SAB Goblin Fireball 280

Written by Chris Mulcahy Capable and affordable 3-D helicopter Product review As seen in the December 2017 issue of Model Aviation.

Bonus Video

Specifications

Model type: Electric flybarless 280-size helicopter Skill level: Beginner to advanced Main rotor diameter: 626mm Tail rotor diameter: 139mm Length: 580mm Height: 170mm Weight: 26 ounces without battery Power system: SAB Direct Drive Motor System Radio system used: Futaba 16SZ Flight duration: 3 to 5 minutes Needed to complete: Flight battery, receiver Price: $449

Pluses

• Low parts count. • Inexpensive canopy and tailboom. • Wide performance envelope.

Minus

• Tiny parts can be challenging to assemble.

Product Review

When I bought my first-generation SAB Heli Division Goblin 700 many years ago, I never imagined that someone would be able to miniaturize it into a 280-size machine. And yet, here we are! SAB had a number of ideas in mind when it designed this helicopter, including a low parts count, an inexpensive repair bill after a crash, and of course, without sacrificing performance. Something that is unique about this aircraft is the direct-drive motor. As the name suggests, it drives the main rotor directly without the need for gears, pinions, or belts, thus reducing the overall parts count.

The low parts count and inexpensive replacements make the SAB Goblin Fireball 280 ideal for beginners and pros alike.

The Fireball comes as either a kit and motor, or as a combo that also includes the speed controller and servos. You can’t buy the Fireball without the motor because it is a special motor designed specifically for this helicopter. I built the combo version, which included the three SAB DS12C cyclic servos and the SAB DS12T tail servo. The included 60-amp ESC is also a SAB brand. For my build, I added a Futaba CGY750 gyro (yes, it fit!), a Futaba R3001SB telemetry receiver, and used Pulse 6S 1,250 mAh 75C flight batteries. All of this was guided by my Futaba 16SZ radio.

The Build

As with all SAB kits, the parts are in numbered bags that correspond with each step in the instruction manual. The included manual is a small, full-color printed booklet that guides each step of the build. The first step, believe it or not, is the tail servo. It was at this point that I realized I should plug in my receiver, gyro, and servos, and center the servo arms on each servo. The tail servo is simply sandwiched between the two molded side frames. I then flipped it upside down and added the one-piece molded landing gear.

The servos and gyro have been installed.

The tail assembly was next. This is probably the only part of the assembly that will test your patience and dexterity because the parts are tiny! The tail grips contain their own set of bearings and thrust bearings, just like the main rotor head, and each must be assembled. I initially used the same grease on the thrust bearings that I use on all of my helis. I found out that this grease was too much for the tiny thrust bearings, so I removed them, cleaned them, and used a little light oil to lubricate them before reassembly. The tail pitch slider was preassembled at the factory, so there was no need to disassemble it. There are a few preassembled parts, and this is noted in the instruction manual. There is no need to take them apart again. The tail assembly consists of the carbon-fiber vertical fin on one side and an aluminum side plate on the other. The tail is belt driven and the belt must be looped over the tail shaft before final assembly. It is important to mention here that where metal parts screw into plastic parts (such as the uniball into the tail blade grip), the parts must not be overtightened to prevent stripping out the plastic. If you strip the plastic, you will have to replace the part. The tail assembly is attached to the plastic tailboom, which costs roughly $9 to replace. The tail assembly is slotted so you can tension the belt correctly after the tailboom is attached to the main frames. The tail rotor pushrod needs to have the threaded ends glued into the carbon-fiber pushrod, and it is important to let the glue fully cure before trying to twist on the ball links. The tailboom assembly is attached to the main frames with a single barb that slides into a socket—no pins or screws. When you push it all the way in, the barb clicks in place, preventing the tailboom from coming out. It’s a simple, easy, and effective design.

The antistatic wire was installed on the tailboom.

The tension from the belt also helps to hold the tailboom in place. This means that during a crash, if the tailboom doesn’t break, it can pull out from the main frames without damaging them. This brings me to the unique motor assembly. There is no main gear, no autorotation hub, and there are no pinions. There is a large-tooth wheel that attaches to one end of the motor to drive the tail belt, and the other end bolts to an aluminum main plate. The ESC is seated inside on the floor of the main frames before the motor and main plate are bolted into the main frames. The left and right belt tensioners are assembled, both of which ride on bearings, and are attached to the main frames. The cyclic servos are attached to their support assemblies and are bolted to the top of the aluminum main plate. Again, be careful not to strip any plastic.

