Regen braking: confirmed! - Page 3 - RC-Monster Forums

teknorc · 02.25.2009, 12:52 PM

Quote:

Originally Posted by Arct1k

I also think people are getting confused between energy transfer in this thread.

The car when moving has kinetic energy : E = Mass * Velocity * Velocity

That kinetic energy can only either be transferred into heat, electrical energy or potential energy (coasting up a hill) (ok light too)...

In the case of a mechanical brake it is always transferred into heat in the brake pad whilst with motor breaks some is transferred into electrical energy.

Second consideration is Newton - i.e. equal and opposite forces required to stop the vehicle.

In a mechanical setup the force is supplied by brake disk which is pressured by a servo which is powered by the battery.

In an electrical setup the force is supplied by the motor - This is where is gets interesting! How is the force generated!?*&^!

Option 1) Through converting the motor into a generator? Which would generate electricity and through losses heat but "not take" energy from the battery
Option 2) Applying power to the motor with an opposing polarity which would "take" energy from the battery
Option 3) Or a fancy combination of both...

Guessing how smart patrick is it is 3... Thats my take...

Option 3 is my guess too. I acknowledge that regenerative braking is happening (I'm really not arguing that point, reread my post

). Brian's test proves there is extra energy for a brief time while braking. But I think some other power or force is also needed to stop the car in most situations, that's all I am trying to say.

lutach · 02.25.2009, 01:41 PM

I think that regen can be more of a marketing thing than anything else. What I've noticed is that the ESC will send send energy to the motor to brake it and that can be seen in most graphs, but there might not be any AMPs going back to the battery. Our little motors as you guys know are basically like an alternator and can be used to make electricity. An alternator can be modified to be a motor and I've seen some. Even in a full size electric vehicle, regen is more for marketing. Now what is different about a full size car is that they can coast much more then our R/C vehicles and that might help them put back a little energy into their pack, but not enough to give it a good charge. So regen braking is more marketing then something practical for our hobby. Brian, a good test to see is spinning a brushless motor and see what kind of reading you get from it.

BrianG · 02.25.2009, 01:59 PM

For sure, the regen braking doesn't do a whole lot to add to runtime. I think the main reason is to provide a place for the energy to go, the added runtime just happens to be a collateral benefit.

Way ahead of you lutach: http://www.rc-monster.com/forum/showthread.php?t=4997

It appears I didn't post it, but I do remember making a three-phase bridge rectifier and capacitor filter and it did provide a decent amount of power (don't have the numbers though).

Arct1k · 02.25.2009, 02:04 PM

iirc patrick mentioned up to 35% eff - note this is of the braking effort only...

I don't really think of it as a marketing thing as actually is saves the ESC / Motor from heating up...

lutach · 02.25.2009, 02:05 PM

Quote:

Originally Posted by BrianG

For sure, the regen braking doesn't do a whole lot to add to runtime. I think the main reason is to provide a place for the energy to go, the added runtime just happens to be a collateral benefit.

Way ahead of you lutach: http://www.rc-monster.com/forum/showthread.php?t=4997

It appears I didn't post it, but I do remember making a three-phase bridge rectifier and capacitor filter and it did provide a decent amount of power (don't have the numbers though).

Yes, I did see that one, but it kind of slipped my mind with so many other good threads. I don't thing for the millisecond of this regen it would be beneficial for adding any amount of energy back into the pack. The moment we use the brakes to slow down we basically loose more energy mainly because it will take more to get up to speed.

lutach · 02.25.2009, 02:09 PM

Quote:

Originally Posted by Arct1k

iirc patrick mentioned up to 35% eff - note this is of the braking effort only...

I don't really think of it as a marketing thing as actually is saves the ESC / Motor from heating up...

What I meant by marketing is when a company uses it as a form to sale the product. Yes, the energy does go to the place it came from and it might loose a little due to wires, connectors, resistors, traces, capacitors and more wires and connectors. So pack might not see anything at all in a way if you count the losses for the regen energy to get there.

Arct1k · 02:18 PM

Agree - I've never seen castle or anyone touting "regen breaking"... But do think that it is a key item and differentiator in enabling the ESC and motor not to heat up...

I agree with tekno that it is obviously going to be cooler without motor breaking as the energy will be lost as heat in the disc/pads rather than the motor.

BrianG · 02.25.2009, 02:14 PM

Quote:

Originally Posted by lutach

...The moment we use the brakes to slow down we basically loose more energy mainly because it will take more to get up to speed.

Of course, but you have to get back up to speed whether you use motor or mechanical brakes. It's obvious that the amount you put back in during braking will be FAR less than you use to accelerate, but a few more mAh is a few more mAh, and maybe a couple seconds more runtime.

Believe me, the intent of the original post was not to start a heated debate about gains in runtime using motor braking. It was just me playing around and tinkering. But, I have seen several posts in the past where this question was asked, so I thought it would be nice to have a tested result instead of theorized.

Arct1k · 02.25.2009, 02:22 PM

Brian - this is one of the more fun threads for me - a chance to use a fraction of my engineering background!

lutach · 02.25.2009, 02:41 PM

Quote:

Originally Posted by BrianG

Of course, but you have to get back up to speed whether you use motor or mechanical brakes. It's obvious that the amount you put back in during braking will be FAR less than you use to accelerate, but a few more mAh is a few more mAh, and maybe a couple seconds more runtime.

Believe me, the intent of the original post was not to start a heated debate about gains in runtime using motor braking. It was just me playing around and tinkering. But, I have seen several posts in the past where this question was asked, so I thought it would be nice to have a tested result instead of theorized.

I like things like this. The more the better and a heated debate will never come up in here. I've also seen post asking this question and this should keep people informed. This is a nice thread, you got an A+

.

lutach · 02.25.2009, 02:44 PM

Quote:

Originally Posted by Arct1k

Agree - I've never seen castle or anyone touting "regen breaking"

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

MetalMan · 02.25.2009, 05:17 PM

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?

lutach · 02.25.2009, 05:38 PM

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.

02.25.2009, 06:04 PM

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?

lutach · 02.25.2009, 07:43 PM

Quote:

Originally Posted by Bolt_Crank

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.