Understanding ESC freewheeling
 

Hi Guys,

Last night I really digged myself into the ESC freewheeling. I was really curious as I saw this function on my new HW Quicrun 1080 but only found a few posts in this theme. My information are mostly from helicopter forums.

So as long as I understand:
If I let go the throttle or use the motor at low RPM, there will be an amount of unused/left current cycling between my motor and ESC. This has to do something with the magnetic field collapsing in the motor which I don't really understand... This is called "wheeling". This current usually would heat up both motor and ESC.

If I enable freewheeling on my ESC it will pump this current into a MOSFET.
This is really useful, becouse this will let:
1./ Run both motor and ESC cooler
2./ Lets me run the motor continuously at lower RPM

Is it true?
I'm running a CC01 which is a bit overgeared from the factory so this would be a great function. Also as I understand, there is no problem with running this function all the time, even on trail runs - as helicopter drivers run this function all the time.

And one more thing is that are these left currents pumped back into the battery or they stay in the ESC? I run NiMH packs which have less charging capacity than LiPo's... but as I read there is no problem with freewheeling on NiMH packs.

Every more information would be really helpful on this theme...

Re: Understanding ESC freewheeling
 

I read up a bit on this as well as I just installed a HW1080 in my TRX-4. I think you summarized what I read pretty well.

I suspect though, that the residual currents are dissipated through the ESC and not sent back to the battery. At this point, the electronics required to make this a "regenerative" system would be prohibitive in terms of the footprint they would require.

This would be a good question to post to JRH's "Have Tech Questions Will Answer" thread further below in the Electronics section though. I suspect he can provide a much more concise answer. "thumbsup"

Re: Understanding ESC freewheeling
 

Brushed motors turn into generators if you turn them with a drill. If the ESC uses the power generated it adds drag to the motor, this drag can slow the motor down.
I believe turning on freewheeling uses the power generated from the motor to charge the battery when the motor is coasting.
I would think turning freewheeling on would produce more heat, but speculation, as I don't know how it works.
Seems backwards to me though, turning on freewheeling adds drag to the motor so it has more control downhill.
I always turn freewheeling on for the downhill control.

Re: Understanding ESC freewheeling
 

"I believe turning on freewheeling uses the power generated from the motor to charge the battery when the motor is coasting."

Are we sure about this? I really don't think the ESC is "smart" enough to do this. There we need to be balancing occurring, etc.

Re: Understanding ESC freewheeling
 

My understanding is active freewheeling can be accomplished by pulsing both neg & positive leads. It actually reverses for a moment to dissipate the voltage spike. Most ESC's just pulse the negative lead & use internal diodes to deal with the voltage spike. The effect is a very low voltage drop as the energy escapes, whereas thru a diode there's a voltage drop. I believe this is also considered regenerative braking.

HW says with it off the motor accelerates faster, and with it on there's more low-speed efficiency & linearity. That would make sense since it's partially braking it in-between pulses. Motors tend to be jumpy at low speed since that's where they make peak torque. FYI full brake is done by grounding both leads.

Re: Understanding ESC freewheeling
 

I continued my search and I'm pretty sure that there is no energy pumped back to the battery...

But it is sure that when auto freewheeling is enabled, the run time will last much longer. It's true that the acceleration is more linear like when you set punch control to a minimum level but that wont hur't you on a trail run.

I'm really surprised that there is very few information on this topic because in my opinion this is one of the most important feature on a crawler ESC. There are so many problems occure because of overheating due to slow driving and overgearing.

Heli drivers wrote that when this function is enabled they can easily do 3D fly on 30-40% throttle continouosly without any trouble. And I think that this is also true for crawling/trailing.

Last night I enabled this function and drived around very slow for a while and the motor and ESC stayed ice cold. I will thest it out in the weekend.

Re: Understanding ESC freewheeling
 

"I continued my search and I'm pretty sure that there is no energy pumped back to the battery..."

The more I've looked the more I tend to agree with TDanny. It would appear the excess is basically burned off at the ESC heatsink. I don't want to hi-jack this post. TDanny - I really think you should pose this question to JRH over in his Have Tech Questions - Will Answer thread. As I stated earlier, I'm confident he can provide us with a much more concise answer.

http://www.rccrawler.com/forum/elect...answer-53.html

Re: Understanding ESC freewheeling
 

"The effect is a very low voltage drop as the energy escapes, whereas thru a diode there's a voltage drop. I believe this is also considered regenerative braking."

