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Old Oct 27, 2012, 05:56 PM
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Austria
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Originally Posted by HappySundays View Post
I just did an experiment to check. You are correct in that the regulators don't sink current. So the problem is simply that they don't *share* current.

I opened up a 25A SS-series ESC that has the laughable BEC current rating of 3A. I measured each of the two parallel regulators by disconnecting one.
Reg 1 = 4.88V, Reg 2 = 4.99V. Together the output is 4.99V.
Incidentally for the 34mA load I was using, 65mA was required at the input, showing the rather poor efficiency of the linear regulators.

Ok so the problem with SS series regs and other badly-designed ones is that - as they don't use current-sharing resistors only ONE reg is actually on at any time. This explains why I could feel one heating up, then the other, as each went into thermal shutdown or overcurrent limit, then the other.

The regulators used in the SS the device is an LF50A in the D-PAK package. The datasheet rates them as "up to 500mA" but they are internally limited to 1A.
I note that it claims a worst-case 500mA load regulation of 25mV, which means that in my example, even at 500mA the 4.99V reg would not sag enough to enable the lower 4.88V one.

With a fully-charged 3S LiPo at 12.6V, 500mA would dissipate a massive 3.8 Watts. The D-PAK has a junction-to-ambient rating of 100 degrees per Watt but in the SS, they are soldered to a tiny pad to aid dissipation. It's hard to guesstimate the thermal resistance but let's be generous and say it's twice as good and so 50 degrees * 3.8W = 190 degrees C.
At 100mA the disspation is 760mW and the heat rise about 38 dgrees C. That sounds about right as the things warm up extremely quickly.

For a laugh, let's work out what would happen if some one believed that 3A rating printed on the HobbyKing SS-Series ESC wrapper...
Let's also be generous and say that the higher regulator sags to the point where both regulators are supplying power.
At 3A, 22.8W is dissipated across the pair of ESCs. 11.4W each. This would cause each to rise to... oh look 570C... and they desolder themselves off the board lol. Of course they would shut down before that but you can see that the rating is completely fraudulent.

So to summarise, with these kind of linear regulators, they won't indeed fight each other when connected in parallel, but they are unlikely to help each other either, due to the fact that...

1. They have excellent load regulation and so won't sag.
2. There are no current-sharing resistors to *induce sag* and...
3. A BEC power lead will not result in significant sag.
24AWG wire will drop 5mV per foot at 100mA,
26AWG wire will drop 8mV per foot at 100mA,
28AWG wire will drop 13mV per foot at 100mA.
So basically, ESCs with linear regulators suck and are completely unsuitable for parallel use as they are unlikely to share current unless designed to do so. However I can no longer see why there is any problem connecting them in parallel as long as you realise that quite possibly only one, 500mA regulator is powering your *whole system*. If you're good with that, no problems.
Excellent reading

So for make a good quality linear BEC is important to source voltage regulators that are perfectly matched in order to put them in parallel

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Old Oct 27, 2012, 06:33 PM
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Australia, QLD, Brisbane
Joined Nov 2011
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Originally Posted by HappySundays View Post
Sorry but that's not right. The assumption has been made that the problem is that only one reg is actually supplying power. Partly true, but not the actual problem.
This is the actual problem:
Let's imagine one reg wants to output 4.90V and the other 5.1V. Lets also imagine that some cheap-ass fool has tied them together directly.
The higher one tries to pull up the lower one and the lower one pulls down the higher one. And how does this actually manifest?
Linear regulators regulate by sinking and sourcing current. The lower one will sink current to try and pull it down, the higher one sources it to pull it up.
So the result is that both regulators pour as much current as they have available into getting the output voltage that they want (but can never have).
Eventually, one will shutdown through either over current or overheating and the other will temporarily "win". Briefly.
It may be that cabling helps current sharing but I would hardly call it perfect. More like "lucky".
You might want to check on that, I was always under the impression that a linear regulator like a 78xx series could not sink current, it counted on the load doing that, it could only source current.

Some other regulators have a minimum sink current that the user must supply or the regulator wont regulate properly.
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Old Oct 27, 2012, 06:36 PM
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Originally Posted by HappySundays View Post
28AWG wire will drop 13mV per foot at 100mA.
So basically, ESCs with linear regulators suck and are completely unsuitable for parallel use as they are unlikely to share current unless designed to do so. However I can no longer see why there is any problem connecting them in parallel as long as you realise that quite possibly only one, 500mA regulator is powering your *whole system*. If you're good with that, no problems.
Don't forget the connector resistance. Servos also draw current in pulses, creating severe, short term, voltage drops. Then there is redundancy etc, etc.

