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Discussion Starter #1 (Edited)
Hello,

I own a 1980 Mini 1275GT that has been sitting in perpetual restoration mode due to a lack of time and currency to complete the job. This has given me time to think about the direction I would like the project to proceed in once I gain sufficient finances to resume.

I have a diploma in electrical engineering, my brother is an automotive engineer ("mechanic") by trade, and my father made a career out of fabrication and custom panelwork.

I am considering converting my Mini to an electric vehicle as a "restomod", and hope to retain the famous handling characteristics of the car in the process. I expect that, once the project is complete, the car would be used mostly for fun (on a track or one of New Zealand's several twisty, hilly backroads), or possibly for short-range commutes.

My proposed specification would be to have an electric drivetrain that delivers performance on par with the stock 1275cc A-series drivetrain (i.e. similar specs for maximum torque and power; 54 hp (40 kW) at 5300 rpm and 65 lb⋅ft (88 N⋅m) at 2550 rpm, according to Wikipedia); so as not to overload the original suspension and steering components. Since the A-series engine and gearbox are combined into a single housing, I would be considering opting for direct drive to the front wheels; either through a differential or by using two motors directly coupled to the original driveshafts; unless there is an overwhelmingly good reason to couple an electric motor to a transmission.

Besides the engineering challenges, my main motivation for considering electric conversion over a traditional restoration with an original-equipment drivetrain is to eliminate the noise from the passenger cabin; which will make driving the car much more enjoyable.

This project is still very much in the planning stages, so at this point in time I am looking for general advice and to determine the feasibility of such a project.

Thanks
 

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Since the A-series engine and gearbox are combined into a single housing, I would be considering opting for direct drive to the front wheels; either through a differential or by using two motors directly coupled to the original driveshafts; unless there is an overwhelmingly good reason to couple an electric motor to a transmission.
The torque output of an electric motor is related to the size of the motor, so a motor with enough torque to drive the wheels directly is very large and heavy. The overwhelmingly good reason to use some sort of reduction drive (a gearbox, although people have used chains and sprockets or toothed belts and pulleys) is that it allows you to use a much smaller motor to get the same torque to the wheels. Another aspect of this is that the big high-torque motor requires a lot of current, so you can use a controller of much lower current capacity to run the smaller motor.

In first gear, the 65 lb⋅ft (88 N⋅m) output of the 1275 GT's engine would be multiplied by 3.32 by the first gear, then 3.105 by the final drive, becoming 670 lb⋅ft (907 N⋅m); to match that would require an enormous motor. Even in top gear, the engine plus transmission can put 202 lb⋅ft (273 N⋅m) to the wheels around 2500 rpm engine speed.

That means (usually) a gearbox, but doesn't necessarily mean a multi-speed gearbox (transmission). Production EVs use a single-speed transmission (gearbox), but they also use high-voltage AC motors which can produce their rated power over a very wide speed range, and nearly up to their maximum rotational speed. Some DIY EV conversion builders find it helpful to have more than one transmission speed (more than one gearbox ratio), because low-voltage motors have a relatively narrow powerband, so it helps to be able to shift to keep the motor at a suitable speed to produce enough power.

The pinion and ring gear set of a typical final drive unit is one stage of gear reduction; the differential itself doesn't provide any gear reduction, but when people say "differential" they often mean the whole final drive unit.

I agree that the classic Mini gearbox is a poor choice for an EV, although it has been used.
 

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Hi TechGeekNZ

Where are you? - I assume NZ!

I'm an old mini fan - I was tempted to convert a mini - but I made a Locost type roadster instead

Where abouts?
 

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Anyone interested in a classic Mini conversion should be aware of the types of conversions already done... here are a few I found in a quick search (I was curious about the transmissions used):

Ian Motion
  • appears to use single motor on single-ratio transaxle
  • Range 150 km*
    Max speed 120 km/h
    Charging time 7 hours

    18 kWh lithium-ion battery
    47HP water-cooled synchronous motor
    3 kW on-board charger
    Type 2 charging plug
    TFT instrument display

dbrive.ch
  • induction motor rated at 22 kW continuous
  • belt drive to original Mini transaxle
  • 10 kWh battery of 32 CALB 100 Ah LFP cells

evmini.ca
  • HPEV AC50
  • Honda Civic transaxle
  • 32x ThunderSky Lithium Ion 100AH cells (so 10 kWh) filling the trunk - this is terrible for weight distribution
  • given how completely clueless seemed to be about both cars and this specific project at the beginning, I'm really impressed that it was completed

