[NSRCA-discussion] Metal Servo Arms

Fri Aug 31 09:16:58 AKDT 2007

http://www.nelsonhobby.com/cnc.html

See this link too.

Jim W.

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Earl
Haury
Sent: Friday, August 31, 2007 11:57 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Metal Servo Arms

The Al arms are quite resistant to twisting - but you're correct that
the nylon wheel is plenty strong and the Al wheel stronger than either. 

A few years back I tested the strength of the JR 8411 Al spline and the
equivalent nylon spline coupled to stock & H9 Al arms. The test involved
making an adaptor to set over a single arm and position an inch-lb
torque wrench directly over the shaft. An output gear / shaft was
clamped in a vise and the torque wrench used to measure the "give" point
and the failure point with different combinations. All exceeded the
torque rating of the servo.

Nylon shaft & arm: "Give" @ 320 oz in and failure @ 480 oz in - the
spline shaft twisted and slipped, arm spline damage (yet there was
enough binding to retain some control transfer).

Nylon shaft & Al arm: "Give @ 320 oz in and failure @ 560 oz in - shaft
spline total failure.

Al shaft & nylon arm: No "give" point. Crisp failure @ 560 oz in - arm
spline total failure.

Al shaft & Al arm: No "give" point, Crisp failure @ 1600 oz in - no
spline damage, shaft broke below spine.

Earl

	----- Original Message ----- 

	From: twtaylor <mailto:twtaylor at ftc-i.net>  

	To: 'NSRCA Mailing List'
<mailto:nsrca-discussion at lists.nsrca.org>  

	Sent: Friday, August 31, 2007 9:09 AM

	Subject: Re: [NSRCA-discussion] Metal Servo Arms

	Last night I was playing with them, they fit the plastic output
gear just fine. I was trying to get them on 8411sa's with the metal
splines. I finally did but they won't go down as far as a nylon arm.
Using a magnifying glass I could see where the alum arm is fully seated
internally. Just looks different than with the plastic arm, as the arm
doesn't cover the entire part of the splines at the bottom like the
standard arm does. I'm using this on elev with the MK bearing fitting.
I'm going to replace the rudder arm with a H9 as well.

	Tim

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________________________________

	From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of
vicenterc at comcast.net
	Sent: Friday, August 31, 2007 9:57 AM
	To: NSRCA Mailing List; NSRCA Mailing List
	Subject: Re: [NSRCA-discussion] Metal Servo Arms

	Earl,

	I wonder if the aluminum single arm will twist more than the
round nylon wheel in similar loads and conditions.  Using MK link (which
are very close to the plane of the wheel) with round nylon wheels has
been working very well for me.  The reason why the nylon wheel is strong
is because the structure is closed.  Of course aluminum wheel would be
stronger than nylon wheel.

	--
	Vicente "Vince" Bortone

		-------------- Original message -------------- 
		From: "Earl Haury" <ejhaury at comcast.net> 

		The nylon servo arms are quite adequate when used with a
clevis that applies the force in line with the plane of the arm (typical
pin clevis). Pushrod ends that bolt to one side of the arm move the
force off the plane of the arm and thereby impart a twisting force to
the arm. (DuBro type ball links are the extreme.) Add a bunch of
vibration to the normal loads and the nylon arm may eventually fail - a
wheel is a much better choice if one uses the nylon accessories. In
addition to better withstanding the twisting forces of offset linkage,
the aluminum arm is more substantial for screw mounting the ball / ball
bearing end.

		Jim is correct regarding the H9 arms on JR servos -
there seems to be more variation in the spline of the output than the
spline of the arm. (An arm tight on one servo may fit nicely on
another.) OTOH, I've found the H9 arms to fit Futaba servos consistently
well.

		Earl

			----- Original Message ----- 

			From: vicenterc at comcast.net 

			To: NSRCA Mailing List
<mailto:nsrca-discussion at lists.nsrca.org>  ; NSRCA Mailing List
<mailto:nsrca-discussion at lists.nsrca.org>  

			Sent: Friday, August 31, 2007 7:28 AM

			Subject: Re: [NSRCA-discussion] Metal Servo Arms

			For pattern I always use the nylon servo arms
that comes with the JR servos.  I am not sure why you need the metal
servo arms.  Usually I use the round one for aileron and elevator.  For
rudder I use the heavy duty arm that JR offers (comes in the 8611
servo).  I never have problems with the nylon servo arms in pattern
application.

			Regards,

			--
			Vicente "Vince" Bortone

				-------------- Original message
-------------- 
				From: Bob Richards <bob at toprudder.com> 

				I've used the H9 arms and the SWB arms.
No comparison, I will continue to use the SWB arms.

				Bob R.

				Kelly Regan <kelly.regan2 at verizon.net>
wrote:

				Not an answer to your question but I
find the SWB arms much nicer
				since they are split. They use a a 2/56
clamp screw and nylon locking
				nut to draw the clamp tight around the
spline of the servo shaft.

				twtaylor wrote:
				>
				> I bought some Hanger 9 alum servo arms
and when I put them on they are 
				> VERY hard to get to pull down on to
the servo. Is
				>
				-- 

				________________________________
				Kelly Regan
				Home Page: www.reganspace.com
				________________________________

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