Rivian reduced electrical wiring by 1.6 miles and 44 pounds

I like to imagine some kind of engineering “meet cute” whereby, one random day, the headlights engineer and the parking radar engineer happen to be working on the front of the car together. Their eyes meet:

“hey, I’m John — I didn’t know you had an ECU here!”,

“hi, I’m Claire — wow, you have an ECU right up front too? It’s, like, right next to mine and we never knew!”

“I know, crazy right?! Hey this is going to sound really forward and I don’t normally do this but I’m only running at 70% compute capacity. I don’t suppose you need any real-time budget this evening?”

“So funny you should ask, I was just about to run a whole bunch of heavy new wiring to…”

And in a story as old as time they get ECU married and raise their control loops in the same front-of-vehicle ECU together instead of living their separate, lonely, ECU-right-next-to-each-other-and-they-didn’t-know-it lives.

For those unfamiliar with Conway's law, I am arguing that how the car companies have organized themselves--and their budgets--ends up being directly reflected in the number of ECUs as well as how they're connected with each other. I imagine that by measuring the amount of excess copper, you´d have a pretty good measure for the overhead involved in the project management from the manufacturers' side.

(I previously worked for Daimler)

With domain-based ECUs, a failure means your locks OR windows OR windshield wipers stop working.

With zone-based, it could be the entire "west" zone that stops, which means you can't unlock the driver's door, open the windows, adjust the seat, and maybe even the ventilation fans don't work

I actually thought a lot of that was already on the CAN bus anyway, but my knowledge of cars stops there so maybe someone can fill in the gaps. Seeing only three "zones" is actually surprising to me. As I was reading I started forming the idea of a single bus cable that went around the car, with I/O modules anywhere there were physical buttons/lights/etc. There would just have to be a cost+weight balance of where it makes sense to stick a small I/O module vs run individual wires back to a bigger module. My assumption is as technology advances it becomes cheaper to have more small I/O modules with very short wire runs to buttons, but it doesn't seem like this is what they're doing.

I am also making the assumption this is "dumb I/O", and somewhere there is a "door lock" program that handles all locks/buttons. In the main computer you'd run all the domain programs individually/isolated, but there would still be a single program responsible for each domain, eg: all the locks (eg: considering button presses, fob buttons, door state, moving or not, etc, and act on the locks accordingly).

From a pure software point of view, if the east/west/south ECUs are actually doing the logic for their respective parts of the car, that seems like a nightmare to build: the code would end up being all partial and distributed. In the worst case you end up with bizarre bugs like "if you open the passenger door, then open the tailgate, then close the passenger door and press the lock button, the driver's door will lock but the passenger won't until you first unlock then shut everything" (which gets reported as "the locks are unreliable, some will randomly just not work every few days").

https://news.ycombinator.com/item?id=38576612: The move to 48V means much less power is lost (power loss = (IxI)xR ), cables can be much smaller, cables and terminals can be much lighter and much less copper can be used used.

Discussion: Tesla shares 48V architecture with other automakers: https://news.ycombinator.com/item?id=38557203

https://electrek.co/2019/07/22/tesla-revolutionary-wiring-ar...

"In order to facilitate the automation of manipulating cables, Tesla has been reducing the length of wiring harnesses in its vehicles.

Musk said that Model S has about 3 kilometers of wiring harnesses and Tesla brought it down to 1.5 kilometers in length for the Model 3.

But that’s just the beginning. Tesla is working on a whole new wiring architecture for future vehicle platforms and they aim to bring it down to just 100 meters starting with the Model Y."

If Rivian wants to add a new feature that doesn't 'fit' on the AIO ecu, then what? Replace it and re-certify ALL of its functions?

A good example is the ABS controller which is usually just a Bosch COTS ECU.

You wouldn't even want to implement that for yourself.

Next step: Each wire only goes to the nearest box. I'm curious how the Tesla unboxed architecture will eventually play out. I understand that eventually, the ECUs will be split up, so you have some aspect of each ECU in each corner of the vehicle. Part of the "lights" function is in front-left, part of it in the back. Wires only go to the nearest box.

A powerful vision, with the potential to further reduce wiring. Complex until you get a distributed brake ECU.

Am I reading this wrong, or are these actually five categories?

> 1.6 miles and 44 pounds

pure copper density at 9000 kg/m3, wire diameter assumed at 1mm, length at 3000 m (1.8 mi, approx) gives 21 kg, approximately 46 lb. math checks out.

> the company claims a 20 percent savings in material costs and 15 percent reduction in its carbon footprint between Gen 1 and Gen 2.

surely this is not just due to the reduction of copper. copper is around 10 USD/kg at bulk.

now let's see if we can address the copper length number. can 1.6 mi (< 3000 m) of copper be saved from wiring alone?

The car dimensions are 2m x 5m. That means, in the worst case, two ECUs placed at opposite ends will need 5m of wire (half of perimeter). There were 17 ECUs originally. Call it n = 20, and if we wire dense (in the graph sense), we get n^2 = 400. So, in the absolute worst case, the densest possible graph would have had 5m x 400 = 2000 m of wire. The claimed wire saving is significantly (but not by an order of magnitude) larger than this. I would say this passes the smell test (albeit barely), but original wiring must have been truly inefficient.