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Old 12-20-2008, 03:47 PM   #1
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servo torque rating

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This is for the electronis gurus out there.

question about servo

Lets use the Hitec 645 as an example, it has a torque of 133 oz, does it mean it can move a surface of close to 8 lbs of weight ? or is there a diff. translation to this rating. the reason i ask is because, i have one on my plane (rudder) and it bzz at the end of the travel which is cause by a bit stiffness on the hinge, but i'm sure that the cause is nowhere near the 8lbs mark.

thanks in advance

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Old 12-20-2008, 04:47 PM   #2
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Re: servo torque rating

Sounds to me like a bit of a bind in your travel. I would decrease the throw until the buzzing stops. I found that even if your servo is at full throw, if you apply some pressure with your hand it will buzz as it tries to hold its position. A good test to try, is to place a servo with an arm under some books and then activate the servo. you will be surprised at what it can move. But this is only a test...
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Old 12-20-2008, 05:20 PM   #3
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Re: servo torque rating

The buzz is caused by the servo stalling. It comes to the limit of the rudder throw but is still trying to go more, which it can't, so it is said to be stalled and you will hear that buzz.

If your radio has EPA (End Point Adjustment) you can easily reduce the amount of travel of the servo itself. Go into your EPA settings and just back off the servo throw enough to stop the buzzing.

When a servo is stalled/buzzing it is drawing more than normal current so if left in that condition, you battery pack could drain faster, giving you less flight time etc, so its best to always correct that situation!

From my understanding, an analogue servo only produces its full torque rating at full throw. So if you only move the servo half of its throw, its only giving you 1/2 of its available torque, 3/4 throw then 3/4 of its full torque etc .

Thats one of the main differences between analogue and digital servos. A digital servo will give you full torque from its first degree of movement right through its entire range of throw. 1/4 throw, full torque...1/2 throw, full torque etc etc.

But anyways, like I previously said, you definitely want to eliminate that buzzing because of the adverse effect it has on your availible battery power!

Hope this helps explain things somewhat for you!
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Old 12-20-2008, 06:11 PM   #4
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Re: servo torque rating

The buzzing problem was cured by adjusting the EPA.And if the explanation that the torque rating only apply to the full throw, that explain then why it will buzz in between the center to full throw. The stalling was not caused by max. travel of the rudder but the stiffness of the hinge (CA hinge). more that few drops were applied, that made stiffer than usuall, i did a small test, i pulled the rudder by a fish scale, and i reach the max throw of the rudder in half weight than the torque specified.
I did this out of curiosity.

thanks for explaining this Gary.

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Old 12-20-2008, 10:21 PM   #5
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Re: servo torque rating

you have to realize that you only put half the units...

it's oz-in not just oz.

Torque = Force x Distance to fulcrum x sin (a)

Also, keep in mind that in this case the oz rating is the unit for force, not weight.
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