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Engine brake/folding props on Sky Climber

#1
I bought a Sky Climber a few months back and from day one I had problems with "windmilling" when I cut the throttle. The general advice was, buy a better ESC. So I did! I purchased a generic 30A Hobby King unit, including the programming card, activated the "brake" feature... but today, the same thing happened! GRRRRRR!

I confirmed the ESC is set correctly (3 beeps for cells, 2 beeps for brake on startup), flew into a 30 kmph headwind today and the prop refuses to fold. On the ground, the prop stops spinning at zero throttle, but not so in the air. I notice that there isn't really any resistance on the prop on zero throttle, so where is my brake?

Could it be a fault with the motor? Do I have a dodgy ESC? How do I test it?

I'd really like to figure this out before the warm thermal weather arrives!

Cheers,
Max
 
#2
I'm not sure how to test it, I would just go through the steps to turn it off then back on.

A side note- I think a video of me trying to program an esc through the transmitter would be rather humorous.. to someone.

"Wait.. what.. how many beeps?" "Was that a long beep?" "Is the microwave on?" "MY FINGERS!! MY FINGERS!!" "Do we have any bandaids?"
 

quorneng

Active member
#3
If it doesn't fold you definitely haven't got the brake set on assuming of course the blades do fold freely!
The problem is you have to go the correct programming sequence exactly to change it.
You will know when the brake is on because once the ESC has armed the prop will be noticeably stiffer to turn by hand (but watch your fingers!).
The brake is not a motor feature but entirely down to the ESC as it short circuits the motor coils as soon as the throttle is at zero. This means the faster the motor is spinning when the throttle is closed the greater is the brake effect.
 
#4
The problem is you have to go the correct programming sequence exactly to change it.
I hooked up the programming card once more to be sure, it's definitely acknowledging the change.

You will know when the brake is on because once the ESC has armed the prop will be noticeably stiffer to turn by hand (but watch your fingers!).
I did notice after programming it again, that the motor does appear to lock up in the opposite direction, but only intermittently ie. If I throttle on and off a few times. Most of the time it spins freely in both directions. I'm wondering now if the throttle is always going back to "zero" (That's what it reads on the transmitter... and their is no response on the motor).

The brake is not a motor feature but entirely down to the ESC as it short circuits the motor coils as soon as the throttle is at zero. This means the faster the motor is spinning when the throttle is closed the greater is the brake effect.
Thanks for clarifying that. Does this mean it is constantly drawing the battery power at zero throttle? I kind of thought the idea of the brake was to reduce wind resistance by utilising the folding prop and thus conserve some battery power to get more air time.
 
#5
I'm not sure how to test it, I would just go through the steps to turn it off then back on.

A side note- I think a video of me trying to program an esc through the transmitter would be rather humorous.. to someone.

"Wait.. what.. how many beeps?" "Was that a long beep?" "Is the microwave on?" "MY FINGERS!! MY FINGERS!!" "Do we have any bandaids?"
I know what you mean... before I had the programming card, I was thnking I might need to study music. The music cycles so quickly between the functions, that I wasn't sure if I was setting the last A-A-A-A tone or the C-C-C-C tone. In the end, my ESC was just sounding like a corny battery operated greeting card. Christmas in July! Woo hoo!
 

quorneng

Active member
#6
The ESC only shorts out the motor coils. It does not apply any current to them so with the throttle closed it takes no power other than that to drive the BEC (if you are using it).

I set the brake on most of my planes that glide well whether or not they have a folding prop.

I do have one ESC (out of about 25!) that I cannot get to set the brake on (yet the other program functions work ok) so it is not an unknown fault.
 

quorneng

Active member
#8
MountianFlyingWV
The blades should easily flop down under their own weight. If they don't it will never fold in flight even with the brake on.
 

xuzme720

Dedicated foam bender
Mentor
#9
Basically: too tight=rigid prop=no fold

If it's too tight then you negate the folding aspect and it will probably windmill with or without the brake on. The brake on the air ESC's is not like the brake on car/surface ESC's as no current is used to brake, it's only shorting 2 phases of the windings which make the motor have more resistance to turning.
Does that help?
 
#10
I'm not really sure how much resistance it should have when 2 phases are shorting... it seems pretty much the same as the first ESC, which is bugger all. I assume if it shorts, then I should be able to run a test with a multimeter to confirm the brake setting is working by testing the 3 wires to the motor?

It's definitely not too tight, the blades flop around and generally get in the way everytime I rest it on a flat surface! I'll try buying one more ESC... can't hurt having another spare.
 

quorneng

Active member
#11
Maximus
The test is simple but needs care to do!
With the motor running at full speed how fast does it slow down when you snap the throttle shut?
Then compare it to how long it takes to slow down by simply disconnecting the battery (so no brake).
The difference should be easily noticeable.
On one of mine with a 10" prop it takes at least twice as long when disconnecting the battery.
 
#13
Thanks for the tips on testing. So I finally got around to testing and here's the verdict...

When the battery is disconnected, the engine brake is ON! Okay, so I know that's impossible based on what we've already said, but there is HEAPS more resistance on the prop when the battery is disconnected. So I'm a bit more confused now.
 

xuzme720

Dedicated foam bender
Mentor
#14
That is actually normal. There is a residual magnetism or charge in the windings after a run when the batt is disconnected. Come back later on and spin the prop and you'll find that it will spin more freely after that has dissipated.
 
#15
That is actually normal. There is a residual magnetism or charge in the windings after a run when the batt is disconnected. Come back later on and spin the prop and you'll find that it will spin more freely after that has dissipated.
Spot on about the residual magnetism. Bit of a shame I can't utilise this effect to get my brake! My only dilemma now, is whether I buy another Hobby King ESC, or try a brand name unit. Seems a bit of a waste to have to buy another programming card.
 

xuzme720

Dedicated foam bender
Mentor
#16
Most ESC's can be programmed with your throttle stick and counting the tones/beeps/ etc.
I'm like our Mr. Bixler in that I'm very cheap! I keep thinking about getting a card, but with so many different ESC's, I don't want to limit myself to just one brand or type. I mean, I have my favorites that are my goto, but what about next week? Anyway, I would just not worry about the programming card and get whatever ESC will work for what you're doing right then. Most of the HK esc's are workable and might even work with your current card;which one did you get?
 
#17
Eureka! It works!! I decided to take your advice and try the throttle stick programming. This will highlight my Noob qualities, but..

The instructions say, "one beep to the open of brake, two beeps to the close of the brake." I mistakenly thought that "close" meant the brake was on. I also must have misunderstood the instructions on the programming card. I assumed that the jumper needed to join the pin marked "on" but again, it's the opposite of what I thought.

So anyone buying a Hobby King 30A UBEC, the startup tone clarifys the settings and is:
1. First beeps when powering up indicate the number of cells detected in your battery pack
2. The next series of beeps indicate two beeps for brake off OR one beep for brake on.

Yours Noobfully,
Max