Evils’ Younger Brother
Earlier his year, SAB Heli Division, makers of high-quality rotor blades, introduced their first helicopter, the Goblin 700. Rather than copying existing designs they decided to break free and introduce something that is completely unique. Their gamble paid off and the Goblin 700 was an instant hit. Not resting on their laurels, SAB decided to slightly shrink the airframe, but still allow the same power systems used in the 700 class machine. The result is the Goblin 630, an insanely powerful helicopter that is strong enough to take the abuse of hardcore 3D flying. Let’s take a look at what the Goblin 630 is all about!
The SAB Goblin 630 defines a new size class of RC helicopters. It has all the power and authority of a 700-class helicopter with the quickness and agility of a 600. With the recommended power system, it is absurdly powerful and totally awesome to fly. The unique construction with the wrap around canopy and the large tail fairing make it exceptionally easy to track in the sky, even during super fast speed runs.
Need To Know
MANUFACTURER: SAB Heli Division
DISTRIBUTOR: Heli Direct
TYPE: Flybarless 3D electric
FOR: Intermediate to advanced pilots
PRICE: $789.99 airframe only; $1199.95
with blades/motor/flight batteries
What We Used
TRANSMITTER: Futaba 8FG, FUTK8010
RECEIVER: Futaba R617FS, FUTL7627
CYCLIC SERVOS: (3) Savox SC-1267SG, savsc1267sg
TAIL SERVO: Savox SB-2272MG, savsb2272mg
GYRO: MSH iKON flybarless controller, IKN1001
MOTOR: Quantum 4135- 530KV, 4135-530
ESC: Castle Creations ICE 120HV ESC, 010-0085-01
RECEIVER BATTERY: Hobbico Life 2S 2100mAh, HCAM6435
FLIGHT BATTERIES: (2) Pulse 6S 3700mAh 45C LiPo, PLU45-37006
FLYING WEIGHT: 10.1 lb. (4586g)
LENGTH: 50.79 in. (1290mm)
HEIGHT: 14.96 in. (380mm)
WIDTH: 8.82 in. (224mm)
ROTOR SPAN: 56.22 in. (1428mm)
ROTOR DISK AREA: 2482 sq. in.
ROTOR DISK LOADING: 9.38 oz./sq. ft.
TAIL ROTOR DIAMETER: 10.94 in. (278mm)
RADIO: Flown with Futaba 8FG transmitter and a Futaba R617FS 7-channel receiver
SERVOS: Three Savox SC-1267SG super speed, steel gear servos for cyclic, Savox SB-2272MG high speed brushless tail servo
GYRO: MSH iKON Flybarless Controller
POWER SYSTEM: Quantum 4135- 530KV outrunner brushless motor and Castle Creations ICE 120HV
BATTERY: Hobbico Life 2S 2100mAh receiver pack, Two Pulse 6S 3700mAh 45C LiPo flight packs
MAIN ROTOR RPM AT HOVER: 1900
DURATION: 3-8 min, depending on power system used and flying style
MINIMUM FLYING AREA: RC flying club or large park
Components Needed To Complete
Brushless motor, ESC, 6+ channel radio system with heli programming, three cyclic and one tail servo, two 6S 3500-4000mAh LiPo batteries, BEC or suitable receiver battery and suitable connectors for the batteries
Material: aluminum box frame gear box and carbon fiber side frames
Type: Two-stage transmission with timing belt on the first stage and helical gear second stage
Servo linkage type: Direct swash to servo linkage
Grips: Machined aluminum
Head block: Machined aluminum
Links: Rigid links off blade grip pitch arms
Swashplate: Machined aluminum with steel balls
Mainshaft: 12mm steel
Drive system: Timing belt drive with spring loaded tensioner
Auto capable: Yes, tail is driven during autorotation
Tail pitch slider type: Aluminum with brass sleeve
Tail blade grips: Machined aluminum, with dual radial and single thrust bearing
Tail case: Carbon side plates/aluminum standoffs with ball bearings
Boom strut material: Molded carbon fiber/epoxy composite
Tail fins: Carbon fiber
Main rotor to motor: 1:9.7 (21T pinion/204T main)
Main rotor to tail: 1:4.66
• Prepainted canopy and tail fairing provide a unique look, low drag and great visibility in the sky.
• Very robust two-stage transmission encased in rigid aluminum frame.
• Crazy powerful with recommended power system.
• Wrap around canopy can be tricky to remove and install.
• Main flight battery must be partially extended off battery tray to get proper CG.
The main rotor of the Goblin 630 is a slightly scaled down version of the 700’s head, but is still remains very beefy. It is fully CNC-machined, with both radial and thrust bearings incorporated to handle the flight loads. The grips and main rotor center block come already preassembled out of the box with all necessary bearings and fasteners installed. The feathering spindle is a stout 10mm in diameter, while the mainshaft is 12mm in diameter and is hollowed out for less weight. Rather than having a separate swash driver, the inner star of the swashplate is driven by rigid pitch links that are connected directly to the main blade grips. The pitch links have left handed threads on them so they work like turnbuckles, allowing very fine length adjustments to get the blade tracking perfect.
