How to Install a Steering Servo
in a Fast Electric, Radio Controlled Boat
By Ralph von Eppinghoven
Metro Marine Modelers Toronto, Canada
For a hard copy of this article you can
download the PDF version and print it out.
SECTION 1: INTRODUCTION
Steering and handling of Fast Electric (FE) boats is controlled by
the steering servo. A good solid installation of the servo, in a
manner that it can easily be removed for servicing or replacement,
is often an overlooked area of FE boat building. There are numerous
methods of installing servos in hulls and some common ones are:
attaching the servo in the hull using double sided tape, gluing wood
blocks in the hull and screwing the servo into the blocks, and even
directly gluing the servo to the hull bottom. There are pros and
cons to all of these methods, but extra care and a strong servo
installation is required for high power, brushless, motor set ups
and larger offshore boats. This article describes a simple, low
cost, and very strong method of installing servos into hulls in such
a way that they can easily be removed for servicing. The components
of the servo mount are shown in Photo 1.
Photo 1: The components used to mount the steering servo in the
The basic idea of this servo mount is to glue a small wood sheet
into the hull floor that has blind nuts pre-installed under the
sheet. Then the servo is screwed onto a right angle aluminum
bracket. One trick is to glue two small pieces of wood with blind
nuts onto the aluminum bracket so it is very easy to screw and
unscrew the servo mounting screws no struggling to hold the nuts
in place on the bracket. Then the entire aluminum bracket and servo
is then simply screwed into the wood sheet on the hull.
SECTION 2: REQUIRED MATERIALS
The following materials are required to make the servo bracket and
install it in a hull.
-Minimum ¾ X ¾ X 1/16 thick right angle Aluminum stock
-5/32 minimum thickness aircraft plywood
-# 2-56 X ½ cap head screws and blind nuts Great Planes part No.
GPMQ3500 Blind Nut Bolt Set
-# 4-40 X 3/4 cap head screws and blind nuts Great Planes part
No. -GPMQ3503 Blind Nut Bolt Set
-Du-Bro EZ-Push Rod Connector
-Medium thickness CA Glue
-220 grit sand paper
SECTION 3: ALUMINUM SERVO BRACKET
The following steps describe how to make the bracket and install the
servo in the bracket. Small, plywood, backing pieces with blind nuts
are installed to eliminate the need to fumble with nuts while
installing or removing the servo from the bracket.
3.1 Making the Bracket:
The aluminum angle bracket must be sized to fit the servo to be
used. For most standard servos, ¾ angle stock is adequate. Larger
servos will require larger stock. An opening must be cut into the
vertical face of the angle stock to allow the servo to be screwed
into the bracket. For a standard servo this opening is 1-5/8 wide
and it is the full ¾ depth of the angle stock. Care must be taken
to NOT make the opening too wide otherwise the servo screws will not
have enough aluminum material to fasten to.
Measure the servo width (it is approximately 1-5/8 for a standard
servo) and mark this dimension on the vertical face of the aluminum
angle stock. Leave at least 1/2 of stock on either side of the
opening to ensure the angle bracket is strong enough to hold the
servo. Cut the angle stock using a Dremel tool with a cutting wheel,
and hand file it to achieve the correct final dimension. Test fit
the servo frequently while you are working to make sure the opening
is not too large. Photo 2 shows the aluminum bracket with the
correct size opening cut into it.
Photo 2 Front view of the aluminum bracket
Photo 3 Back view of the bracket with blind nuts
In order to fasten the bracket to the wood
mounting sheet in the hull, it is necessary to drill two 1/8
diameter holes in the horizontal portion of the bracket. The holes
must be positioned to be clear of the servo and servo arm as shown
in Photo 2, in order to easily remove the entire assembly from the
hull after final installation.
Once the correct size opening has been cut into the right angle
aluminum stock, temporarily place the servo into the bracket
(similar to Photo 3), and mark the servo mounting holes on the
aluminum bracket. Remove the servo and drill 3/32 diameter holes so
that the #2-56 cap head screw can pass though the aluminum. Cut two
small rectangular pieces of 5/32 aircraft plywood and glue them to
the back of the aluminum bracket using medium CA glue. Roughen the
aluminum with sandpaper where it is to be glued. As shown in Photo
3, the wood pieces may need to be slightly larger than the bracket
sides in order to hold the #2-56blind nuts. Test fit the #2-56 blind
nuts on the wood pieces to ensure the correct size of wood.
