RC Helicopters

Author: James Wang

Nick Maxwell kneeling outdoors with an XLPower Specter 700 V2 NME helicopter.

RC HELICOPTERS

XLPOWER
700-SIZE
HELICOPTERS

By James Wang | heloeditor@gmail.com

THIS MONTH, I will discuss the XLPower Specter 700, Specter 700 V2, and Specter 700 V2 Nick Maxwell Edition (NME) RC helicopters.

The original Specter 700 came out in 2020. It is easy to build, the parts and bolts fit perfectly, it fits 12S to 14S batteries, the components are rugged and can handle aggressive 3D flying, and the handling quality is excellent and repeatable. The Specter 700 V2 provides some refinements, but the Specter 700 V2 NME is even better.

The NME main rotor is made from harder 7075 aluminum, while the original and the V2 rotor hubs are made from 6061 aluminum. The 6061 aluminum is known for its excellent corrosion resistance and weldability. The 7075 aluminum’s exceptional strength and hardness is ideal for high-stress applications.

The original and V2 versions use a 15mm-tall main gear, while the NME features an 18mm-tall CNC-cut, precision helical main gear that runs smoothly and can handle powerful motors. The NME tail-rotor hub is mounted on a tapered-tip tail-rotor shaft to ensure true spinning.

XLPower’s designer worked closely with 3D pilot Nick Maxwell to create the 700 V2 NME. There is also a new Specter 700 V2 World Champion edition, a 700 nitro version, and a stretched Wraith E 760 V3 760-size helicopter that is capable of handling up to 760mm main rotor blades. These models share many design features. For now, let’s focus on the 700 V2 NME version, which is what I am most familiar with.

The airframe design permits the use of nearly any diameter high-performance brushless motor on the market. The 9.636.1 gear ratio is ideal for 500

Kv to 540 Kv motors with a 12S battery. XLPower offers optional pinions to vary the ratio between 10.6.1 and 8.3&8.1.

Nick uses a Scorpion HKIV-5025-520 Kv motor with a Scorpion 200-amp ESC. I used the same motor but with a YGE 250-amp ESC. I really like that the motor pinion is supported by two aluminum bearing blocks, which helps reduce the moment load on the motor’s internal bearings. Every time we roll or flip a helicopter, the precession force generated by the spinning

Close-up of the CNC-machined helical main gear and motor. — The CNC-machined, 18mm-tall helical main gear is one of the thickest and best-made main gears. The helical pattern increases the load-carrying ability by increasing the contact surface between the main gear and the motor pinion gear.

The CNC-machined, 18mm-tall helical main gear is one of the thickest and best-made main gears. The helical pattern increases the load-carrying ability by increasing the contact surface between the main gear and the motor pinion gear.

Close-up of a helicopter swashplate and rotor control mechanism. — This shows the 1-to-1 control geometry. When the swashplate tilts, it changes the main rotor blade pitch angle by the same angle. This makes cyclic control responsive and suitable for 3D flying.

This shows the 1-to-1 control geometry. When the swashplate tilts, it changes the main rotor blade pitch angle by the same angle. This makes cyclic control responsive and suitable for 3D flying.

Nick Maxwell and Ra Kabun standing with XLPower helicopters at an event. — (L-R): Nick is with Ra Kabun, the founder of XLPower and creative designer of the XLPower helicopters.

(L-R): Nick is with Ra Kabun, the founder of XLPower and creative designer of the XLPower helicopters.

motor puts a strong, sideward moment on it, which is absorbed by the motor shaft and motor bearings. This and the motor bell being slightly out of balance are the root causes of motor bearing failures.

The robust 15mm-diameter hollow, main rotor shaft is supported by two bearings that are mounted in a one-piece machined aluminum block that sits above the main gear. A third bearing is added below the main gear. The drivetrain system is bulletproof.

Each main rotor-blade grip is supported by a radial ball bearing, then a thrust bearing, and followed by another radial ball bearing. This radial bearing is a double-row angular contact bearing, while most models use a single-row radial bearing. Having two rows of rolling elements allows the bearings to carry higher radial loads compared with their single-row counterparts. Combined with a 10mm-diameter blade spindle, the helicopter feels very solid in flight. The swashplate is excellent and has minimal play because it uses a 10mm-tall angular bearing.

Specter 700 V2 helicopter rotorhead, frame, and mechanics — The rugged Specter 700 V2 rotorhead, main frame, and mechanics. The battery mounting system permits easy installation of 12S to 14S batteries.

The NME and the V2 World Champion edition use 1-to-1 control geometry, which means that the two rotating pushrods from the swashplate to the main blade grips are perfectly vertical and parallel to the main rotor shaft. Hence, when the swashplate tilts 10°, the main blade pitch changes by 10°. The 1-to-1 geometry does not affect the sensitivity of collective control, but it increases the cyclic-control sensitivity.

All three electronic cyclic collective-pitch mixing (eCCPM) servos are mounted vertically beneath the swashplate to provide a short and direct run from the servo arms to the swashplate. Nick recommends mounting the steel ball on the servo arms at 15mm from the servo shaft center and using +15°/-15° collective travel. I am using +13°/-13° collective travel. Set the ESC governor to give 1,600 rpm for normal mode and 2,200 rpm for idle-up mode. The main rotor comes assembled, but it’s better to take it apart, add grease, and reassemble it.