# Regenerative braking



## JRP3 (Mar 7, 2008)

Many people like the experience of driving with mostly the A-pedal only, and you can make a slight neutral zone in the pedal throw that allows coasting. Most cars have at least some regen on the A-pedal, the Curtis controllers allow you to program how strong it is. Some people prefer to have regen only on the brake pedal.


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## cruisin (Jun 3, 2009)

JRP3 said:


> Many people like the experience of driving with mostly the A-pedal only, and you can make a slight neutral zone in the pedal throw that allows coasting. Most cars have at least some regen on the A-pedal, the Curtis controllers allow you to program how strong it is. Some people prefer to have regen only on the brake pedal.


The proper way is to attempt to design the use of regen as close to a production car as possible, since that seems to work the best. Minor regen with throttle off, varible regen from 0-100% with the first 2" of brake pedal movement before the disk brakes are activated. In most cases the disk brakes will never be used, like most if not all hybrids, except during a panic stop. Brake light must be re assigned to the regen pot so that it is activated by the regen. The use of a regen pot with a 2 wire switch works well.


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## ishiwgao (May 5, 2011)

cruisin said:


> The proper way is to attempt to design the use of regen as close to a production car as possible, since that seems to work the best. Minor regen with throttle off, varible regen from 0-100% with the first 2" of brake pedal movement before the disk brakes are activated. In most cases the disk brakes will never be used, like most if not all hybrids, except during a panic stop. Brake light must be re assigned to the regen pot so that it is activated by the regen. The use of a regen pot with a 2 wire switch works well.


So far, I'm still unable to find a 0-5V pot box that can move 2" first before activating the brakes. I've found one that moves 40 degrees, but i think that's a bit too much too. Any suggestions on which 0-5V pot I can use for braking, so that I can move first using regen then continue somemore using the brake pads?


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## johnsiddle (Jun 22, 2011)

Thanks guy's
How harsh does regen tend to be?

If I arranged a dead spot near throttle closed and then full regen at closed would the nose dig into the ground as soon as regen came on or is it a bit more progressive? although I plan this going on a 2.5 ton truck and nothing happens quickly on that.

I think I will have the brakes turn the inverters off and switch to full regen, although if regen is as good you guys say I think by the time you have to use the brakes the saving will be quite small.

I could design in progressive braking using a second pot starting at the end of the dead spot.... I will think about that one.

Thanks guy's
John


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## cruisin (Jun 3, 2009)

ishiwgao said:


> So far, I'm still unable to find a 0-5V pot box that can move 2" first before activating the brakes. I've found one that moves 40 degrees, but i think that's a bit too much too. Any suggestions on which 0-5V pot I can use for braking, so that I can move first using regen then continue somemore using the brake pads?


 
Here is a picture of the setup I use and install in customer cars. It works very well as the brake pedal is ajusted to use the regen pedal for the first 2 inches, then brake disks. Pot has 2 wire switch for brake lights when activating regen.


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## ishiwgao (May 5, 2011)

crusin any details about pricing and dimensions?


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## cruisin (Jun 3, 2009)

ishiwgao said:


> crusin any details about pricing and dimensions?


$125.00 and is about 5" square without the pedal.


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## JRoque (Mar 9, 2010)

Hi all. Crusin, where's the mechanical link to the hydraulic brakes? Do you have a picture that shows it?

JR


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## tomofreno (Mar 3, 2009)

I also like control of regen through the accelerator pedal since it gives one-pedal control of both acceleration and deceleration with no need to move your foot between two pedals, except for a panic stop. Using the brake pedal for regen seems it gives about the same end result during a panic stop. Most of the initial brake pedal travel is used to control regen. So in a panic stop you push the pedal down through max regen setting then apply mechanical brakes. With regen on the accel pedal, during a panic stop you let up the accel pedal fully applying max regen setting, then hit the mechanical brakes. Regen is actually applied slightly more quickly in this case, as all that is required is lifting your foot.

