MexAir RC X4MR 250 User manual

X4MR250 MexAir RC
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X4MR Manual
(See our website www.mexairrc.com for our upcoming video series on X4MR Construction))
Introduction
Congratulations on your purchase of the MexAir RC X4MR 250 FPV Race Quadcopter. This quad has
some very unique design features that allow for advanced flight characteristics. The built-in
configurations enhance maneuverability, speed and load handling capability. Some of these are
described below and throughout the build sections of this manual. Besides the advantages described
below are the less obvious materials making up the airframe. Most quality multirotors use some form of
carbon fiber in their design. We have chosen the more costly but highest quality aerospace quasi-
isotropic carbon fiber. Rather than describe the benefits of this material, especially when used in
conjunction with a light-weight core, you may wish to simply “Google” the terms to find the vast amount
of technical data supporting the use of this grade of carbon fiber in light-weight rugged, rigid, and strong
applications.
MexAir RC, located in Central New York, is the designer and manufacturer of the X4MR 250 Class
Racing Quad airframe. We specialize in the design and construction of the airframe. Since the various
electronic components and peripherals are widely available through many sources, our focus is on
providing a unique platform for the already available devices. The experienced builder will already know
much of the information –but we decided to cover details not always found in build manuals –
especially considering some of the unique features of the X4MR.
The X4MR carbon fiber laminated airframe design, materials, and methods of construction create an
assembly that allows for:
Enhanced aerodynamics due to the ability to embed wiring within airframe structural
components thus reducing turbulence and drag
Elimination of the typical “lightening holes” in areas of the airframe to improve strength and
rigidity, additionally reduce turbulence, while at the same time reducing airframe weight when
compared to typical solid carbon fiber frame materials used in many other multirotor copters
Reduced induced vibration through use of vibration damping body & arm core material –
resulting in better video quality
Electronic component placement flexibility due to:
oease of mounting additional accessory items to the CF frame using simple self tapping
screws
Completed X4MR Airframe
Total Weight as
Pictured: 111 Grams

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oadditional space on certain surfaces of the frame when using embedded wiring
Top and bottom plate mounting using thru-layer tie-rods and fasteners creating a rigid structure
required by high power motor systems
Variable motor arm positioning that allows for
oFine adjustments to center of gravity
ovariable motor placement to enhance maneuverability
omotor arm “swing away” deflection on a hard-hit thus reducing crash damage potential
The X4MR 250 kit includes all the frame components and fasteners necessary to construct a 250 class
racing quad using electronics of your choice. You will receive the airframe in an already assembled state.
We have done this for you so that you can see how the frame should look when completely assembled.
It is expected that you will disassemble some of it during the build. The instructions that follow assume
that you simply received the kit in a completely disassembled state.
The airframe comes configured to mount the supplied Power Distribution Board with the included PDB
standoffs and predrilled main frame mounting holes. This PDB mount allows for “piggy-back” mounting
of a 30.5mm controller board using additional standoffs. The frame body already has embedded wire
leads to solder the included LEDs to both the front and rear to assist in visual orientation during flight.
The motor arms have internal wire cavities that allow for embedding the motor wires up to the main
frame and the speed control bottom plate.
X4MR Kit Contents: (See Accompanying Pictures)
1. Main Frame Body w/preinstalled LED wiring
2. Motor Arms (4)
3. Top Plate [To mount FPV Gear]
4. Bottom Plate [To mount ESCs]
5. Camera Plate [To mount forward looking camera]
6. Landing Gear Legs, Boots, and Mounting Hardware (4 sets)
7. Power Distribution Board [3oz copper PDB for higher
current applications]
8. LED Boards, 4S LiPo Capable (Front & Rear)
9. PDB Mounting Standoff Set
10. Plate Mounting Standoffs/Hardware Set
11. “Hook & Loop” Battery Strapping Material
12. Alternate 3mm motor mounting screws (16) if your motor screws will not fit properly
13. Double Backed Insulating Tape
1
2
3
4
5

