Servo Arms Universal Servo Arms Made in the USA

Large R/C jets, gliders, scale, and aerobatic aircraft models are becoming quite popular. These aircraft usually all have one thing in common, they probably need heavy duty servo control arms and longer arms to provide additional control surface travel.

The typical plastic servo arms that are supplied with servos have two problems. Many times they don’t provide sufficient throw and can have too much flexing under high load conditions. We have developed a new single truss design that has the necessary strength and rigidity required for the large and high speed aircraft. This new design is also lower in cost.

NELSON heavy duty SSA125 single servo arm mounted on a JR8417 servo. Arm is made from 1/16" thick 2024T-3 aircraft aluminum. It is attached to standard JR servo wheel with four 2-56 screws with elastic stop nuts. A heavy duty 4-40 ball link is mounted on the underside of the servo arm.

Our servo arms are made from 1/16” thick aircraft quality 2024T-3 aluminum. The servo arm is attached to the top of a typical round plastic or metal servo wheel. Four legged servo arms can be used too. Over many years of use and thousands of applications of our servo arms, we have found that the attachment of our servo arms to the standard factory supplied plastic servo wheels is very reliable and suitable for almost any size radio control model airplane including 50% size aerobatic airplanes and 200 MPH jets and pylon racers.

NELSON DSA250 2 1/2" double servo arm mounted on the smaller Airtronics servo wheel. New holes were drilled using the servo wheel as a pattern. Similar to the SSA arm series except for the double arms and additional ball links.

The servo arms are attached to the servo’s wheel with four 2-56 screws and held in place with four subminiature 2-56 elastic stop nuts. A NELSON RCL87 heavy duty 4-40 ball link is attached on the underside of the servo arm and is held in place with 4-40 screw(s) and a subminiature 4-40 elastic stop nut(s). The design allows for the movement of the ball link when 45+ degrees of control surface travel is required.

JOINING SERVOS IN TANDEM

Joining servos in tandem is quite common with rudder control systems in the larger aerobatic aircraft. When joining servos for this application it is very important that the servos are matched perfectly so that the servos don’t bind or fight against each other. This can cause excessive power drain and even can cause damage to the servo motor and amplifier.

One can find servos that are evenly matched in control travel, but one overlooked condition usually cannot be corrected. That is the relationship of the servo spline and the actual neutral position of the servo. The spline can be off as much as a 1/2 a tooth. This may not seem like a lot, but when the servo is rotated large amounts of 45 degrees, this error can be significant causing a bind between the servos.

The NELSON HD servos can be installed so there is no binding caused by the error in the neutral position of the servo spline. This is accomplished by installing the servo arm on the primary servo in the normal manner. The servo arm on the second servo is temporarily installed on the second servo. With the radio turned on and the controls in neutral, check to see if the the neutral on the second servo is exactly parallel to the primary servo. If there is an error, then remove the servo wheel from the second servo and rotate it 45 degrees or so. Then place our servo arm in the center of the wheel and drill a new set of holes into the wheel. Now the second servo arm can be mounted exactly in the correct neutral position. If a 3rd or 4th servo is utilized, then follow the same process as noted first by matching the 3rd servo to the 2nd servo and similar for the 4th servo.This is obviously some extra work, but it important to keep the neutral alignment exact between the two or more servos.

As new servos are introduced to the hobbyist, we will offer servo arms for these new servos. Most likely our NELSON HD Universal Servo Arms can be easily fitted to the new servos. However, some of the new servo types, such as the jumbo servos will require a more robust servo arm and a stronger method of attachment for our servo arms.

NELSON DSA500H 4" jumbo double servo arm mounted on a Hitec #5735MG servo. The 1/16" thick aluminum arm is attached to the 2" blue colored aluminum arm supplied with the servo with four 4-40 screws and elastic stop nuts. This is an extremely heavy duty servo arm system.

Offered is a selection of servo arms for the new jumbo size servos such as produced by Multiplex and Hitec. This selection will most likely increase in number as customers request larger servo arms for this type of servo.

These type of servos are very powerful and careful attention to the method of attaching larger auxiliary servo arms must be carefully considered. Our Jumbo Servo Arms are designed to allow the full power of these type of servos.

The Jumbo servos are becoming more popular all the time. Call for prices and availability and what new sizes are available.

The Hitec jumbo servo is supplied with a machined aluminum arm, blue in color, that is about 2 inches wide. Our Hitec jumbo arms attach directly to this arm in a very secure manner with four 4-40 screws and elastic stop nuts.

Two Hitec jumbo servos can be joined together with one or two short 4-40 threaded rods with a similar arm attached to the second jumbo servo.

The Multiplex Jumbo Speed servos can be fitted with our Multiplex HD servo arms. These arms are attached to the Multiplex Jumbo Double Arm as supplied with the servo. Like the Hitec servo attachment, four 4-40 screws with elastic stop nuts firmly hold our servo arms to the servo’s nylon output arm. With modifications, our Jumbo Servo Arms can be used with other type servos. However, we do not consider our Jumbo Servo Arms to be of the universal type.

