Pack that puts weight on sides of hipbelt?
- This topic has 28 replies, 17 voices, and was last updated 4 years, 9 months ago by
.
-
The old, I’m talking early 1970’s, Adventure 16 external frame backpacks made in San Diego had a sort of “wing” that extended out from the frame to about the center of your body that the hip t belwas attached to. So it swiveled around that point.
Adventure 16, Alpinlite, and Jansport all offered models with “side bars.” Only the Jansport “D” series side bars swiveled. The Alpinlite and Adventure 16 side “wings” were fixed/welded.
The concept worked “ok” but never really caught on. Because they were immovable, the Adventure 16 and Alpnlite frames only fit a small variety of hips. The Jansport D series was far more popular because the wings could swing in and out (like a gate), had multiple attachment points for the hipbelt, and as a result fit nearly everyone. However, the D-wings connections weren’t very robust. In 1977 the wings on my Jansport D3 blew apart on a 2.5 mos long AT walk. The D series lasted into the 1980’s but the “D” was eventually replaced with a solid aluminum wing.
The concept works, but it’s not a simple element to properly design and implement.
Here’s a pick of the circa 1977 Jansport “D” wing pulled off the net:
The shafts of the delrin “U” frame on the old ULA OHM 1.0 seated in 2 pockets sewn to the hipbelt wings just forward of where they attached to the main compartment. That transferred the weight to the hipbelt. The only problem with the 1.0 was that the hipbelt wings were too small, and did not spread the weight over a large enough surface to be comfortable for long days. That said, I carried 30# in that pack comfortably for several hours at a time, at which point I had to take a break. Unfortunately, when the OHM 2.0 came out, the much larger hipbelt wings were attached to the center of the pack with velcro in the lumbar area, and the weight was no longer transferred to directly to the hipbelt wings at the sides of the main compartment. This led to sagging and a less optimal weight transfer. I’ll never understand why they didn’t just enlarge the hipbelt wings and stay with the 1.0 weight transfer system. In the end, I purchased a 2.0 hipbelt and modified my OHM 1.0 to use the larger 2.0 hipbelt wings with the old transfer system. Best of both worlds. Carries like a dream with no sag.
Note where the poles seat in pockets at the back of the hipbelt wings in this picture of an original OHM 1.0. It is not my pack, just a picture lifted off the net. Now picture that pack with the much larger 2.0 hipbelt wings and you have a pack that will comfortably carry 30# , maybe a bit more, while weighing 24 oz, stripped, in a medium.
Re: “. . .having the attachment point of belt to frame at the sides means that your hips cannot move up and down in their normal manner . . .”
The Stephenson design solves this problem by attaching the belt to the frame at only three points: At the small of the back, and at the points of the sidearms, furthest from the pack, forming a triangle. So each side of the belt is free to move independently up and down as one walks:
And each side of the belt rests on each hip bone (the ILIAC crests, not the hip joint), so the weight does not rub against the hips. The attachment at the small of the back is recessed, so only the belt, not the frame, contacts the back.
The attachment at the small of the back is a key element of the design, as it keeps the center of gravity over the lumbar area, and not further backward, causing the pack to rotate rearward, and place much more pressure on the shoulder straps, as was the case with the Jansport D model packs. and some others with sidearms.
A number of methods of attachment at the small of the back have been tried, including fittings that rotate 360 degrees: but only slight freedom to rotate at the small of the back is needed for the belt to rotate freely with the hips, which is actually more desirable to assist keeping the pack upright; and more elaborate attachment methods are not needed.
A modification allows the arms to rotate freely, and snug the belt as tightly as desired against the hips, as on this butterfly frame with a suspended mesh backband:
But using the Jansport fittings for the sidearm hinges requires 5/8″ tubing, too heavy for a really light frame; so in progress is a butterfly, or hourglass-shaped frame from prebent Easton 340 tube, which is less than half the weight of the Jansport tube. Roger Caffin was kind enough to use his homemade ‘Rolling Jenny’ device to prebend some Easton tube to the desired amount for the side arms and hourglass part of the frame.
Another lesson was the need to keep the sidearms several inches up from the pack bottom, again to limit top heavy rotation of the pack sideways. Using the common feature of bottom side pockets for water bottles also moves the center of side rotation upward, further helping to keep the pack upright..
Still another lesson in going to lighter tube was that the cross bars behind the belt must be strong and rigid enough to keep the sidearms from opening slightly so that the snugness of the belt is lost. A front buckle like Stephenson’s will solve this; but making the belt keep snug without a buckle makes for much greater comfort. .
The greatest thing about this design is that with a contoured hipbelt of ordinary width, slipping of the belt is a thing of the past, and all of the pack weight is transferred to the hips, with none on the back. The greatest drawback is that the frame must be more tailored to the wearer’s hips and body size, so while great for MYOG, probably not marketable. But there is more freedom for variation than initially thought.
Will post on MYOG when the frame is done, with more photos.
As an aside , I could be totally stupid but to me the way to balance the weight on your back is to put weight on the front. The same reason why a weight on the left side is balanced by one on the right.
Yes , I do realise that people with large stomach bones are already equipped with the balancing weight.
- You must be logged in to reply to this topic.