Fred
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Old Oct 27, 2012, 06:38 PM
<Marty>
United States, KY, Springfield
Joined Jul 2011
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just had my maiden flight a few minutes earlier...i have to say wow...super stable and very quick , climbs like a rocket..really surprised me how easy it is to handle but it could be cause i am used to flying Heli's for years now..one thing i noticed is when i yaw with the tri facing out it tends to want to go back to the position i started the yaw from...kind of like heading hold i guess..is there some adjustment that would make it hold the position when i release the stick when yawing in stead of it wanting to yaw back to the previous position?


next project is building a H copter for fun..
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Old Oct 27, 2012, 11:50 PM
<Marty>
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Joined Jul 2011
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quick question....how can i tell what board i have? i got it from a rcg member and he got it in a trade but listed it as a older board...looks exactly like this one it does have the atmel328 chip on it....http://www.hobbyking.com/hobbyking/s...ga328_PA_.html

but i tried to load the settings from the board and it wouldn't load them...so i tried to flash it with the KK 4.7 and it had a error and wouldn't flash...this board has a dsm rx soldered directly to it and mounted to it with double sided tape...does the rx have to be unhooked before it will flash? cause when i hook up the usbasp to the board the led on the rx lights up but nothing on the board...i know the board works cause i already hooked it up and tested it...
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Old Oct 28, 2012, 12:00 AM
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Australia, NSW, Sydney
Joined Feb 2011
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Quote:
Originally Posted by Erknie View Post
You might want to check on that, I was always under the impression that a linear regulator like a 78xx series could not sink current, it counted on the load doing that, it could only source current.

Some other regulators have a minimum sink current that the user must supply or the regulator wont regulate properly.
Read up a couple of posts. You missed my test and findings
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Old Oct 28, 2012, 12:15 AM
Dixie Normious
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Quote:
Originally Posted by magic_marty View Post
quick question....how can i tell what board i have? i got it from a rcg member and he got it in a trade but listed it as a older board...looks exactly like this one it does have the atmel328 chip on it....http://www.hobbyking.com/hobbyking/s...ga328_PA_.html

but i tried to load the settings from the board and it wouldn't load them...so i tried to flash it with the KK 4.7 and it had a error and wouldn't flash...this board has a dsm rx soldered directly to it and mounted to it with double sided tape...does the rx have to be unhooked before it will flash? cause when i hook up the usbasp to the board the led on the rx lights up but nothing on the board...i know the board works cause i already hooked it up and tested it...
I would sure like to see apic of the DSM2 RX soldered directly to the KK v3.
I've never seen that before? So not sure if that is causing the issue with the flash or not.
I flashed my freinds V3 early this year...But depending on what Version of the flash tool you have there is a process you have to do...
sorry its been sometime now and i forget!!
I do believe you have to flash with a order flash tool version before you can flash it with the newest (at the time it was ver.60) on the KKV3

lazyZ directed me how to do it and it worked

Head over to here...may get a quicker response
http://www.rcgroups.com/forums/showt...5#post18609175
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Old Oct 28, 2012, 12:37 AM
<Marty>
United States, KY, Springfield
Joined Jul 2011
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here is the picture used in the classified add...they removed the header pins and used jumper wires then stuck the rx to the board with double sided foam tape...really clean setup..
http://www.rcgroups.com/forums/attac...mentid=5237937


i tried unsoldering the neg wire so the rx would not get power but still no joy when trying to read or flash the board...
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Old Oct 28, 2012, 12:38 AM
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Canada, BC, Vancouver
Joined Dec 2011
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Hello, RCGroupers.

I am enjoying the functionality of this KK2 board on 1.2 firmware, most of it is quite intuitive. I do have a question though which I hope hasn't been answered somewhere in the 389 page thread though.

If I power off my Spectrum DX6i transmitter while the KK2 is in "Armed" mode, the throttle will go up to 100% . Is this the KK2 thinking that signal is lost and it is trying to prevent the model from plummeting to the ground? If the KK2 is in "Safe" mode and in "Receiver Test", it shows full throttle happening there as well.

Thanks.
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Old Oct 28, 2012, 12:51 AM
Dixie Normious
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Originally Posted by Thumb Pilot View Post
Hello, RCGroupers.

I am enjoying the functionality of this KK2 board on 1.2 firmware, most of it is quite intuitive. I do have a question though which I hope hasn't been answered somewhere in the 389 page thread though.

If I power off my Spectrum DX6i transmitter while the KK2 is in "Armed" mode, the throttle will go up to 100%. Is this the KK2 thinking that signal is lost and it is trying to prevent the model from plummeting to the ground? If the KK2 is in "Safe" mode and in "Receiver Test", it shows full throttle happening there as well.

Thanks.
Becareful there... thats why its always good to take Props off. only last week was i helping my freind set his KK2.0 that i sold him up. We calibrated escs as normal and worked fine. we decided to do it again as someone wanted to see the process.