The Lynch Atlantis
  • Motor: Lynch type LM200 7.5R, 8.5Kw on 48V
  • original Mini transaxle
  • Batteries: 8 x 6V 225 AH lead-acid
  • claimed performance:
    Max. Speed: 60 mph
    Max. Gradient: 1 : 4
    Range: 50 miles
  • this is a golf-cart level of conversion; the performance claim seems implausible to me

1972 Mini Cooper E.
  • D&D 6.7" brushed DC motor
  • chain drive to original Mini transaxle
  • 30x 100AH CALB LFP cells (10kWh) in the trunk
  • may not have been completed

Classic Mini A.C. Electric Conversion
  • likely aborted project

... and more links from another thread:
 

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Although I haven't seen anyone do this, there is a transmission approach that might not need much custom fabrication: use a motorcycle engine conversion kit for the Mini (example: Lynx).

They typically use a chain drive (from the output of the motorcycle transmission, but from the electric motor in this case) to a differential, with a subframe and bearings to hold the differential and shafts. The fabrication would be mounting the motor instead of the motorcycle engine... plus of course all of the usual mounting of controller, charger, and battery. This would be a single-ratio reduction, and would be noisy compared to a gearbox but maybe not bad. It would require the same chain maintenance as a chain-driven motorcycle.
 

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Discussion Starter #6
Hello everyone. Thanks for the warm welcome and very useful info!

The torque output of an electric motor is related to the size of the motor, so a motor with enough torque to drive the wheels directly is very large and heavy. The overwhelmingly good reason to use some sort of reduction drive (a gearbox, although people have used chains and sprockets or toothed belts and pulleys) is that it allows you to use a much smaller motor to get the same torque to the wheels. Another aspect of this is that the big high-torque motor requires a lot of current, so you can use a controller of much lower current capacity to run the smaller motor.

In first gear, the 65 lb⋅ft (88 N⋅m) output of the 1275 GT's engine would be multiplied by 3.32 by the first gear, then 3.105 by the final drive, becoming 670 lb⋅ft (907 N⋅m); to match that would require an enormous motor. Even in top gear, the engine plus transmission can put 202 lb⋅ft (273 N⋅m) to the wheels around 2500 rpm engine speed.

That means (usually) a gearbox, but doesn't necessarily mean a multi-speed gearbox (transmission).
That's very useful, Brian. I haven't yet done any serious number crunching (this idea is still very much in its formative stages); and that gives a very good starting point.

The thing about learning theory is that it often doesn't give a sense of the scale of things in practice; a 40 kW electric motor that could develop 900 Nm without the mechanical advantage offered by gearing sounds like it would be a very big machine indeed ;). It does gets me thinking, though; what would be the drive ratio of the gearbox built into a typical induction motor? Could that be sufficient to drive the wheels, either directly or through a typical final drive (and differential) unit?

I admit I don't know quite as much as I'd like to about the pure mechanical aspects of cars (that's very much my brother's domain; although my own mechanical skills aren't too bad, simply by virtue of owning a car manufactured by BLMC); however, upon reflection, it's obvious that the torque figure of interest is the one where the rubber meets the road, after the engine's torque has been multiplied by the transmission. So, to match the performance of the original vehicle (prior to many of its original horses escaping), that would be the figure I'd need to replicate with an electric drivetrain?


Production EVs use a single-speed transmission (gearbox), but they also use high-voltage AC motors which can produce their rated power over a very wide speed range, and nearly up to their maximum rotational speed. Some DIY EV conversion builders find it helpful to have more than one transmission speed (more than one gearbox ratio), because low-voltage motors have a relatively narrow powerband, so it helps to be able to shift to keep the motor at a suitable speed to produce enough power.
That is a brilliant explanation for why many of the EV conversions I read about retain the manual transmission from the original car, even though theory would suggest it is unnecessary. Not only is it a convenient way to obtain the required drive ratio; but it is also an effective way to use a lower-powered motor.

Given my background theory in electrical machines (induction motors, mostly), and given the widespread availability of all manner of readily-available induction motors (in everything from domestic appliances to industrial machines), that would seem the natural choice. I also like the sound of a machine that produces (close to) maximum torque right across its speed range; the acceleration (and deceleration) of the resulting vehicle would be phenomenal :D.

Now, controlling the thing (and managing the batteries) would be an entirely different matter; and that, I believe, is where the real engineering challenge will be.

Given that they have no permanent magnetic field, I was somewhat surprised to learn that induction motors can also function as generators, by operating in the negative slip region. Since, in practical terms, this simply means the magnetic field induced in the rotor is rotating faster than the supplied stator field; it suggests an effective means of governing the vehicle's speed, i.e. set the frequency of the motor drive based upon the position of the accelerator pedal. A faster stator field causes the motor to speed up (motoring), while a slower field causes it to slow down (regenerating).

