Cruise Control still follows throttle pedal

[CorneliusRox]

When I set cruise control and then slowly let off the throttle, the car decelerates as if I had not set cruise control at all. Then when I'm about 5mph slower than the speed I set, it'll all of a sudden launch back to the set speed.

Does anyone else have the same experience? Is there a way to fix this? Can anyone explain the dynamics here so I can maybe change my behavior to counter it?

SIDE QUESTION: Is there a 'resume' function for cruise control?

 

[ShawnA]

Hi @CorneliusRox ,

Generally the cars will not engage cruise control while you are varying the speed with the throttle.
When you set cruise control release the throttle, the car may decrease speed a little and then will climb
to your set speed. If anything very different than this occurs, your car needs service...

To resume cruise control - pull the lever used to set cruise control one time...

Good luck,

Shawn

 

[FirstInTown]

My 2020 MX LR+ does the same thing. How hard is it to engage cruise and release trottle w/o slowing down while releasing foot? Apparently very hard in a Tesla. Anoying, because the car has so much power, when the throttle comes back automatically after the slowdown, it is a bit jerky. Should be able to program around this, if it was a priority, but must not be.

 

[CorneliusRox]

Generally the cars will not engage cruise control while you are varying the speed with the throttle.
When you set cruise control release the throttle, the car may decrease speed a little and then will climb
to your set speed. If anything very different than this occurs, your car needs service...

To resume cruise control - pull the lever used to set cruise control one time...

That's what mine does, it's just not what I feel it should be or what any of my other cars do. There's just no way to set cruise and not have a dip then? I used to use the offset and I don't think I noticed it then, but I got sick of that.
I'll have to try the resume pull. I thought it just set a new speed but maybe I'm pulling it too far?

My 2020 MX LR+ does the same thing. How hard is it to engage cruise and release trottle w/o slowing down while releasing foot? Apparently very hard in a Tesla. Anoying, because the car has so much power, when the throttle comes back automatically after the slowdown, it is a bit jerky. Should be able to program around this, if it was a priority, but must not be.

Yeah, these are my thoughts exactly. It seems like an issue and the car is so jerky with the throttle that it comes across as non-refined.

 

[thewishmaster]

I notice the same behavior. Basically trained myself to let go of the throttle a bit later to let the automated throttle catch up. Guessing it is built to gradually ramp up the speed irrespective of the current speed/throttle position to avoid surprises in the other direction

 

[ShawnA]

Hi @CorneliusRox ,

There is a way to set CC without the dip, but you may find it more of a pain than the dip.
Set cruise control to current speed with pull on lever, then bump the lever up quickly
for a 1 mph increase or slowly for a 5 mph increase (multiple bumps) to get where you want it to be.....

Good luck,

Shawn

 

[laceyboy]

You will experience your car slowed down after you activate cruise control if your car is closer to the car ahead of you than preset distance.

 

[CorneliusRox]

You will experience your car slowed down after you activate cruise control if your car is closer to the car ahead of you than preset distance.

Of course. This scenario I am talking about happens without adaptive cruise control input.

 

[laceyboy]

If so, then I don't have this issue with either my MY or MX

 

[rxlawdude]

If so, then I don't have this issue with either my MY or MX

Nor in our MY or M3, both with FSD.

 

[CorneliusRox]

Nor in our MY or M3, both with FSD.

That's a good point. I don't have FSD. I wonder if that's a factor.
@FirstInTown do you have FSD?

 

[laceyboy]

That's a good point. I don't have FSD. I wonder if that's a factor.
@FirstInTown do you have FSD?

My MX has FSD but not MY. So I don't think FSD has something to do with the issue

 

[johnm]

When I set cruise control and then slowly let off the throttle, the car decelerates as if I had not set cruise control at all. Then when I'm about 5mph slower than the speed I set, it'll all of a sudden launch back to the set speed.

Does anyone else have the same experience? Is there a way to fix this? Can anyone explain the dynamics here so I can maybe change my behavior to counter it?

SIDE QUESTION: Is there a 'resume' function for cruise control?

"then slowly let off the throttle" Why not release the pedal quickly?

 

[CorneliusRox]

"then slowly let off the throttle" Why not release the pedal quickly?

Mostly because if you think you hit it but you didn't and let off quickly, it's pretty violent (if you're not expecting it).

 

[gearchruncher]

This is just the way a PID control system works.

The vehicle is above the set speed, so the power command reduces. The longer it is above the set speed, the more it reduces, the (I)ntegral term in PID. Of course, nothing is happening because the actual power command is the greater of the cruise control or the accelerator pedal, so it just keeps decreasing to zero.

When you suddenly let off, the cruise command is much lower than needed. The (D)erivitatve term catches this pretty quick, but it can only react to the sudden slow down of the vehicle. It has no way to see this coming, as there is no direct tie between power command and speed (it changes with hills, wind, etc).

The way around it is to let off the accelerator slowly so that you give it a second or two just below the set speed for the I term to wind back up and take over from the pedal. You can feel it take over as the car actually speeds up as you keep backing off.

All my vehicles do this (Tesla or not). I've never driven a car that doesn't do it, but I could see how you could add some smarts based on the fast change in throttle position. That increases the complexity of the system, which can add some real safety and design challenges, which is why I assume they avoid it.

There's zero reason to think FSD vs EAP vs AP would have any impact on how cruise control would return to the set speed after a sudden accelerator change. This happens even when you don't have autosteer on and are just using TACC. I bet it even happens to people without TACC and just "dumb" cruise.