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Other “stuff”typically installed on a racing multirotor frame includes:
Flight Controller Board
Motors
Propellers
Speed Controls (ESCs)
FPV Gear and cameras
Batteries and Battery Connectors
In some frame designs, including the X4MR, there are varying options for positioning and mounting
components. We listed options for those that have shown to be useful and tested successfully with the
X4MRs we build in-house.
Recommended Options:
Voltage Regulator(s)
oNote: If you do not have 5V and/or 12V supplies that may be necessary for your camera
systems, these can be handy add-ons wired direct to the supplied PDB.
Satellite receiver vs. standard receiver?
oTesting with a Spektrum satellite receiver showed no adverse effects on range or signal
reception. It is a good lightweight alternative to traditional receivers due to small size
and less wiring as might otherwise be necessary. It can be mounted almost anywhere
on the X4MR airframe.
General Guidance to make assembly faster, easier and safer:
1. Read through the assembly instructions completely PRIOR to beginning construction.
2. Inventory all kit supplied parts, your electronics and tools, organizing them according to your
intended build. Do not forget about any general supplies such as solder, heat shrink, small tools,
etc.
3. Use small amounts of blue loctite thread locker on all metal-to-metal screw contact surfaces,
especially motor mounting screws.
4. “Dry-fit” and test all electronics and FPV gear, to the extent possible during the build, so
disassembly will not be required after you have completed the frame assembly.
5. Pre-plan purchase of motors that have sufficient motor wire length and diameter to allow for
embedding the wires into the motor arms. The minimum length of the leads should be 4 inches.
The wire diameter, including insulation, should be a maximum of 1/16” (~20 gauge) to fit into
the arm holes. If larger, the holes can be widened as described in this manual. Alternately, any
wire length or diameter can be used by surface mounting them.
6. Take care in soldering components to prevent shorting between solder pads or overheating any
sensitive electronic components.
7. Although the skills, techniques, and “hazards” associated with this build are typical for many
hobby related activities, we always strive for safe and efficient construction techniques. We
therefore repeat here what you have likely learned from your previous experiences:
a. The X4MR airframe kit does not require any drilling for the typical build. If drilling
holes in the carbon fiber (CF) for self tapping screws or larger component attachments
use a sharp drill bit and work with light pressure and a relatively high speed drill. CF can
not be “punch marked” for drilling. A small electric rotary tool or drill press is
recommended to prevent the bit from “wandering” as you start the hole. Wear
appropriate safety gear, including air mask/filter, if creating carbon dust.

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b. Always wear appropriate safely gear or take other precautions during any operation
that could create a hazardous condition –including soldering, drilling, cutting and
grinding.
8. Carbon fiber is a conductive material. Never allow bare battery terminals or other
powered connections to physically come into contact with the carbon fiber or metal
components of the frame. Contact may create short circuits that may damage
electrical components and/or become a fire hazard. Always insulate powered
terminals from the frame using nonconductive materials such as electrical insulating
tape, heat shrink tubing, or plastic/nylon standoffs or mounts.
9. NEVER attempt to screw any component into the carbon fiber frame without first
carefully drilling the appropriately sized hole at the fastener location. Self tapping
screw/bolt hole sizes are slightly larger than the inner diameter of the threaded
portion of the fastener. When tightening a self tapping fastener, it may be necessary
to start tightening it, back it out slightly, repeating this process until the fastener is
threaded to the proper depth. This creates a threaded hole that should hold firmly
without any other aid. For added assurance, use the time-tested technique of
“hardening” the laminate core material AFTER you create the threads using the self
tapping fastener. Remove the fastener from the hole and carefully drip 2 –3 small
drops of thin CA into the hole. The CA will “wick” into the core thread area and harden
the core material. Allow sufficient time (usually only a couple of minutes) for the CA to
completely dry prior to reinserting the fastener. You do not want to glue the fastener
permanently in the hole! Hardening the laminate core material, although not typically
necessary, is only done if you intend to insert a threaded fastener that will be
tightened across the laminated surfaces causing significant compressive forces on the
laminate structure. Hardening reduces “dimpling” the surface when compressed. The
laminate structure is sufficiently strong and some dimpling is not a bad thing –it
actually acts to further reduce the possibility of fasteners loosening. Excessive
tightening is unnecessary.