Since this would be a function of the controller, it should also simplify the implementation of regenerative braking to assist the Mini's stock (non-servo-assisted) front disc and rear drum brakes (I may tweak things to favor regenerative braking over mechanical braking, but there's no way I'd even consider completely ditching the hydraulic brakes).

Anyone interested in a classic Mini conversion should be aware of the types of conversions already done... here are a few I found in a quick search (I was curious about the transmissions used).
Although I haven't seen anyone do this, there is a transmission approach that might not need much custom fabrication: use a motorcycle engine conversion kit for the Mini.

They typically use a chain drive (from the output of the motorcycle transmission, but from the electric motor in this case) to a differential.
Thanks for all those useful links; I will likewise be interested to learn what replacement transmissions were used. Interestingly, the A-series engine actually uses a timing chain to connect the camshaft to the crankshaft; so I wonder just how much a chain drive would compare to the original A-series power unit (along with its distinctive gearbox whine) in terms of noise :cool:.


Where are you? - I assume NZ!
Hi, Duncan. I live in the Manawatu, so I'm rather spoiled for choice of excellent driving roads, and of course Manfeild Motorsport Park.

It looks like I have quite a lot to think about, and plenty of research to do; but thanks very much for pointing me in the right direction. Let's see if we can get this project rolling :).
 

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Another, more recent discussion of Mini conversion possibilities... but mixed up with MGB ideas:
Smart Fortwo Electric Drive as Mini/MGB donor?
Most of the earlier Mini project links are from the era in which common practices were to assemble LFP cells to build a battery pack, and to use aftermarket motors. Recent trends are to use salvaged EV battery packs, and (to a lesser extent) to use salvaged EV motors or complete drive units.
 

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... what would be the drive ratio of the gearbox built into a typical induction motor? Could that be sufficient to drive the wheels, either directly or through a typical final drive (and differential) unit?
A motor doesn't typically have a gearbox built into it. If you're referring to the complete drive unit (motor + gearbox + differential) of a typical modern production EV... the only common EV using an induction motor is the Tesla Model S/X, and it has a roughly 10:1 ratio of motor speed to axle speed. Since the motor can run at least 12,000 rpm and the tires are tall, top speed can be high. Most other EV motors are configured to run a bit more slowly, so (for instance) the Nissan Leaf overall ratio is about 8:1.
 

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I admit I don't know quite as much as I'd like to about the pure mechanical aspects of cars (that's very much my brother's domain; although my own mechanical skills aren't too bad, simply by virtue of owning a car manufactured by BLMC)...
This forum's membership is an interesting mix, with long time auto enthusiasts who can rebuild an entire vehicle but are completely new to electronics (beyond the "plug in the black box" level), to electronics experts who can build anything from scratch but have no idea how anything in a car works, to computer programmers who can create complex logic in code but have never really touched the actual physical devices that do the work, and every combination in between.

Fortunately, everyone can fill in the gaps for everyone else. :)

... upon reflection, it's obvious that the torque figure of interest is the one where the rubber meets the road, after the engine's torque has been multiplied by the transmission. So, to match the performance of the original vehicle (prior to many of its original horses escaping), that would be the figure I'd need to replicate with an electric drivetrain?
Yes, but since that changes with each gear and depends on the shape of the engine or motor's torque-versus-speed curve, it's hard to pick a single value.
 

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Given my background theory in electrical machines (induction motors, mostly), and given the widespread availability of all manner of readily-available induction motors (in everything from domestic appliances to industrial machines), that would seem the natural choice.
Induction machines have become nearly ubiquitous since AC power distribution was adopted. Familiarity and availability are significant factors... they're the only reasons that the cars now branded "Tesla" started with induction motors, and why the company used that name

I also like the sound of a machine that produces (close to) maximum torque right across its speed range; the acceleration (and deceleration) of the resulting vehicle would be phenomenal :D.
The same characteristics can be true to some extent of almost any type of motor, but especially brushless motors (anything other than a brushed DC motor) which are less limited in voltage.

Almost any motor produces relatively constant torque up to some transition speed, limited by the current which can be supplied by the battery, handled by the controller/inverter, and tolerated (in heating terms) by the motor. Above that transition, if there's enough voltage available then they are generally limited to constant power battery capability and cooling of the motor and electronics; that's constant power, not constant torque, so torque drops off with speed (power = torque x rotational speed = force x linear speed = voltage x current).