The main chassis of Goblin 630 shares many of the same parts of the Goblin 700, with the exception of the ESC mount. Instead of being machined aluminum, it is made out of a piece of flat carbon fiber, to save some weight. Otherwise, the main chassis is identical to that of the 700. Rather than use the main carbon side frames as stressed members, the Goblin mounts all the critical parts to a series of CNC machined aluminum blocks. This ensures that the parts that see the highest loads are also the strongest and most rigid. It also ensures that the gear mesh between the main gear and its pinion is near perfect. A two stage transmission is used between the motor and the main rotor. With an effective gear ratio of 9.7:1, it uses a high-strength timing belt drive for the first stage and helical gearing for the second stage. The tension of the belt is set by a built in spring; all that is required to properly tension the belt is to loosen the motor mounting plate from the frames, allow the spring to push the mounting plate to the intended position and then retighten the screws.
Power for the tail rotor is taken off of the intermediate shaft that sits between the motor and the main shaft. Rather than having a round tailboom and boom supports, the Goblin uses a molded carbon fiber tail fairing that is much larger than a regular tailboom. Because of its larger size, it is extremely stiff all by itself and doesn’t require tail boom supports. In addition, the larger cross-section allows much larger tail pulleys, increasing tail belt life and power transmission capacity.
The rear tail box is composed of carbon fiber side plates separated by round aluminum standoffs. Rather than sliding the entire tail assembly, only the tail box slides on the tail fairing to tension the belt. A second belt tensioner is mounted in the chassis to set the proper belt tension. The tail box is adjusted on the tail fairing until the flat side of the tensioner is even with the side of the frames. This really simplifies the process of obtaining the optimum belt tension.
The tail rotor is as equally robust as the main rotor. Rotating on a 6mm diameter shaft, it’s all metal and fully ball-raced. A carbon fiber pushrod transfers motion from the boom mounted tail servo to the metal bellcrank. A plastic bracket supports the pushrod mid span to keep it from flexing.
The manual does a great job of providing suggestions as to where to mount all of the electronic components. The ESC installs on a tray in the bottom front of the frames, and there are several ways to mount the receiver and flybarless controller. I used the included gyro mount that sits just behind the mainshaft and it holds both the iKON flybarless controller as well as the Futaba R617FS receiver that I used.
For the swash servos, I used three Savox SC-1267SG servos. Having metal gears, they are rated an astounding 291oz./in. of torque with a .11s/60 degree transit time. Be sure to mount the servo arms in the proper orientation prior to attaching them to the helicopter as once they are installed, it becomes very difficult to access the servo arm mounting screws. For the tail servo, I used a Savox SB-2272MG servo. At 7.4V, it has a blazing .032s/60deg transit time, with a stout 97 oz./in. of torque.
The manual lists several different motor/ESC combinations and recommended pinions depending on the flying style desired. I used a Quantum 4135- 530KV outrunner brushless motor driven by a Castle Creations ICE 120HV ESC. Two Pulse 6S 3700mAh LiPo packs provide electrons to power the motor while I used a Hobbico LiFe 2S 2100mAh pack to power the receiver and servos.
In The Air
After a quick pre-flight to ensure that everything is working in the proper direction, it’s time for the Goblin to take into the air. I set the Castle Creations 120HV into governor mode and the first thing to do was to adjust the throttle curves unit to get a reasonable head speed. I gradually increased my flat line throttle curves until I got the head speeds that felt about right. Here were my results that I was able to extract using the data logging feature of the Castle Creations 120HV:
(0% to 100% scale)
|Main rotor RPM||Current draw (A)|
Due to the rigid pitch links in the rotor head, the head dampers have to be very stiff to prevent over flexing the pitch links. Unfortunately, stiff head dampers and low head speeds result in wobbling of the main rotor. The cure is to gradually increase the head speed until the wobble goes away. On the Goblin 630, this happened around 1900 rpm. With a measured current draw of about 20A, flight times can approach eight minutes of smooth, non-3D flight.
Once I was able to dial in a proper head speed, I was really able to appreciate at how locked-in the Goblin felt. I used all the default settings of the MSH iKON flybarless controller and they worked flawlessly. Per the iKON’s manual, the basic settings should be near optimal for most pilots, with advanced settings available for those looking to push the iKON even further.
The large wraparound canopy and tail fairing makes the Goblin very easy to see in the sky. Because of the dual-stage transmission, the main gear outside diameter is much smaller than those found in single-stage transmissions. Because of this, the canopy can be made much narrower, resulting in much less drag. At full tilt, the Goblin 630 has to be one of the fastest ships around. Everybody at the field was amazed at the high speed passes that I was making over the runway.