I get where you're going here. But, if it's simply mitigating voltage drop, I'm not sure it can be referred to as regenerative. Efficient - Yes. Regenerative - My guess is No.

Re: Understanding ESC freewheeling
 

From HW direct.......
Tech Guru CS (HOBBYWING)

Feb 1, 10:52 AM PST

Hello,

It has to do with how the motor responds up and down hills. It's very difficult to explain, but mainly it "holds" on inclines, and declines a lot better when in motion.

It's fairly direct to "feel", so it would be worth trying an up and down hill section, starting and stopping slowly, with the feature, on, and that same route again, with the feature off. Usually only takes a few "up and downs" to feel the difference.
HOBBYWING
Innovation Powered by Passion

And i asked for layman's terms....lol

Re: Understanding ESC freewheeling
 

So, based on their explanation, there is no regenerative effect.

Re: Understanding ESC freewheeling
 

I was guessing on the charging the battery part. And there would be not much charging being done as the current is so small, it would just make sense as a dissipation destination for the extra current.
Honestly I only care about the effect it has on the driving, which is as hobby wing has stated, "declines a lot better when in motion" or downhill control.
I want my drag brake to lock up the tires, so there is no coasting down hill, to go down hill i pull the throttle, with freewheeling i have control, without freewheling it would free roll down hill as soon as any throttle is applied faster then i would like.

Re: Understanding ESC freewheeling
 

Set it and forget it. It works for crawling. ;-)

Re: Understanding ESC freewheeling
 

It’s sort of similar to the brushless freewheeling types, but not with associated increases to esc efficiency. Voodoobrew’s explanation is pretty much right.


At low throttle, the esc clamps the motor freespinning by the same method of regen break. This increases heat in all parts of the system, as it is not contributing work but is increasing amperage flow. It does keep the motor from “free running” as much.

Re: Understanding ESC freewheeling
 

John is this the same as Holmes Hold or?????

Re: Understanding ESC freewheeling
 

I dont think so, dont they just call in "regenerative braking"? I thought HH was basically 4x drag brake.

Re: Understanding ESC freewheeling
 

Holmes Hold is a reactive brake that actively pushes back. Not at all the same.

Re: Understanding ESC freewheeling
 

So yesterday I had some time to play with the settings. Man, this function is really awsome :D I'm starting to understand after a bunch of forum reads and videos...

So if I'm correct...
When you normally drive your car at low RPM, there are a number of unused current cycling around your motor and ESC because of the magnetic field, which your motor generates and holds.
Active freewheeling drives this unused current to a MOSFET and this not only makes the system to run more efficiently (cooler with more runtime...), but also generates an active braking effect in the motor. (One video explains why this happens...)

So this works like driving a real car downhill in lets say 1st gear. It wont let the car run faster than you push the throttle. This is an active braking effect whyle the car is in motion against the drag brake, which only works when you complitely let go the throttle.

Re: Understanding ESC freewheeling
 

In a brushed system it lowers efficiency and makes everything run hotter, it’s just recirculating more current to oppose the rotor inertia. In a brushless it can boost part throttle efficiencies because diode losses are the majority of heat, and the goal is to remove diode losses and shunt current through the mosfet instead.

Re: Understanding ESC freewheeling
 

I think you are wrong. The Quicrun is a brushed ESC supposed to run only brushed motors.

This is the description right from the ESC manual:

15. Freewheeling
For regular vehicles, we recommend disabling this function. With it disabled, your vehicle can have quick acceleration. For a crawler (simulation model), we suggest enabling it. With it enabled, you
crawler can have better linearity during a low-speed running and also less heat.

Re: Understanding ESC freewheeling
 

I'm not an electric engineer, altough I used to learn some electronics in high school.
But as long as I understand it right, the point is on the effect that the active freewheeling couses the magnetic field of the motor to collapse way faster. This gives you a more efficient and cooler drive and the braking effect is only a consequence.

The magnetic field (freewheeling) is the nature of electric motors brushed and brushless also. If you force this field to collapse, there you get efficiency and also braking the motor.

Also the braking effect only occures in crawlers (and wheeled vehicles), because in a helicopter, your rotor will spin as fast as you set your throttle so you wont notice any braking. And when you let go the throttle the active freewheeling will also turn of. And after then your rotor will turn freely. But in crawlers we have the drag brake to stop the car while it is not in motion.