NELSON DSA350M 3 1/2" double servo arm mounted on a Multiplex jumbo servo. The arm is attached to the 2" white nylon arm supplied with the servo with four 4-40 screws and elastic stop nuts.

New servo arms are being added to our product line on a regular basis. If you don't see what you need call us and we perhaps can make a custom servo arm for your application. Normally there is no charge for custom servo arms because others may be able to use your servo arm design.

Bottom view of our DSA350M 3 1/2" double servo arm attached to a Multiplex double servo arm.

Two Airtronics servos slaved together with a DSA125-90AF (90° double arm with 1 1/4" arms) and a SSA125AF single arm. One of many ways to joining servos in tandem.

Listed below are three groups of the standard arms

that we offer, the single, double, and offset.

NELSON Heavy Duty Single Servo Arms
JR-Hitec Digital Std.- Multiplex Std.
ITEM NO.	DESCRIPTON	QTY. PKG.	PRICE
SSA100	Single Servo Arm 1"	1	$7.95
SSA125	Single Servo Arm 1 1/4"	1	$7.95
SSA150	Single Servo Arm 1 1/2"	1	$7.95
SSA175	Single Servo Arm 1 3/4"	1	$7.95
SSA200	Single Servo Arm 2"	1	$7.95
Single Servo Arms: Airtronics-Futaba Std.
SSA100AF	Single Servo Arm 1"	1	$7.95
SSA125AF	Single Servo Arm 1 1/4"	1	$7.95
SSA150AF	Single Servo Arm 1 1/2"	1	$7.95
SSA175AF	Single Servo Arm 1 3/4"	1	$7.95
SSA200AF	Single Servo Arm 2"	1	$7.95

 

NELSON Heavy Duty Double Servo Arms
JR-Hitec Digital Std.- Multiplex Std.
ITEM NO.	DESCRIPTON	QTY. PKG.	PRICE
DSA200	Double Servo Arm 2"	1	$8.95
DSA225	Double Servo Arm 2 1/4"	1	$8.95
DSA250	Double Servo Arm 2 1/2"	1	$9.50
DSA275	Double Servo Arm 2 3/4"	1	$9.50
DSA300	Double Servo Arm 3"	1	$9.50
DSA325	Double Servo Arm 3 1/4"	1	$9.50
DSA350	Double Servo Arm 3 1/2"	1	$9.50
DSA375	Double Servo Arm 3 3/4"	1	$10.50
DSA400	Double Servo Arm 4"	1	$10.50
DSA420	Double Servo Arm 4.2" (metric)	1	$10.50
DSA450	Double Servo Arm 4 1/2"	1	$10.95
DSA475	Double Servo Arm 4 3/4"	1	$10.95
DSA500	Double Servo Arm 5"	1	$10.95
Airtronics-Futaba Std.
DSA200AF	Double Servo Arm 2"	1	$8.95
DSA225AF	Double Servo Arm 2 1/4"	1	$8.95
DSA250AF	Double Servo Arm 2 1/2"	1	$9.50
DSA275AF	Double Servo Arm 2 3/4"	1	$9.50
DSA300AF	Double Servo Arm 3"	1	$9.50
DSA325AF	Double Servo Arm 3 1/4"	1	$9.50
DSA350AF	Double Servo Arm 3 1/2"	1	$9.50
DSA375AF	Double Servo Arm 3 3/4"	1	$10.50
DSA400AF	Double Servo Arm 4"	1	$10.50
DSA420AF	Double Servo Arm 4.2" (metric)	1	$10.50
DSA450AF	Double Servo Arm 4 1/2"	1	$10.95
DSA475AF	Double Servo Arm 4 3/4"	1	$10.95
DSA500AF	Double Servo Arm 5"	1	$10.95

 

NELSON Heavy Duty Jumbo Double Servo Arms
Hitec Jumbo Digital
ITEM NO.	DESCRIPTON	QTY. PKG.	PRICE
DSA250H	Double Servo Arm 2 1/2"	1	$9.50
DSA275H	Double Servo Arm 2 3/4"	1	$9.50
DSA300H	Double Servo Arm 3"	1	$9.50
DSA325H	Double Servo Arm 3 1/4"	1	$9.95
DSA350H	Double Servo Arm 3 1/2"	1	$9.95
DSA375H	Double Servo Arm 3 3/4"	1	$9.95
DSA400H	Double Servo Arm 4"	1	$9.95
DSA420H	Double Servo Arm 4.2" (metric)	1	$9.95
DSA450H	Double Servo Arm 4 1/2"	1	$10.50
DSA475H	Double Servo Arm 4 3/4"	1	$10.95
DSA500H	Double Servo Arm 5"	1	$10.95
Multiplex Digital Jumbo
DSA250M	Double Servo Arm 2 1/2"	1	$9.50
DSA275M	Double Servo Arm 2 3/4"	1	$9.50
DSA300M	Double Servo Arm 3"	1	$9.50
DSA325M	Double Servo Arm 3 1/4"	1	$9.95
DSA350M	Double Servo Arm 3 1/2"	1	$9.95
DSA375M	Double Servo Arm 3 3/4"	1	$9.95
DSA400M	Double Servo Arm 4"	1	$9.95
DSA420M	Double Servo Arm 4.2" (metric)	1	$9.95
DSA450M	Double Servo Arm 4 1/2"	1	$10.50
DSA475M	Double Servo Arm 4 3/4"	1	$10.95
DSA500M	Double Servo Arm 5"	1	$10.95

