TedMo

Just don't understand why JR/Spectrum do not provide any longer servo arms with their servos? All they have are the sound ones and the short 4 arm type. I have servos and arms from all other manufacters that also include thos e far longer than what Jr have. Of course none of those will fit a Jr servo . I just installed my Spectrum digital servos in my wing for the ailerons and found they do not protrude out of wing enough to connect to the pushrod. Only solution I have is to put other servos in their place that have longer output arms. Seems odd that JR doesn't include them or do they even have them?

ChuckW

Unless it is just a simple trainer or sport plane, I almost always use Dubro or some other longer, higher strength servo arm regardless of the brand of servo I'm using.

gotprops

JR does sell longer servo arms. I got some from the LHS for $2 a pair. Here is a link on Horizon http://www.horizonhobby.com/Products...ProdID=JRPA215

Brandon

TedMo

Thanks to both of you I didn't know they were available, great.

w8ye

My Feedback: (16)

I use the Dubro arms on all my servos

The Ghost

Remember, that the longer the servo arm the less power you will get from the servo.

Cheers

jaka

Hi!
Why longer servo arms??? The longer the arms are the weaker the servo gets!

BarracudaHockey

My Feedback: (11)

Depends on what you're trying to accomplish. Considering the torque rating of todays digital servos, if control throw is what you're after (3d style plane) then the torque you loose isn't worth worrying about.

ChuckW

Also, there is the OP's issue. The arms included with the servos aren't long enough to work easily with the servos mounted flush with the wing. I agree that it is best to use the shortest arm possible that will still achieve the desired throw but there are those situations where a little longer arm is necessary or nice.

airbusdrvr

Longer arms do not a make a servo weaker.

exeter_acres

My Feedback: (2)

they do not... correct...

but you do not get the full torque with arms longer than 1"

its a physics thing

BarracudaHockey

My Feedback: (11)

If you ever get a hankerin to test this, hard mount a servo on a table, get you a bag to fill with shot or sand, and play with different servo arms, you'll see it stalls at less weight the farther out you go on the arm.

ChuckW

Kinda like changing gears in your car or on your bicycle.

airbusdrvr

So, would it be a generally correct statement that the longer the servo arms, the less torque(that is the way most servos are rated) a servo will produce?

http://en.wikipedia.org/wiki/Torque

w8ye

My Feedback: (16)

Someones missing point here by the fixation of only looking at the Servo Arm.

You must also consider the control horn on the device bering controlled

Ultimate torque must consider the rating of the servo, the length of the servo arm, the length of the control horn, and the size of the end device being controlled

You can have a 2" servo arm and a 2" control horn and the torque is the same as a 3/4" servo arm and a 3/4" control horn

To run longer arms and horns tends to lesson the free play and therefore flutter potential on a control surface without sacrifice of torque as long as you keep the ratio the same.

jaka

Hi!
Yes!
The longer the arm is the less torque you get!
That's why you should always use as short servo arm as possible, within reason of course, because in some applications (3D) you need as much throw as possible.

darrolair

If a servo has a rating of 100 in. oz., and a 1 1/2 in. servo arm is placed on the servo, what is the torque rating of this servo?
If the same servo has a 2 in. arm placed on it, what is the torque rating? Regardless the length of the control horn, how much rated torque does the 100 in. oz. servo loose with longer arms?
Darrolair

w8ye

My Feedback: (16)

The torque rating for the servo is the same in both cases

But in the first instance it will only push/pull 75oz at mid point with the push rod and in the second case it will only push/pull 50 oz at midpoint with the push rod.

jester_s1

w8ye has it 100% right. With a given control horn, you lose torque by using a longer servo arm. But you can get it back by going to a longer horn. The length of either isn't the issue. It's the ratio of lengths between the two of them.

To solve the problem the OP is having, I had a Goldberg Skylane 62 which had very sensitive ailerons with the dual wing mounted servos. I wound up bending the pushrod in order to let it go into the slot so as to be able to use the nearest hole on the arm. Going to giant scale horns would have worked too, but I didn't like the looks of them.

mikekosatka

My Feedback: (7)

Longer servo arms ( without changing any other part of the equation) will give you more deflection (travel) and higher speed. It's all a trade off, but back to the original question there are longer arms available. I personally like the loks, weight and strength of the aluminum ones. Don's Hobbys WWW.donshobbyshop.com carrys several kinds including Dubro hd ones ,plus all kinds of good stuff. If you call and talk to Don ( a great guy) he is happy to give great advice and actually knows what he's talking about.