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Aug 31, 2013, 08:01 PM
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aymodeler's Avatar
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Help!

Which Motor for a Sig Somethin Extra?


I'm stuck trying to find a good motor option for a Sig Somethin Extra conversion. The glow specs call for a .40 - .50 two stroke. There is not a lot of ground clearance, so 12" prop is probably max (unless I put her on longer legs). I'd like to pull at least 700 watts, more would always be better.

I've seen a lot of threads here, but most of them are at least 5 years old with older technologies or motors that are no longer available.

I'm looking at these two setups, but I am open to other options. Any suggestions out there?

Turnigy G46, 670Kv, 5S LiPo with an 12x6 prop

RimFire .46, 800 Kv, 5s LiPo with a 10x5 or 11x5 prop

Al
Last edited by aymodeler; Aug 31, 2013 at 09:33 PM.
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Sep 01, 2013, 06:05 AM
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scottc39's Avatar
I have used both motors on 5 cells and they were very good to me in power and speed .
the plane specs give a weight of close to 5 lbs so either motors will kick butt on that plane and 5 cells
Sep 05, 2013, 08:19 PM
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I had planned to build one some time ago, but felt the kit was a bit fragile for my likes.. I had planned to use a B P Hobbies U3520-6 with either a 3s, or 4s power. I currently use that combination in 4 different planes, all kit built, and 50"s ws, and find it to be a very satisfactory selection.
Arnie
Sep 05, 2013, 08:38 PM
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Cool plane, Id watch the floor sheeting. I lost one on its maiden day when the rx battery fell from the plane. Took the os70 fs with it too
Sep 08, 2013, 04:46 AM
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aymodeler's Avatar
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Thanks for the feedback. I'm leaning towards the RimFire since it's higher Kv will allow me to run a smaller prop (which I am thinking will be a better choice for this bird).
Sep 15, 2013, 11:39 AM
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6S power is more regular than 5S. You can create it with 3S in series.

This plane should have enough fuselage space for 6S 5,000 mAh batteries, so why not put a 55mm electric on it? This will get you around 10 pounds of thrust, and you can still fly it at 1/2 throttle to make it look like it has a Rimfire 46 in it.

Remember that the cubic inch rating was for nitro in the the 1960's. Manufacturers that put out nitro sized electric motors often seriously suggest under powering electric planes.

If the Sig will carry the weight, don't be afraid to put 150 watts per pound on it, or 200 watts per pound. Buy a motor that can use whatever voltage you can make from your current batteries. Multiples of 3S and 6S are better than trying to buy odd cell size batteries.
Sep 16, 2013, 06:32 AM
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aymodeler's Avatar
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wuest, thanks for the suggestion. I was originally looking for a 6S setup, but could not find a combo that worked with a 12" prop. Motors with a high enough Kv (700-800), couldn't handle the voltage or the current at 6S.

Can you suggest a motor prop combo that would work? I could put her on longer legs to spin a bigger prop, but I'm trying to avoid that.

Al
Sep 16, 2013, 08:00 AM
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scirocco's Avatar
IMO Kv700-800 is way too high for 6S, in a 5--6lb model even with only a 12" prop

For 6S, the Hacker A40-8L and A40-10S both have Kv=610. That would give you around 800W peak with a 12x6, and way under max rpm for the A40 series of 16k

For 4S, consider the OS 5010-810, at about 650W with a 12x6, or for more speed, about 620W with an 11x8. Lot of infor from Ken Myers here: http://www.theampeer.org/ampeer/ampm...r13.htm#REVIEW

For a cheaper 6S option, consider the Turnigy G46-550 with a 12x8. The spec says 4-5S, but as long as the rpm is not excessive and current is within limits, 6S vs 5S is not a concern. Consider that the G60 series with Kv up to 500 suggests up to 7S, ie about the same max rpm as Kv=550 on 6S.
Sep 17, 2013, 08:57 PM
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aymodeler's Avatar
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Quote:
Originally Posted by scirocco
IMO Kv700-800 is way too high for 6S, in a 5--6lb model even with only a 12" prop
Agreed. I was actually looking at a smaller dia prop when I was coming up with that Kv.