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Construction of the X4MR Airframe
1. LEDs (LED Boards supplied with this kit can be run direct to 4S LiPo power without any
voltage regulator)
a. The preinstalled LED power leads feed through the body of the frame and exit the
frame conveniently below the PDB position. Do not permanently connect the power
side of the leads to the PDB or power source at this time. Permanent installation
should be done after final placement of the PDB, any necessary voltage regulators,
and speed controls.
b. Place the main frame body upside down. First, gently push the LED wires a slight
amount into the wire exit hole and then pull gently to see how much slack wire you
have to work with. Note the slack amount. Strip the remaining insulation leaving the
amount of insulation you determined as slack.
c. Cut the excess bare wire leaving about ¼” bare. Tin the bare end.
d. If your kit was supplied with single color wires, trace the wire from the LED location
to the planned source end with an ohm-meter. Mark both the positive (+) and
negative (-) wire ends at the main body hole (the large elongated hole). You can
always trace the polarity later during the build if you forget to do it now. If supplied
with colored wires, the red (or white) wire will always be intended as the positive (+).
The other wire is the negative (-).
e. Solder the LED board to the wires paying attention to the proper polarity. Measure
and cut a small strip of supplied double backed tape the same size as the LED board.
[This is very sticky stuff! You may want to handle it with the tip of a small hobby
knife blade rather than your fingers.] Apply the sticky side between the wire holes
on the body underside. Remove the remaining tape backing.
f. At this time you should be able to push the soldered wires of the assembly slightly
into the body so the board will lay flat to the tape. Readjust as necessary.
g. Verify that the bare metal of your solder joint is not touching the carbon frame body
and the board is fully insulated from the body by the tape.
Wires Fully Extended
Partially into Body
Insulation Stripped
Soldered to Board
Double Backed Tape Applied to
Bottom of Board or Frame
Tape Backing
Removed, wires
pushed into holes &
LEDs Pressed Into
Place

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2. There are two possible locations to mount the PDB and/or controller board. Note that
there are six standoff hole locations. Use either the forward or rear sets depending on your
needs. The rearward set places the controller more toward the center of the body –closer
to the center-of-gravity. Flight testing using a Naze32 in both forward and rearward
positions did not seem to affect performance –so it becomes a matter of personal
preference. Install four PDB standoffs “upside-down” as shown in the accompanying figure.
The nylon screw is hidden within the frame body minimizing any possibility of interference
with motor arm placement. The female end of the standoff is placed over the 3mm hole on
the main frame top and the screw is inserted into the frame 5mm hole from the underside.
Hand-tighten the posts to their respective screws by holding the screw in place with a
screwdriver. Complete tightening using the screwdriver while holding the standoff in place.
Take care not to over-tighten the standoff and shear off the screw. For added assurance to
prevent the screw from ever backing off, a small dab of RTV/Silicone Seal can be placed on
the threads using a toothpick. The screw can be removable if necessary. Alternately, a drop
of CA can be used while the frame is held upside-down. This will be permanent and any
future standoff removal will require breaking off the standoff and replacing it with a new
one.
3. Installing the motors
a. Verify the appropriate length of your motor screws and always mount them so there
is sufficient thread into the motor frame, but not so much as to touch the internal
components. Doing so will damage your motor. If your screws will not work and
you have motors with 3mm mount threads, the set of 3mm motor screws included
in the kit will likely work for you.
b. For screws less than 3mm diameter you may need to install the screws with a flat
washer to increase their contact surface area against the CF skin.
Screws Placed in
5mm Holes From Bottom
Screws Pushed Through
To Other Side (Top)
Standoff Placed over 3mm
Hole on Top & Threaded to
Screw