I would make the max applied regen adjustable. My max is set to 55%. If I applied 100% I think it might cause the car to skid. It would certainly be dangerous on ice or snow. On a quick stop the 55% setting gives me up to around 160A regen. I also have it tapered to give lower percentage at higher speeds. Without that the max current would be higher.


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## ishiwgao (May 5, 2011)

JRoque said:


> Hi all. Crusin, where's the mechanical link to the hydraulic brakes? Do you have a picture that shows it?
> 
> JR


yeah I would like to see that too.


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## JRoque (Mar 9, 2010)

Hi Tom. Hopefully that won't retrain your body into associating braking with the accel pedal since that's already a problem for some - and I have a smashed gate and a mother-in-law to prove it 

Another thing, if max regen is applied when accel pedal is at 0, does that mean your car won't easily roll back when stopping on a slight hill? If so, doesn't that use energy - like DC injection - to attain max regen? Or maybe the controller doesn't apply regen below a certain RPM?

Personally, I wouldn't want the car to behave any differently than current ICE cars so others can drive it without having to adapt. I also believe max range can be attained by letting the motor freewheel and only only use brake (ie: regen) when you need to stop/slow down. You can probably learn how to keep the motor in a neutral zone and using little power but that's another thing to relearn. 

Isn't a 2" travel on the brake pedal before mechanical brake is applied a bit too long? If your regen goes out (as in your pack is already at max volts) then that's 2" of pure panic not having the car brake when expected. Perhaps a small regen travel, 1" maybe, and ending right before mechanical braking kicks in so there isn't a gap would be best; pure guess of mine.

JR


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## cruisin (Jun 3, 2009)

JRoque said:


> Hi all. Crusin, where's the mechanical link to the hydraulic brakes? Do you have a picture that shows it?
> 
> JR


Where is the what? There is a hydraulic brake pedal that activates the regen pedal for the first 2" of travel as shown in the picture.


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## cruisin (Jun 3, 2009)

JRoque said:


> Hi Tom. Hopefully that won't retrain your body into associating braking with the accel pedal since that's already a problem for some - and I have a smashed gate and a mother-in-law to prove it
> 
> Another thing, if max regen is applied when accel pedal is at 0, does that mean your car won't easily roll back when stopping on a slight hill? If so, doesn't that use energy - like DC injection - to attain max regen? Or maybe the controller doesn't apply regen below a certain RPM?
> 
> ...



2" is NOT too much of travel. Hybrids have that much and more on some. Your brake pedal has 1/2" stock, so another 1 1/2'" is not too much. 1" does not give the driver enough movement for 0-100% of regen. 100% of regen will skid the rear wheels of a light car. The disk breaks almost NEVER come into play. My disks have rust on them from lack of use. H ybrid disk breaks will outlast the car in most cases.


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## JRoque (Mar 9, 2010)

Hi. Ok, I see. I hadn't seen that pedal cluster before and, as I remember it, the OEM VW cluster looks different. 

So you adjusted the link from the brake pedal to the master cylinder so there's additional play? And they used the play to actuate the regen box? Or were those 2" already there?

JR


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## cruisin (Jun 3, 2009)

JRoque said:


> Hi. Ok, I see. I hadn't seen that pedal cluster before and, as I remember it, the OEM VW cluster looks different.
> 
> So you adjusted the link from the brake pedal to the master cylinder so there's additional play? And they used the play to actuate the regen box? Or were those 2" already there?
> 
> JR


The brake pedal free play was adjusted to about 2" to allow 2" travel for the regen. When driving, it will act just like a production Hybrid, which is the way it should. This is important in designing a EV conversion, as much like a production car as possible. Others will like it better, will quickly adapt to it, and more than likely have a higher resale value.


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## tomofreno (Mar 3, 2009)

> Hi Tom. Hopefully that won't retrain your body into associating braking with the accel pedal since that's already a problem for some - and I have a smashed gate and a mother-in-law to prove it


 It hasn't over the last two years, and I've had a couple panic stops in that time. Not sure why you think it would. The brake pedal is still the brake pedal. Regen works for slowing, or gradually stopping, but STOP still means BRAKE.