At an all up weight of just over 10 pounds, I was a little concerned the Goblin would feel heavy in the sky. However, my first collective push with the Goblin quickly put that to rest. In fact, the Goblin feels extremely light on the sticks and starts and stops maneuvers nearly instantly. With the Quantum 530Kv motor and default gearing, my governed head speed was approximately 2100 rpm in my stunt flight mode. At this head speed, the 630 is extremely nimble and is virtually asking to be thrown around the sky. Current draw averaged around 50A with mixed pitch pumping and smooth 3D, which results in flight times of almost five minutes. According to the manual, the maximum recommended head speed is 2350 rpm, which will make the collective response even stronger at the expense of much higher current draw. Honestly, the 630 can do everything in the book even at 1900 rpm and I really don’t feel any need to go past the 2100 rpm that I used during my flights.
At all the head speeds that I tried, the Goblin tracks extremely well through all maneuvers. The combination of the precise mechanics, high quality electronics, and the iKON flybarless controller, make the 630 really groove into fast flight. I loved making high-speed backwards inverted passes over the field and the incredible stability provided by the iKON really inspired confidence as I brought the passes lower and lower to the ground. While fast passes over the field are fun, the 630 was designed from the ground up to be a hardcore 3D machine and it excels at it. Roll and flip rates are incredibly quick, yet also very controllable. It feels as though the airframe has almost no inertia in the air, as rotation starts the instant the cyclic is moved and it also stops the instant the stick is returned to center. Likewise, collective response is just amazing and the power system used has some much torque the setup is nearly unboggable. Tic-tocs appear as if the helicopter is bouncing between two walls. As expected, tail control is solid, holding like the proverbial vise, regardless of going forward, backwards, or sideways.
In the air, I couldn’t find any faults with the 630, but turnaround time between flights is a little longer than I normally like. The main flight packs are designed to be installed from the front of the helicopter, which necessitates removing the canopy. Since the rear of the canopy wraps relatively tightly around the main shaft, it can be a little tricky to get on and off. I found it best to move the swash all the way down and then rotate the main rotor so that the blades are perpendicular to the body. Then the top edges of the canopy can slide above the swashplate with the least amount of flexing. While this entire process takes a little bit longer than some other pod and boom helicopters, the Goblin’s design offers many of the drag reduction benefits of a full fuselage with only a fraction of the effort.
• While many of the assemblies are already prebuilt, it is worthwhile to disassemble them to check for Loctite and for grease in the appropriate areas.
• The torsion spring for the tail belt tensioner has a short leg and a long leg. The manual omits which way it goes, but the proper direction is with the long leg facing down.
• The cutout for the tail rotor servo in the tailboom was big enough for the housing, but there wasn’t clearance to get it in with the servo harness sticking out of it. I used a Dremel tool with a 3/8 inch sanding drum to create clearance for the harness.
• The main swash servo is mounted against the top of the servo’s mounting flange. The Savox servos that I used had a plastic rib that protruded above the rubber grommets. I trimmed off this rib so the servo would sit on the rubber rather than rocking on the plastic rib.
• The pitch links are slightly rocking back and forth every rotation of the main rotor and the only flexibility comes from the metal threads on this part. Be sure to keep the threads on the pitch links well lubricated with grease.
• Sand the edges of the carbon fiber frames prior to assembly, with extra care around the areas where wires will be near edges. This is to prevent the edges from cutting into the insulation of the wires.
• The Quantum motor’s shaft had to be trimmed to prevent it from protruding into the battery area. I poked the shaft through a plastic sandwich bag and then taped the bag prior to using a Dremel cut off wheel to trim the shaft to the desired dimension. The bagging prevents metal chips from finding its way into the bearings and into the motors innards.
• There was a little excessive drag from the tail pushrod support against the tail pushrod. I used a small round file to slightly increase the opening to make it fit more smoothly. I also put a light coating of grease on the pushrod to further reduce friction.
I really enjoyed building and flying the Goblin 630. With a high level of pre-assembly, the build goes quickly. Once in the air, the flight performance in phenomenal! It’s definitely got a unique look and will turn heads at the flying field. The electronics that I used also performed perfectly and the motor/ESC combination system provides insane amounts of power. In my book, SAB is two for two when it comes to producing awesome helicopters and I look forward to seeing what they come up with next!
CASTLE CREATIONS castlecreations.com, (913) 390-6939
FUTABA futaba-rc.com, (800) 682-8948
HELI DIRECT helidirect.com, (877) 439-4354
HOBBICO hobbico.com, (800) 682-8948
IKON ikonflybarless.com, (877) 439-4354
PULSE BATTERY pulsebattery.com, (877) 439-4354
QUANTUM quantummotors.com, (877) 439-4354
SAB HELI DIVISION goblin-helicopter.com, (877) 439-4354
SAVOX savoxusa.com, (800) 622-7223
Words: Tony Yap
Photos: Walter Sidas/Tony Yap