Quote:
Originally Posted by scirocco
For 6S, the Hacker A40-8L and A40-10S both have Kv=610. That would give you around 800W peak with a 12x6, and way under max rpm for the A40 series of 16k
The A40 might be a good fit. eCalc claims that I am over the voltage limit with 6S for both the 8L and 10S and claims the 10S is over the power limit. What are you using to get the power estimates?

Quote:
Originally Posted by scirocco
For 4S, consider the OS 5010-810, at about 650W with a 12x6, or for more speed, about 620W with an 11x8. Lot of infor from Ken Myers here: http://www.theampeer.org/ampeer/ampm...r13.htm#REVIEW
On the surface, this seem to be close to the RimFire .46. Also interested in how you are calculating power estimates. eCalc does not have any data for the 5010-810.
Sep 18, 2013, 08:28 AM
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scirocco's Avatar
Quote:
Originally Posted by aymodeler
Agreed. I was actually looking at a smaller dia prop when I was coming up with that Kv.



The A40 might be a good fit. eCalc claims that I am over the voltage limit with 6S for both the 8L and 10S and claims the 10S is over the power limit. What are you using to get the power estimates?



On the surface, this seem to be close to the RimFire .46. Also interested in how you are calculating power estimates. eCalc does not have any data for the 5010-810.
Re the A40s - ecalc says "The Motor Voltage is close or over to the Limit - please verify the max. allowed Motor Voltage" From experience and the rpm limits, I know the A40s are good on 6S, so I'm happy I've verified the max voltage. BTW, ECalc gives that warning a lot - I'm not sure what its criteria are, but as long as rpm are not excessive I don't worry anywhere near as much about voltage as being conservative on current limits and treating batteries gently. The other Ecalc warning to safely ignore, at least in typcal systems up around over 100W/lb, is the static thrust and prop stalled warning. It always appears on high pitch/diameter ratio props, and while the prop may be stalled, it still develops a lot of thrust, and at the rate of acceleration on the ground at such high power levels, unstalls very soon

Oops, typo when I wrote 10S, it's the 12S that has the same Kv as the 8L. The 10S at Kv=750 would be way too hot.

For the OS, I just put the constants Ken Myer determined useing DriveCalc in his review into a custom motor in Ecalc, and checked for reasonableness against Ken's results. So far I've used the OS 5025-375, 5020-490 and 3820-1200 and been very happy with the results and thus value. The 3825-750 is in a new build SuperCub 25E waiting to be finished, and the 5010-810 is in the drawer just in case.

I should switch across to DriveCalc myself, but I'm too slack to figure out how on a Linux machine and Ecalc I find gets me in the ballpark over many systems
Sep 26, 2013, 06:42 PM
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aymodeler's Avatar
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Well after overthinking and agonizing on this for way too long, I opted for a Scorpion 4020-10. With a 630Kv on 6S it should give me about 870 watts at 12,400 RPM with an 11x7 prop. That should be more than enough power, but if I want to get a bit more crazy, I can prop up to 12x6 and get just under 1,000 watts at around 12,100 RPM.

I had my mind made up on the Hacker A40-8L, but none were to be had in stock. The Scorpion seemed to have similar specs and was in the same price range and actually a bit higher max power, so that's where I ended up.
Sep 26, 2013, 10:37 PM
Electric baptism 1975
DavidN's Avatar
I run several Scorpion 4020-10. Our field altitude is 1300ft. My set up is 4s TP3850 45C APCe14x8.5 CC ICE 75, giving 56amps & peak 60 on verticals. Only about 4amp drop over the flight. This agrees well with Castle's ecalc WITH BATTERY SET AT FULL.
Using the same settings suggests you could see almost 50 amps & 1100 watts. Take an 11x6 & 10x6 with you. Check amps on wattmeter or logging before you fly. A few times I have found that I am drawing way more than expected in a new set up eg a Hacker A50 10s setup that drew 1775 watts instead of the 1250 on Hacker's charts.


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