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Created expressly for tail-rotor duty of helicopter models ranging from 500 through 800-class, this ultraspeed, narrow-band, standard-size, HV (high voltage) servo is water-resistant and features a brushless motor. Made of high-impact engineering-polymer, it's significantly lighter than an all-aluminum servo. Designed with tank-like durability in mind, this servo is a great choice for 3D-pilots conscious how every single gram adds up. Is it the right servo for you? Just eyeball the features to see how well it matches up with your requirements.
Features at a glance:
- CNC-machined 6061-T6 aircraft aluminum motor-section for superb cooling of the HV motor.
- Lightweight engineering-polymer- an über-strong Nylon 6,6 like what's used in Glock handgun frames.
- Assembled with ten grade 12.9 Allen-head machine-bolts - not el cheapo Phillips-head screws.
- Metal gears - stronger, last longer, and more crash resistant - 25-spline - Ø5.96 (Futaba compatible).
- Brass gear-shaft inserts - these reinforce the servo top case to preclude the holes getting wallowed out.
- Brushless motor - no matter the claims, it's our experience these are much more reliable than coreless-motors.
- Million-cycle Nobel potentiometers - the best money can buy - ensuring many years of service.
- High voltage - rated for 2S LiPo or LiFe battery packs versus old fashioned NiCds
- Fully-captured o-rings - for resisting water and exhaust oil - after all, exhaust fumes and pop-up rain showers happen.
- Dual ball bearings - ensures the high precision lasts for many years to come.
- Epoxy potting compound - for better vibration resistance - competitors often use none.
 
Accessories - included are an assortment of three 25-spline
(Futaba-compatible) servo arms (cross, star, and round). They're made of tough
fiber-filled engineering polymer, which is better than ordinary plastic arms
because they're super strong and won't deflect under flight loads. Along with
rubber grommets, brass eyelets, four truss-head screws, and one M3x6mm long
machine screw, they complete the included hardware package.
- Standard assortment of 25-spline (Futaba-compatible)
servo arms, eyelets, dampers, and wood screws
Since the tail rotor servo usually mounts aft of the main rotor, our goal was
to reduce the weight of our HV brushless tail-rotor servo by using
engineering-polymer instead of aluminum. Making the job harder is the tail
rotor servo constantly moves with incredible quickness, so the design had to be
ultra rigid. And to preclude wear, we needed to reinforce the polymer so the
servo would last just as long as one made of metal. By dint of great
engineering, we succeeded . . . here's how.
Engineered-polymer upper and lower case with brass inserts -
the S120BLHV foundation, the center case, is CNC-machined from a solid billet of
6061-T6 aircraft aluminum. Like a radiator, it keeps the powerful HV-motor nice
and cool. To save weight we use fiber-filled Nylon 6,6 (an engineering-polymer
like that used in a Glock handgun) because it's ery strong and
resists stresses imparted by the constant motion generated by a gyro.
To assure durability equal to an all-metal case, we resorted to reinforcing
the polymer with brass inserts created with a Swiss lathe pressed into
molded pockets for the steel gear-shafts. End result? The precision and
durability of aluminum without the weight.
- Bronze inserts where the steel gear shafts ride in
the polymer upper-case ensure long lasting precision gear-mesh.
Gear train - all metal gears makes this servo
strong. Material selection makes it tough. Exotic titanium-ceramic (TiCN)
armoring of the 7075-T6 output gear (same aluminum-alloy used in components of
the upper receiver of an M-16 rifle) means this massive gear has an 800%
increase in wearing surface hardness. Combination-gears mate C86300
manganese-bronze with 4140 chrome-moly steel for optimum strength and wear
characteristics.
- TiCN/7075-T6 output gear, plus bronze/4140 chrome-moly
steel combo-gears perfectly match durability with strength.
O-rings - have you noticed how some really expensive servos
don't have o-rings? The claim is electric models make them superfluous. Since
getting caught in a pop-up rain shower isn't unheard of, and re-purposing servos
into a nitro-powered model a year later happens all the time . . . do you buy
that line of reasoning? We figure it's because the manufacturer pockets a few
extra bucks - but leaving o-rings out comes at your expense because keeping
water, fuel, and exhaust residue out of your servo is important. Wanna know why
the S120BLHV is fully o-ringed? Simply because our engineers make these
decisions instead of our accountant.
- Now you see them, now you don't . . . fully captured
hidden o-rings make the case resistant to water, fuel, and oil.
Nitty gritty - it's said the measure of a man is what he
does when nobody is looking - take our servo's measure the same way. Ever
disassemble a servo? They typically use four long-ass Phillips head screws,
which come up from the bottom, sandwich the center section, and actually thread
into the plastic top-case, right? However, an S120BLHV is built better. How? To
begin, we use grade 12.9 Allen-head machine-thread bolts instead of el
cheapo screws. Six come in from the top plus four more from the bottom, and
instead of sandwiching the center case, the ten bolts actually thread into the
aluminum. The result is a far more rigid assembly that's so much better . . .
it's not even fair to compare!
.
- Note how an S120BLHV servo is assembled with Allen-head
machine-bolts vs. el cheapo Phillips-head screws!
Packaging - nestled within a high density foam insert for
protection, each S120BLHV servo arrives packed in a jewel case. Since good looks
never hurt, we use red polymer to show off our brand and laser-etched our logo
into the polished aluminum center-case. These servos look great - think in terms
of the fit and finish equal to, or better than, servos selling for more than
$200. Bottom line? For the craftsmen who appreciates our high standards because
we pay attention to the smallest detail, we hope you'll be as proud to install
them in your model as we are to make them.
- We proudly brand our product with the ProModeler logo .
. . and hope you'll be as proud of them as we are.
Hooking up servos to the control surfaces sometimes require heavy duty servo
arms. Since one size doesn't fit all, we offer two completely different
approaches. One approach features servo arms CNC-machined from a solid billet of
6061-T6 aircraft aluminum. Broached to fit our 25-spline output shaft (Futaba
compatible), these are perfect for applications ranging from throttle and choke
to flight controls of models as large as 42%. The other approach relies on
uber-strong fiber-filler engineering-polymer (in both single and double arm
style) to handle the loads. Pick your poison!
- PDRS004 - this 20mm aluminum arm is great for throttle
or choke, as well as cyclic and tail rotor controls on helicopters.
- PDRS007 - this 22mm long 4-hole heavy duty arm is a
great for general purpose use.
- PDRS008 - this 51mm long double-side 4-hole heavy duty
arm is a handy.
Nominal Voltage*: 6.0 - 7.4VDC
Operating Voltage: 5.5 - 8.4VDC
Torque:
90 - 120 oz-in
Speed: 0.05 - 0.03 sec/60°
Frequency: 760µs/560Hz
Dead
band: 2µs
Weight: 73.5g
Wire: JR/265mm
NOTE: deciphering the parts code - PDRS120BLHV means:
- PDR = ProModeler
- S =Servo
- 120 = oz-in - torque
- BL = brushless motor
- HV = high voltage
*Nominal voltage - for a LiPo cell, it's 3.7V/cell (or 7.4V
for a 2S pack). Yes, a 2S pack fresh off charge reaches 8.4V - but the voltage
depresses nearly as soon as you load it. This is why we offer specs at nominal
voltage. What this means in a practical sense are specs generated at real world
voltages because inflating specs is a fool's game (and a matter of questionable
ethics). Remember, the figures don't lie . . . but the liars
figure!
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