Remember when Elon Musk said batteries would come out of the Tesla Gigafactory as fast as “bullets from a machine gun”?

The hinted (and newly discovered) automation technique is somewhat similar. It would be simplified as: "making modules as fast as bullets on a machine gun belt."

Yes, a machine gun belt. Each bullet is attached to the belt but in this case, the battery cells are the bullets and the machine gun belt is the cooling ribbon that Tesla uses to cool the pack.

Schematic of Tesla Model S Battery Module

Schematic of Tesla Model S Battery Module

In Model S, a ribbon-shaped cooling tube snakes its way through the pack to cool the cells (ref). In Model S and X packs, the cooling snake is not physically attached to the cells. In the Tesla Model 3 battery module, the cells are physically attached to the cooling ribbon.

How do we know this?

An article describes Tesla's funding for battery pack automation equipment. Apparently, the article which first appeared on Teslarati has since been taken down - presumably because of the sensitive internal material pertaining to Tesla.

The article mentions one major expenditure that stands out:

Perhaps this new battery pack automation technique -- which was likely intended to speed up the process -- was the main culprit in the Tesla Model 3 production bottleneck

Perhaps this new battery pack automation technique -- which was likely intended to speed up the process -- was the main culprit in the Tesla Model 3 production bottleneck

Cell to Tube Attach (CTA): $30.7M

That's new. The cells were never attached to the cooling tube in the Model S, but apparently, they are now in Model 3.

How exactly the cells are attached is not known for sure, though speculation suggests that the cells are glued to the cooling tube. Speculation also assumes that this gluing procedure is where the Tesla Model 3 production bottleneck is.

Gluing the cooling tube to the cooling ribbon accomplishes two things:

  1. It allows for better cell cooling because the heat transfer coefficient is higher.
  2. It allows for speedy assembly of the cells into a module as opposed to manually inserting the cells.
This completed machine gun belt is then snaked in an "S" shape to form the module.

It's so simple and obvious I don't understand why we didn't think of it earlier.

*Fellow engineer Keith Ritter also contributed to this article