I never seen Castle, but I've seen a few from my few years of R/C that have mentioned such thing.

Just more to add to this smoldering fire:
http://img.photobucket.com/albums/v1...age_graph3.jpg

In this situation I was hard on the throttle to get to top speed quickly, and then I would SLAM on the brakes. Think the red circles are indicating regen. braking?

Just more good info. I have posted graphs also showing such volt spikes. One this I did notice in 2 runs I made was, first trying to see if the regen has any benefits which doesn't and the second was just plain simple smoothness which gave me the longest run time.

Hard race braking probably uses a lot more power than it puts back into the batteries, or more gets transformed into heat...

But what about slow, easy braking? Slamming on the brakes and releasing right away isn't going to put much usable energy anywhere but heat... That could be why there's longer run times on a track with mechanical braking.

Maybe someone with a data logger can do some tests, and try it with moderate braking instead of panic stops?

Tried that with drag braking, but didn't see anything significant.

A few weeks ago I posted some eagletree data and noted the current being put back into the battery in the second post of this thread. http://www.rc-monster.com/forum/showthread.php?t=18458

Regenerative breaking is very simple the way I see it. If you recall that motor torque is proportional to current, and that torque is negative during breaking, your are going to get negative current, or in other words, current that is charging the pack. When you charge a pack, the voltage increases.

If it doesn't make sense how a motor would create negative torque on its own without using power, think of what happens when you physically try to spin a motor faster than its kv*volts. It begins to push against you. You can drastically reduce the kv of a motor just by adding a resistor or equivalently, switching the esc on and off the same way it switches with different throttle amounts. This is just a guess based on general knowledge of circuits. I don't know the specifics.

Ok that guy made a test and still No true regen brakes in ezrun 150.
He made test device/stand. In one side motor spinning other motor which was he tried to brake. Yeah, he noticed regen spikes (Voltage and negativ current) but those spikes are realy short, impulse lenght was 0.002s-0.007s so no true regeneration there, just some spikes thats all.
Seems ezrun 80a make same spikes

Patrick - Please could you put us out of our missery with a nice technical explanation!

I wonder if Patrick even looks in this forum. After all, it's the CC section...

Maybe move the thread to CC area?

lol, I suppose it could be moved, but it initially had nothing to do with a CC product - it became that way when one person asked "Does the MMM do this?".

I hear ya, but thats just about as consistent and repeatable as I will be able to get in a real world test. This is something that I just observed when I went from mechanical brakes to motor brakes in my truggy. I was trying to just simplify the system as the mechanical brakes werent giving me any lap time benefits on the high traction indoor track. So when I took the mechanicals off I noticed I used a little more mah. I wanted to understnad what was happening. it could have been differences in the track layout or the traction from one day to the next so I did my little experiment to try and eliminate all of the other variables except the mechanical/motor brake difference. What I saw confirmed my suspision. Not a highly scientific or overly controlled experiment, but the results were clear enough that I am assuming what I am seeing is real.

I'm not arguing that regen braking isnt happening, I'm just wanting to understand if it means anything at all to the runtime. my suspision is that the motor brakes take energy to work. Of course... I have no real proof of that except for my little experiment and what I personally have observed.

I didnt mean to totally derail your thread Brian, but at this point I do hope that we get some input from someone who truely understands this all. I had the same discussion with Mike and we didnt come up with a real answer either.

FYI: I went and found my notes from my test. I know its not a huge sample size or a super controlled test but it seems like pretty simple clear result to me. I dont think I would have the time to put together something that would be statistically significant and completely controlled. Its enough to convice me personally.

Setup was:
RC8T, 1515/2.5D, MMM, 5s lipo, 15/50 gearing.
Lipo Pack #1 was a 5s 4300mah Neuenergy 25c
Lipo pack #2 was a 5s 5000mah Zippy Flightmax 30C


Track was a medium/small sized track. (125ft x 75ft with a 100ft straight) indoor high traction clay surface with alot of quick burst straights and sharp 180 corners. The layout required alot of braking to get around it quickly.

mah usage on a 5 minute run with mechanical brakes:
Pack #1 =1122mah Pack #2 =1146mah

mah usage on a 5 minute run with motor brakes:
Pack#1 =1241mah Pack #2 =1296mah

Pack #1 results 1241-1122=119 119/1122= 10.6% increase in mah used with the motor brakes.

Pack #2 results 1296-1146=150 150/1146= 13.1% increase in mah used with motor brakes.

The ESC probably has to use some of the power to actually stop the motor.

The only way to do a real test would be some type of automated setup that places a consistent load on the motor for the whole run, and applies brakes with the same intensity and duration. There could be slight variations in each run (exact grip of terrain, acceleration ramp, how slow you brake before accelerating again, etc) which will skew the results. The definition of a good test is comparing using a consistent and repeatable process.

