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Dec 31, 2012, 12:12 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
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Quote:
Originally Posted by jaccies
Hi Ron ,

Not solved yet 2 questions from other members , what is your opinion Ron :

-1) So which Rule of Thumb holds " extra low esr 220uF for every 4inch/10cm extra length/distance between battery and ESC "
Twisted, non-twisted, or both?
my opinion is this rule is for the 2 wires close together, not twisted ...
Twisted, non-twisted was not mentioned with that rule of thumb. Twisting the wires is just an extra.

Quote:
Originally Posted by jaccies
... 2) Does current draw vs. battery capacity have an relationship? ...
It's the wires the cause the inductance, not the battery (a huge capacitor)

Vriendelijke groeten Ron
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Dec 31, 2012, 06:46 PM
Registered User
Quote:
Originally Posted by panther3001
After what I've read in Post 1 I disagree. This link (https://www.rcgroups.com/forums/show...2&postcount=32) from Post 1 states that "on robots running two or more motors on one battery. 2 feet battery wires to non opto coupled controls will make motors hunt." This indicates that the back-EMF pulses caused by long battery leads can indeed affect motor response and timing, thereby causing motors to "hunt" or jitter slightly. Based on this information, in a multi-rotor, this could potentially show up as instability I now believe.
interesting , thanks for correcting me
Dec 31, 2012, 06:49 PM
Registered User
Quote:
Originally Posted by Ron van Sommeren
Twisted, non-twisted was not mentioned with that rule of thumb. Twisting the wires is just an extra.

It's the wires the cause the inductance, not the battery (a huge capacitor)

Vriendelijke groeten Ron
thanks Ron for info
but if say current is 5AMp or current is 50AMp for a motor
has the amount of current no effect?
Dec 31, 2012, 09:26 PM
Registered User
Quote:
Originally Posted by jaccies
interesting , thanks for correcting me
No problem. Though I think what I said is true (see Post #525), I'd like to add one clarifying point that may enlighten us more on the situation (in case a more knowledgeable reader comes across this and wants to comment).

The clarifying point is this: The "hunting" motor that was referenced, due to the long battery leads and therefore back-EMF pulses, was apparently a sensored motor. It was on a robot, and robots generally use sensored motors in order to get accurate motor positioning. In other words, if I understand correctly, a sensored robot motor can be commanded to rotate to an exact position and stop, or even to back up (kind of like a servo motor). Since virtually all RC motors used for propelling an aircraft are not sensored, I wonder if back-EMF pulses could still affect it. however, my hunch is still yes.

PS. When I say "back-EMF" pulses, I think I could also say "back-EMI" pulses interchangeably (note: EMF = Electric & Magnetic Field; EMI = Electromagnetic Interference).
Jan 20, 2013, 05:52 PM
Registered User
I was looking at specs for Panasonic FM series and I see that some have a different inductance (330 uF, 35V).

http://www.digikey.com/scripts/dksea...3=159&PV63=371

Which would be preferable (or does it matter?) 26 or 30 mOhm?
Thanks a lot!!
Jan 20, 2013, 07:00 PM
Scout CX | mCX2 | mSR | 120SR
North_of_49's Avatar
don't robots use stepper motors... controled by arduino etc.?
Jan 20, 2013, 07:03 PM
Registered User
Quote:
Originally Posted by North_of_49
don't robots use stepper motors... controled by arduino etc.?
yeah, beats me. Beyond my knowledge/expertise at this point.
Jan 20, 2013, 07:04 PM
Registered User
Quote:
Originally Posted by GMPheli
Which would be preferable (or does it matter?) 26 or 30 mOhm?
Thanks a lot!!
The lower the mOhm the better.
Jan 20, 2013, 07:52 PM
Registered User
My speed control has 220uF 35V caps. Panasonic fm's this size have either 38 or 41 mOhms impedance. 220uF 50V have 30 mOhm. 330uF 35V have 26 mOhms. And 330uF 50V have 22mOhms. Of these choices what would be best? There must be a reason why it is recommended that you duplicate the existing size, so the 220 uF 35V 38 mOhms?

