Motor braking.

[GriffinRU]

Originally Posted by zeropointbug

The software engineers of the controllers are putting 'assumptions' into the algorithms, if you catch what I mean? It's hard to explain this. But also, maybe it's monitoring current levels, and there is a max?

A simple braking alg. would prob do some pretty decent braking effect. But who knows how sophisticated they are, or maybe they are simpler than one might think?

I don't think so, but it is Ok to assume that :)

[zeropointbug]

what do you mean?

[zeropointbug]

NVM then

[Serum]

what the.... the MOTOR takes the abuse,

Yeah, if the motor stops dead immediately, but that's not the case. since you are trying to slow down the vehicle and not locking its tires.

Go figure boy..

Use the motor as a generator to slow down the vehicle, that's the principle of braking.

[Serum]

Simple and short, my opinion on braking.

BL motor braking: (most likely mechanics)

first: a shorted motor has incredible resistance from turning, and, the faster it spins, the more resistance it has.

- Using full motor shorting for braking would undoubtedly flip an R/C car over it's lid with ease.

- So, you need to control this shorting in order to control the motor shaft resistance, to create an average resistance or torque.

-Along came PWM... the controller sets up the FET's to unify all motor phases to create a short. So the controller will change PWM duty cycle depending on throttle position... so anywhere between say 1% to 95% (for ABS, guessing) duty cycle for proportional braking.

-These latest controllers (like the Quark) most likely have some good algorithms for braking.

This is just my simple theory on motor braking, not going into detail what happens in FET's.

And this is correct.

BTW, the ABS can 'easely' be programmed; if a motor turns, it's a generator, and by the amount of energy it produces the speed of the turning motor can be determined. Slowing a vehicle down usually take a certain amount of time and the controller can measure the energy that the motor is still producing.

Who ever ran a quark on a rather direct drive vehicle (short gearing ratio) and a low KV motor knows that the brakes work too hard. It's just a matter of software, this software assumes a certain brake power is needed.

Again; that guy at schulze (who developped his brushless controllers) told me the energy was stored back into the batteries. No need to think he was wrong. He seemed very interested in my runtime of my savage, when i told him i was going to use the mechanical brake instead of the motorbrake. So something must be happening with the batteries, agree?

And zero; if the energy is stored in the motor like you suggested, why does a controller get hotter if you use the motorbrake? (the motor would get hotter too, no doubt, but with your theory ONLY the motor would get hotter.)

@ artur; why does the controller need to know the possition of the rotor? all three phases can be shorted with PWM instead of going the complex route of following the stator.

[zeropointbug]

Did I say the motor is only takes energy? that's true, most of it, esc I would assume takes some, obviously a little from internal resistance (not much), and switching, and losses from whatever else goes on with the FET, like Artur said there is a voltage drop in FET?

I have said it before that braking IS hard on a ESC, but when you look at total energy , the esc probably dissipates small percentage of energy.

I can see regenerative braking, but let the question be asked whether the efficiency when motor is acting like generator is great enough to produce a voltage high enough to charge batts. It might depend of motor? Do you think?



"Yeah, if the motor stops dead immediately, but that's not the case. since you are trying to slow down the vehicle and not locking its tires.

Go figure boy..

Use the motor as a generator to slow down the vehicle, that's the principle of braking."

-What are you saying?

[Serum]

It might depend of motor? Do you think?

That would be determined by the internal resistance (inherent with KV) of the motor.

The motor generates energy once the vehicle is running; some motors KV value are determined by spinning the rotor at X rpm to make 1V. Don't know if this AC is measured over 2 wires or if it's the sum of all three phases.

Basically every electric motor that uses magnets can be used as a generator. It produces energy once it spins. This is the reason why shortening the wires affect the turning resistance of the motor.

You said it yourself; if it spins faster, it has more resistance with the wires shortened.

If you have no batteries attached and you spin the wheels at 60-70mph and the truck is geared for 20mph i am pretty sure the controller will burn.

