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Author Topic: Picking a Motor  (Read 867 times)

Offline Glenn Kirms

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Picking a Motor
« on: June 08, 2020, 10:21:20 AM »
I have an old Sig Shoestring with a 32" wingspan that I would like to convert to electric.  I already bought one motor from Brodak which was decidedly too small so I'm at a loss on what size motor, amp, timer and battery to mount on this plane.  If anyone has suggestions what I can purchase from Brodak it would be much appreciated.

Offline Tim Wescott

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Re: Picking a Motor
« Reply #1 on: June 08, 2020, 11:57:24 AM »
Bigger than what you bought before.

"Too small" in what way?  What happened?  A "too small" motor with an adequate ESC and battery will pull a plane smartly enough -- it'll just burn up in the process.  Is that what happened?
AMA 64232

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

Offline Tim Wescott

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Re: Picking a Motor
« Reply #2 on: June 08, 2020, 12:00:21 PM »
And tell us what you want to do -- the Shoestring certainly isn't going to be a hot stunt prospect.  Are you looking for a trainer, a racer, or what?  What sort of speed to you want to attain, and what sort of flight time?
AMA 64232

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

Offline Tim Wescott

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Re: Picking a Motor
« Reply #3 on: June 08, 2020, 12:05:50 PM »
If it's powered by a .15, then a motor that'll swing an 8" prop with authority should work well.
AMA 64232

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

Offline Glenn Kirms

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Re: Picking a Motor
« Reply #4 on: June 08, 2020, 02:46:15 PM »
Bigger than what you bought before.

"Too small" in what way?  What happened?  A "too small" motor with an adequate ESC and battery will pull a plane smartly enough -- it'll just burn up in the process.  Is that what happened?
[/quote

I don't have anything on it right now.  I have a Superclown and Ringmaster but they came with the motors so I didn't have an issue in deciding what motor.  For the Shoestring I just want to pick an appropriate motor for moderate flying with the appropriate battery, timer and amp.  I really don't have any idea what to pick to mount on this plane.

Offline Mike Alimov

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Re: Picking a Motor
« Reply #5 on: June 08, 2020, 07:36:28 PM »
I would think the Shoestring setup should be pretty similar if not identical to the Ringmaster and the Super Clown. Unless you have very specific requirements, why not copy what you already have.

Offline Tim Wescott

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Re: Picking a Motor
« Reply #6 on: June 08, 2020, 09:05:29 PM »
If anything those setups will be a bit big -- but the nice thing about 'lectric is that you can easily tone it down, just by putting on a smaller prop.

Once you've established how much the thing draws you can easily go down to something lighter.

In your shoes, I'd be strongly tempted to borrow the setup from the Ringmaster or S. Clown as my first cut at getting it in the air, and use the amount of charge I put back into the battery after a flight as guidance to how much smaller I can go.
AMA 64232

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

Online Ken Culbertson

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Re: Picking a Motor
« Reply #7 on: June 08, 2020, 10:01:49 PM »
Tim has hit on the "problem" with electric to a first timer.  I had the same questions and it took a couple of years before I realized that the *motor* was just one piece of the power train in electric where it is the entire power train in IC.  The ESC will drive the motor at whatever RPM you ask it to and burn itself up trying if you ask for too much for the prop.  That is why we prefer larger motors running well below capacity.   

Ken
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Offline William DeMauro

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Re: Picking a Motor
« Reply #8 on: June 09, 2020, 05:36:26 AM »
I would think the Shoestring setup should be pretty similar if not identical to the Ringmaster and the Super Clown. Unless you have very specific requirements, why not copy what you already have.

Exactly what I was thinking!!! 
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Offline CircuitFlyer

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Re: Picking a Motor
« Reply #9 on: June 09, 2020, 07:48:09 AM »
Sounds like the RSM Distribution competition 15 power package may be a good place to start.  I'd post a link here if I could.

If any one knows how to copy a link to a product on RSM's goofy web pages please let me know.

Paul
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Spinning electrons in circles in Mississauga, Ontario, Canada DIY Control Line Timers - www.circuitflyer.com

Offline Glenn Kirms

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Re: Picking a Motor
« Reply #10 on: June 09, 2020, 11:48:47 AM »
If anything those setups will be a bit big -- but the nice thing about 'lectric is that you can easily tone it down, just by putting on a smaller prop.

