Elon Musk on the effects of jitter on Tesla Autopilot

[sheppard]

I'd never heard of jitter discussed outside the context of DACs (and only in the audiophile context) until today, when I saw Elon discuss it within the context of Tesla Autopilot.

To summarize, when Autopilot wants to tell the car to, for example, turn the steering wheel X degrees left, it wants the turn to happen at a verify specific moment in time and jitter (Elon also calls it "variable latency") adds unpredictability to when it will actually happen. A steering wheel adjustment 100ms earlier or later than intended when traveling at 100mph can matter.

It's reassuring to see that not just audiophiles but even the CEO of one of the most valuable companies in the world cares about it too!

 

[K3RMIT]

Makes sense to me. i thought all the heavy living was done on board
if I get him it’s real time over wifi geezz
but most new cars dont have a steering column so we are all driving a video game.
correct me if I’m wrong

 

[microstrip]

I'd never heard of jitter discussed outside the context of DACs (and only in the audiophile context) until today, when I saw Elon discuss it within the context of Tesla Autopilot.

To summarize, when Autopilot wants to tell the car to, for example, turn the steering wheel X degrees left, it wants the turn to happen at a verify specific moment in time and jitter (Elon also calls it "variable latency") adds unpredictability to when it will actually happen. A steering wheel adjustment 100ms earlier or later than intended when traveling at 100mph can matter.

It's reassuring to see that not just audiophiles but even the CEO of one of the most valuable companies in the world cares about it too!

Jiitter can have different meanings according to context. In electronics and radio it has the meaning we use in DACs - phase noise of the clock signal. However in data communications jitter can mean variation of the delivery time of the message - " variable latency" as you wrote.

 

[K3RMIT]

I think his jitter is more lantecy then noise
I can’t see how noise matters in this case. his point my be why the delay takes place

 

[K3RMIT]

Ill say this im not ready to let a car drive me at 70 mikes am hour no way
traffic yea

 

[Steve Williams]

Ill say this im not ready to let a car drive me at 70 mikes am hour no way
traffic yea

I own two Teslas with autopilot. I have to tell you that it is a knuckle buster to turn it on. It makes all of the correct turn but there is jitter and last second turns that for me makes autopilot crazier than an E ride at Disneyland. My fingers are microns from the steering wheel. I see it as the future . It just isn't "the now" but seeing the refinements with each new Tesla computer update, there is no doubt in my mind that the age of driverless cars is soon upon us

 

[Tim Link]

100ms latency is not too bad in terms of a reaction time for a car, or a person. I think I read somewhere that they did tests on people who were very good at fast action video games. They told them to press the button as soon as they saw a flash of light, or heard a beep. It's hard to hit that button any faster than about 200ms after receiving the signal. The brain has to process the signal before it can then send it's own signal out to the thumb to push the button. People have reaction times in games that seem much faster than that, but it turns out those are done predictively, not waiting for the actual input to be received. They're anticipating what their opponent will do, and blocking or dodging before actually seeing the attack initiated. The car will have to do the same thing we do, apply the correction earlier in anticipation of an upcoming situation. On-line video games are doing some pretty fancy things to deal with on-line latency in fast action games. Understanding how people's perception works allows them to make the game seem to be much more responsive than it really is.

If the car is sometimes making an input 100ms too early, that suggests it already is making anticipatory reactions trying to take into account it's own latency, which may vary and cause it to do something too early.

 

[msimanyi]

@Steve Williams I'm revealing some demographics here, but how many of our readers understand your reference to an E-ticket ride?!!

 

[Tim Link]

I own two Teslas with autopilot. I have to tell you that it is a knuckle buster to turn it on. It makes all of the correct turn but there is jitter and last second turns that for me makes autopilot crazier than an E ride at Disneyland. My fingers are microns from the steering wheel. I see it as the future . It just isn't "the now" but seeing the refinements with each new Tesla computer update, there is no doubt in my mind that the age of driverless cars is soon upon us

Plain old cruise control makes me a little nervous. When I hit that resume button and the car takes off on it's own, I'm always watching very closely to make sure it stops accelerating at the right time.

 

[Steve Williams]

You have to be an old fart to know what an E ride was. Or better yet can you name them all

 

[Steve Williams]

@Steve Williams I'm revealing some demographics here, but how many of our readers understand your reference to an E-ticket ride?!!

You have to be an old fart to know what an E ride was. Or better yet can you name them all