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Old May 16, 2006, 04:37 PM
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Carl's Avatar
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Question
Servo spline tooth count

What is the different teeth count and size of the various servos that we use. Is there a chart that lists the different brands of servos?

Carl
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Old May 26, 2006, 05:30 PM
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Old May 27, 2006, 10:05 AM
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This chart lists servos but I don't think it gets down to counting spline teeth. Why would you want to know that?

http://www.fatlion.com/sailplanes/servochart.html
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Old May 27, 2006, 11:26 AM
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having an odd number of teeth in the spline facilitate finer adjustment capability. With even number, if you rotate the arm on the pline 180 degrees, you will be at the same relative position. If you have an add number of teeth, you can get a minute difference when you try to rotate the arm 180 degrees, it won't fit until you move it a bit more one way or the other. That is why Futaba (has an odd number of splines) has the numbers on some of their servo arms. You can get finer adjustments and (by noteing the number on the arm you are using) repeat it or --by changing to another numbered arm--get a minute change.
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Old May 27, 2006, 11:47 AM
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Rodney, Wow!! I'd figured out the numbers on the arm bit and noticed the difference between a 180 degree rotation on some servos but I'd never really stopped to think how and why! Thank goodness for subtrim on the Tx to get us where we want to be if it can't quite be done mechanically.

I've been trying to set up a closed loop rudder this morning and can't get the servo arm on the Futaba servo to sit at 90 degrees to the servo. Me thinks if I rotate the arm 180 deg it might just square up. I'll go try it.

Is it only Futaba that's odd - the splines that is?
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Old May 27, 2006, 11:54 AM
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Quote:
Originally Posted by Rodney
having an odd number of teeth in the spline facilitate finer adjustment capability. With even number, if you rotate the arm on the pline 180 degrees, you will be at the same relative position. If you have an add number of teeth, you can get a minute difference when you try to rotate the arm 180 degrees, it won't fit until you move it a bit more one way or the other. That is why Futaba (has an odd number of splines) has the numbers on some of their servo arms. You can get finer adjustments and (by noteing the number on the arm you are using) repeat it or --by changing to another numbered arm--get a minute change.
Do not use a servo arm with a different spline than the servo's output shaft. the different spline will not give proper engagement and would be in danger of the arm slipping in flight.

It might feel like it will work... but you can be losing over 90% of the tooth contact area.
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Old May 27, 2006, 12:27 PM
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Standard Hitec servos have 24 teeth. Standard Futaba servos have 25 teeth. Don't know about minis, micros, or other brands.

Bill
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Old May 27, 2006, 01:41 PM
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Quote:
Originally Posted by fhhuber506771
Do not use a servo arm with a different spline than the servo's output shaft. the different spline will not give proper engagement and would be in danger of the arm slipping in flight.

It might feel like it will work... but you can be losing over 90% of the tooth contact area.

That's right. Futaba arms 'feel' as though they are ok on a Hitec servo as you tighten them down but they aint....
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Last edited by guy mckenzie; May 27, 2006 at 01:41 PM. Reason: typo
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Old May 27, 2006, 03:59 PM
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I never said that you could interchange manufacturers brands, If anyone interreted my comments as such, I am sorry. I just assumed everyone knew that without being told, bad assumption on my part. I was just explaining the advantages/dissadvantages of having an even or odd number of splines. To the best of my knowledge, Futaba, DAD and Cirrus arms are interchangeable, and Hitec and Hobbico are also interchangeable on the standard size servos. When you get into the miniature ones, I am not sure any are interchangable.
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Old May 27, 2006, 06:27 PM
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Quote:
Originally Posted by guy mckenzie
That's right. Futaba arms 'feel' as though they are ok on a Hitec servo as you tighten them down but they aint....
Some of the smaller ones are interchangable.

The Hitec HS-55 arms fit on the Futaba 3110 micro servos... both have 15 tooth arms, and I have swapped them successfully. There is a very, very slight pitch diameter difference, making a tiny bit snugger fit on one vs the other, but the tooth count is the same and they will work.

FWIW, I have found the 3110 is a much better servo for essentially the same cost... slightly smaller and lighter, slightly faster, with about 20% more torque. I tried them and never looked back after having two HS-55's failing to center or step properly right out of the box...
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Last edited by Tom Frank; May 28, 2006 at 02:55 PM.
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Old May 28, 2006, 11:45 AM
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Thank you for the response. I use Hitec, Cirrus and Eflight servos in the HS55 size on most of my fleet and I was wondering on the interchange ability of the servo arms. I did know that some manufactures used even and some odd number of teeth for adjustment purposes.

Carl
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