Once you've established how much the thing draws you can easily go down to something lighter.

In your shoes, I'd be strongly tempted to borrow the setup from the Ringmaster or S. Clown as my first cut at getting it in the air, and use the amount of charge I put back into the battery after a flight as guidance to how much smaller I can go.

I've ordered a 2200kvh motor with a small battery and esc so I'll see how that goes once they arrive.  If not I will use the same motor as my Superclown with a rear mount and just use the smaller prop for it.  Thanks to everyone for some guidance.

Online Ken Culbertson

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Re: Picking a Motor
« Reply #11 on: June 09, 2020, 12:51:08 PM »
I've ordered a 2200kvh motor with a small battery and esc so I'll see how that goes once they arrive.  If not I will use the same motor as my Superclown with a rear mount and just use the smaller prop for it.  Thanks to everyone for some guidance.
That combination is fine for sport flying but if you plan to do any serious maneuvering be warned that the recovery time with a 2200kv motor will be slow.  When you say a small battery are you referring to the mAh rating or the voltage(cells). mAh only governs how long you can fly, it is the cells count that tell you how well and that pesky "c" number tells you how quickly the ESC can deliver the extra juice the motor is asking for.

good Luck and let us know how it works out - Ken
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USAF 1968-1974 TAC

Offline Tim Wescott

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Re: Picking a Motor
« Reply #12 on: June 09, 2020, 01:04:31 PM »
That combination is fine for sport flying but if you plan to do any serious maneuvering be warned that the recovery time with a 2200kv motor will be slow.

Based on?

In general a high kv motor will require less voltage and more current to do the same job; as long as the wires are thick enough and the ESC and battery capable of delivering the current, there shouldn't be an overall difference in behavior.

When you say a small battery are you referring to the mAh rating or the voltage(cells). mAh only governs how long you can fly, it is the cells count that tell you how well and that pesky "c" number tells you how quickly the ESC can deliver the extra juice the motor is asking for.

Well, it's more complicated than that -- for a given C rating, two batteries of the same physical size, matched up to the correct motor for that pack, should result in equivalent performance -- even if one is 3 cell and the other 6.  Actually finding motors and ESCs to match over that wide of a range ain't gonna happen without a lot of work.

In general smaller systems are designed for lower voltages, because the overhead of thicker wires is less for a smaller plane than the overhead of more cells.

I've ordered a 2200kvh motor with a small battery and esc so I'll see how that goes once they arrive.  If not I will use the same motor as my Superclown with a rear mount and just use the smaller prop for it.  Thanks to everyone for some guidance.


Tell us which motor and pack -- what matters is the power the motor can put out (which depends on kv, current rating and your pack voltage) and the RPM it can achieve (which depends on the kv and pack voltage).  Just quoting kv isn't sufficient information.

(And my small may be your huge, and visa-versa -- I know guys for whom a "small" motor is one that you can actually carry around in a 1/2-ton pickup, and others for whom a "large" motor is actually bigger than your thumb.)
AMA 64232

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

Online Ken Culbertson

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Re: Picking a Motor
« Reply #13 on: June 09, 2020, 01:31:37 PM »
In general a high kv motor will require less voltage and more current to do the same job
Which is basically what I said in different words.

Well, it's more complicated than that
I was trying to keep it simple.

In general smaller systems are designed for lower voltages, because the overhead of thicker wires is less for a smaller plane than the overhead of more cells.
Precisely why his selection is fine for sport but borderline for heavy aerobatics.

I may be missing something here.  Do you know of any of the top flyers that use anything much over 1000kv?  The most I have ever used is around 940 and my best results were in the 700's.  Electric is like herding cats LL~

Ken
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Tim Wescott

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Re: Picking a Motor
« Reply #14 on: June 09, 2020, 01:58:47 PM »
I may be missing something here.  Do you know of any of the top flyers that use anything much over 1000kv?  The most I have ever used is around 940 and my best results were in the 700's.  Electric is like herding cats LL~

Ken

Well, no, but he's trying to find a motor for a 32" wingspan plane with a solid wing, that's designed for basic training, or to be raced with a .15.

For a 650-700 square inch, 4 1/2 pound stunter (with a built-up wing), your best results are probably to be had with a 6 cell battery.  The matching motor for that will have a kv of around 700-900 RPM/volt.
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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