# Autopilot getting dangerously close to car when going downhill



## pcenginefx (Sep 12, 2017)

Has anyone else gotten a change in autopilot behavior when using it going downhill? I go the same way to work every day and there is one part of my drive which goes downhill at a pretty good grade. Cars are usually in front of me and if autopilot is engaged and the traffic slows down, my M3 isn't braking soon enough to give the right amount of space and does a hard brake at the very last second, usually at the point where I'm afraid I'll ram the car in front of me and I take over.


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## mswlogo (Oct 8, 2018)

What distance do you have it set to? I put mine on Max (7 cars?).


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## pcenginefx (Sep 12, 2017)

mswlogo said:


> What distance do you have it set to? I put mine on Max (7 cars?).


For local roads it's generally 1-4. Even so it seems to fail on braking soon enough even with say 4 cars when going downhill.


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## gary in NY (Dec 2, 2018)

Even at the max, sometimes the following distance feels too close for me. I'm driving rural roads most of the time, so I like distance between cars. You can't always do that in heavy traffic without getting cut off constantly. But, I hadn't noticed anything odd on hills.


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## MelindaV (Apr 2, 2016)

pcenginefx said:


> Has anyone else gotten a change in autopilot behavior when using it going downhill? I go the same way to work every day and there is one part of my drive which goes downhill at a pretty good grade. Cars are usually in front of me and if autopilot is engaged and the traffic slows down, my M3 isn't braking soon enough to give the right amount of space and does a hard brake at the very last second, usually at the point where I'm afraid I'll ram the car in front of me and I take over.


this reminds me of one of my first times driving thru downtown Seattle, stopped behind a pickup at a light, (in a manual 5speed) and when the light changed and the truck moved forward, the boards he had in the bed of the truck, hanging over the tailgate, rolled out onto the street. It was one of the streets like this


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## Niki-and-I (Nov 18, 2018)

Could it be that it was too cold or charged to 100% and it did not have much regen available? (just thinking what could do this). I have a long downhill section on my commute (not as steep as Melinda's but not too far off) and I have never seen autopilot getting closer to the next car than in any other place.


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## Bokonon (Apr 13, 2017)

pcenginefx said:


> Has anyone else gotten a change in autopilot behavior when using it going downhill?


What firmware version are you on, and what firmware version were you on previously when the distance wasn't as close? And about how fast is the speed of traffic, and by how much does it slow down?

I have a very steep hill up and down on my commute (1/4 mile+ in each direction), and I usually go through with Autosteer on. Speed limit is 50 mph, but traffic is usually going about 35-40 during commuting hours. On the return home, traffic typically slows down to a halt near the bottom of the hill, and I've found that Autopilot (on 2019.5.15 and prior) brakes sooner than I would have, and also uses the friction brakes earlier/more than I would have. (Sometimes I'll even disable Autosteer and handle the deceleration myself just to eke out all the regen I can from that grade.)

So, I'm curious about the various reasons why our experiences might diverge...


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## MelindaV (Apr 2, 2016)

Niki-and-I said:


> Could it be that it was too cold or charged to 100% and it did not have much regen available? (just thinking what could do this). I have a long downhill section on my commute (not as steep as Melinda's but not too far off) and I have never seen autopilot getting closer to the next car than in any other place.


AP will use the friction brakes, so if regen is limited, it will still brake when it needs to.


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## Scubastevo80 (Jul 2, 2018)

I've commented in another thread that I'm also seeing AP issues on follow distances. I used to keep it at 2-3, now I need to constantly adjust between 1-4. In some cases 1 is too far, and in others like you indicated, 4 may needed to avoid being too close.


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## pcenginefx (Sep 12, 2017)

Bokonon said:


> What firmware version are you on, and what firmware version were you on previously when the distance wasn't as close? And about how fast is the speed of traffic, and by how much does it slow down?


I'm currently on 2019.5.15. I'm pretty sure I remember experiencing this on the previous FW update as well but not the one before that.

In my specific situation, there is a slope I go down for a few hundred yards before leveling out. There is a stop light at the bottom of the hill so traffic usually comes to a halt when I get on the slope. Speed limit is 35mph. I'll post up a video of the part in question next time so that you can see it.


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## Trappist-1e (Oct 21, 2018)

On 2019.5.15, I've experienced this recently with my family in the car. Going downhill I have mine set to distance of 1. The car was going about 50mph when it detected the car in front, tries to brake but not hard enough, it was getting close at a good speed, so I had to brake with my feet. Ended up about 1 foot behind the car in front of me, it looked like it was going to hit.


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## pcenginefx (Sep 12, 2017)

trappist1e said:


> On 2019.5.15, I've experienced this recently with my family in the car. Going downhill I have mine set to distance of 1. The car was going about 50mph when it detected the car in front, tries to brake but not hard enough, it was getting close at a good speed, so I had to brake with my feet. Ended up about 1 foot behind the car in front of me, it looked like it was going to hit.


Yeah this is exactly what I'm experiencing right now. It's like it isn't braking hard enough to stop the car from hitting the car in front of it coming up (and I'm alone in the car).


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## Trappist-1e (Oct 21, 2018)

@pcenginefx forgot to do a Bug Report at the time because I was making sure everyone was okay. My dad and mom who are still iffy about cars driving themselves were definitely startled.


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## RichEV (Sep 21, 2017)

pcenginefx said:


> I'm currently on 2019.5.15. I'm pretty sure I remember experiencing this on the previous FW update as well but not the one before that.
> 
> In my specific situation, there is a slope I go down for a few hundred yards before leveling out. There is a stop light at the bottom of the hill so traffic usually comes to a halt when I get on the slope. Speed limit is 35mph. I'll post up a video of the part in question next time so that you can see it.


How does it behave with more conservative stopping distances (4)?


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## pcenginefx (Sep 12, 2017)

RichEV said:


> How does it behave with more conservative stopping distances (4)?


Will actually try 4 next time I can get it to happen again. This morning I made it through the stop light at the bottom of the hill without stopping so >_<


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## pcenginefx (Sep 12, 2017)

Here are two videos - first one going down said hill and having autopilot brake behind a truck, the other video braking behind same truck but on level ground. Both on autopilot, both set for car distance of "4". There is an obvious distance difference between the two brake instances:
Video 1 (brake distance going downhill):





Video 2 (brake distance on level ground):


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## ADK46 (Aug 4, 2018)

It's as though the desired brake/regen application force is calculated solely from speed and distance, without taking into consideration the additional force necessary to resist gravity. The result is not only a surprise to the driver, but to the AP system itself. I'm sure there is an inclinometer in the car (there's one in my phone and even my watch); the gravity force is simply grade times weight. I'm afraid I've come to expect this of Tesla's AP software - I don't think they have anyone assigned to work on the basic goal of driving well in simple situations. I'd much prefer that they suspended work on FSD until they get the basics working perfectly.


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