Any regen braking will be minimal when compared to pack capacity to be sure. I would be surprised if regen braking exceeded 5mAh to be honest. For one, the voltage generated while braking has to exceed battery voltage for reverse (charging) current to flow. If braking gently, the generated voltage may not be high enough to generate any charge current, or just slightly over the battery voltage and won't generate appreciable amounts of charge current. Two, the duty cycle (time braking vs time running) of braking vs running is tiny, probably in the 5% range or most likely less. Three, our motors are most likely way more efficient when in "motor mode" as opposed to "generator mode".

Again, this isn't a thread to say we should all use motor brakes to get more runtime, this thread just says "see, this ESC does have regen braking". I personally prefer motor braking because it is "fade-free", simpler, and layout is cleaner. I really wouldn't care if motor braking used more power than mech brakes as long as it didn't exceed 5%.

What are you using to measure the mAh? If you are using an eagletree data logger, which measures reverse current as positive, it WILL say that your are using more mAh than you actually are when using motor breaks. My eagletreee says my pack uses about 4,000mAh during a run when it takes less than 3,600mAh from the charger. From this it is quite obvious that there is regenerative breaking, because some mAh are being reused and are thus being counted more than once.

Was my previous post not read? It seemed to have been skipped over. The ESC implementing low throttle when the motor is spinning fast is how motor breaks actually work. You may think that wherever position of the trigger correlates to throttle but that is not the case with car escs. This was the issue with the old MGM compros. The throttle input from the reciever was exactly correlated to the throttle outputed by the ESC causing the motor to "break" when going from high throttle to low throttle.

mah put back in the battery with the charger. Was my first post not read. lol:lol:

Sorry to resurrect a really old thread... but I saw that people were asking me to jump in and "pay my respects" so to speak... (And I'm having trouble getting to sleep tonight!!)


Regenerative braking does occur in all Castle ESCs. And yes, the actual braking action is achieved by just shorting the windings together through the FETs.

What happens is this -- the ESC shorts the windings of the motor, and forces the motor to start acting like a generator. Remember that a turning motor generates a specific voltage -- back EMF. This voltage is actually the voltage induced in the windings by the moving magnets.

Because the motor windings are shorted, the voltage drops to a very low level (usually less than .1V) and current rises very high, very quickly (often hundreds of amps.) As energy is generated (by the drag created by the voltage difference) current rises, and energy is circulated through the windings and the FETs - -- And a large magnetic field (with a LOT of energy) is stored in the winding.

After a short time, the FETs turn off -- and this is when the regeneration occurs. The current that was flowing through the windings suddenly has nowhere to go. Inductors (like a motor winding) abhor a change in current, so the stored energy (in the motor winding magnetic field) forces the voltage to rise until the winding current can continue to flow. The current flows from the battery negative, up through the body diodes of the low side FETs, through the motor winding, back through the body diodes of the high side FETs, and into the capacitors (and battery...)

This is similar to how a boost converter works:

http://en.wikipedia.org/wiki/Boost_converter

(stolen from the Wiki:) The key principle that drives the boost converter is the tendency of an inductor to resist changes in current. When being charged it acts as a load and absorbs energy (somewhat like a resistor), when being discharged, it acts as an energy source (somewhat like a battery). The voltage it produces during the discharge phase is related to the rate of change of current, and not to the original charging voltage, thus allowing different input and output voltages.

But instead of a supply, there is a magnet passing the coil that creates the current source.


Hope that clears it up for you all!

Awesome post Patrick. I don't know how accurate some of the data recorders are, but they usually show some sort of upward spike in the voltage. I also noticed that sometime an amp spike can occur as well, does that mean it's actually amp going back into the pack?

Yes, that amperage is going back into the pack during braking. Many data loggers do not have the ability to measure negative currents, so some just show zero current (like the Phoenix ICE data logger -- it does not have reverse current measurement, so it shows zero current during regen.) And some will show positive current, even though the current is negative. It depends on how the current sensing is achieved.

For example the Eagletree 150A uses a Hall-Effect sensor that is unidirectional. It would be nice to upgrade the HE sensor to a bidirectional version of the IC, but my email to ET asking about that is as of yet unanswered.

Sounds good. Thank you for coming in here to explain it to all of us.

We made the decision on the ICE controllers to use a unidirectional current sense to increase the accuracy (dynamic range) of the current sense. Eagletree may have made the same choice for the same reason.

My English isn't very good, and the translator is even worse. But doesn't shorting means connecting + and - together? But, that can't be possible, there should be a fire then, right? So what does shorting actually means?

Thank you,

Patrick

I might be wrong, but I don't think the shorting Patrick meant is the same as a + and - shorting of a battery for example. It's basicaly 2 motor phases shorting to achieve braking. I'll be waiting for the experts to answer it in more details though :lol:.

