Let's do away with mechanical brakes?

It's time to challenge the controller gurus even more. It sounds like we're finally making some headway on variable regen, which is to be applauded. I want to keep the pressure on though and say let's make the weight, cost, and maintenance issues of mechanical brakes go away on the driven wheel. Since regen has to cut out as rpms get too low, we should have some type of plug braking pick up the slack. I don't think that's quite enough though to do away with the mechanical brakes, so maybe to increase braking force even further the controller should send pulses to the windings in opposition to the turning wheel to create more braking torque. I realize that will use so energy, but big deal, since I'm sure the net including regen will add to range, and the weight and cost savings along with a more simple overall system (other than programming in the chip and some wiring to dissipate heat to the frame for plug braking) is worth it. I have little doubt that EVs of the future will have all wheel drive and no mechanical brakes at all, so why not do it now?

Definitely need a minimum of two motors and two batteries and two controllers for redundancy

You need a motor on the front for sure

The problem is if you have a big bldc motor a shorted winding can cause the wheel to lock. Right now I wouuld never use a big bldc motor on my front wheels

Ac induction are superior in this manner because their is no permanent flux

The way around the problem with bldc is to use multiple stators per motor so if one stator were to fail the braking torque due to the single short is not enough to cause the vehicle to lose control

Brakes are pretty much useless on the rear of a bike most of the time. You only need em if ur front wheel locks before the rear end comes up or u need to initiate a slide

The front would only require a small motor, because it would be used intermittently only for braking and acceleration. Let's start with just the drive wheel and leave the front mechanical brake for now.

Mechanical brakes can have failures too, yet we don't see redundant disk brakes. This just needs to be made to a similarly low failure rate which should be quite simple with no moving parts. It's just a matter of recovering and storing as much of the energy as possible, and dissipating the rest as heat, and since we can make much of that conversion to heat outside the motor, then heat dissipation is a relatively minor issue. My bike draws 27kw peak, and accelerating from a stop the motor probably doesn't reach 50% efficiency until at least 35-40mph, so my drive system is dissipating lots of heat without issue. I can think of an number of enhancements to my cooling approach, so it's nowhere near optimum. With no heat problems now, that means I can take on lots more heat from braking and reject it with heat buildup.

Give me the control system to make electronic braking adequate enough to eliminate the need for a mechanical brake on the drive wheel, and leave the heat issues for me to solve.

What you want pretty much already exists but if you want to brake down to zero you need to apply a negative torque (when the motor is no longer generating enough voltage alone, regen is max but you want to slow more than regen allows). BMW does this on the i3. You can drive with only the throttle. At zero speed it applies the mechanical brake just to comply with the law

Tesla doesnt do this because it wastes a bit of power (the same reason they dont support wireless charging)

Maxed out regen at high speed damages the battery but F1 has shown it is possible with the right cells (but those cells only have to last less than one season)

Mechanical brakes have failures also, which is why you need both front and rear brakes by law on motorcycles. Also note almost every country requires all new cars to be built with a split dual circuit hydraulic braking system so if one circuit fails the other takes over

We need a cheap china controller with a Lebowski plug-in option. Only use the china controller as a power stsge. New board to handle inputs and brain. The real thing to work on is minimized torque ripple (besides the whole pronlem of a bldc motor locking up due to a short)

The Mission RS race bike is faster with regen off around Laguna Seca because the mechanical brakes are smoother. The torque ripple will cause a lose of traction for an equal rate of decel. Less of a problem with a car with heavier wheels and motor and brakes and...that acts as a flywheel smoothing out motor torque ripple

John in CR said:

Since regen has to cut out as rpms get too low, we should have some type of plug braking pick up the slack. I don't think that's quite enough though to do away with the mechanical brakes, so maybe to increase braking force even further the controller should send pulses to the windings in opposition to the turning wheel to create more braking torque.

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since v2.10 my controller IC can do (not-strength-reducing) strong regen braking all the way down to motor stop. It does this by seamlessly applying negative voltages (or: applying voltages that would make the motor run in reverse) in order to keep the regen-current flowing at full amplitude.

John in CR said:

I realize that will use so energy, but big deal

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No, it will still charge the battery, even at low rpm

John in CR said:

I have little doubt that EVs of the future will have all wheel drive and no mechanical brakes at all, so why not do it now?

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I disagree. What if, like me, you live on top of a hill and you start your trip by braking (for about 50m height difference) and your Lipo cells are already at 4.2V ? The choice between a LiPo fire or not braking, what would you do ?
What if you have temperature protection installed which automatically reduces phase current ? Then it will start to automatically reduce braking force, a big nono I would say.

For me: never without some sort of mechanical backup.

