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Old Apr 18, 2010, 01:59 AM
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mikmerl's Avatar
Athens, Greece
Joined Apr 2010
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Question
If a folding prop, doesn’t fold

If a folding prop does not fold when the throttle is cut and it ends up lazily freewheeling.
Other than the reduced flight performance of the glider, can it have an adverse affect on the motor-ESC-battery.
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Old Apr 18, 2010, 02:06 AM
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tinkrerpilot's Avatar
Puyallup, WA
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Depends if the ESC you are using has a brake function and if it activated or not. Which in case would be the free wheeling prop.
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Old Apr 18, 2010, 02:54 AM
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Quote:
Originally Posted by mikmerl View Post
If a folding prop does not fold when the throttle is cut and it ends up lazily freewheeling.
Other than the reduced flight performance of the glider, can it have an adverse affect on the motor-ESC-battery.
Not as far as I know, it doesn't.

Consider all the thousands of models out there that aren't fitted with folding props. Whether the brake is activated or not, and dependent on airspeed, they'll tend to freewheel when throttled off.

tim
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Old Apr 18, 2010, 04:32 PM
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Marietta, GA
Joined Jun 1999
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No effect. It's desirable on sport models, helps slow them for landing..
..a
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Old Apr 18, 2010, 04:56 PM
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The 'Wack, BC, Canada
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If by some chance your ESC doesn't have a brake mode then you can often figure out how to wind a small and light rubber band around the hub and blades such that it encourages the fold but won't hold them in hard. Then all you need to do is after the motor cut raise the nose a little to slow down to near the stall point for a moment. The prop freewheeling will slow enough to let the blades fold thanks to the rubber band. From there you'll be fine until you power up again.

If it's a hotliner which won't slow down enough try a stronger rubber band or upgrade to an ESC with brake function.
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Old Apr 18, 2010, 08:16 PM
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Marietta, GA
Joined Jun 1999
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I flew my Falcon for a long while on a Jeti motor which couldn't fold the prop.

I just stalled it at the top of every climb!
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Old Apr 18, 2010, 10:00 PM
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Joined Jun 2009
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Hi Mikmerl
I think your question is is referring to the fact that the freewheeling prop turns the motor into a generator and you want to know if this will damage your speed control or battery during a long sailplane flight. Good question IMHO. I don't know if this is a problem with aircraft ESC"s. Many if not most CAR ESC's are designed to use this to actually put charge back into the battery. Maybe some of the electronics experts here will have some knowledgeable input.
Hope the Sun is shining in Greece, Still raining in TX :>(
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Old Apr 19, 2010, 11:09 AM
The Kid
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Detroit, MI
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Quote:
Originally Posted by TeamTigerPaw View Post
Hi Mikmerl
I think your question is is referring to the fact that the freewheeling prop turns the motor into a generator and you want to know if this will damage your speed control or battery during a long sailplane flight. Good question IMHO. I don't know if this is a problem with aircraft ESC"s. Many if not most CAR ESC's are designed to use this to actually put charge back into the battery. Maybe some of the electronics experts here will have some knowledgeable input.
Hope the Sun is shining in Greece, Still raining in TX :>(
Some brushed ESCs 'way-back-when' had regenerative braking. But, to the best of my knowledge this is not possible with brushless motors. This is because the ESCs arent designed to convert AC current back into DC (brushed is DC to DC, as far as I know).

I don't think you'll run into any problems, regardless of whether the above rambling is correct

Kid
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Old Apr 19, 2010, 11:41 AM
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Athens, Greece
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Tigerpaw we have at least 300 days of sunshine annually, fantastic for model airplane/helicopter flying.
You were right, I was wondering if there is a damaging effect to the onboard components such as the actual motor, the ESC or even the LiPo.
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Old Apr 19, 2010, 11:58 AM
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The 'Wack, BC, Canada
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Quote:
Originally Posted by Thekid3418 View Post
Some brushed ESCs 'way-back-when' had regenerative braking. But, to the best of my knowledge this is not possible with brushless motors. This is because the ESCs arent designed to convert AC current back into DC (brushed is DC to DC, as far as I know).

I don't think you'll run into any problems, regardless of whether the above rambling is correct

Kid
The braking on the brushed controllers did not put the power back into the batteries. Instead it was just a single additional MOSFET that would come on and short out the motor terminals. By putting a short circuit across the output of the freewheeling motor it produced a strong drag due to the EMF of the coils.

On brushless motors they don't have this shorting out option. But most of the better ESC's intended for sailplane use do have a brake option. Instead of shorting out the leads from the motor, which would work but require more MOSFETS on the ESC, they just switch small amounts of power to the motor out of phase. In effect they try to make it suddenly run backwards using small amounts of power. This provides a good braking function.

As for damage to the ESC during freewheeling it's not an issue at all. Thanks to the very few turns of the motor the voltages produced by the motor are very low and well under the max blocking voltage of the MOSFETS used for the power switching. You can try this for yourself. Hook a voltmeter across any two leads and spin the motor with an electric drill. It'll only produce a few volts at most. You'll need to use an AC volt scale since brushless motors are AC devices.
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