Perhaps even sooner, but the idea is obvious i guess.

schulze tells the world about the loose contact; he told me that a loose contact is worse on braking than on accelerating; this combined with the fact of his 'store the energy in the batteries' made sense to me.

[GriffinRU]

Originally Posted by Serum

And this is correct.
@ artur; why does the controller need to know the possition of the rotor? all three phases can be shorted with PWM instead of going the complex route of following the stator.

To be in sync with rectification provided by diodes, otherwise there will be less energy put back to battery.

To charge the battery you need current. Higher current means higher energy density, in battery system means more energy being put back in battery in short time.
Now when you discharge battery under normal driving (acceleration...) battery voltage goes down based on voltage drop associated with internal resistance. Internal resistance related to battery chemistry and driven how fast this chemistry goes. This mean that for a short period of time their would be a nice current going to the battery via diodes (or FET's if controlled, very efficient) due to the earlier voltage drop on battery and it's time period will be driven by battery recovery time and vehicle dynamics (it can slow down faster).

As simple as charging battery with 100C for a 0.1 sec...
That's also explains why nice cap is always helps, but that is different story on parallel thread :)

Schulze's comment about loose contact business very well explained in App. Note I mentioned earlier, but as for braking I haven't check their soft yet if their controller does that or its given for free with built-in diodes.

[Serum]

Good, I thought you and zero both shared the opinion on the fact that the motor took the punishement during braking, that's why i asked.

I never lost the 'store energy in the battery' theory out of sight; i thought you and zero both did. But i just read your earlier posts again, and saw you agreed on another thing with zero;

Originally Posted by GriffinRU

Much faster, at least 2 times faster then number of PWM steps times switching frequency.

I checked the spec sheet and it can go upto 5000 samples per second in high resolution mode. Surely it has to capture _something_ if it is there, even if it is recorded intermittently...

[zeropointbug]

So, then, can 'potentially' all the energy from momentum be put back into batteries IF voltage is high enough through rectification, or can only half be utilized, with diodes?

This is the part I am still stuck on.

Maybe we should get an esc engineer representative on here to explain how there controller braking works. Maybe from CC, or S&T?

I'm sure some of these theories are correct in way, but whether engineers use them or something diff, who knows? just a thought

[zeropointbug]

Originally Posted by Serum

Good, I thought you and zero both shared the opinion on the fact that the motor took the punishement during braking, that's why i asked.

I never lost the 'store energy in the battery' theory out of sight; i thought you and zero both did. But i just read your earlier posts again, and saw you agreed on another thing with zero;

Is it not a good idea for ppl agree with me?

[zeropointbug]

Originally Posted by Serum

That would be determined by the internal resistance (inherent with KV) of the motor.

Use impedance instead, some ppl might be confused when you use internal resistance.

Originally Posted by zeropointbug

I'm sure some of these theories are correct in way, but whether engineers use them or something diff, who knows? just a thought

Yes, they are correct. The main problem I have with the regenerative braking theory in the context of our setups is that not a single controller that I know of makes any provision for setting the exact battery chemistry type and cell count or even warns about the use of lithium based packs if motor braking is used.

If ESCs are performing regenerative braking they need to warn users about how to configure their product correctly to accomodate their battery chemistry under braking conditions. Anything less is a serious danger!

[silentbob343]

There is a guy over at rcuniverse under the screen name Novak2 that is pretty good about relaying technical questions to the Novak engineers. He's about the only one I know of off hand.

Originally Posted by Aragon

Yes, they are correct. The main problem I have with the regenerative braking theory in the context of our setups is that not a single controller that I know of makes any provision for setting the exact battery chemistry type and cell count or even warns about the use of lithium based packs if motor braking is used.

If ESCs are performing regenerative braking they need to warn users about how to configure their product correctly to accomodate their battery chemistry under braking conditions. Anything less is a serious danger!

The Quark 33A allows the user to select NiMH/NiCD or Li-Poly, but I believe it is only for purposes of LVC.