"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

What are servos to use on 1/2a ?

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Old 08-12-2014, 12:24 PM
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TampaRC
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Default What are servos to use on 1/2a ?

With all the new micro servos out there now, what is a good torque rating for something like a 21oz. Mach None with a TD ?


The 6 gram servos have around 13 ounce inch and the 9 gram servos have about 22 ounce inch. What torque would you recommend for elevator for example?
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Old 08-12-2014, 12:29 PM
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I like the Hitech HS65-HB, but there are many other good servos available too, just stay away from the cheapest HK and Tower servos etc...
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Old 08-12-2014, 12:58 PM
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I'm looking for the most appropriate torque numbers.
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Old 08-12-2014, 02:01 PM
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I think there is more to it than torque. Some servos have weak gear trains but good torque while others do not hold up well to the vibration of small glow motors.

I would not be afraid of a 15 to 20 oz torque servo in a 1/2a plane given a strong gear train and resistance to vibration .

I agree with the previous poster that HS 65 servos are great for 1/2a or even a bit larger. I personally prefer HS81 servos over HS65 servos because they are a bit cheaper and a bit stronger but at the expense of size and weight. They are slightly heavier and larger.

The problem is that many micro servos are designed for use in electric aircraft and are often not robust enough for the harsher environment of 1/2a glow planes. Unfortunately the only way to know for sure is to give a servo a try and see how it holds up OR by asking others what has worked for them.

Neither I nor my 1/2a friends have had good luck with HS55 servos in glow planes, they soon succumb to the vibration and cause random problems followed by total failure.

Last edited by 049flyer; 08-12-2014 at 03:31 PM.
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Old 08-12-2014, 06:39 PM
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HS-65MG has long lasting and durable metal gears
One of the slimmest micro servos available
High efficiency
Neodymium magnet motor
The HS-65MG was created for fast Park Flyer models, electric micro
planes, and features a top
ball-bearing
for long life and positive centering


Weigth: 0.44oz (12.5g)
Speed: 0.14sec/60 @ 4.8V
0.11sec/60 @ 6V
Output Torque: 24.99 oz-in (1.8 kg-cm) @ 4.8V
30.55 oz-in (2.2 kg-cm) @ 6V
G Mighty Feather Metal Gear Micro Servo with
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Old 08-13-2014, 05:50 AM
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You'd have to dig hard to find a definitive answer to "what is the right amount of torque".

The HS55 is an example of a servo with sufficient torque but a crappy gear train. The HS65HB has proven to be more than adequate for any 1/2A aircraft so is a go-to choice for many. I agree that the gear train and vibration resistance are bigger issues. I have yet to see an example of a 1/2A that stalls the elevator servo in flight, unless it is due to stiff hinges and/or crappy linkages.

You probably need less torque than you think.. you can fly a 170mph .50 delta with elevons on 48 oz-in servos. But it is generally not recommended..
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Old 08-21-2014, 11:11 AM
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MJD and COX are right on with the Hitec HS-65HB servo. The 65 with the karbonite gears are very very strong. I think they are better than the MG metal gear ones in that they have less slop in them. i have used them on 25 size glow planes and have had no issues.

as for torque just remember in the old days we flew 60 size pattern planes with only 35-40 ounces of torque...

If your control surface and push rod set up is very free you need less torque. for 1/2A plans film covering hinges are the best. your control surfaces with push rods hooked up should move under their own weight. if not then they are too stiff. They CA hinges are way to stiff for 1/2A models IMO.
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Old 08-21-2014, 03:02 PM
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The only way to witness a servo lose the "torque battle" with a control surface is to watch the diameter of real tight, consecutive loops get larger as the battery wears down.
It simply doesn't take much torque to fly a 1/2A plane, whether you are doing 3D type stuff or going 100 mph.
The torque rating on most "1/2A servos" I've ever seen is enough to turn a pinion shaft on an automotive rear axle assembly.
Gear toughness and the servo's tolerance for vibration is what matters.
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Old 08-21-2014, 06:50 PM
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I have heard it said that a good rule of thumb is 1 oz of servo torque for every square inch of control surface area.
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Old 08-26-2014, 08:59 AM
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I've gone to using HS-65HB servos for 1/2A after having HS-55 servos fail. I find the weight difference minimal on a 1/2A ship, but knowing I won't have a failure is worth the little weight gain there is. Also, like has been said, a hinge system with as little friction as possible is desired - for this I've found Dubro pinned hinges work best for me (just remember to add a bit 3-n-1 oil to the hinge joint before gluing in place). I've also used MonoKote hinges and sewn hinges with great success.

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