> Another thing, if max regen is applied when accel pedal is at 0, does that mean your car won't easily roll back when stopping on a slight hill? If so, doesn't that use energy - like DC injection - to attain max regen? Or maybe the controller doesn't apply regen below a certain RPM?


 Not sure what you mean by "0". With the accelerator pedal released, the car will roll backward on a hill with it in gear, as there is no applied torque. I have a transmission so I can also take it out of gear. I usually come to a stop mostly with regen, then apply my brakes near the end - and hold them on if on a hill so the car doesn't roll backward, with the car in gear and zero battery current.


> Personally, I wouldn't want the car to behave any differently than current ICE cars so others can drive it without having to adapt.


 Yes, I can see that, as it does take some getting used to. Took me about 20 minutes to get comfortable with it the first time I drove, and my first reaction was Hey, this is COOL! I still get a kick when I drop down from a mountain pass easing the pedal up to slow and pushing it down to accelerate as I go through the switchbacks never touching my mechanical brakes, and watching the "Ah used" decrease.


> I also believe max range can be attained by letting the motor freewheel and only only use brake (ie: regen) when you need to stop/slow down. You can probably learn how to keep the motor in a neutral zone and using little power but that's another thing to relearn.


 Relying on your imagination again rather than experience. It's easy for me to hold the pedal so the battery current varies by less than +/- 2A for as long as I usually have the opportunity. Usually I can only drive for less than a minute or so before I come up on someone going slower, or someone slows in front of me, or I have to slow for a curve, or slow as I enter a lower speed zone, or speed up in a faster speed zone, or press the pedal further to go up a grade or release it a bit to slow going down a grade to keep pace with traffic over rolling terrain, or stop for a stop sign or traffic light. I use regen to slow in all those cases, and only use the mechanical brakes near the end of stopping typically. 

I find in my car that the myth that you can't coast with regen, or it is very difficult to do so, is not true. I have no trouble coasting. I've tested it on a short grade - went down holding the pedal for zero battery current, then went down with the car in neutral. The car attained about the same speed at the bottom in both cases. So I can coast down that grade freely same as you would with a DC motor, or ease up the accelerator a bit to slow if I overtake the car in front of me, or press the accelerator to speed up if a semi is riding my rear bumper.

As I have said before, the only way I see that regen can be less efficient than coasting with a DC motor is if you modulate the kinetic energy of the vehicle, meaning repeatedly slow it up with regen, speed up pushing the accelerator... continually cycling this way when you should be just cruising along at one speed, or you over-correct in slowing, then have to speed up, etc. You loose energy in every period of this modulation since you get back less through regen than it takes to accelerate the car through the same delta v. But if you have good pedal control and hold close to zero current when you want to coast and use regen to slow in all the cases I mentioned above, there is no way it can be less efficient.

But some, like cruisin, prefer regen on the brake pedal and that's fine with me. Just sayin' why I like it on the accelerator.


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## johnsiddle (Jun 22, 2011)

Thanks Tomofreno, that gives me a lot to consider, I didn't think that regen would be so effective. It is deffo a facility to be incorporated.

Regards John


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## johnsiddle (Jun 22, 2011)

tomofreno said:


> I also like control of regen through the accelerator pedal since it gives one-pedal control of both acceleration and deceleration with no need to move your foot between two pedals, except for a panic stop. Using the brake pedal for regen seems it gives about the same end result during a panic stop. Most of the initial brake pedal travel is used to control regen. So in a panic stop you push the pedal down through max regen setting then apply mechanical brakes. With regen on the accel pedal, during a panic stop you let up the accel pedal fully applying max regen setting, then hit the mechanical brakes. Regen is actually applied slightly more quickly in this case, as all that is required is lifting your foot.
> 
> I would make the max applied regen adjustable. My max is set to 55%. If I applied 100% I think it might cause the car to skid. It would certainly be dangerous on ice or snow. On a quick stop the 55% setting gives me up to around 160A regen. I also have it tapered to give lower percentage at higher speeds. Without that the max current would be higher.