It will still charge the battery with negative voltage but would it have been more efficent to coast to a stop?

Long term mechanical brakes will go extinct, but maybe not for another 20 years
Even then there will be many holdouts
Also hacking to consider. Must have pysical access to hack mech brake
Electronic can be hacked from a distance

I havent run a rear mech brake in years but it will be a long time before I give up my front mech brake

flathill said:

It will still charge the battery with negative voltage but would it have been more efficent to coast to a stop?

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As long as the mechanical power goes back into battery charge, I would say it's more efficient than coast.

but if you get into the nitty gritty of 3rd order effects.... the regen braking charges the battery but also heats the motor, higher temp means
higher winding resistance meaning efficiency drops (especially for the next take-off)

Electronics cannot be hacked from a distance if they don't incorporate some sort of receiver (exception: large scale EMP event from nuclear blast )

Some electronics can covertly be operated and programmed at a distance with no "receiver" but its a secret
(Dont know this for sure but have seen funding and research to do exactly this)

If only trying to temp disable not hack...The most common attack would be a EMP style attack that scrambles all the signals. It doesnt have to be a full scale EMP that actually damages the circuit, only enough to scramble the comms. Def want a faraday cage if you are going to rely on ebrakes only but shielding against terahertz wave software define radio is not easy

Lebowski said:

John in CR said:

I realize that will use so energy, but big deal

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No, it will still charge the battery, even at low rpm

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That's pretty awesome, Lebowski 8)

Lebowski said:

What if, like me, you live on top of a hill and you start your trip by braking (for about 50m height difference) and your Lipo cells are already at 4.2V ?

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If you short all 3 phases to each other (turn on the 3 lowside FETs) you'll get strong braking even at low speed (it does this with my inrunner at least) and no current will flow to or from the battery but heat will build up in the motor, wires and FETs. If the motor and controller is sufficiently cooled, would this approach pose any problems?

then you have no control over the braking force, your speed will depend on hill percentage...

I'm on top of the hill, same as Lebowski, so, I'm game for testing.

Lebowski,

Your concerns are why I think plug braking should be part of the system, then when the battery can't take the charge current the energy gets dumped to resistors probably in the form of heating element wire with the frame as the heat sink. The fully developed system of the future would limit speed according to the braking capacity. Because it all adds little to no weight and no parts subject to wear, its seems inevitable.

WRT your system's ability to send charge to the battery all the way down to a stop, does that help with respect to the motor's decreasing efficiency as a generator with decreasing rpm so we get less heat. Am I even looking at that correctly when the motor is a generator, ie the same as a motor starting at 0 efficiency from 0 rpm, when it's a generator it's efficiency moves toward 0 as rpm goes to 0?

I really need Big Lebowski's running my ebikes. Is the development to a stage where I can do it economically, and without having to learn about electronics? ie order X,Y, and Z parts, solder them in place, and snap in your MCU. If not, then how can I help make it happen?

ie order X,Y, and Z parts, solder them in place, and snap in your MCU. If not, then how can I help make it happen?

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+1

Why not do something cool with the wasted energy if the battery is full (doubtful) like sending lightning across the back or a tesla coil type device?

Futterama said:

If you short all 3 phases to each other (turn on the 3 lowside FETs) you'll get strong braking even at low speed (it does this with my inrunner at least) and no current will flow to or from the battery but heat will build up in the motor, wires and FETs. If the motor and controller is sufficiently cooled, would this approach pose any problems?

Click to expand...

Lebowski said:

then you have no control over the braking force, your speed will depend on hill percentage...

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You could PWM it...

Two problems I foresee.........your going down a large hill, regen is slowing you down....your battery gets to its fully charged state and the high voltage shut off kicks in and stops regen......you fly down the hill with no brakes.

Or two.....your flying down a hill, and your batteries give out or your main circuit breaker goes, you then have no brakes.

Regardless, we still need mechanicals for when the electrical system fails. It does not need to be robust; only enough to bring the EV to a safe stop within a reasonable amount of time, and last for a reasonable lifetime since it is not the primary brake. It could also double as the holding brake on an inclined stop. Surely this would weigh a lot less than the dual rotor & caliper presently employed on motorcycles.

As for the full battery condition at the top of the hill:
That is an edge case. The smart move would be to dissipate as heat if the HVC kicks in. Again this system does not need to be robust. However if it is the case where you live at the top of the hill, then I'd tune the charging system down a notch so your regen works properly to top off the battery.

~KF

The electrical system should have a failure a lot lower than mechanical brakes, and in this case dual failures would be required at the same time, since 2wd is needed to be able to get rid of all of the mechanical brakes. Battery full was covered by the requirement of plug braking that automatically and seamlessly kicks in as needed.