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c. When initially dry-fitting the motor in the following sections and on final tightening
of the motors, verify that the motor shaft is centered in the arm shaft hole and that
there is sufficient clearance from any shaft hardware. Some motor shafts have a clip
or setscrew that secures the shaft in the motor. Visually verify that the clip/setscrew
will not contact the edge of the hole. Turn the motor rotor by hand and again verify
sufficient clearance all the way around.
d. Embedded Wire Option (for typical 20 gauge motor wires –size for many high power
2000KV motors)
i. It is possible to widen the three motor wire holes for wire sizes greater than
20 gauge using a small, round needle file inserted at an angle toward the
arms body end. The hole is already predrilled at an angle to allow pushing
the lead through and toward the body without binding. The intent here is to
ultimately thread the leads into the three holes and into the arms cavity and
out to the body end leaving sufficient wire to reach the solder pads or
connectors with some excess. The excess allows the arm to pivot to its
maximum angle without tightening or binding.
ii. Align the motor mount holes to the motor mounting slots of the arm with
the motor wires facing the three motor wire holes in the arms. Verify that
there will be sufficient wire to reach your intended ESC solder pad locations
or connector. A minimum wire length of about 4 inches is necessary. If not,
use the “Surface Wire Option” described below. A solder joint will not fit
through the hole unless the hole is widened as described above.
iii. If your wires have pre-installed connectors, they must be removed. If the
wire insulation is not uniquely colored, note which wire is threaded into each
hole by tagging or marking the bare end after each is pulled through. This
will aid in attaching to the correct pads on the ESCs for proper motor
rotational direction. This step may not be necessary should your ESCs have a
reverse motor option and you plan on setting direction using this ESC feature.
iv. Avoid kinking the wire/insulation while snaking the motor wires into the
holes and out the other end. There is a curvature to the channel so it may be
necessary to give the end of the wire a slight bend to follow the curve near
the exit of the channel. First insert the outermost motor wire into the
corresponding hole. Gently push the wire through the arm until you can pull
it out at the body end. The middle wire is next then the third. It may take a
couple of tries until you get the hang of it –and yes –it can be done! You
may need to manipulate the wires past the leg hole in the arm if it hangs up
there. You will be able to see the wire through the leg hole and manipulate it
Needle File to Open Motor Wire
Holes ONLY if Necessary

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from the outside with a thin/blunt pointed object. Do not cut off any excess
motor lead at this time.
v. Bolt your motors to the arms while carefully pulling from the body end any
excess wire loop at the motor.
e. Surface Wire Option –easier to install , but less aerodynamic
i. Lay out your wires as described above to determine where you will fasten
the wires to the arm. Drill small holes all the way through the arm on
opposite sides of the wires to securely mount them to the arm using small
“tie-wraps”.
ii. If using this option, you may also consider surface mounting your motor ESCs
directly on the arm surface. Again, this will additionally increase drag and
turbulence and expose the components to possible unprotected crash
damage.
iii. Bolt your motors to the arms and fasten the wires as appropriate for your
configuration.
4. ESC installation
a. Prior to permanent attachment, note the depth of the bottom plate below the main
body frame. The depth below the mounted motor arm and the bottom plate will be
about 9.7mm. The depth between the main frame and bottom plate is about 14
Enough Wire
Laid Out with
Some Excess
3 Motor Wires
Through
Motor Wires in
Place

X4MR250 MexAir RC
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mm. This allows ample space for ESC mounting. If not already done, dry-fit the
arms and bottom plate to the main frame should there be any doubt.
b. For unwired/bare ESCs, with the exception of the motor wires, pre-wire your ESCs.
Use enough wire to reach their intended termination. A bit of excess length is
recommended until the PDB, flight controller, and other peripherals are fitted in-
place.
c. Slip the appropriate length of heat shrink over the ESCs and beyond the ESCs over
the input power leads and signal/ground leads PRIOR TO SOLDERING the motor
wires (to be soldered on later). This will allow for soldering the motor wires later
and THEN moving the heat shrink over the ESCs prior to final shrinking.
d. TEMPORARILY place the ESCs onto the bottom plate so that the motor pads face the
side of their intended motor arm. [There are other options available including PDBs
intended for ESC mounting.] You may solder the motor leads to the ESCs at any
convenient point during final frame assembly. After soldering the motor leads,
move the heat shrink tubing completely over the ESC to cover all exposed bare
wiring and solder joints. Shrink the tubing at this time.
e. Firmly mount the ESCs to the bottom plate using double backed tape (“servo tape”)
supplied with this kit or mount using any other suitable method.
14mm
9.7mm
View of Spacing Between Bottom
of Body and ESC Mounting Plate

