Edf not at same power/rpm - RC Groups
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Dec 27, 2017, 07:10 PM
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orvie6's Avatar
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Edf not at same power/rpm


I have two freewing 70mm EDF units. Running a 3000mHa 4 cell battery through two 80 amp Aerostar speed controls. Both fans have same kv. motor and about the same amount of run time. On my newest twin, one motor runs stronger than the other. Speed controls both hooked up to single battery. One fan connected to throttle. Other one to Aux1 through transmitter mix. If I switch connections around, same motor is stronger. Any advice?
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Dec 27, 2017, 07:32 PM
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davecee's Avatar
Quote:
Originally Posted by orvie6
I have two freewing 70mm EDF units. Running a 3000mHa 4 cell battery through two 80 amp Aerostar speed controls. Both fans have same kv. motor and about the same amount of run time. On my newest twin, one motor runs stronger than the other. Speed controls both hooked up to single battery. One fan connected to throttle. Other one to Aux1 through transmitter mix. If I switch connections around, same motor is stronger. Any advice?
Which connections are you switching? ESC to transmitter or ESC to motor. perhaps one ESC is set up differently, eg timing?
Dec 27, 2017, 09:47 PM
Registered User
orvie6's Avatar
I believe I may have a bad motor. Switched escs and problem still there. Tested on same channel with both escs on problem motor. Same results. I also noticed that as I tested each motor seperatly, the 'problem' motor had a lower volume beep when pluging in the battery.
Wayne
Dec 28, 2017, 09:54 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by orvie6
I believe I may have a bad motor. ...
Several motor tests
  1. Determining whether magnets still have original strength, by determining whether Kv motor parameter (in rpm/volt) is still the same, several simple straightforward methods
    www.bavaria-direct.co.za → motor constants
  2. Drytesting brushless motors - WFF (RCG user vollrathd)
  3. Overheated magnets result in lower magnet strength (irreversible! ), which in turn results in higher Kv. Motorcurrent is proportional to Kv cubed
    Higher current → hotter motor → weaker magnets → higher Kv → higher current → hotter motor → weaker magnets → higher Kv → higher current ⟲⟲⟲ etcetera etcetera, temperature runaway
  4. Opening an outrunner for visual inspection
  5. Generator test, only using a power drill and a voltmeter
    (Re)winding and building motors - RCG (sticky) → opening post → #40 Generator test
Vriendelijke groeten Ron
Dec 29, 2017, 03:11 PM
Laughs at un-boxing videos...
basicguy's Avatar
A couple of years ago I bought 3 turnigy motors. Two of them were pretty close about 2% apart the 3rd had a 25% lower kv. It is unlikely that you you will get two truly identical motors so fine tuning is important.

On my radio I can trim each motor by putting the two speed controls on different channels.

You should calibrate each ESC by starting the receiver with the transmitter at full throttle.
Dec 29, 2017, 03:43 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by basicguy
... the 3rd had a 25% lower Kv. ...
Since current drawn is proportional to Kv³ (and proportional to voltage²) that would give a change in current by factor (0,75)³ = 0.42.
Power drawn is also proportional to Kv³, it would change by same factor.

Four simple methods for checking/comparing Kv motorconstants
www.bavaria-direct.co.za
→ motor constants
→ Kv constant

Prettig weekend Ron

Opgenomen stroom is rechtevenredig met pitch¹, #bladen¹, spanning², Kv³ en diameter⁴.
Opgenomen vermogen rechtevenredig met pitch¹, #bladen¹, spanning³, Kv³ en diameter⁴.
Last edited by Ron van Sommeren; Dec 29, 2017 at 05:33 PM.


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