Automatic Brake Lights

[Adoepner]

Since our car decelerates aggressively in B (compared to an ICE vehicle coasting), I wanted to have a way to automatically trigger the brake lights to help save from being rear-ended.

Today I installed a GearBrake Smart Brake Light Module (https://gearbrake.com/). They are really cheap.

I installed the GearBrake in parallel with the pedal switch. I didn't want to potentially lose the brake lights if the module fails for some reason. Here are some wiring notes:

GearBrake Green (ground): Any available ground point under the dash.

GearBrake Red (+12V): Teal wire (one of 4 largest gauge wires in the key switch bundle, this wire is HOT when the key is in the ON position).

GearBrake Yellow (Brake signal out): White wire from brake pedal switch.

GearBrake Blue (Brake signal in): used only to calibrate the module. Needs 5x +12V pulses within the first 10 seconds on the first power up. This triggers the module to find level.

The quick install sheet that came with my module made no mention of using the blue wire. The instructions on the website use the blue wire to put the GearBrake module in series with normal brake light activation.

Sensitivity is set by tilting the module after calibration. I have mine set so that it just barely activates when coasting in ECO.

Notes on the I-Miev key switch wiring harness:

Red - always HOT
Teal - ON
Purple - ACC
Yellow - START

Andrew

 

[Don]

Since our car decelerates aggressively in B (compared to an ICE vehicle coasting), I wanted to have a way to automatically trigger the brake lights to help save from being rear-ended.

To each his own, I guess - Glad you're happy with your brake lights flickering on and off - Gladder still I'm not following you!

I drive in B mode 100% of the time and I don't find the deceleration to be 'aggressive' by any means - Certainly not as aggressive as downshifting manual transmission ICE's which I have done for . . . . maybe 50 years! Never been rear ended because . . . . I watch my mirror before I begin to slow down The iMiEV is also not nearly as aggressive as the max regen paddle in my 2017 Chevy Volt - Oh, how I wish our iMiEV's had a max regen paddle. I think touching the brake pedal just enough to turn on the brake lights does give you max regen and I've considered a mod to put a switch on the shifter tied into the brake lights just to give more regen, but I've never got around to experimenting with it

For me, I'm glad the brake lights don't come on until i press the brake pedal. Few things annoy me more than the car in front of me flickering it's brake lights on and off and on and off - VERY distracting . . . . and you never know when they actually are thinking about slowing. Usually it's just the 'left foot brakers' who keep their foot on the brake pedal all the time so they can kill their fuel economy by pressing both pedals at the same time! I *think* my Volt flickers it's lights sometimes with it's overly sensitive application of the brake lights - Need to find a way to mod that to be more like the iMiEV - No brake lights for weak regen and only apply them when I'm actually slowing down at a pace which requires them. The US Federal Government has a standard for how rapidly you're slowing and whether or not it requires brake lights - The iMiEV in B mode doesn't decelerate quickly enough to meet that threshold, which is why we only have brake lights with the brake pedal

Don

 

[JoeS]

I share Don's comments and concerns as I like to think that I keep one eye on the rear-view mirror and always have the option of tapping the brake to flash my brake lights.

Following Teslas down my winding road to town is often infuriating as many drivers don't practice nuanced control over their go-pedal and their brake lights come on unnecessarily and inordinately often.

That said, I bought one of these gadgets because I'd like to support what looks like a small company and it appears, sadly, that they're having a fire sale. There must be some other uses for this thing...

 

[Adoepner]

The latest free info I could find on the web on the subject of automatic brake light regulations in the US was this article from 2016: https://www.bellinghamherald.com/news/traffic/rules-of-the-road/article53707810.html. According to the author, the US Government does not have a brake light deceleration standard ( ... that may have changed since 2016). Based on the UN code linked in the article (http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R13hr2e.pdf), automatically activated brake lights should NOT be activated unless the deceleration is above 0.7 m/s2, may be optionally activated between 0.7 and 1.3 m/s2, and must be activated above 1.3 m/s2. I just measured my car's coasting deceleration in B from 60 km/h to 30 km/h using the very scientific method of a stopwatch and eyes on the speedometer. The average of several runs produced an assumed linear deceleration between those speeds of 1 m/s2.

I don't want to annoy other drivers, but I also don't think it is unreasonable for the brake lights to come on when coasting in B. ECO, I agree is debatable and I have adjusted the system to only operate in B. I tested the system with a piece of white paper loosely taped over the high-mount brake light and a small portion of the upper rear windshield so I could observe the brake light while driving. I don't find it that annoying, but that is just me.

I am getting some nuisance, momentary flashes on really bumpy roads. I will try re-calibrating the unit. If that doesn't fix it, I think I'll add a small time-delay so that the signal needs to be of a certain duration to actually activate the lights, off the top of my head I'm thinking 0.2 to 0.3 sec. Teslas incorporate a delay of up to 0.59 sec (https://www.sae.org/publications/technical-papers/content/2020-01-0883/).

 

[JoeS]

Andrew, thanks for the links, especially the latest info about measuring Tesla's response time. About the same time delay as a driver moving foot from accelerator to brake? Not surprised that damping is needed to smooth out the bumps (pun intended).