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5. Frame Assembly
a. Assemble the balance of the frame as you complete the final wiring of your
electronics. See the accompanying photos for airframe standoff placements. Note
that the upper standoff CF tubes are embedded into the main frame. They insert
into the upper side of the main frame body and rest on the lower skin surface. Prior
to insertion, check that the hole is clear of any obstruction. When finally tightened,
this creates a very rigid frame. Temporary and partial frame assembly may be
desired as you progress through assembly.
CF Tube Standoff Configuration
(Steps 5a through 5e Completed)
b. Final tightening of the frame standoffs is done after all soldered / permanent
equipment is installed. The camera plate must be inserted into the front upper and
lower slots completely while the forward standoff fasteners are loosely fitted. The
camera plate should rest squarely on the main frame body and top plate surfaces.
Camera Plate Configuration

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c. With the motor arms held loosely in place, thread the aluminum cone nuts onto
their respective threaded rod (rear arm) and 4-40 SS screw (front arms). The cone
nut should be threaded on so it will leave sufficient thread for spacers and
engagement with the knurled nuts. See the preceding pictures. All standoff knurled
nuts should then be tightened snugly by hand. Note that the supplied cone nuts
holding the rear motor arms in place are tightened by turning the top knurled nut.
The front arm set is tightened by turning the supplied 4-40 steel screw. Do not over-
tighten.
d. Attach the bottom plate using the aluminum spacers and nylon thumb-nuts. Each
motor arm uses a 5mm spacer and the middle spacers are made up of two 7mm
spacers each or a 9mm plus 5mm spacer (depending on what is supplied in your kit).
Tighten the plate firmly. Readjust the hardware placement if necessary.
e. Take the main frame by hand and apply a moderate twisting force to the main frame.
The frame should feel solid as if it is one piece. If there is any noted slipping or twist,
verify that all standoff fasteners are properly tensioned.
f. Landing Gear Installation [Note: Nylon landing gear can be cut to desired length]
i. Embedded Motor Wires
1. Looking through the landing gear holes you will likely see that the
motor wire(s) may interfere with the landing gear (LG) installation.
Using any thin blunt object simply move the wires to the side and out
of the way. There is enough space in the cavity to make room for the
LG. Install the LG screws.
ii. Surface Mounted Motor Wires
1. If the wires cover the landing gear (LG) holes, move the wires apart to
make room for installing the LG and prevent pinching a wire under
the LG head. Install the LG screws. The wires may be moved back
and rest on top of the LG head.
iii. Slide the plastic boot over the leg. The boot may fit tightly and may need to
be “worked” onto the leg. When installed, it should not come off easily. If
loose, remove the boots and place a small amount of RTV / Silicone Seal or
similar pliable glue to the lower threads of the legs. Fit the boots back over
the leg and stand the completed airframe on a flat surface until the glue
hardens securing the boots in place.
Landing Gear Screw and Boot Installed

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g. Final Adjustment of Motor Arm Position & Tension
i. The motor arms are designed to intentionally pivot at the single mounting
point.
ii. The motor arm is typically mounted at about 60 degrees from the main
frame (see picture below). This is a good starting point for most applications.
Verify that your propeller will not interfere with the main frame standoffs.
The arm length is designed to accept a 5 inch prop without interference.
There should be no noted “slop” and the arms should feel firmly seated in
position, yet should pivot with moderate force. Tighten/loosen the arms as
necessary so that they are firmly seated but can pivot with moderate force.
Do not over-tighten to cause excessive dimpling of the laminate or possibly
sheering the aluminum threaded rod.
PROPER ANGLE AND ANGLE TEMPLATE
iii. Repeat the above steps when realigning the arm(s) after a crash. Inspect for
damage to the arm or frame. Always repair or replace broken structural
parts prior to use.
iv. The positioning of the motor arms can be varied from 60 degrees to affect
flight characteristics, including the location of the center of gravity (CG).
Contact Us:
MexAir R/C
Ph: 315.532.6826
Web: www.mexairrc.com
Mexico Air, Sea & Land Radio Control Hobbies, LLC
329 Pople Ridge Road
Mexico, New York 13114