Hi again,
What is your battery pack voltage? 160A is a hell of a lot of current.
John


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## JRP3 (Mar 7, 2008)

His pack voltage is the same as mine, 115 nominal. I've gotten over 200 amps of regen from my setup, which is still only 2C for my 100 amp cells. I agree with everything Tom said about A-pedal regen, as do most Tesla and MiniE owners, we all love it, and it's not that hard to hold a no current in or out position for coasting.


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## mizlplix (May 1, 2011)

Just food for thought;

In the electric open wheeled series of a few years ago, the drivers were used to the easy transition from brake to throttle in a normal ice racecar and when the electric car was set to regen when the throttle was let up, they would wind up backwards, not being ready for the rear wheel change in rolling resistance.

But, they adapted perfectly when regen was set up in the first part of brake pedal travel , it acting like they were expecting. They didn't want to retrain......

My car will do both but is set up currently for regen on throttle down. 

My first thought is to mimic the old way of driving close as I could. But my second thought is that is a unique vehicle. A new way of operating it is not a big deal. try both before deciding.


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## JRP3 (Mar 7, 2008)

There is a problem when the "old way" is considered best because it's familiar. There is an inherent suggestion that people can't learn and adapt, and that doing so is a bad thing. Quite the opposite in my opinion.


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## mizlplix (May 1, 2011)

Kind of like the way our government is run? Don't tell the public the truth, they don't want to know, only to feel safe.

A while back, on another EV site, the mod. Removed a thread about a simple battery charger. Their reason? The average reader does not understand the subject very well and might get hurt with this information .

I too agree, old tried and true is not necessarily better. If this were so, we would still be living in caves.


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## DavidDymaxion (Dec 1, 2008)

Jack Rickard mentioned a pressure transducer that transmits 0 to 5 V for a regen signal.


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## ken will (Dec 19, 2009)

In my driving experience:
I learned to drive on a go-kart with a centrifugal clutch, when you let off the throttle you had no drag from the motor.
I have owned 1 automatic car, which had very little drag from the motor when you let off the throttle.
I have had many cars trucks, and motorcycles with a standard transmission, that all had different amounts of drag when you let off the throttle.

So, for me, .. a small amount of drag from regen. when I let off the throttle, ( maybe 10-20% ) and then the rest of regen. for the first 2" of brake, would be the most natural.


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## neorules (Sep 14, 2011)

cruisin;259560100% of regen will skid the rear wheels of a light car. [/QUOTE said:


> has anyone come up with a way to use the antilock brake sensor to modulate the amount of regen so that at high speeds you don't get wheel lock?
> 
> JC


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## JRP3 (Mar 7, 2008)

I've wondered if regen might be somewhat self regulating in that respect, once the wheels stop turning there is no regen, and once they gain traction again and start turning regen comes back. I don't know if this would happen fast enough to provide an anti lock feature or not.


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## neorules (Sep 14, 2011)

JRP3 said:


> I've wondered if regen might be somewhat self regulating in that respect, once the wheels stop turning there is no regen, and once they gain traction again and start turning regen comes back. I don't know if this would happen fast enough to provide an anti lock feature or not.


Well I heard all vehicles 2012 and later must have Stability control standard I thought. So that means if you are taking an off ramp at speed and touch the brakes the back end "shouldn't" come around since the stability control would immediately start braking the outside front wheel just enough to cause a tiny plow condition and hopefully allow the driver to regain control...

At least that is what I thought they meant.

so maybe some form of electronic Anti lock brakes are the future...


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## DavidDymaxion (Dec 1, 2008)

It is naturally that way on a sepex motor, and yes the response is extremely fast. For years I have called it "a natural form of traction control." However, it's not down to 0 rpm, it's with respect to a key speed. Above key speed = regen, below = motoring. It's similar with AC. BTW it works the other way, too, if the wheel suddenly hits a slippery spot on acceleration, and suddenly speeds up, it loses torque. It's neat that it is inherent, analog, fast, and a proportional response.


JRP3 said:


> I've wondered if regen might be somewhat self regulating in that respect, once the wheels stop turning there is no regen, and once they gain traction again and start turning regen comes back. I don't know if this would happen fast enough to provide an anti lock feature or not.


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