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Offline Motorman

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« on: February 08, 2018, 09:59:24 AM »
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« Last Edit: December 05, 2021, 09:18:56 AM by Motorman »

Offline Mike Haverly

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Re: Motor Saggs
« Reply #1 on: February 08, 2018, 11:22:21 AM »
That's a bad way to break in a battery.  The better way is to use a good charger that will cycle the batteries for you.  Charge at 1C and discharge at a lesser rate at least twice.  What you are doing is not good for them.
Mike

Offline Fred Underwood

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Re: Motor Sags
« Reply #2 on: February 08, 2018, 11:41:06 AM »
Used ESC and possibly failing?  Does the ESC get hot?  I think that one was before datalogging so no temperature recording?  Does it feel hot, or IR temperature reading?

My understanding of TP recommendation is about 3 - 4C discharge for break in as you are trying.  My guess is that a lower rate is also ok - a couple of cycles partially up and down before flying. 
« Last Edit: February 08, 2018, 01:11:37 PM by Fred Underwood »
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Offline Fred Underwood

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Re: Motor Sags
« Reply #3 on: February 08, 2018, 01:19:43 PM »
My simple non-engineer understanding - motor speed is controlled by switching power on and off, not by lowering voltage.  The time of on vs off controls the "average voltage" and motor rpm.  The ESC doesn't really lower voltage for throttle control, but controls the pulse width.  Yep ESC for dummies, by one.

More heat is generated in the ESC at lower rpm, partial throttle. 

For the real explanation this may help, ESC portion is toward the bottom.
http://www.rcuniverse.com/articles/uncategorized/greg-coveys-ampd-issue-21-brushless-basics/

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Offline Fred Underwood

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Re: Motor Sags
« Reply #4 on: February 08, 2018, 03:16:22 PM »
Break in according to TP is no more than 3 - 5C.  You could also lower your rate, since no minimum is required, if I am interpreting correctly. 

It takes a long time at charger discharge rates, unless you hook up regenerative discharge/charge.  OTOH, you don't have to fuss with the discharger and you can set cycle charge and discharge voltages. Some of the inexpensive chargers are quite limited as to discharge rate and no regenerative capability.  You mentioned i306b so you have a reasonable rate.
Fred
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Offline Tim Wescott

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Re: Motor Sags
« Reply #5 on: February 08, 2018, 05:03:36 PM »
My simple non-engineer understanding - motor speed is controlled by switching power on and off, not by lowering voltage.  The time of on vs off controls the "average voltage" and motor rpm.  The ESC doesn't really lower voltage for throttle control, but controls the pulse width.  Yep ESC for dummies, by one.

More heat is generated in the ESC at lower rpm, partial throttle. 

For the real explanation this may help, ESC portion is toward the bottom.
http://www.rcuniverse.com/articles/uncategorized/greg-coveys-ampd-issue-21-brushless-basics/

Yes, motor speed is controlled by switching power on and off.  No, it's not that simple.

The motor has inductance, which means that the current doesn't change immediately in response to voltage changes.  ESCs these days switch rapidly enough that the output voltage is somewhat averaged -- so it kinda-sorta acts like a constant voltage.

If you DID switch things slowly enough for the motor to come up to full current on each cycle, then the motor would be the one feeling the pain, not the ESC.  ESC's get hot because the transistors act like little resistors when they're on (conduction losses), and because they can't snap from being on to being off instantaneously, meaning that in the middle there's a medium current and a medium voltage across the thing (= lots of power for a little time, known as switching losses).  .  ESC designers pull their hair out trying to minimize both kinds of loss at the same time.

So you're saying lower rpm makes the ESC work harder, seems I've heard that somewhere before. I could try a 9-4 and 10,000 rpm and see what that draws out.

After all that refutation -- yes, lower RPM will make the ESC work harder (there will be higher switching losses, if nothing else).  Checking the ESC temperature every twenty seconds or so for a couple of minutes after a run may tell you something interesting, as the heat migrates out from the inside.  If keeping a fan on the ESC (aimed to flow through the heat sink) helps, then it's an ESC issue.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.


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