Frame Design

Using Osprey Sirrus 24 pack’s trampoline back as inspiration, Measured length of metal frame rods and diameter with caliper.

Frame measures 60 inches (5 feet) + diameter  is 3/16 inch

Cross Beams measure 21 inches (1.75 feet) + diameter is 1/8 inch

Frame assembly plan sketches

 

I decided that for my first prototype I would just hack the Osprey and use its frame, and for future prototypes I will try to make my own frame. David at Metalliferous warned me that my frame will not be as good without a good jig and pressure machines to push the aluminum into place.

 

Full bag – pre hack

 

Hack open

resulting frame + straps that I will use for my suspended load prototype

Suspension Design

 spring constant lbs/in is 8.3

With my first order of springs, I ordered so one spring has this spring constant. Now I realize I will need at least 2 springs in parallel for each side of a handle (if handheld) or at least one for each strap (if backpack).

 

As you can see, these are very long.

under load springs/ waistbelt idea

“There’s a rule we have in engineering machine design: everything is a spring.  Any material, if you push on it enough, will squish.  Different configurations of materials will do this differently – whether it’s the material in your video, an inflated ball, foam, metal springs, etc.  There are a ton of ways to add springiness to your bag.  I think it’s important to do a survey of options, but choose 1 or 2 to really prototype with and ignore the others so you don’t get distracted.  You can always go back and redo, but if you push forward with 15 different options you may stall more than you move.”

– Dustyn

Final Project Step 2: Suspension Plan

Suspension Bag Overview

Suspension bags move in the opposite direction of the wearer. When you walk normally, your hips move up and down, and your bag moves with you. This movement causes extra force on your joints, especially when you’re carrying heavy laptops and devices. Suspension bags can effectively reduce the force you’re joints feel. Professor Larry Rome at University of Pennslyvania proved this method can reduce the total peak vertical force on the wearer’s body by 60%.

Progress to Date

I aim to apply Rome’s principles to daily urban bag loads and perform more extensive testing. To determine if a spring-mounted suspended-load-carrying system was a viable option for reducing fatigue experienced by my demographic, I performed an initial feasibility study with biomechanics professor Dustyn Roberts. I hypothesized that load-carrying systems using springs and suspension to counteract the vertical force of loads will cause less fatigue. After assembling and testing a prototype of the load attached to extension springs, preliminary results (attached) showed the mass moving out of phase with the carrier’s gait as expected.[i]

 

Next Steps

My preliminary results proved that suspension works with handheld loads. Next I want to make suspension work for bags worn on the back since young professionals like to carry bags both on their backs and in their hands. 

Timeline

Rapid Prototyping & Testing

I will develop the bag following an iterative design process involving continuously creating and testing prototypes, then reevaluating and making adjustments.

 

1. Make Suspended Load Backpack (in addition to my current handheld prototype)

The first step is to buy materials and develop a succession of suspended-load bag prototypes. Increased friction between the backpack and back will require trial and error testing of springs and bungees.

 

2. Test

I will measure fatigue by testing ground reaction forces during gait when a person holds the bag on the back versus in the hand. I should be able to visualize differences between fixed and spring-mounted bags in the pressure patterns if fatigue is reduced. I will also test different designs’ distribution of pressure forces on the back.

 

Refinement & Finalization

As I receive test results, I will update the bag design accordingly. Moving forward, I intend to distribute final prototypes to my target demographic to test if their load carrying improves, and then hopefully move from prototypes into production.

 

 

---

[i] Holtz, Melissa, and Dustyn Roberts. Design of Suspended Load Backpacks for Young Urban Professionals. American Society of Biomechanics Submission, 9 Mar. 2012.

 

Final Project Step 1: Best Possible “Locked” Bag

Best possible “locked” bag based on biomechanic principles

1. Convertible strap bag so can have option of different strap positions

2. adjustable lumbar padding

padding of different thicknesses have velcro sewn to them and then there is a velcro panel in the bag the padding pieces can lock into.

3. Super lightweight, super strong material

I’m working with a new, lightweight, superstrong, waterproof, and durable material called Dyneema, which substantially reduces the bag weight.

However, these functionalities have limited effect.

Only exercise was found effective for preventing self-reported back pain in seven of eight trials (effect size 0.39 to >0.69). Other interventions were not found to reduce either incidence or severity of BP episodes compared with controls. Negative trials included five trials of education, four of lumbar supports, two of shoe inserts, and four of reduced lifting programs.

– Value-based care in the management of spinal disorders: a systematic review of cost-utility analysis. Indrakanti SS, Weber MH, Takemoto SK, Hu SS, Polly D, Berven SH. Washington University in St Louis School of Medicine, St Louis, MO, USA.