BTW, we had talked a bit about this quite a few years ago -

http://myimiev.com/forum/viewtopic.php?f=22&t=1895

 

[Don]

Sensitivity is set by tilting the module after calibration. I have mine set so that it just barely activates when coasting in ECO.

What activates the brake lights? Is it a decelerometer of some sort or . . . . ? Adjusting the sensitivity by tilting the module would seem to change depending on whether you're going uphill or down

I had a rotary engine Mazda which had a decelerometer that locked up the seat belts. It was a steel ball in a spring cage which was set so that a certain amount of deceleration (in any direction) caused the ball to move (with a click) and that energized a solenoid that locked the seat belts (also with another click) so you couldn't lean forward at all - The clicks literally drove me nuts, which is why I know how the decelerometer worked . . . . after I cut it apart! :lol:

IMO. what's needed is a system which trips based on the amount of current being regenerated back into the battery. Many years ago, Joe put a clamp meter on the correct wire which gave all of us some idea of what the ammeter in the dash was telling us. IIRC, full scale deflection when standing hard on the accelerator was about 150 amps and enough regen current to peg the meter in the opposite direction was only about 75 amps, but full regen was much more

Rather than having flickering lights (my primary objection is that any brake lights that happen with little or no slowing just put following drivers to sleep, since the brake lights keep activating but the car isn't slowing, so subconsciously, you begin to ignore them, which is worse than no brake lights at all) what you would want is a light activated by some exact amount of regenerated current. This wouldn't be that hard to do with a simple Arduino circuit and a few loops of wire around the cable on the car to sense regen current and activate the lights only when some threshold is exceeded, say maybe 100 amps or so - 75 amps (when the needle goes down full scale) isn't very much slowing, so I assume you'd want more than that

In 50 years or so of driving manual transmission ICE's, the thought never occurred to me to want my brake lights actuated when I'm downshifting to slow down . . . . and I've never been rear ended, nor has there ever been a time when that came close to happening - If I had somebody close on my tail, I would give them one flash of my brake light before I selected a lower gear and began slowing . . . . and hopefully, over those 50 years, a few million other drivers learned not to count on brake lights to alert them so they don't rear end other cars, as there are certainly plenty of cars with completely non-functioning brake lights out there - Especially in a state like Mississippi where we currently have absolutely no form of mandatory vehicle inspection system in place

On my road motorcycles, I did add a simple circuit which gives 3 flashes and then solid red on the brake lights . . . . and I also ditched the filament bulbs for much, much brighter LED's in the tail light - If somebody rear ends your bike, you're probably dead, but I still had total control over the brake light when I wanted it illuminated or not. It's much easier to slow by downshifting on a bike (almost necessary, as you need to cycle through each gear to get to first so you can move away after a complete stop) and you CAN downshift and flash a brake light anytime you want/need to by gently pulling on the front bake with your right hand

I do hope you get this system you bought working to suit you . . . . but adding any delay seems counter productive if you're depending on it to keep you from getting rear ended - A quarter second delay with an inattentive driver on your tail could be the difference between getting hit and not getting hit. Probably better to watch him in your mirror and give him the brake pedal early and often

Don

 

[Adoepner]

I'd expect there is a single-axis accelerometer in the GearBrake. The calibration of the unit at the start allows it to find level and remove acceleration due to gravity. The unit is then tilted slightly to adjust for sensitivity (adding or removing some influence of gravity). Hills will definitely affect the unit: going downhill will make the unit more sensitive, going uphill will make the unit less sensitive. It may have been nicer to have an adjustment pot on the unit to vary the sensitivity after calibration and leave the level alone, but that's not the way it was built. The designers went for simple and cheap ... and they achieved that. As JoeS mentioned, there is a firesale on at $5 a unit.

Yes, any delay at all is not ideal, but so are false activations. It was interesting to read that Teslas incorporate a delay - this tells me that they likely also use an accelerometer-based system. I found a cheapie variable delay relay on ebay. When it arrives from China, I'll play with it a little. I intend to add the minimum delay required to get rid of "bumps."

An ammeter on to measure regen current is a great idea, but I don't have the skills to implement it, and certainly couldn't do it for less than the current cost of a GearBrake and timer. A few things to consider with this approach: regen current is likely limited when the battery is 1) too cold, 2) to hot, or 3) already at a high state of charge.

Andrew

 

[PV1]

My Bolt uses some formula of current speed and regen power to control the brake lights. In the 45-60 MPH range, the brake lights seem to activate with 21 kW or more of regen. The lower the speed, the threshold decreases. Down below 5 MPH, 2 kW of regen is enough to activate them, and they shut off once below 1 MPH. With this, it's darn near impossible to stop the Bolt without brake lights coming on like we can with the i-MiEV (regen down to 10, then pop into Neutral and use the handbrake to stop).

Like Teslas, the Bolt also has the slightest delay of activation, but this is there to prevent brake light flash by quickly letting off the throttle and re-applying (something I do a lot to keep my foot calibrated so I don't have to watch the dash as much).

As for accomplishing regen-based brake lights in the i-MiEV, an Arduino reading the CAN bus or doing current sense on the high voltage feed to the MCU could replicate this, but as was said before, the GearBrake is a simple and affordable option for those that want it. I personally enjoy being able to slow down without lights to gauge the following driver's attention, but I always drive with an eye on the rearview anyway (saved me more times than I care to think about).