In modern EVs, the transition point is only 1/4 to 1/3 of the way up the speed range from stall, so for most of the motor speed range the full rated power is available; below the transition speed torque is constant so power drops off as the speed drops, but acceleration is limited by traction anyway so that's okay. Providing enough voltage for high motor speed at full power is the reason that typical modern EVs run 360 V to 400 V battery packs. Even Toyota's non-plug-in hybrids, which have small NiCd batteries running between 200 and 300 volts, use a voltage doubler before the inverter so the motors can run with higher voltage.

Now, controlling the thing (and managing the batteries) would be an entirely different matter; and that, I believe, is where the real engineering challenge will be.
Yes, but the challenge has already been handled to a large extent by the designers of the motor controller (and the battery management system), whether that is salvaged from a production EV or part of the design of home-built hardware using someone else's plan.

Given that they have no permanent magnetic field, I was somewhat surprised to learn that induction motors can also function as generators, by operating in the negative slip region. Since, in practical terms, this simply means the magnetic field induced in the rotor is rotating faster than the supplied stator field; it suggests an effective means of governing the vehicle's speed, i.e. set the frequency of the motor drive based upon the position of the accelerator pedal. A faster stator field causes the motor to speed up (motoring), while a slower field causes it to slow down (regenerating).

Since this would be a function of the controller, it should also simplify the implementation of regenerative braking to assist the Mini's stock (non-servo-assisted) front disc and rear drum brakes (I may tweak things to favor regenerative braking over mechanical braking, but there's no way I'd even consider completely ditching the hydraulic brakes).
Almost all of the electrical power supplied to the utility grids is from induction generators in power plants, whether hydro or thermal or wind powered. :)

I get the speed-controlling theory, and that's the sort of reasoning that works with fixed-frequency industrial power supplies (to provide a relatively constant machine speed) or with a variable-frequency drive without speed feedback... but in practice it doesn't work well in a vehicle. The normal approach in an EV is for the accelerator pedal position to be interpreted as a torque or power request (the two are the same, except for the speed multiplier). Speed limiting or cruise control is handled the same way as with an engine, using a secondary control loop: if the vehicle goes faster than intended, power is reduced, and vice versa.

It is possible to drive without friction brakes, entirely using the motor(s); however...
  • this generally isn't legal for a road vehicle (friction brakes mechanically/hydraulically linked to the pedal are required)
  • for reliability, it would be unwise
  • when near zero speed actively powering the motor in reverse would be required to stop, and using power to apply holding torque with the motor would be required to remain stationary
  • brakes are needed on all wheels, so friction brakes are still required on a two-wheel-drive vehicle

Although regenerative braking doesn't return a huge amount of energy, it is certainly desirable. The big challenge is coordinating it with friction braking, so that braking is smoothly controlled, sensible to the driver, balanced (braking just one end of the car is bad for handling and stability), and doesn't use more friction braking than necessary. Anti-lock braking system and stability control system behaviour must be considered as well, although I think most DIY conversions give up on these features even if the original vehicle had them. In an older vehicle with a simple hydraulic braking system (assisted or not), one problem is how to keep the friction brakes from applying on the powered wheels when regenerative braking is active; I haven't seen anyone address this in a DIY project.

It is now popular to have "one pedal" driving, in which zero accelerator pedal application is treated as a moderate degree of braking. It is a challenge to make this feel right to the driver, especially since the right amount depends on driver and driving conditions.
 

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Interestingly, the A-series engine actually uses a timing chain to connect the camshaft to the crankshaft; so I wonder just how much a chain drive would compare to the original A-series power unit (along with its distinctive gearbox whine) in terms of noise :cool:.
Timing chains don't transmit much power compared to the engine (or electric motor) output, but noise was one reason that the automotive industry moved from timing chains to timing belts for overhead-cam engines a few decades ago; however, they have almost entirely moved back to timing chains to avoid the need for occasional belt replacement. Most pushrod engines have always used a timing chain, although heavy-duty and racing engines tend to use gears instead.

Many transmissions have used a drive chain (particularly in transverse automatics, but also in the early Toyota Prius hybrid and some oddball manuals), and most traditionally configured transfer cases in production 4WD vehicles use a drive chain for transmission to the front axle. The noise isn't generally noticeable, even in relatively quiet vehicles.

Properly installed, a timing chain or internal transmission chain doesn't make much noise, but these homebuilt transmission chains might be another matter.
 

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Discussion Starter #12
I neglected to mention that I found this on the subject of Mini aerodynamics. Although I would like to preserve the basic appearance of the car, I will certainly consider making some aerodynamic mods such as de-seaming (especially given that the roof gutter and side seams are rotting anyway) and boxing in the underside with a metal plate. I might also consider a bodykit, so long as it's done tastefully :).

