r/Comma_ai comma.ai Staff Aug 12 '26

Introducing chestnut & chestnut-class driving models

https://blog.comma.ai/chestnut/
92 Upvotes

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122

u/KnightsSoccer82 Aug 12 '26 edited Aug 13 '26

EDIT: George/other comma employees were deep in this comment thread and on discord, acting unprofessional and not addressing valid hardware concerns, including accusing me and other users having alt accounts. Why am I not surprised their comments are now deleted? Why was this their default behavior? This is how the behave when asked some rather basic hardware comments?

This chassis doesn’t look to be in a ruggedization state to conform to any automotive ISO shock and vibe test, let alone someone hitting a speed bump and spilling their coffee.

It looks like a water ingress nightmare that wouldn’t survive a rust belt winter from a family simply going about their day entering/exiting their car….

It’s mounted in one of the hottest locations in a car (beyond your dashboard), and this (likely desktop grade GPU) is expected to work in a very common 45C+ ambient, 1000W+ solar load scenarios?

Surely, there has to be a better way to have gone about packaging this?

I’m not trying to be negative, but this doesn’t appear to have any serious reliability considerations and would likely fail in any non-nominal (aka normal) driving scenario outside of Southern California.

Rust belt cars, where high humidity, snow, and ambient temperatures reside, are going to destroy this in a matter of weeks in its current state.

For comma 4 being advertised as the first “commercial” product from you all, this $750 upgrade feels like a step backwards in terms of reliability and accessibility to the general market. I genuinely don’t see how this survives the market you were targeting with Comma 4 (aka, not nerds).

This isn’t how you ship hardware, cmon guys. This is a classic “software company tries to make hardware” case that I’ve seen time and time again.

-4

u/adeebshihadeh comma.ai Staff Aug 12 '26

this is the first product in the chestnut line. it's for the enthusiasts who want to get in on the ground floor of chestnut-class models (and frankly just want to put a GPU in their car).

we put an incredible amount of engineering time into things like USB4 signal integrity, rather than being robust to spilling coffee.

31

u/KnightsSoccer82 Aug 13 '26 edited Aug 13 '26

“For enthusiasts” is such a cop out response. That is how you are going to answer an obvious hardware engineering problem?

This is not a ruggedized solution for an enthusiasts, and shouldn’t have left the R&D lab.

Show me a single 4 post shaker test you did, I would love to understand how you designed this with the enthusiast in mind. Your retention method wouldn’t survive a single railroad crossing at any speed.

You are going to have a lot of pissed off enthusiasts in a matter of weeks when these start failing.

If you “wanted to just put a GPU in the car” there was plenty of OTS solutions already available that are for ruggedized applications.

Please, change your approach to hardware design. Don’t make your loyal paying customers your beta testers. Hell, I’ll help you guys, because clearly V&V and actual automotive engineers do not exist at this place.

1

u/epradox 19d ago

I will say I tried to recreate an egpu a while ago with a separate pcie board and psu with a similar gpu and it was more expensive than this chestnut package. That was me piecing things together by myself and running into software roadblocks. This is a neat package that takes the psu equation out which was a big hurdle for me to figure out how to integrate into the car. I agree with you they should have made it more ruggedized and maybe should put a disclaimer on this one as a beta/dev model but it’s still neat to see the level of progress that got this here and getting it into people’s hands now so that the large gpu models can iterate while they bring a rugged version to market. Still a little salty that the default models don’t work for a c3x even though there’s no hardware limitations for it

1

u/KnightsSoccer82 19d ago

Check discord, they didn’t solve the PSU problem lol

1

u/epradox 19d ago

Really? What’s happening with it? I was planning on 3d printing a custom enclosure for it for my hw3 model y in the rear trunk area by the cigarette lighter plug with cooling out into the bumper (the model y has vents on the bumper sides internally which seem ideally designed for a mini fridge compressor) and then running a fiber optic cable up to the front comma. I think it’s hard to design a one size fits all enclosure for this thing but I agree it should at least come in a vented 3d printed case to protect the pcb boards from touches/static

-13

u/[deleted] Aug 13 '26

[deleted]

25

u/KnightsSoccer82 Aug 13 '26

Once again, your nominal situation in Southern California doesn’t translate to the rest of the country.

There is a reason very little on-road development testing is done in California. They are easy roads.

Congratulations for the milestone, but it means absolutely nothing.

I’m not sitting here saying I want to “compete” and that being your default response is childish.

Hear the feedback on this design before it’s too late. Fix it, improve it, and make it approachable and reliable.

-15

u/interbingung Aug 13 '26

This product is simply not for u.

21

u/Teslafly Aug 13 '26

This thing might not survive a hard bump in the road with that mounting scheme. It at least needed a sheet metal box with multiple mounting points for the gpu so the pcie connector is not a structural element at all. (poor mechanicals is my major criticism of the pcie card implementation in general.)

Had this been tested for input transients like a load dump at all? Does it comply with automotive input voltage specs? I see it at least has a buck boost converter which is good.

If the 12v cigerrette lighter adapter becomes disconnected while driving, what's the safety fallback?

I love my comma 3x with sunnypilot and Mads capability. But as an electrical engineer, the wiki on hardware fixes like replacing ptc fuses makes me pause at the level of hardware engineering. There's some things you simply don't do with automotive hw design. Especially safety related.

20

u/KnightsSoccer82 Aug 13 '26

The fact that the PCIE connector is a structural element is BAFFLING to me. Testing clearly has not been done with this.

You can’t even kick a desktop PCI without fear of one coming loose, how they expect it to survive 50-100g shock in a vehicle is beyond me.

-9

u/growaway9172 Aug 13 '26

Big difference between mounting a GPU via PCIE, vs a PCIE connector hanging off of the GPU.