The motor installed in the main frames, with belt and tensioners in place.

At this point, the rotor head is assembled. Each blade grip has its own set of bearings and thrust bearings, and the head spindle floats in rubber O-ring dampers in the head. There is a unique part called the bearing support assembly that consists of two bearings and a feeder. It is a keyed component that connects to the motor. The feeder damper keys to the motor shaft that drives the feeder. A setscrew attaches it to the bottom of the main shaft. The direct-style swashplate is much like the first-generation Goblin 700. The pitch links from the servos to the blade grips are not adjustable, and neither are the links from the servos to the swashplate. This should make setup simpler. With this last assembly finished, the build is almost complete. All that is left is to attach the rest of the electronics and take care of the wiring. If you’re like me, you will spend more time with the wiring than on the actual helicopter assembly! The plastic canopy is secured to the helicopter with magnets and a decal sheet is included. The flight battery is held under the front tongue of the main frames using Velcro and a strap. I installed my CGY750 controller on the back of the helicopter and mounted the sensor on the top of the front tongue. I had to level out the mounting plate for the sensor because the front tongue is angled slightly down. Using any kind of mini gyro would be ideal here, given the helicopter’s small size. Routing and tidying up the wiring wasn’t as bad as I expected, and there are places to install zip-ties and the included wire keepers. As an addendum to the manual, there is an antistatic wire kit for the tailboom. Some people say you will need it; others say you won’t. Erring on the side of caution, I installed the antistatic kit. This attaches a wire from the aluminum tail hub at one end of the tailboom to the aluminum main motor plate on the side frames. This prevents any potential static buildup from the belt from causing problems with your electronics. You could probably sit down in the morning and have this kit ready to fly later that day. Or you could, as I did, spread it out over a couple of evenings after work. The build time is short, but enjoyable.

Programming

Following the instruction manual, I set up my throttle curves with a flat curve of 60%, 75%, and 85%, for 3,000, 3,800, and 4,200 rpm respectively. I don’t have a swashplate level tool that is small enough for the Fireball, so I used the center pitch marks on the head and blade grips to level the swashplate. I rotated the head and made adjustments until I was satisfied that it was as level as I could get it. With none of the links being adjustable, it was an easy way to set it up. I started out with my gyro gain settings as stated in the manual, which ultimately proved to be too high for my model.

Flying

The first flight was spent setting up the gyro. Because the stock settings were too high, I had to significantly lower them. I’m not a huge fan of setting up small helis because they always seem so finicky compared with their larger counterparts. After I lowered the gyro gains, however, it started behaving itself. For the CGY750 gyro, I ended up with 30%, 20%, and 18% on the tail, and 30% across the board for the cyclic pitch. After the gyro was dialed in, I got to have some fun with it. Although there is a more powerful motor available for the Fireball, the stock motor has plenty of power. You can cruise around at 3,000 rpm and do all of your 3-D maneuvers, albeit slower. You will extend your flight time to 4 or 5 minutes in this mode. The Fireball wakes up at 4,200 rpm and becomes a snappy little speed demon. This small helicopter feels like a heavier one in the air. It can be fast and will quickly become small in a straight line, but the bright canopy and decals help with orientation. It has a lot of pop when going up, but needs most of the collective to pop in the opposite direction of gravity when coming down. It’s an extremely agile 3-D flier, but can be tamed to be a gentle sport flier. The biggest difference between the Fireball and other helis is autorotations. It has no auto hub, so will it autorotate? Surely when you hit throttle-hold the motor will stop, thus stopping the rotor head? These thoughts ran through my mind before actually flying it. While hovering low to the ground, I turned on throttle-hold and, surprisingly, the rotors kept spinning long enough for me to bring it in for a nice, soft landing. Does this mean that you can do an honest-to-goodness autorotation with the Fireball? I’m just not brave enough to find out yet. My flight times at 4,200 rpm were 3.5 minutes using the 1,250 mAh Pulse batteries. I found myself flying at 4,200 rpm most of the time because it was just so much fun. After I became comfortable with the Fireball, I found it to be a more stress-free type of flying because I wasn’t as concerned about the possibility of a crash as I am with my larger helis. It is a capable little helicopter and extremely fun to fly! —Chris Mulcahy [email protected]