Internally, the gauges will likely be replaced with modern, electronic instruments; mostly for the convenience of working with them, but also because I have reason to believe the car's original speedometer no longer works properly.

After reading the story about the ForkenSwift, I like the idea of rigging up the choke cable as a quick disconnect, and I could certainly utilize some of their ideas about working on a shoe-string budget.

Something that hasn't yet been mentioned is heat dissipation. How much cooling is likely to be needed to keep the electric systems in serviceable order? What approaches have been used to solve this problem?

Somewhat related to this is New Zealand's temperate climate. If I intend to use the car in any season other than early autumn or late spring, it will need a heater (for winter) and (preferably) an air conditioner for all seasons (the car will get hot in summer and, as I recall; the Mini's stock window de-mistor was barely adequate to clear the front window, never mind the side ones, in winter ;)). I have heard of some cars using a small heat pump for this purpose; does this seem plausible?
 

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Discussion Starter #13
The bulletin board software doesn't support nested quotes? Pity :cool:.

A motor doesn't typically have a gearbox built into it. If you're referring to the complete drive unit (motor + gearbox + differential) of a typical modern production EV... the only common EV using an induction motor is the Tesla Model S/X, and it has a roughly 10:1 ratio of motor speed to axle speed. Since the motor can run at least 12,000 rpm and the tires are tall, top speed can be high. Most other EV motors are configured to run a bit more slowly, so (for instance) the Nissan Leaf overall ratio is about 8:1.
This is terrific information. You obviously know a thing or two about engineering yourself ;).


This forum's membership is an interesting mix, with long time auto enthusiasts who can rebuild an entire vehicle but are completely new to electronics (beyond the "plug in the black box" level), to electronics experts who can build anything from scratch but have no idea how anything in a car works, to computer programmers who can create complex logic in code but have never really touched the actual physical devices that do the work, and every combination in between.

Fortunately, everyone can fill in the gaps for everyone else. :).
I tend to think of myself as a programmer with a screwdriver and soldering iron. If I can't fix it in software, I'll fix it in hardware; or vice versa :).


Almost any motor produces relatively constant torque up to some transition speed, limited by the current which can be supplied by the battery, handled by the controller/inverter, and tolerated (in heating terms) by the motor. Above that transition, if there's enough voltage available then they are generally limited to constant power battery capability and cooling of the motor and electronics; that's constant power, not constant torque, so torque drops off with speed (power = torque x rotational speed = force x linear speed = voltage x current).
That seems like perfectly reasonable and solid engineering to me.


Providing enough voltage for high motor speed at full power is the reason that typical modern EVs run 360 V to 400 V battery packs.
I like this; we aren't making any toy power drill here. More volts equals less amps for the same power; although I am going to have to give some serious thoughts to where I'm going to put all those cells, and how to protect them if the worst-case scenario occurs :cool:.


Yes, but the challenge has already been handled to a large extent by the designers of the motor controller (and the battery management system), whether that is salvaged from a production EV or part of the design of home-built hardware using someone else's plan.
Even if I do take the sensible approach of using someone else's controller design, I will most likely want to make a few customizations to it; that's just the way I think.


Almost all of the electrical power supplied to the utility grids is from induction generators in power plants, whether hydro or thermal or wind powered. :)
It's quite interesting that this wasn't mentioned in my electrical engineering curriculum; but I can certainly see the logic here, not least of which is that an induction machine would be able to accept minor variations in the input frequency without affecting the synchronous frequency.


I get the speed-controlling theory, and that's the sort of reasoning that works with fixed-frequency industrial power supplies (to provide a relatively constant machine speed) or with a variable-frequency drive without speed feedback... but in practice it doesn't work well in a vehicle. The normal approach in an EV is for the accelerator pedal position to be interpreted as a torque or power request (the two are the same, except for the speed multiplier). Speed limiting or cruise control is handled the same way as with an engine, using a secondary control loop: if the vehicle goes faster than intended, power is reduced, and vice versa.
That was one of my thoughts, too. It would also make the vehicle behave similar to the direct mechanical linkage from the accelerator pedal to the carburettor; i.e. more pedal = more fuel = bigger bang = more torque.


It is possible to drive without friction brakes, entirely using the motor(s); however...
  • this generally isn't legal for a road vehicle (friction brakes mechanically/hydraulically linked to the pedal are required)
  • for reliability, it would be unwise
  • when near zero speed actively powering the motor in reverse would be required to stop, and using power to apply holding torque with the motor would be required to remain stationary
  • brakes are needed on all wheels, so friction brakes are still required on a two-wheel-drive vehicle
I never could figure out how modern vehicles do away with the simplicity and redundancy of a cable-operated handbrake. If the vehicle's service brakes fail, you're basically screwed.


