Good servo for a Butterfly - RCCanada - Canada Radio Controlled Hobby Forum
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Old 06-11-2015, 05:49 AM   #1
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I am: Gerard Gagnon
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Good servo for a Butterfly

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I started yesterday my Butterfly and I have no idea witch servo to use, they are so many choice, from what I can read a slow trainer like this one doN,t need fancy digital, but what about torque ? I will probably use an electric motor with a 4s lipo, but it's not sure at 100%, ao option for both electric and 0.15 will be great

thanks, Gerard

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Old 06-11-2015, 06:16 AM   #2
Dale Hunter
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Re: Good servo for a Butterfly

Anything similar to these HiTec ones would be fine.
40 oz servo's were pretty much the norm when this airframe was conceived.
Hope this helps.
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Old 06-11-2015, 06:46 AM   #3
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Re: Good servo for a Butterfly

If your build is the Dynaflite Butterfly, I am using these HS 225MG which are serving me well.. Getting the sailplane as light as possible is required and using a 4s lipo is pushing it a bit. good luck on the build.
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Old 06-12-2015, 09:53 AM   #4
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Re: Good servo for a Butterfly

One 'rule of thumb' - suggested by Ampeer, an online blog on electrics - to aim for torque power 50% (or more) of the all up weight of the plane; so if the model weighs 80 ounces, use a servos with 40oz/inches or more.

In this kind of trainer - servos in the fuselage compartment under the wing; roomy fuselage, lots of wing area, slow flyer, "basic"/no frills analog servos would be fine. IMHO, an ounce more of less located around the center of gravity, is not critical in this kind of plane.

good luck,

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Old 06-13-2015, 07:19 AM   #5
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Re: Good servo for a Butterfly

HS81's or HS85's would be my choice. They are compact, quite light and powerful for their size. My #1 choice for under 3 meter gliders. I have been using them with great success in even larger planes.

As for battery sizing, that depends totally on the motor/prop combination you choose and how long you want your flight times to be. You need the right balance between cell count, motor kv ratting and prop size.

I have an old timer smaller than the Butterfly that runs 4 cell 1000mAh packs that gets 20 minute flights and I also have a 2 meter glider with 2 cell 2000mAh packs that gets 45 minute flights. Both have very similar performance and watt draw. Different motor specs and props.

Look up motors in the 175 watt range (yes I know they are not publishing that spec much anymore)and follow the cell count and prop size recommendations. For you plane you will want a lower kv/big prop motor.

I will look one up for you and show you what I mean.


Brushless Outrunner
Motor Type:

370/400 Range
Motor Size:

9x6 to 12x6
Prop Range:

7.2-12 v
Voltage Range:

890 rpm
RPM/Volt (Kv):

.20 ohms

.69A @ 8V
Idle Current:

4 mm
Shaft Diameter:

2.5 oz

28 mm

33 mm

14 A
Continuous Current:

Max Burst Current:

6-10 cells
NiCd/NiMH Cells:

2-3 cells
Li-Po Cells

Max volts are 12 and max amps 14 for 168 watts.

The recommended prop sizes are:
9 x 6 ( with the 3 cell battery) and
12 x 6 (with the 2 cell pack)
These are the extremes that still fall within the specs of the motor and are starting points so somewhere in between will be your happy spot.
Pick a cell count that suites you (availability/present charger size etc), invest in a watt meter, get a few props in the size range for your cell count and experiment till you get the performance you are happy with.

Experience tells me that around 150 watts will be a comfortable power level for a rank beginner with this plane. Nice climb without getting all twitchy on you!

Put the battery and ratio gear as far forward as you can on this plane as it has a long tail moment to balance out. You may even need to put some sort of extension on the firewall to get the motor weight further out and avoid a lot of extra lead added.

Good choice of bird by the way, have fun and don't forget to turn the motor off and go thermal hunting!

Hope this helps. Merv
Hang time does not apply to ceiling fans, light fixtures, overhead door tracks or basketball nets!

Last edited by OLD PRAIRIE RED NECK; 06-13-2015 at 08:19 AM.
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