How does it know if your hands are on the wheel?

[Patrick W]

Any ideas how the system knows if one's hands are on the wheel?

When I get the message saying to put my hands on the wheel sometimes just lightly touching the wheel with one hand works. But sometimes I have to grip the wheel hard. And other times I need to move the wheel slightly. All of the preceding with gloved and bare hands.

Also, anyone noticed lately the "Put hands on wheel" message is not always accompanied by a chime? Ignore the message and eventually the chime sounds but seems like in the past a chime always sounded when the message appeared.

 

[Vger]

At some point Tesla explained that it is by micro-torque measurements of the steering mechanism. Apparently when you hold the wheel, you impede the adjustments the steering motor is making even just slightly. It can measure that and "tell" that you are there.

 

[S4WRXTTCS]

My conclusion after a few thousand miles of driving with it is that it doesn't.

Instead it measures torque applied in one direction or the other.

90% of the time I get the "hold steering wheel" is in corners because in corners it can cheat.

and yeah it does cheat.

50+ miles of straightaway and nothing, but one mild corner and it pops up.

 

[Todd Burch]

The steering is controlled not by basic motors but by servos. Servos are like motors, except that they are capable of being set to a specific rotation angle.

The car knows that you're there by sensing that more torque is needed to rotate than is required just by the wheel/steering shaft alone.

In other words, you have to apply a bit of rotational force to the wheel for it to recognize you--it is not touch-based at all.

And the car's not "cheating"...the reason you see the message more often in turns (especially sharp ones) is because autopilot's uncertainty about the action to take increases in a sharp turn. (A "sharp" turn to autopilot is not necessarily sharp by manual driving standards).

 

[donv]

I always have to jiggle the wheel a bit. Sometimes quite a bit.