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Old Jan 02, 2013, 03:59 PM
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Originally Posted by gionag View Post
juuuut when do do you think the 35a version will be available ??

thanks
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Old Jan 03, 2013, 01:27 AM
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Quote:
Originally Posted by gionag View Post
juuuut when do do you think the 35a version will be available ??

thanks
Hi,

i dont know it exactly .. i think it may be in about ~1 month. as i said i still working on the layout, the 35A will also have a shunt for current measurment and limiting on it


regards

Felix
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Old Jan 03, 2013, 08:39 AM
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Hi,

i was asked what difference it would be compared to "normal" ESCs..
so i think one of the most important things is the active freewheeling.
here is a good video i found that explains its basic advantage.
How BLDC Active Free-wheeling (Synchronous Rectification) works.. (10 min 27 sec)


there are also differencies how active freewheeling is used. as far as i know the most ESCs that has it (like kontronik and YGE) uses it just for getting rid of the diode losses. to do this thay turn off the opposite "active freewheeling fet" as soon as the stored coil current stops flowing.
but if you keep this fet on as long as the "main PWM fet" is off, you will get also a brake effect that will hold the motor on its speed.
so with this type of active freewheeling the ESC regulates in both ways.. not just when it accelerate the motor... also when you slow it.

and that gives a positive effect to the whole control circuit of a multicopter.
a side effect of this is that the energy that becomes free when it brakes the motor will flow back to the lipo. some call it regenerative braking because of that. but its not the same as it is used on car ESCs.. they act like a generator if the throttle is at zero.

the main problem of active freewheeling is to turn the opposite "active freewheeling fet" on as soon as the main fet is turned of. but it must be done with a accurate timing. if it is turned on to early it will short circuit the lipo and generate a lot of losses. if you wait too long the positive effect is gone.

a drawing which shows the PWM of both fets of one phase:


so there are some requirements for a fast (effective) active freewheeling..

1. fast switching fets (the faster thay are the less dead time is needed)
2. a accurate jitter free PWM (the more jitter you have the larger must be the deadtime to prevent short circuits)

i tried to take the best HW for both .. the MCU does HW PWM..also complementary. so there is almost no jitter. and the fets are driven with fast gate drivers.. so thay can switch with about 27ns typically (according to data sheet)

the most HK ESC's dont have fet drivers and also don't use active freewheeling at all..


regards

Felix
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Old Jan 05, 2013, 04:20 AM
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hi,

i made a video that shows its motor compatibility:
UltraESC motor test (6 min 40 sec)

its german but i basicly discribe what motors that are.. so

1. a 2208 9 slot 6 magnetpole 1250kv
2. 3005 18 solt 20 magnetpole minicroco (1100kv)
3. 2208 12 solt 14 magnetpole (1000kv)
4. MT3506 (12 slot 14 magnetpole)
5. 1811 9 slot 12 magnetpole (~2900kv)


ill do a special one for the MT3506 with 4S soon


regards

Felix
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Old Jan 05, 2013, 05:22 AM
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Felix, thanks for those last two posts.

I understand more about the ESCs now and especially active freewheeling.

How does the ESC know the optimum timing to turn off the freewheeling fet? Is this a manual setting or is the stored current sensed by the ESC?

Is the extra (braking) time the 'freewheeling fet' is left on set by the 'braking force' setting in the GUI?
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Last edited by Soma; Jan 05, 2013 at 06:18 AM.
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Old Jan 05, 2013, 05:54 AM
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Quote:
Originally Posted by gionag
juuuut when do do you think the 35a version will be available ??

thanks
hi,
i cant tell that for sure .. im just on the last steps of the layout. so we may also need prototypes of that one to configure the software for it .. i will post it here when i have a release date.


Quote:
Originally Posted by Soma View Post
How does the ESC know the optimum timing to turn off the freewheeling fet? Is this a manual setting or is the stored current sensed by the ESC?
Hi,
ist the same time that it waits for turning it on.. so for example if the deadtime is 1us. it turns the opposite "active freewheeling fet" on if the main PWM fet is off for 1us. and it turns it off 1us before the main PWM fet goes on again.

as shown in the picture the deadtime is used on both flanks.

Quote:
Originally Posted by Soma View Post
Is the extra (braking) time the 'freewheeling fet' is left on set by the 'braking force' setting in the GUI?
no the braking force acts like a normal brake.. if the throttle is at zero it brakes the motor. so it is independent from active freewheeling

ill make a nother video to show the difference


regards

Felix
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Old Jan 05, 2013, 06:16 AM
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Thanks Felix!

Good explanation, I get it now

You had given enough information but I missed that connection before.

Cheers!
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Old Jan 06, 2013, 08:27 AM
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and some more tests

here to show the MT3506 @14V
UltrESC & MT3506 default settings (0 min 58 sec)


here you can see the difference between active freewheeling (regenerative braking)
and the normal brake (brake force in the gui)
Ultra ESC brakes (1 min 46 sec)



regards

felix
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Old Jan 06, 2013, 11:52 AM
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Definitely interested in this product. Good work!
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Old Jan 06, 2013, 02:04 PM
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Yah, good stuff!
Looks like these babies can take & serve a punch.

Now that you opened your ESCinema, what about some of the protective functions?
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Old Jan 06, 2013, 03:57 PM
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Thanks Felix,

The vid comparing active freewheeling to braking was enlightening.

Very snappy with the freewheeling. Very interesting indeed.
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Old Jan 07, 2013, 06:35 AM
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Great work!

I'm a bit curious about the regenerative/active breaking. Wont that raise the bus (LiPo) voltage which could harm the LiPo or the electronics if the voltage gets to high? Or maybe the LiPo's can swallow the excess current easily keeping the bus voltage fairly stable? Would really like to hear about your findings/measurements on this.
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Old Jan 07, 2013, 07:03 AM
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Quote:
Originally Posted by kinderkram View Post
Yah, good stuff!
Looks like these babies can take & serve a punch.

Now that you opened your ESCinema, what about some of the protective functions?
Hi,

yes ill add a fet self test at startup for both ESC's. the 35A one will also have a current limiter(because it will have a shunt). and for now if you dont chose a much too big motor (or propeller) it wont get damaged because in case of startup or blocking it will always reduce the PWM (throttle) to a fixed low value untill the motor runs. and as you may seen in the video.. if it cant get the motor to spin it will disarm after ~3 seconds. this will make the startup process a bit slower but as multicopters always have a minthrottle it wont be a problem here

and as the used fets have enough reserves (100A each on the 20A and 200A each on the 35A) it also want make problems when you fast throttle the motor up. so there is no ramp needed.

Quote:
Originally Posted by tobbeanton
Great work!

I'm a bit curious about the regenerative/active breaking. Wont that raise the bus (LiPo) voltage which could harm the LiPo or the electronics if the voltage gets to high? Or maybe the LiPo's can swallow the excess current easily keeping the bus voltage fairly stable? Would really like to hear about your findings/measurements on this.
thanks

the actual lipos has a very low internal resistance so thay will hold the voltage in the normal case.. in my tests with a 2200mah 25c the biggest spikes are arround 0.2v. and on multicopters when you slow some motors fast you normaly speed up other ones so thay will take the free current.

you may want to look at warthox videos he does the fastest speed changes and it dont makes any problems.

regards

felix
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Old Jan 08, 2013, 01:21 PM
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This freewheeling thing is just brillant.
I'm now in a hurry to test 'em

Really nice work Juuuut
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Old Jan 08, 2013, 02:55 PM
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