Once the plywood backing pieces are glued onto the bracket, drill
the mounting holes through the plywood using the holes in the
aluminum bracket as a guide. Carefully press or tap the #2-56 blind
nuts into the holes on the plywood backing pieces as shown in Photo
3.2 Installing the Servo in the Bracket:
The servo can now be installed in the bracket using #2-56 cap head
screws, lock washers and flat washers. The blind nuts, fixed in
place on the plywood backing, make it very easy to install the
servo. In this example, the servo is installed with the rubber
grommets and brass sleeves around the mounting screws to provide
isolation from vibration. This is optional for FE boats, but is
normal practice for RC boats that have gas or nitro engines. Photos
4 and 5 show the finished bracket with the servo installed in place.
Photo 4: Front view - Servo in bracket
Photo 5: Side view Servo in bracket
SECTION 4: WOOD MOUNTING SHEET
Now that the servo bracket has been fabricated and assembled, all
that remains is to securely fasten the bracket to the boat hull.
Rather than glue the bracket directly to the hull, a wood sheet will
be glued into the hull and then the aluminum bracket will be screwed
on to the sheet. The wood sheet provides a large gluing area in the
hull and thus allows for a very strong bond to the hull, while the
use of screws to fasten the bracket to the sheet allows ease of
servo removal for maintenance or repairs.
Select the location within the hull where the servo is to be
installed. Typically this will be near the stern of the FE boat and
in such a position that a simple straight push rod can be used to
control the rudder arm. Photo 7 shows a typical location for a
hydroplane model boat. There must be sufficient space to accommodate
the servo, bracket and a plywood sheet under the aluminum bracket.
4.2 Wood Base Sheet::
The small plywood sheet to be glued in the hull should be at lease
5/32 thick, and should be slightly larger than the base foot
print of the aluminum bracket. The larger the sheet, the stronger
it will be glued in the hull.
Trace the outline of the aluminum mounting bracket, and the base
plate holes, onto the stock plywood. Trace a slightly larger outline
around the bracket outline and cut the plywood to these traced
dimensions. Test fit the aluminum mounting bracket and drill 1/8
diameter holes through the plywood base at the marked hole locations
for the bracket.
Turn the wood base over and press or tap the #4-40 blind nuts into
the underside of the base sheet. Make sure the blind nuts are flush
with the bottom of the wood sheet. The underside of the finished
base sheet, with the blind nuts installed, is shown in Photo 6. Test
fit the servo bracket and screw the bracket onto the base sheet
using the #4-40 cap head screws, lock washers and flat washers. The
screws will be longer than required and will protrude beyond the
bottom of the wood base sheet. Mark the screws where they protrude,
remove them and cut them to the correct length so they do NOT extend
beyond the bottom of the wood base sheet when the screws are fully
Photo 6: Underside of the plywood sheet with #4-40 blind nuts
4.3 Installing the Sheet
The servo mounting location should be prepared for gluing of the
wood sheet by sanding the surface with 220 grit sandpaper and wiped
clean. Test fit the wood base sheet, with the servo and bracket, in
the hull to find the correct final mounting location. Mark this
location in the hull. Remove the aluminum bracket from the wood
sheet to avoid any CA glue from getting onto the #4-40 screws.
Roughen the underside of the wood base sheet and glue it onto the
hull using medium CA glue. Be careful not to get CA glue on the
blind nut threads. Photo 7 shows the wood base sheet glued into the
Photo 7: Wood base sheet glued in hull
SECTION 5: INSTALLING THE SERVO
After the base sheet has been glued into the hull, simply screw the
aluminum mounting bracket (with the servo already installed), onto
the base sheet.
Install the desired servo arm on the servo and pushrod connector on
the arm. In this example, an adjustable arm is shown in Photo 8. The
adjustable arm makes it easy to obtain the desired rudder throw by
shortening or lengthening the arm as desired. As shown in Photo 8, a
Du Bro E-Z connector will be used to attach the pushrod to servo
Photo 8: The completed servo mount installed in a hydroplane hull
The techniques descried in this article can be
used to install a steering servo in a hydroplane hull as shown in
Photo 8 or a monohull as shown in Photo 9.
Photo 9: The completed servo mount installed in a mono hull
This method of installing servos has been developed with tips and
guidance from fellow FE racers at Metro Marine Modelers in Toronto,
and other RC hobbyists. I wish to acknowledge and thank all those
that have given me helpful suggestions and advice over the years.
Thank you to Steven Vaccaro of Offshore Electrics for posting this
article so others may pick up some tips and get hooked on Fast
Electric RC boats.