That's right; I am 100% sure Patrick did NOT mean to short the battery leads. That would be "bad". He did mean shorting the motor leads together via the FETs. Try this sometime: spin a motor by hand and note the resistance. Then, somehow ties all three motor wires together and spin it again. You'll see how much more resistance there is. And the faster the motor is spinning, the more resistance it will have when the wires are shorted.

Ok... But if I brake with my ESC, it also goes like "connecting all three wires together", but then it goes via the FETs and no energy goes through them?

I'm guessing the FETs don't stay shorted (otherwise the brakes would lock up), but pulse on/off. It's when the FETs switch off when the voltage charges the batteries.

Hmm, that would be pretty logical. And how more often they switch on/off how harder you break, right?

Actually, it's not so much "how often", but what percentage of "on" vs "off" they are.

Thanks for posting that Pdelcast (Patrick?), a good explanation for the not so tech savy.

Byte, yes the FET's do not continuously short the motor windings out, it uses the same principle as working normally as a motor, it's called PWM (pulse width modulation) and basically the more braking you input on your Tx, the wider the 'pulses', and hence more braking action. PWM is usually at a set frequency, but not always, and if it is variable, will change according to motor speed. Some controllers vary PWM in normal forward/throttle operation, usually to increase efficiency at lower rpm's, as the higher frequency PWM you go, the more heat is created because of eddy currents.

I'm just wondering how much this "regen" actually can effect run time. it cant be much.

I understand that when you spin the magnet inside the coils the motor acts like a generator. But wouldnt it act like a generator while its just coasting too? Why does it take shorting the motor phases to generate energy? Just not making sense to me.:neutral:

If you lock up the tires when stopping, then the motor is then no longer spinning so it cant be generating any power to send back to the battery, but it must consume some energy in order to keep the motor from spinning. How can it not take engergy to prevent the motor from moving?

I guess I am still not clear on this.

I'm just wondering how much this "regen" actually can effect run time. it cant be much.

Not much no, very small amount, it's not really optimized in these R/C applications vs. real electric cars regen brakes.

I understand that when you spin the magnet inside the coils the motor acts like a generator. But wouldnt it act like a generator while its just coasting too? Why does it take shorting the motor phases to generate energy? Just not making sense to me.:neutral:

Yes, when you are coasting there is potential between all three phases, however there is no current, hence no power being produced. The way the braking works is basically a 'controlled' short, you spin a motor in your hand, and it spins quite freely, then short out the leads and you have a dead short, that is basically the most braking action you can get from the thing. The FET's just control this by 'pulsing' the shorting action, thus the amount of braking effect.

If you lock up the tires when stopping, then the motor is then no longer spinning so it cant be generating any power to send back to the battery, but it must consume some energy in order to keep the motor from spinning. How can it not take engergy to prevent the motor from moving?

Despite what you may THINK you are seeing, the wheels really aren't locked up, they are spinning a little bit, and that little bit is basically the motor doing 100% braking action under those circumstances. And you are correct in your assumption that the motor cannot be generating potential when it is not moving... it's just that the motor IS moving, just very slowly, it doesn't take much to induce a potential into the windings, and thus currents.

I guess I am still not clear on this.

I haven't read the thread, but...
I luv my eagletree:yes:

this is a maxcraps pack....





next is jason hills losi truggy with mechanical brakes/clutch, losi 1700 system, 5s batt
high amps: 141.90
low voltage: 15.97
Mah: 2300
watts: 2395

note the regenerative braking on jason's truggy http://www.rctech.net/forum/classic_...es/redface.gif
http://i272.photobucket.com/albums/j...asongraph1.jpg
http://i272.photobucket.com/albums/j...asongraph2.jpg
http://i272.photobucket.com/albums/j...asongraph3.jpg

ET graphs do show voltage peaks during regen, but you can't see the current spikes because they are negative currents and the current sensor in the ET only measures positive currents.

but you can see it a little with the voltage spikes...

my question is, how come it has those voltage spikes with a mech. brake setup and a clutch:diablo:

Voltage jumping back up after going from under load to no load?

Battery voltage can jump like crazy going from full load to no load...

no... some of the peaks are above the voltage of the pack starting out....

I've seen my truck go from the 12 - 13 volts when sitting without the truck running, to 16 - 17 volts when I turned off my rack-o-lights... Though, that might be a strange backflow due to the relays themselves...

Could it be that breifly the motor is still doing high rpm hence the clutch is still engaged :whistle:

When you go quickly from any throttle to neutral, the magnetic field in the motor will collapse and generate a small voltage. Won't be near the amount that a brake setup has though, unless the motor IS in fact doing a little braking without you realizing it.

Relays are coils and generate inductive kickback when shut off. Most circuits simply place a reverse-biased diode in parallel with the coil to shunt that spike.