Thanks Again!!!!!
Jan 20, 2013, 09:45 PM
Scout CX | mCX2 | mSR | 120SR
North_of_49's Avatar
Quote:
Originally Posted by panther3001
yeah, beats me. Beyond my knowledge/expertise at this point.
In my DSLR cinematography hobby that's how we get precise movement on our camera sliders for doing time-lapse... the technology is borrowed from robotics.
Jan 21, 2013, 03:55 PM
Registered User
Quote:
Originally Posted by GMPheli
My speed control has 220uF 35V caps. Panasonic fm's this size have either 38 or 41 mOhms impedance. 220uF 50V have 30 mOhm. 330uF 35V have 26 mOhms. And 330uF 50V have 22mOhms. Of these choices what would be best? There must be a reason why it is recommended that you duplicate the existing size, so the 220 uF 35V 38 mOhms?

Thanks Again!!!!!
yes, that makes sense to me. Considering all that, I'd say use the 220 uF 35V 38mOhm Panasonic FM capacitors. One trend you'll see is that in general, just as for LiPo batteries, as you increase the size (uF for capacitors, or mAh for LiPos), the internal resistance (mOhms) will decrease. That is why they recommend using a low impedance capacitor (to minimize resistance, hopefully matching what is already on the ESC), yet they also recommend using the *same* size and voltage of capacitor as what is already there in order to *distribute the load.* Ex: if you added a 500uF 35V 18mOhm capacitor to a 220uF 35V 38mOhm capacitor, my understanding is that the 500uF 35V 18mOhm capacitor will now be doing *more than its fair share* of the voltage regulation per unit capacitance, since it has a lower internal resistance. This will make it wear out a bit faster than it should. By using the same specs as the existing caps, you allow them to equally distribute the load and job of voltage regulation, allowing them all to remain cool and last longer. Now, this is my theoretical understanding, with little practical experience and no experimental data to back up that claim. It makes sense to me though.
Jan 21, 2013, 03:59 PM
Registered User
Quote:
Originally Posted by North_of_49
In my DSLR cinematography hobby that's how we get precise movement on our camera sliders for doing time-lapse... the technology is borrowed from robotics.
Ah, so you're using robotics stepper motors for this then?
Jan 21, 2013, 04:12 PM
Registered User
PS...to the whole thread: since capacitors are simply 2-dimensional high-speed electron storage devices (oftentimes using high-speed electrolytic chemical reactions), they can be equated to 3-dimensional batteries (low-speed electron storage devices, requiring slow chemical reactions) in an interesting way: By definition, 1 Farad = 1 A*s/V (http://en.wikipedia.org/wiki/Farad), so you can convert Farads to mAh like this: mAh = (cap*10^-6*V/3600)*1000. Ex: Question: What is the battery equivalent of a 3000uF capacitor at 5V? Answer: (3000uF x 10^-6 * 5V/3600 sec/hr) x 1000 mAh/Ah = 0.00417 mAh. Therefore, a 3000uF capacitor at 5V is approximately equal to a 0.004 mAh 5V battery. The difference is that a capacitor can store or release energy MUCH FASTER than any battery. In this way, they help keep current and voltage more consistent and act as low-pass voltage filters. Here's a couple interesting plots I made using the above and similar mathematical relationships. (see attached)
Jan 21, 2013, 05:16 PM
Scout CX | mCX2 | mSR | 120SR
North_of_49's Avatar
Quote:
Originally Posted by panther3001
Ah, so you're using robotics stepper motors for this then?
Not me, personally, yet. I don't have much interest in time-lapse... I did do a few but shot statically, just to try it out. Alot of guys in the hobby (or professionally) are doing motorized time-lapse.
Jan 26, 2013, 06:33 PM
Retardedly intelligent
foam and tape's Avatar
New question Instead of linking brushed motors together over long distances will this work to suppress voltage spikes across the line


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