Regen braking: confirmed!

[jhautz]

This is cool Brian. I always wanted to do this test myself but never really had a good enough multimeter to do it. Especially after a little experiment I did myself a couple weeks ago. I have actually been meaning to start a thread on this very topic. I have heard for a long time that they did have regenerative braking in just about all ESCs but never saw any proof of the fact.



I'm hopeing someone can answer why it is that I see 10-15% better milage when I run mechanical brakes? This is on the same truck on the same day on the same track with the same setup and batteries. I did some testing the last time I went out for a practice day and wanted to see what effect the mechanical vs motor brakes had on run time. I ran 2 5 minute runs with the mechanical brakes on 2 different packs, and then took the mechanical brake off, and charged the packs back up recording the amount of energy I put back in each one. Then ran two 5 minute runs with the mechanical brakes taken off and used motor brakes. I tried to drive just as hard with both brake setups and ran 2 trials on each just to add a little extra data.

But for sure, both runs with the motor brakes used more mah from the packs than the runs with the mechanical brakes did.

A day or 2 after I actually did this I realized I could have used my eagle tree to get better data. Next time I will do it that way.



I just dont get it, the evidence would support the opposite effect being true. Longer run time with motor brakes.

Wondering if anyone has any thoughts?

[teknorc]

Originally Posted by jhautz

This is cool Brian. I always wanted to do this test myself but never really had a good enough multimeter to do it. Especially after a little experiment I did myself a couple weeks ago. I have actually been meaning to start a thread on this very topic. I have heard for a long time that they did have regenerative braking in just about all ESCs but never saw any proof of the fact.



I'm hopeing someone can answer why it is that I see 10-15% better milage when I run mechanical brakes? This is on the same truck on the same day on the same track with the same setup and batteries. I did some testing the last time I went out for a practice day and wanted to see what effect the mechanical vs motor brakes had on run time. I ran 2 5 minute runs with the mechanical brakes on 2 different packs, and then took the mechanical brake off, and charged the packs back up recording the amount of energy I put back in each one. Then ran two 5 minute runs with the mechanical brakes taken off and used motor brakes. I tried to drive just as hard with both brake setups and ran 2 trials on each just to add a little extra data.

But for sure, both runs with the motor brakes used more mah from the packs than the runs with the mechanical brakes did.

A day or 2 after I actually did this I realized I could have used my eagle tree to get better data. Next time I will do it that way.



I just dont get it, the evidence would support the opposite effect being true. Longer run time with motor brakes.

Wondering if anyone has any thoughts?

The motor is still using power to stop. In other words, ESC braking is not free. The 'regenerative' part is that it can recapture small (if not tiny) amounts of power in between the pulses while the braking power is applied. After all, a force is essentially being applied in the opposite direction to bring the car to a stop, just as it would if it was starting from a standstill. This is also why motor brake setups run hotter since the motor is working in both directions. Also, braking force is usually applied more abruptly than while accelerating. AFAIK, a single mechanism (the motor) can't function as a generator and a source of power at the same time. You must use power to brake the car. I'm not an electrical engineer, but I know a few things about physics and the forces that are present and being applied in this scenario simply can't be ignored.

Please correct me if I'm wrong here because our results coincide with jhautz and others that have found mechanical brakes to be more efficient. I'm not arguing that some energy isn't being harnessed or regenerated while braking, I'm saying that it does in fact use power to brake and that the overall net of the system is negative, not positive. Mechanical brakes are obviously using power as well (servo), but compare a servo's energy requirements to a 1/8th brushless motor's requirements and I think the picture becomes clearer.

[jhautz]

Thats what I was always thinking. I can see how coasting off power would actually spin the motor and make it act like a generator. That makes sense to me. But braking to me always seemed like it would take energy to offset the energy that the truck already had in its momentum.

[tom255]

Originally Posted by teknorc

The motor is still using power to stop. In other words, ESC braking is not free. The 'regenerative' part is that it can recapture small (if not tiny) amounts of power in between the pulses while the braking power is applied. After all, a force is essentially being applied in the opposite direction to bring the car to a stop, just as it would if it was starting from a standstill. This is also why motor brake setups run hotter since the motor is working in both directions. Also, braking force is usually applied more abruptly than while accelerating. AFAIK, a single mechanism (the motor) can't function as a generator and a source of power at the same time. You must use power to brake the car. I'm not an electrical engineer, but I know a few things about physics and the forces that are present and being applied in this scenario simply can't be ignored.

