Bead Cord Update

As you know, GravityLight has been put through rigorous testing over the past few months, both in our workshop and out in the field.

Back in 2014, we tested an early version of the device (GL01) in 1000 households across 26 countries to assess functionality and ease of use. We collated feedback on the designs from the people who matter the most – the families who will rely on them to replace kerosene lighting in their homes – to ensure we’re creating a solution with a positive impact and stands the test of time.

To recap, we discovered back then that our initial design needed improving. Some people struggled to lift the 12 kilos of weight required to get the lights going, especially in the dark. Our designers tackled this by adding a bead cord that works as a pulley, making the lights safer, easier and more inclusive to use.

As testing of our new GravityLight progressed, we were delighted to see that significant gains had been made in its robustness, durability and lifespan - the graph below plots the current output of the various gearbox builds that we put through accelerated life testing. The purple line, build 5, exhibited the best stats - with the current improving in the first phase and remaining consistent throughout the first year of product use.

However, as the tests progressed, they turned up an issue with the bead cord. Further along in the product use cycle - around the 200 day mark - as the cord is used, we noticed that it's stiffness and rigidity would change, becoming softer, and therefore causing it to interact with the GravityLight in a different way. The bead cord would begin to tangle, causing the light to go out. 

The Early Design: Bead Chamber Build

The original design for GL02 employed the use of a 'bead chamber' to capture the cord and keep it neatly contained. From the images and footage below, you can see the tangle occurs inside the bead chamber. 

Second Design: Carriage Build

As the tangle was occurring in the bead chamber, we decided that the next logical step was to remove this component and collect the beads using a 'bead carriage' - illustrated in the renders below. 

Carriage Build: Tangling

The bead carriage build improved performance, although tangles were still occurring during product testing - an example of this can be seen in the video below. 

Variations of Carriage Component

To address this, we designed various iterations of the bead carriage component, seen in the gallery below.

Minor Tangle

However, none of the alternative carriage component designs eliminated the tangling issue. Early on in the product life cycle, the tangles are relatively minor and easy to fix - as demonstrated in the three videos below.

Severe Tangle

Further along in the product life cycle, the tangles would become much more severe, often taking long periods of time to resolve. Clearly this is not acceptable, particularly as GravityLight will be the only light source in many homes. It is unreasonable to expect users to resolve tangles as severe as the examples shown in the videos below - especially in the dark. 

Going Forward: The Pulley Build

As it became apparent that the bead carriage builds were not resolving the tangling problem, we started to think about alternatives solutions that we could use to fix the issue. Keen to avoid a substantial delay, we did this in parallel to testing the various carriage builds.

We are confident that we have identified a robust solution, substituting the carriage for a pulley (as illustrated in the renders below). 

The pulley removes random characteristics from the bead cords, completely controlling the manner in which they are pulled through - ensuring that the beads can not tangle.

We have been testing the pulley in tandem with the rest of the GravityLight unit - to make sure that the overall performance was not compromised by the new factors that the pulley introduced and we are pleased to say that the solution to stop the bead cord from tangling is on track. 

The photos below show SLS prototypes of the new pulley solution being tested on accelerated life rings over the past few weeks. The results have been positive so we will now be commissioning production tooling.