along the way I got pretty sensitized to pack appurtenances interfering with the arms, and although it might just be my particular body, there’s not much clearance between arms and torso to play with and still allow a very natural walk. I’m not sure I’d get used to having those wands running from so high to so far forwards under my arms as on the picture Bill just showed and I guess on the MH packs. What’s your impreesion of them, Bill? Tubes in compression run from high on the pack to far forwards is potentially a very light way to go either under or over the shoulder (note the big triangles), but there are ergonomic issues at least for me.

I resigned myself to not being able to get that superlight giant triangle over the shoulder going but looked to creating a somewhat smaller triangle effect with a molding that wraps around the body and upwards into the pack…sort of like the props but in bent sheet form right up near the body. When I tried with fiberglass I didn’t attempt any sort of intermediate body mold, that much plaster being sort of beyond comprehension and my non-budget as a kid in like 1966 or 67 working with stuff that was lying around. I think I used a bent piece of posterboard or some found round surface for a fiberglass mold, then trimmed the layup so it bit me less and built it up more for strength. I still didn’t have the stuff to get the waistband right.

The hard molded subframe fit near to my hips for arm clearance and carrying the weight down from higher on the pack seemed to make better sense on my body then and still does…and it could create much of the effect of running props out from under the armpits with fewer clearance issues. 2006 adults are a lot better equipped to actually execute a workable version these days, though, and more.

It’s just great that you’re doing all that pack fabrication, Bill. I’m excited to see what you’ll be able to do with laminating. You’ve already practiced nearly every other skill needed to pull this off.

I’ll try to remember to post a picture of that little computer when there’s one out. We should be seeing a lot of variants of these small Intel-based computers hitting the market over the next year.

[BPL Subscriber]

“Vertebra”…I like that! A marketer in our midst!

As to the need for wands, Dale, I think that’s why the waistband section really wants to be rigid up to the vertebra, with whatever padding is needed where it touches the body. The upper edge of the waistband assembly (girdle?) would more or less replicate the path of the wands, only closer to the torso. The system would depend on the vertebra being pretty stiff in the crunch and de-crunch direction to transfer weight into the girdle.

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