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Old Nov 04, 2012, 09:21 PM
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taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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Return of The Scorpion powered Sig 1/4 Cub

Hi Gents!
I've been flying a Sig Clipped wing quarter scale Cub since the maiden in March of '09 with a Scorpion 4020-16 swinging a 15/8 prop.
I've got two 5000 mah, six cell lipos and a 100 amp scorpion esc.

I've got a question for any experts on big heavy motors...
The motor, as shown in the vid below, will swing the 15/8 light prop easily and does fine on the aborted landing test of going from full to idle the suddenly back to full throttle.

The second prop in the vid is a heavy 16/8 that runs just a well as the 15 and pulls an extra pound of thrust for only 2 more amps.

But!
After going to full idle, then suddenly back to full throttle, it squeals like a wounded pig and does not pick back up.
The ESC is set to auto select. Would manually setting it to a low setting like 5 degrees make a difference in acceleration, maybe setting it to a slow spool up like for a chopper?
Thanks for any advice.
Nick
Scopion prop test (1 min 14 sec)
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Old Nov 04, 2012, 11:17 PM
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Doug Bartley's Avatar
Canada, ON, Owen Sound
Joined Oct 2008
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Most of the Scorpions if not all run better on mid timing for me, which is somewhere around 12-16 degrees. It may need even more depending on how heavy the new prop is.
Make sure your esc is set on 8mhz frequency too as all Scorp's I've used are designed for it.
It the extra weight in the prop that causes this, quite common really, the motor has no problem spinning up the lighter prop, but loses sync trying to spin up a heavier one.
All the 40 series Scorps I've run have required med or high timing to prevent the stutter/ squealing, the setting is dependant on the prop size. I've run 4020-12, 4020-14, 4020-16 and 4025-12's to date. Doug B
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Old Nov 05, 2012, 10:41 AM
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taildragger1589's Avatar
Lawrenceville, Georgia
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2,354 Posts
Thanks for the info!
I was completely backwards, I thought that the timing was like the distributor timing on a car.
Heavy prop squeal has had me baffled for a while.
Hopefully will be able to test your numbers soon.

Nick
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Old Nov 05, 2012, 04:58 PM
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Canada, ON, Owen Sound
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Hi taildragger: The 4020-16's I've tested all required med timing, I have tested up to a 16/12/ 3blade Graupner 18/10 Apc e without issue (72a). I have two in my 14 lb 84" Buffalo on 12/8/ 3 blades, only 50a per motor.
You should also use normal or hard start, these motors like a good shunt of power to get them spinning and will not respond well to slow starts, esp with bigger props. fwiw Doug B
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Old Nov 05, 2012, 06:19 PM
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taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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Ha!
I had the start up backwards too.
I tell ya, if fuel wasn't so expensive (and messy) I'd dig out my old OS 120 FS, (the first of the series) and put on a 16/6 MAS.
Plenty of power.
But then again, it sure is nice not having to wipe off the goo at the end of the day.
Can't even quote noise difference, since it sounds almost the same.
Can't wait to try the mods, had too many house chores today.

re buffalo: Wow! at 14lbs. she must really move out. My Cub is 13 lbs and though she only has about 30 feet of vertical from straight and level, she has a nice comfortable climb rate with only one pulling 45 amps (47 with the big prop) (search quartercub on youtube to see her fly.)

Nick
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Last edited by taildragger1589; Nov 05, 2012 at 06:25 PM.
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Old Nov 12, 2012, 12:12 PM
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taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
2,354 Posts
Quote:
Originally Posted by Doug Bartley View Post
Most of the Scorpions if not all run better on mid timing for me, which is somewhere around 12-16 degrees. It may need even more depending on how heavy the new prop is.
SUCCESS!!!

Thanks a bunch Doug.
turns out that 15 degrees made the big prop behave as well as the smaller.
Now all I need is calm day above sixty and we're airborne.

Nick
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