Regenerative braking

Regenerative braking

One of the nicest features in driving the MS day to day is - in addition to the dizzying acceleration - the regenerative braking. I wouldn't mind it if it were adjustable to kick in on a steeper ramp that I control with the accelerator, because I think after a few days, I'd know how to handle it. I also notice that it disengages when the car reaches 5 mph. I would be in favor of keeping it active down to a practical standstill.
This is all software controlled, right? So I guess Tesla could give us more detailed fine tuning options, other than standard and low, such as an adjustment of the curve on which it activates and the minimum speed when it disengages. That would help us not only convert the last ounce of kinetic energy, but it would be a quite usable driving tool.
What do you guys think?

Brian H | February 22, 2013

Below 5 mph there's not enough energy to capture to do much more slowing. Brakes are better at the lowest speeds.

And there are 2 settings, max and low. The max dumps 60kW into the batteries. Don't know the low spec.

The rest is physics.

diegoPasadena | February 22, 2013

Brian H:
There is really no physical reason for "5mph". As long as the car is rolling there is kinetic energy. Tesla could just as easily have set it to disengage at 10mph - or 2mph. Of course, the slower the car is moving, the less there is to be harvested. I'm assuming they chose 5mph as the point where additional gains are insignificant. I'd like a lower point of disengagement mostly for the driving, not really for the additional few electrons.

andrigtmiller | February 22, 2013

Having driven mine over the course of the last two days (just received mine on the 20th), I actually like the way it behaves. I wouldn't change anything.

scriptacus | February 22, 2013

Can you stop properly without using the brake at all, or does the 5mph cutoff prevent that?

diegoPasadena | February 22, 2013

At 5mph it just rolls, so you do need to tap the brakes. (This is whole discussion is, of course with creep disabled).
Mind you: I think the car drives absolutely like a dream, and if nothing were to be changed, I'd still think this is the best driving experience ever. But since there *could* be the opportunity to fine tune, I'd love to do it. I guess that goes back to my adrenaline-filled days of European rally racing, where fine tuning was the name of the game. Probably not worth Tesla's effort, I do concede - unless it's easy to do.

jat | February 22, 2013

@diegoPasadena - it isn't that it disengages, but that it simply doesn't extract enough energy to slow the car down much. The kinetic energy is proportional to the square of the velocity, so at 5mph there is less than .09% as much energy to be extracted as there is at 70mph.

If you wanted to stop without using the brakes, you would actually need to feed energy into the motor to counteract the motion of the car.

DTsea | February 22, 2013

diegoPasadena, is exactly right. At 5 mph there is only 4% of the kinetic energy in the vehicle as at 25 mph, and only 1/144th of the energy at 60 mph. It is the same reason your brakes decelerate you more at low speed (per second) than at high speed- the brakes can dissipate energy at a certain rate and so at high speeds that is less of a deceleration. A regen system sized to the 5 mph case would be VERY stiff at any higher speed. Personally I find the tuning perfect- driving in city traffic I hardly use the brakes, but on the highway the decel works great for station keeping at 60 mph too.

peahl | February 22, 2013

100% with, try to get in an BMW ActiveE you will find what you ask for.

Brian H | February 23, 2013

Impossibly stiff. All the regen circuitry can take is 60A, and that's reached at lower speed and then plateaus if you size to 5mph.

Mark K | February 23, 2013

Think there's a conceptual error here.

While it's true that the kinetic energy rises as the square of velocity, you don't need energy to dissipate energy.

If you want regen feel down to zero, there are many ways to do it.

If you put a short across a motor and then try to move the rotor, it is very difficult, even at the equivalent of 1 mph.

That said, the primary load in the car's drive system during regen is the battery. To my knowledge, they dont have a resistive load to dump charge. Depending upon how the drive electronics are organized it may or may not be possible for firmware to slow it with the battery load if the motor output potential is lower than the battery voltage (can't drive charge into a battery when the cell potential is higher than the charge source. An inverter can fix this, but not sure if TM's power drive electronics step up/down the voltage or just PWM the battery output to control current. Think it's PWM.

Still, even in this case, the ABS servo's can be feathered in below 5 mph to automatically gently apply brakes until you stop. This can give you the full one pedal experience if desired.

Cattledog | February 23, 2013

diego - I'm with you, nothing needs to change and it already beats every other driving experience out there. But because we have tasted the electrical good life, we want the better life. For me, that would be a couple things:

1. Slider bar vs. two position setting for regen, like the pano roof so you can dial to the setting you like;

2. A setting where you could set the max (say 60A) for under 45 mph and then the min (say 30A) for 75 mph and over with a linear progression - in this case, one amp of regen per mph. I like to drive on the Max/Standard setting in the city and the Low setting on the highway, but I'd like to have a more fluid transition between the two.

My 2 amps worth.

Brian H | February 23, 2013

A re-volting idea. Excellent!