So turned radio on, put 100% throttle, plugged in battery and BAM all 4 motors spun up WOT...not sure what caused it as we just finished doing it the first time with no drama... Glad the props were off


Na its not the kk thinking the signal is lost and trying to recover or anything...

I would reset your radio/model and re bind with the KK all hooked up. Make sure your Throttle stick is at zero. Depending on what RX your using could be a fail safe issue.
What RX are you using?
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Old Oct 28, 2012, 12:57 AM
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Joined Sep 2008
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Quote:
Originally Posted by HappySundays View Post
I just did an experiment to check. You are correct in that the regulators don't sink current. So the problem is simply that they don't *share* current.

I opened up a 25A SS-series ESC that has the laughable BEC current rating of 3A. I measured each of the two parallel regulators by disconnecting one.
Reg 1 = 4.88V, Reg 2 = 4.99V. Together the output is 4.99V.
Incidentally for the 34mA load I was using, 65mA was required at the input, showing the rather poor efficiency of the linear regulators.

Ok so the problem with SS series regs and other badly-designed ones is that - as they don't use current-sharing resistors only ONE reg is actually on at any time. This explains why I could feel one heating up, then the other, as each went into thermal shutdown or overcurrent limit, then the other.

The regulators used in the SS the device is an LF50A in the D-PAK package. The datasheet rates them as "up to 500mA" but they are internally limited to 1A.
I note that it claims a worst-case 500mA load regulation of 25mV, which means that in my example, even at 500mA the 4.99V reg would not sag enough to enable the lower 4.88V one.

With a fully-charged 3S LiPo at 12.6V, 500mA would dissipate a massive 3.8 Watts. The D-PAK has a junction-to-ambient rating of 100 degrees per Watt but in the SS, they are soldered to a tiny pad to aid dissipation. It's hard to guesstimate the thermal resistance but let's be generous and say it's twice as good and so 50 degrees * 3.8W = 190 degrees C.
At 100mA the disspation is 760mW and the heat rise about 38 dgrees C. That sounds about right as the things warm up extremely quickly.

For a laugh, let's work out what would happen if some one believed that 3A rating printed on the HobbyKing SS-Series ESC wrapper...
Let's also be generous and say that the higher regulator sags to the point where both regulators are supplying power.
At 3A, 22.8W is dissipated across the pair of ESCs. 11.4W each. This would cause each to rise to... oh look 570C... and they desolder themselves off the board lol. Of course they would shut down before that but you can see that the rating is completely fraudulent.

So to summarise, with these kind of linear regulators, they won't indeed fight each other when connected in parallel, but they are unlikely to help each other either, due to the fact that...

1. They have excellent load regulation and so won't sag.
2. There are no current-sharing resistors to *induce sag* and...
3. A BEC power lead will not result in significant sag.
24AWG wire will drop 5mV per foot at 100mA,
26AWG wire will drop 8mV per foot at 100mA,
28AWG wire will drop 13mV per foot at 100mA.
So basically, ESCs with linear regulators suck and are completely unsuitable for parallel use as they are unlikely to share current unless designed to do so. However I can no longer see why there is any problem connecting them in parallel as long as you realise that quite possibly only one, 500mA regulator is powering your *whole system*. If you're good with that, no problems.
Thanx for that effort. You have explained why my SS ESC's have issues.
Rob
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Old Oct 28, 2012, 01:24 AM
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Canada, BC, Vancouver
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Originally Posted by Eastcoast78 View Post
What RX are you using?
Using Spectrum DX6i set to "Plane" mode
SimonK ESC's
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Old Oct 28, 2012, 01:29 AM
Dixie Normious
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Originally Posted by Thumb Pilot View Post
Using Spectrum DX6i set to "Plane" mode
SimonK ESC's
yes DX6i what RX(receiver)?

But try that resetting your model and rebind with Thr at 0 and all EPA's clean/untouched
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Old Oct 28, 2012, 01:29 AM
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Hey everyone. I'm looking for a KK2 guru that can help me get my Kk2 that's on my tricopter super stable and rock solid both in rate mode and atti. I've been messing with the p I gains but I can't figure out how to get it to fly as stable as other people's I've seen. If you can help send me a PM thanks.
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Old Oct 28, 2012, 01:47 AM
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Canada, BC, Vancouver
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Originally Posted by Eastcoast78 View Post
yes DX6i what RX(receiver)?

But try that resetting your model and rebind with Thr at 0 and all EPA's clean/untouched
Took your advice and reset model profile on radio as well as did a rebind, this fixed the full throttle issue.

Thanks for your advice

I was using a HobbyKing Orange RX6 channel receiver.
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