 

NELSON Heavy Duty Double Offset Servo Arms
JR-Hitec Digital Std.- Multiplex Std.
ITEM NO.	DESCRIPTON	QTY. PKG.	PRICE
DSA250-250	Double Servo Arm 2 1/2" x 1/4" Offset	1	$9.95
DSA250-312	Double Servo Arm 2 1/2" x 5/16" Offset	1	$9.95
DSA250-375	Double Servo Arm 2 1/2" x 3/8" Offset	1	$9.95
DSA275-250	Double Servo Arm 2 3/4" x 1/4" Offset	1	$9.95
DSA275-312	Double Servo Arm 2 3/4" x 5/16" Offset	1	$9.95
DSA275-375	Double Servo Arm 2 3/4" x 3/8" Offset	1	$9.95
DSA300-250	Double Servo Arm 3" x 1/4" Offset	1	$9.95
DSA300-312	Double Servo Arm 3" x 5/16" Offset	1	$9.95
DSA300-375	Double Servo Arm 3" x 3/8" Offset	1	$9.95
DSA300-437	Double Servo Arm 3" x 7/16" Offset	1	$9.95
DSA350-250	Double Servo Arm 3 1/2" x 1/4" Offset	1	$10.50
DSA350-312	Double Servo Arm 3 1/2" x 5/16" Offset	1	$10.50
DSA350-375	Double Servo Arm 3 1/2" x 3/8" Offset	1	$10.50
DSA350-437	Double Servo Arm 3 1/2" x 7/16" Offset	1	$10.50
DSA350-500	Double Servo Arm 3 1/2" x 1/2" Offset	1	$10.50
DSA375-250	Double Servo Arm 3 3/4" x 1/4" Offset	1	$10.95
DSA375-312	Double Servo Arm 3 3/4" x 5/16" Offset	1	$10.95
DSA375-375	Double Servo Arm 3 3/4" x 3/8" Offset	1	$10.95
DSA375-437	Double Servo Arm 3 3/4" x 7/16" Offset	1	$10.95
DSA375-500	Double Servo Arm 3 3/4" x 1/2" Offset	1	$10.95
Airtronics-Futaba Std.
DSA250AF-250	Double Servo Arm 2 1/2" x 1/4" Offset	1	$9.95
DSA250AF-312	Double Servo Arm 2 1/2" x 5/16" Offset	1	$9.95
DSA250AF-375	Double Servo Arm 2 1/2" x 3/8" Offset	1	$9.95
DSA275AF-250	Double Servo Arm 2 3/4" x 1/4" Offset	1	$9.95
DSA275AF-312	Double Servo Arm 2 3/4" x 5/16" Offset	1	$9.95
DSA275AF-375	Double Servo Arm 2 3/4" x 3/8" Offset	1	$9.95
DSA300AF-250	Double Servo Arm 3" x 1/4" Offset	1	$9.95
DSA300AF-312	Double Servo Arm 3" x 5/16" Offset	1	$9.95
DSA300AF-375	Double Servo Arm 3" x 3/8" Offset	1	$9.95
DSA300AF-437	Double Servo Arm 3" x 7/16" Offset	1	$9.95
DSA350AF-250	Double Servo Arm 3 1/2" x 1/4" Offset	1	$10.50
DSA350AF-312	Double Servo Arm 3 1/2" x 5/16" Offset	1	$10.50
DSA350AF-375	Double Servo Arm 3 1/2" x 3/8" Offset	1	$10.50
DSA350AF-437	Double Servo Arm 3 1/2" x 7/16" Offset	1	$10.50
DSA350AF-500	Double Servo Arm 3 1/2" x 1/2" Offset	1	$10.50
DSA375AF-250	Double Servo Arm 3 3/4" x 1/4" Offset	1	$10.95
DSA375AF-312	Double Servo Arm 3 3/4" x 5/16" Offset	1	$10.95
DSA375AF-375	Double Servo Arm 3 3/4" x 3/8" Offset	1	$10.95
DSA375AF-437	Double Servo Arm 3 3/4" x 7/16" Offset	1	$10.95
DSA375AF-500	Double Servo Arm 3 3/4" x 1/2" Offset	1	$10.95

 

Work in process. Not shown new Futaba Jumbo Digital.

and other Single Servo Arms.

Revised 4/18/04

NELSON Servo Arms are available from

NELSON Hobby Direct or at hobby dealers.