Please correct me if I'm wrong here because our results coincide with jhautz and others that have found mechanical brakes to be more efficient. I'm not arguing that some energy isn't being harnessed or regenerated while braking, I'm saying that it does in fact use power to brake and that the overall net of the system is negative, not positive. Mechanical brakes are obviously using power as well (servo), but compare a servo's energy requirements to a 1/8th brushless motor's requirements and I think the picture becomes clearer.

Actualy Its consume very little not more than couple amps! One guy in russian forum made tests about regenerative brakeng and he did not recorded any noticable power consumption its just shorting motor windings and power force applies through shorting Impulse lenght and opposite phase switching, power consume mostly for FET drivers, brains then braking. MGM, MMM, MM, Schulze, Quark B125. No one regenerated a power, all regenerated power goes for FET heating.

[teknorc]

Please don't misunderstand. I'm not saying that regenerating isn't happening while braking. There is stored energy in the vehicle to be recaptured. But unless the regeneration or conversion of the stored kinetic energy is 100% efficient, some other energy must be used to stop the car, especially if you are braking hard at high speed. If the conversion was 100% efficient we'd have a perpetual motion machine in our RC cars. Shorted motor resistance is one thing, but we all know how motor brakes can flip a car on it's lid. If shorting was that powerful you wouldn't be able to turn a brushless motor shaft by hand if all three wires were touching each other. This is why I think there is power being applied while braking.

Again, I'm not an electrical engineer, maybe at higher speeds, the shorting becomes more powerful and violent enough to flip the car, not sure. This still doesn't explain why a lot of people are experiencing better run times using mechanical brakes though. I'd like to know for sure from someone who can explain it as well. I've read up on full scale regenerative braking and they all have mechanical brakes to supplement the regenerative brakes for various reasons. One of the reasons cited was to more quickly bring the vehicle to a stop from higher speeds.

So, please, someone explain. If motor braking is indeed free, I have a couple things I want to try to get even more run time

[Arct1k]

Well I'm not disagreeing 100% but have you ever tried shorting a brushed motor - No power input is actually applied but almost impossible to turn over - This is the easiest way to dig a clod....

You don't need to have power to provide breaks when using a motor...

Patrick is the one we need to chime in here...

[jhautz]

Originally Posted by Arct1k

Patrick is the one we need to chime in here...

That would be nice. Someone who actually knows how these thigs work. lol

[Arct1k]

PS http://www.ezonemag.com/pages/faq/a504.shtml

[BrianG]

A looong time ago, I too thought that motor braking was achieved by the ESC partially shorting the phases via PWM. Due to the way ESC FETs are wired to the motors, this would be done by turning on all the FETs going to ground. But, doing this would generate no voltage/current. And as you can see via my original post, the ESC does generate both voltage and current. The numbers don't lie boys. The fact that I got a higher voltage than the supply (battery) and negative current (current flowing into the battery rather than from the battery) both indicate, without a doubt, that there IS regenerative braking.

However, Patrick has said the ESC sends the motor's kinetic back into the ESC and then to the battery. If this is happening (and it is), simply shorting the windings would not accomplish this. Shorting the windings would brake the vehicle, but where is all that kinetic energy going? I'll tell you; either the motor and/or ESC. Neither are sized to simply dissipate that power.

There is a graph (in a previous post) by othello which proves regen braking as well.

Even Mike agrees with the results. He has Eagletree graphs where the mAh consumed is greater than the battery capacity. As well all know, when you have any decent current flow, the mAh used will actually be LESS than battery capacity. So, even though ET doesn't show negative current (does show v spikes though), just the fact you get more mAh is a giant red flag in favor of regen braking.

jhautz: why you get less runtime with motor braking is still puzzling to me. Without a consistent and repeatable test method, results are simply objective. Not trying to shoot ya down, just my $0.02.

Originally Posted by BrianG

jhautz: why you get less runtime with motor braking is still puzzling to me. Without a consistent and repeatable test method, results are simply objective. Not trying to shoot ya down, just my $0.02.

Could it be the result of the quality of the battery packs in use? If low quality packs with higher internal resistance can't take back the load they're feeded during braking, the energy is transformed into heat instead of actually recharging the pack.

[jhautz]

Originally Posted by BrianG

jhautz: why you get less runtime with motor braking is still puzzling to me. Without a consistent and repeatable test method, results are simply objective. Not trying to shoot ya down, just my $0.02.

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.

[lutach]

Originally Posted by jhautz

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.

[SpEEdyBL]

Originally Posted by jhautz

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.

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.

[jhautz]

Originally Posted by SpEEdyBL

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

[Pdelcast]

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!