Although regenerative braking doesn't return a huge amount of energy, it is certainly desirable. The big challenge is coordinating it with friction braking, so that braking is smoothly controlled, sensible to the driver, balanced (braking just one end of the car is bad for handling and stability), and doesn't use more friction braking than necessary.
That does sound like a challenge. However, since the Mini's original equipment 8.4" front discs are not servo-assisted (that didn't happen until about 1989), augmenting it with regeneration doesn't sound like a bad idea. The Mini really needs all the braking assistance it can get :D.

The only time I've ever seen the front wheels of a Mini out-brake the rear is when the car has been significantly shortened (a "shorty") and the original car had front discs :eek:.


Anti-lock braking system and stability control system behaviour must be considered as well. In an older vehicle with a simple hydraulic braking system (assisted or not), one problem is how to keep the friction brakes from applying on the powered wheels when regenerative braking is active; I haven't seen anyone address this in a DIY project.
Needless to say, I will not be messing around with adding anti-lock braking or stability control (the Mini is, quite accidentally, perfectly stable on its own; provided I don't mess up the weight distribution). I fully intend to keep the brake pedal firmly connected to the hydraulic brakes, regenerative or not. The only change I might make there is to increase the travel of the brake pedal so that the hydraulic brakes kick in later in the pedal's travel; leaving a dead zone at the top of travel where electric-only braking can occur. Regenerative braking would then occur over the complete travel of the pedal, augmenting rather than replacing the function of the original brakes.


It is now popular to have "one pedal" driving, in which zero accelerator pedal application is treated as a moderate degree of braking. It is a challenge to make this feel right to the driver, especially since the right amount depends on driver and driving conditions.
The intention would be to have mild regeneration occurring with no accelerator input; mimicing the deceleration and engine braking of the original engine and (manual) transmission.
 

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I never could figure out how modern vehicles do away with the simplicity and redundancy of a cable-operated handbrake. If the vehicle's service brakes fail, you're basically screwed.
Long ago, the handbrake was both for parking and emergency use, but that was before the service brakes were required to have dual hydraulic circuits. Since then, the service brakes have had their own redundancy, so a separate hand- (or foot-) operated brake system is no longer for emergency use; it is just for parking.

This is a good thing, since those parking brakes were never much good for emergency braking.

One issue is that they act on the wrong wheels for traction...

When brakes were all drum, it was easier to fit the cable-actuated mechanism in the single-cylinder drum brakes on the back than the more effective but more complex dual-cylinder (two leading shoe) drum brakes on the front. When front disks came in, it was much easier to run the remaining drum brakes on the rear with a cable than the disks in front. Even with the four wheel disk brakes that are now normal, it's still better to add the weight and complication of a parking mechanism to the rear brakes (which typically have smaller calipers) than to the front brakes.

Regardless of mechanism, it is preferable to run the parking brake cables to the rear wheels than to run them to the front and have them bending with steering action. The end result is that the lighter end of the car (in most cases) has the parking brakes. Even if the vehicle has equal front-rear weight distribution, under braking the load shifts to the front, so the front tires are more effective for braking.

Saab actually put the parking brake on the front wheels for a while, but that was back when they were gloriously weird. :D

So if you really need braking and all you've got is a typical handbrake, you're still screwed.

A related issue is that they act on the wrong wheels for stability...

The most common use of a handbrake, other than parking, is breaking the rear tire traction to spin the car around - it's actually a valid corner entry technique in some circumstances in rally competition. Pulling the handbrake to stop the car in an emergency is bad idea, as the likely result is hitting something while sliding sideways or backward, instead of hitting the same thing going forward, so you're even more screwed.

Those Saabs were popular in rally, and had to add a hydraulic handbrake lever to brake the rear wheels. :)

And they are difficult to use anyway because the lock on:

To be practical as a parking brake, they're always arranged to latch on; so you lose control if used in an emergency because they don't release when the driver stops pulling on the handle.

With the classic handbrake lever the driver can hold the button in, but that's awkward and most people will forget to do that in a panic situation. The handle that sprouted from the dash in the first pickup that I drove was turned to release - that would work better, but is still likely to be confused in an emergency... and it's almost impossible to maintain steering control while reaching for that thing. Then there's the foot pedal with separate release - try steering with your left knee up around the steering wheel to push the pedal while reaching down to the release handle with your left hand... I think you're screwed. The worst is probably the foot pedal which automatically releases when you push it again, leading to an on-off dance that would probably be amusing if it wasn't happening in the lead-up to a collision.


