I Literally Ate Our First Prototype

The Tanktwo string cells (aka space eggs) started it all. In the early days, when people looked at the prototypes and saw what they could do, their jaws dropped. If you’re one of the many who snagged a space egg from a trade show, I promise we won’t track you down ;)

The “too good to be true” technology didn’t come out of thin air. It’s the result of endless rounds of iterations — combining disciplines that span the realms of the physical, electrochemical, electronics, and logics/algorithms/software.

Nobody had even dreamed up anything close to our software-defined battery management solution before, let alone solving any part of it. But there’s always a way. And it doesn’t have to be as jaw-dropping as the outcome.

The string cells have a humble beginning that started with M&Ms, Skittles, and coffee beans.

We nickname our string cells “candies” because we explored how to maximize contact surfaces while minimizing the total volume of the battery pack by pouring an unhealthy amount of M&Ms, Skittles, and coffee beans into transparent containers.

Next, we took pictures to analyze how each piece touches others in this random packing arrangement. After endless modeling and calculations, we came up with the optimal shape — kind of like an M&M and an egg had a baby.

But how do they (literally) stack up to conduct electricity?

After determining the string cell’s optimal form factor, we had to answer some practical questions to turn theory into reality:

How would the cells talk to each other? How would they connect with the sides of the tank to charge and discharge? What are the thermal properties, and how will the battery materials behave?

Juva, our head of R&D and engineering, wrote a CAD planning and simulation tool from the ground up to answer these questions. He “glued” together pieces from a first-person shooter game engine, electric circuit simulation programs, and an advanced 3-d visualization software with chunks of Python code. 🤯

The system allowed us to understand how a system built from individual string cells would behave on its own and work as a unit. We then used the insights to fine-tune the physical attributes, explore the logical connections, and model the behaviors.

One reason why it’s challenging for many to wrap their head around our technology is its multi-disciplinary approach. We tapped into knowledge from different disciplines, and often, we had to learn on the fly to find (or create) the tools we needed to make the next step possible.

While we analyzed the electrochemical, electronics, and logic/algorithms/software aspects with advanced computer modeling, we also created physical prototypes to experiment with the cells’ physical form factor.

These plastic egg-shaped prototypes helped us understand the concept of random packing to maximize the packing density in a given space. The insights allowed us to determine the final dimensions of the string cells to fit the most battery materials (i.e., power) into a string tank.

After relentless modeling and experimentation… it’s show time!

But not a single manufacturer on the planet can cover everything needed to make a string cell. So we visited plants all over Europe and Asia to source the materials:

The shell was made in Finland, and the coating was done in Sweden. Electroplating went to Switzerland, and the circuit board came from Germany. Then, the electronics and final assembly took place in a re-purposed cellphone manufacturing line in Finland with chips from the US and China.

Copper tapes were involved, and there may or may not be a few arts and crafts sessions in our office to make everything come together.

While we were very happy that these initial prototypes worked as expected, we weren’t done yet. How can we scale up the solution by making mass production commercially feasible?

Many technology startups have great ideas on paper. Few can turn them into working prototypes. Even fewer can mass-produce the product profitably — especially with a never-seen-before system like our string cells and string tanks. 

After proving our concept and technology through an “artisanal” way of building the string cell prototypes, we must scale. And we cracked it.

The video below is the birth of the first batch of mass-manufactured string cells using injection molding. Now we’re off to the races.