Regen braking: confirmed!

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]

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.

[SpEEdyBL]

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.

[Arct1k]

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

[BrianG]

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

[Arct1k]

Maybe move the thread to CC area?

[BrianG]

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?".

[BrianG]

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%.

[BrianG]

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.

[Pdelcast]

Originally Posted by BrianG

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.

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.

[bcltoys]

So the MMM is for 6cells right that to me means you should use 4cells to be real safe 5cells max and always at least 35c right or wrong. And nothing but 6.5 connectors or larger. And gear for say 45MPH max.

[BrianG]

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.

Originally Posted by BrianG

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?

[BrianG]

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.

Originally Posted by BrianG

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?