So I say forget the parking brake as an emergency brake. In the very rare event of a service brake failure, use engine braking or regenerative braking to slow down, and use the parking brake or jam it in park (or stall it in gear if you have an engine) for stop the final bit of rolling.


While the cable-operated parking brake is largely gone, the mechanical function is still there. It is just operated by a tiny electric motor on the brake caliper now. That means it is needs power to operate, and can be affected by computer problems, but it will probably still work... and is operated by an easy-to-reach switch. Some even have quite sophisticated control, so if you apply them while moving the system kills the drive power and gradually applies the parking brake - this may work better than the classic hand lever and cable system.

Many cable-operated parking brakes are not functional anyway, because they are not used (in automatic transmission vehicles) and the cables rust in the off position. If applied by someone other than the regular driver, they can stick on. Compare ten-year-old vehicles with electric and cable parking brakes, and I wouldn't be surprised if the electric ones are more likely to be functioning properly.
 

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... since the Mini's original equipment 8.4" front discs are not servo-assisted (that didn't happen until about 1989), augmenting it with regeneration doesn't sound like a bad idea. The Mini really needs all the braking assistance it can get :D.

The only time I've ever seen the front wheels of a Mini out-brake the rear is when the car has been significantly shortened (a "shorty") and the original car had front discs :eek:.

Needless to say, I will not be messing around with adding anti-lock braking or stability control (the Mini is, quite accidentally, perfectly stable on its own; provided I don't mess up the weight distribution). I fully intend to keep the brake pedal firmly connected to the hydraulic brakes, regenerative or not. The only change I might make there is to increase the travel of the brake pedal so that the hydraulic brakes kick in later in the pedal's travel; leaving a dead zone at the top of travel where electric-only braking can occur. Regenerative braking would then occur over the complete travel of the pedal, augmenting rather than replacing the function of the original brakes.
That makes sense, but there are two issues:
  1. it's going to feel weird
  2. if the regen is not full-on by the time the hydraulic brakes hit, there will be less regen than might be possible, but if regen is full-on before there is any hydraulic braking, the front-rear bias will always be wrong. At least this is more tolerable with regen on the front than it would be with regen on the rear only.
Production EVs all seem to use some sort of manual mode control to allow the driver to manage the balance of regenerative and friction braking, whether it's a switch or shifter position or steering column paddle. With a manual transmission and clutch (which no production EV has) you could set a moderate level of regen and shift to change the degree of effect (just like downshifting for engine braking or to change the effectiveness of a diesel compression brake).

In comparison tests the Tesla Model 3 clearly has less off-accelerator regen than competitors such as the Chevrolet Bolt. I believe that this is deliberate, because while using regen without any friction braking Tesla wanted to avoid excessive rear bias; the Model 3 is rear-drive, while the others are front-drive.

Of course AWD EVs have a big advantage in managing regenerative braking and balancing it with friction brakes (because it can regeneratively brake all four wheels), but that's not something that many DIY builders are attempting.
 

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Discussion Starter #17 (Edited)
I am editing this on my phone. Apologies in advance...

I never could figure out how modern vehicles do away with the simplicity and redundancy of a cable-operated handbrake. If the vehicle's service brakes fail, you're basically screwed.
Long ago, the handbrake was both for parking and emergency use, but that was before the service brakes were required to have dual hydraulic circuits. Since then, the service brakes have had their own redundancy, so a separate hand- (or foot-) operated brake system is no longer for emergency use; it is just for parking.
The most common use of a handbrake, other than parking, is breaking the rear tire traction to spin the car around - it's actually a valid corner entry technique in some circumstances in rally competition. Pulling the handbrake to stop the car in an emergency is bad idea, as the likely result is hitting something while sliding sideways or backward, instead of hitting the same thing going forward, so you're even more screwed.
Ah, yes; the good ol' handbrake turn. Pretty much the only thing the handbrake was ever useful for in the Mini; as, even when the handbrake cable and rear brake shoes were properly adjusted, they never did seem to be particularly effective, even for parking :rolleyes:.

... those parking brakes were never much good for emergency braking.

One issue is that they act on the wrong wheels for traction...
I actually did have a sudden and total failure of the hydraulic brakes on my 1989 Toyota Corolla once. It turned out that one of the rear brake shoes had been installed incorrectly and caused brake fluid to leak out of the system until there was insufficient pressure for operation. Fortunately, the failure occurred on a quiet city street and I was able to yank up on the handbrake to stop the car in time. I'm not sure who was the most surprised at the roundabout that day; me, or the driver I was attempting to give way to :eek:.