 

[Daniel in SD]

I have noticed this behavior too. I haven’t quite figured out the pattern. What’s annoying is that I’m sure it flashes the brake lights before accelerating. So if someone is following me I have to feather the accelerator for a long time before cruise control kicks in. It’s weird though that sometimes it seems to engage immediately.

 

[mikes_fsd]

Mostly because if you think you hit it but you didn't and let off quickly, it's pretty violent (if you're not expecting it).

I have noticed this behavior too. I haven’t quite figured out the pattern. What’s annoying is that I’m sure it flashes the brake lights before accelerating. So if someone is following me I have to feather the accelerator for a long time before cruise control kicks in. It’s weird though that sometimes it seems to engage immediately.

This is easy to recreate. It took me a while to find the right balance of applying the accelerator to match the TACC "easing off" accelerator.
How to recreate/test at any time when TACC/Autopilot is engaged:
If you are cruising on AP at 60 mph and want to just feather the accelerator to speed up 1 or 2 mph more.
Basically when you start applying accelerator manually while TACC is engaged, @ 60-70% of the way to matching the set "going speed", the AP/TACC will start "easing off" in what I can only describe as accelerator "control handoff".

I will add one caveat, it is more pronounced on my AP1 car but my FSD Tesla does this as well, just seems the two use slightly different "easing off" curves.

I've learned to just apply the accelerator as if I am trying to speed up by 4-5 mph instead of 1-2, so not gunning it.
This is not noticeable if you want to just fly by someone on the highway, and need to speed up quickly.

Rereading what I wrote: it seems like this is difficult to describe on a forum. Let me know if I can clarify anything, but the easiest way is to go try it out on your car.

 

[mark95476]

You mean gas pedal/accelerator position, right? So 60-70% of accelerator position when going 60 mph.

I use AP all the time and manually accelerate regularly to keep up with traffic flows, especially when we get to lights.

This is easy to recreate. It took me a while to find the right balance of applying the accelerator to match the TACC "easing off" accelerator.
How to recreate/test at any time when TACC/Autopilot is engaged:
If you are cruising on AP at 60 mph and want to just feather the accelerator to speed up 1 or 2 mph more.
Basically when you start applying accelerator manually while TACC is engaged, @ 60-70% of the way to matching the set "going speed", the AP/TACC will start "easing off" in what I can only describe as accelerator "control handoff".

I will add one caveat, it is more pronounced on my AP1 car but my FSD Tesla does this as well, just seems the two use slightly different "easing off" curves.

I've learned to just apply the accelerator as if I am trying to speed up by 4-5 mph instead of 1-2, so not gunning it.
This is not noticeable if you want to just fly by someone on the highway, and need to speed up quickly.

Rereading what I wrote: it seems like this is difficult to describe on a forum. Let me know if I can clarify anything, but the easiest way is to go try it out on your car.

Me neither.

Nor in our MY or M3, both with FSD.

 

[gearchruncher]

Basically when you start applying accelerator manually while TACC is engaged, @ 60-70% of the way to matching the set "going speed", the AP/TACC will start "easing off" in what I can only describe as accelerator "control handoff".

Yep, like I explained above, this is the cruise control PID reducing it's commanded power, as the vehicle is now above the set speed, and the motor power is the higher of the pedal command or the cruise control command. The cruise has no idea you are pressing on the pedal, so it just thinks the car is going too fast due to a hill and reduces power.

It’s weird though that sometimes it seems to engage immediately.

The reason it will feel so different is the derivative term which senses how fast the car is moving away from the set speed. Really minor variations in the speed profile that are imperceptible to humans right before you release the pedal can mean mean the PID loop may have a 0% power command or one that is only a few percent below what is needed to maintain speed.

 

[FirstInTown]

All my vehicles do this (Tesla or not). I've never driven a car that doesn't do it, but I could see how you could add some smarts based on the fast change in throttle position. That increases the complexity of the system, which can add some real safety and design challenges, which is why I assume they avoid it.

NONE of my other cars or any other car I have driven do it like the Tesla.

Lets go back 40 years, and before Throttle-By-wire. The Cruise Control physically controlled the throttle opening on the carburetor or throttle body by holding it open, just like the peddle your foot pushes on does. SO, very easy to set speed, and remove foot and ZERO speed bump to humans, as the throttle was held at the 'current position' by the car cruise control.

Jump forward to throttle-by-wire in cars OTHER THAN TESLA. Lets say my Chevy Volt. In both full-electric or when ICE is running, it is the same. The programmers, having experience with how the older system provided a smooth "bump-less" transition to car control, did programming that allowed the foot to be removed from the pedal and the car to ignore this foot removal and keep a smooth speed while moving from human control to car controlled cruise.

Tesla must have missed the memo on how to do this apparently and their system follows the foot removal by lowering the torque until the foot is fully off.(no throttle plane to really open, so just a torque command). THEN cruise notices the car slowed down just a bit from the set-point and has to juice the torque in a not-so-smooth way to get back to set speed.

It is just programming, other makers with WAY less expensive cars do it so not a price excuse. Appears Tesla just doesn't see it as something important.

(Maybe instead of fart noises, we could have smooth transition to car control in my $100K+ luxury car????)

And while they are 'fixing' this, get rid of the car slamming on the brakes for no reason on TACC cruise. Again, Volt and Caddy SRX don't do this. ('16 Mustang GT (5.0 ICE version) does sometimes freak out and blink red dash " oh my, you are going to hit something", so Ford needs to work on this also.