Comment by phkahler | Hacker News Reader

Comment by phkahler | Hacker News Reader

>> Only try this on an actual car if you know what you’re doing. Even though only two very small patches are made to the model specific calibration values, making changes to your EPS might have unintended consequences.

The author has no idea what he's doing, or more specifically what hazards might be lurking right under his nose. I worked in EPS for 6 years and it's all really cool stuff right up until you download code and it promptly turns left all the way to the stop the first time you touch the wheel. That was a bug ;-) I can't tell you how hazardous it may be to tweak tuning parameters - that depends on a lot of things. Tuning aside, just commanding it over CAN might allow you to do things that wouldn't normally happen and might damage something - i.e. are all protections still in place when taking an external command? I didn't work on this model, or at this company, I'm just saying I've seen a lot of stuff and wouldn't recommend messing around with safety-critical ECUs like this.

I think you are a little bit too harsh here. The author is one of the leading developers at Comma.ai - the company behind OpenPilot. I am closely following the project and regardless of what is your attitude towards OpenPilot, the author is definitely not someone, who jumps into EPS hacking without being aware of implications of his actions.

I have a totally stock EPS that will just apply random full torque left or right if the battery voltage drops below ~10 volts. One would imagine that's a scenario they tested for, but apparently not! It happens very easily on my car when all the electrics are turned on for a few hours while driving with low revs, like driving on a cold dark day on a 40mph road.

The first time I did it, my thumb was dislocated because it was inside the wheel! Didn't realise quite how powerful power steering systems are!

Now I have tape over the heated seats button with a warning to only use them or the rear defroster, not both.

Fun fact: The power steering uses 170 Amps when turning the wheel fast! Of course the voltage drops!

Mind sharing year/make/model of car? That's crazy.

Could a higher capacity battery help?

!!!

Holy cow, that's a crazy failure. Many cars have a zone between idle, and some greater RPM that is essentially a no charge condition. But what a consequence! Having dimmed lights, or an erratic instrumement display is the worst I've seen.

My older Honda has a fairly wide zone, 600 to about 1200 RPM. Annoying on high load days, and I've often wondered why this isn't designed out. Maybe it's wider due to car age and component wear / variation. I've installed a pretty great battery and see a little light dim, and that's about it.

One day I had an alternator failure and some distance to drive to get a new one basically. Made it, but right near the end, the instrument panel would go into reset and the car into some limp mode. Not the end of the world, particularly given I was expecting some failure as battery voltage dropped below 11 volts.

It was close enough to lose instruments entirely, but the engine ran anyway. All in all, it was a pretty graceful failure.

That rando full torque action seems crazy! And at 10! That's definitely a scenario, as you have found out, that can happen enough to seemingly be a problem.

So, what happened! Suddenly, your car is off the road, or what?

Seems like your sore thumb is the least of the potential bad things going on right then.

and it promptly turns left all the way to the stop the first time you touch the wheel.

I bet many have had nearly the same experience with rebuilding a power steering gear... yet that's no justification for taking away control from the things you own.

"Life is risk, risk is life."

> yet that's no justification for taking away control from the things you own

I'm a big believer in owning what you buy, but if what you're buying requires a license to operate and you intend to use it publicly, not to mention the various safety regulations and certifications required just for the product to be legal in the first place (which are likely ignored if not violated while modifying the product), then the justification is "not killing someone else accidentally."

This doesn't mean you can never hack anything, but you should be aware of the risks and potential consequences of your actions.

As long as it's only your own life you risk and not that of others on the road, dependants in your household or something like that that need you to be around, sure.

In this case the EPS already came stock with the functionality to request torque over CAN, that part of the code or the amount of torque was not touched. I agree it would not be a good idea to patch that functionality into an EPS that doesn't come with that from the factory.

One system I know of had to have software to reduce torque at the end stops or it could destroy FETs and shut down. If this system needed such protection, we might wonder if its included when taking external torque commands. I would if I wrote the code, but you never know when operating outside their expected use cases.

It's also much more benign to destroy components than to have actual bugs. And he's not changing software at the source level.

> are all protections still in place when taking an external command

Diagnostic-specific commands are often restricted when the vehicle is in motion. On VW I remember that any "write" command such as an actuator test being declined even for "innocent" stuff such as lights or power windows on the body control module.

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