So if you really need braking and all you've got is a typical handbrake, you're still screwed.

...

To be practical as a parking brake, they're always arranged to latch on; so you lose control if used in an emergency because they don't release when the driver stops pulling on the handle.

With the classic handbrake lever the driver can hold the button in, but that's awkward and most people will forget to do that in a panic situation.
Despite my personal anecdote, I would tend to agree; although with an ineffective brake, you're still less screwed than with no brakes. Obviously, it's very important to know how the vehicle is going to respond in situations like that before attempting such a maneuver. Also, if I hadn't had so much experience pulling handbrake turns on grassy fields in the Mini, I probably would have found a way to screw up my emergency stopping maneuver and hit the oncoming car instead of stopping short of it.

So I say forget the parking brake as an emergency brake. In the very rare event of a service brake failure, use engine braking or regenerative braking to slow down, and use the parking brake or jam it in park (or stall it in gear if you have an engine) for stop the final bit of rolling.
In situations where you actually have time to think about it, using the engine and gears to slow down is by far the better way to do it. May sentient beings have mercy on you if you happen to be driving an automatic without knowing how to force a downshift in such a situation.


While the cable-operated parking brake is largely gone, the mechanical function is still there. It is just operated by a tiny electric motor on the brake caliper now. That means it is needs power to operate, and can be affected by computer problems, but it will probably still work... and is operated by an easy-to-reach switch. Some even have quite sophisticated control, so if you apply them while moving the system kills the drive power and gradually applies the parking brake - this may work better than the classic hand lever and cable system.
It's somewhat reassuring that there is still some redundancy in the system. Although, as you say, it is rather unlikely that a modern dual-circuit hydraulic system will fail completely; so there is still another level of redundancy there.

Many cable-operated parking brakes are not functional anyway, because they are not used (in automatic transmission vehicles) and the cables rust in the off position.
That's a good reason in and of itself to actually use the parking brake when parking an automatic transmission. I wonder why more people don't do that :cool:?


The only change I might make there is to increase the travel of the brake pedal so that the hydraulic brakes kick in later in the pedal's travel; leaving a dead zone at the top of travel where electric-only braking can occur. Regenerative braking would then occur over the complete travel of the pedal, augmenting rather than replacing the function of the original brakes.
That makes sense, but there are two issues:

  1. it's going to feel weird
  2. if the regen is not full-on by the time the hydraulic brakes hit, there will be less regen than might be possible, but if regen is full-on before there is any hydraulic braking, the front-rear bias will always be wrong. At least this is more tolerable with regen on the front than it would be with regen on the rear only.
More very useful things to think about. Thank you!

Production EVs all seem to use some sort of manual mode control to allow the driver to manage the balance of regenerative and friction braking, whether it's a switch or shifter position or steering column paddle. With a manual transmission and clutch (which no production EV has) you could set a moderate level of regen and shift to change the degree of effect (just like downshifting for engine braking or to change the effectiveness of a diesel compression brake).
Another great idea; and a potential use for the clutch pedal?

Of course AWD EVs have a big advantage in managing regenerative braking and balancing it with friction brakes (because it can regeneratively brake all four wheels), but that's not something that many DIY builders are attempting.
I have actually seen a hybrid car (a Toyota Oddysey, perhaps?) that installed electric motors to the rear wheels for the express purpose of providing regenerative braking; so it's not outside the realm of possibility.
 

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I have actually seen a hybrid car (a Toyota Oddysey, perhaps?) that installed electric motors to the rear wheels for the express purpose of providing regenerative braking; so it's not outside the realm of possibility.
The Odyssey is a non-hybrid Honda minivan... you're presumably thinking of the Toyota Highlander (or RAV4, or Lexus RX, or Lexus NX) hybrid version. The Honda Pilot / Acura MDX hybrids are similar. In those cases, the rear drive unit will regeneratively brake, but that's not its primary purpose: it's there to provide all wheel drive when required. The front has comparable or greater regenerative braking capability, in the hybrid drive system (in fact, one of the motor-generators in a Toyota Synergy Hybrid Drive transaxle - called "MG-2" - is typically identical to the motor-generator in the rear, called "MG-R").
 

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Discussion Starter #20
Hi
My mini through it's incarnations

From a 1430 A series to a 170 hp two litre twin cam

To my current electric roadster
Wow, that's an impressive array of mods. Well done with the open-top conversion, and very well done stretching the engine bay around that Lancia motor without converting it to the (slightly roomier) Clubman front-end :).

That roadster is cool; what did you use as a base vehicle?
 
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