Hobby-Lobby Dragonus II ARF

Saturday, January 5, 2008

Chris "JustPlaneChris" Boultinghouse

Specifications:

Manufacturer: RCer
Distributor: Hobby-Lobby, Intl
Type: Mini electric aerobatic helicopter
For: Beginners to advanced pilots
Flying weight (review model): 27.9 oz. / 792g
Length: 26 in. / 660mm
Rotor span: 27.5 in. / 698mm (325mm blades)
Rotor disk area: 594 sq in / .38 sq m
Rotor disk loading: 6.77 oz/ sq ft / 2.07 kg/ sq m
Radio: JR 9303 transmitter with DSM2 module, Spektrum AR6100e receiver, 3 Hitec HS65MG servos on cyclic, and a Futabal 9650 on the tail (GY401 gyro)
Power system: Stock MTM 500XH 3300Kv outrunner, Jeti Spin 33 ESC, and PolyQuest 2150 3S Lipo

Introduction

The RCer Dragonus II, distributed by Hobby-Lobby, Intl, has been gaining a lot of ground in the hot "mini" electric helicopter market. It has features typically only found in larger machines, such as adjustable Bell-Hiller ratios, and a belt drive that uses a pulley on the main shaft rather than a "double stack" main gear and secondary tail drive gear. While the Dragonus has been available for quite a while now, the subject of this review is an ARF version soon to be offered by Hobby-Lobby. So, let's dig in and see what's in the box!

Construction

Since this is the ARF version of the Dragonus, there really isn't much building to do. As you can see, the airframe is completely assembled, needing only radio installation. However, there are a few issues I encountered I'd like to address.

The first thing I noticed was that none of the frame screws had threadlock. You'll definitely want to remove the frame screws (one at a time) and apply a bit of blue threadlock to keep the frame from loosening over time.

As I dug into the manual (same one you get with the kit version) I noticed that the "A" linkages in the pre-assembled head were the wrong length and would not allow proper head movement. I sent an email to Hobby-Lobby, and they have contacted RCer to let them know about the problem. Luckily, I had a spare linkage set so I "borrowed" the correct link rods from myself and kept building.

Another "gotcha" that is fairly well known in the Dragonus community is the fact that Hitec HS65 servos are deeper than whatever servo the frame was designed for. As a result, the wires / grommet will rub the frame. This is easily fixed by modifying the frame with a few passes of a file or Dremel sanding drum. A bit of model airplane fuel tubing split and glued to the frame protects the wires from chafing.

I also noticed that there was a tiny bit of wobble in the center hub assembly. From what I read in the various online forums, this is fairly common and not considered a huge issue. I'm somewhat of a stickler about everything being super smooth though, and this wobble does induce a bit of vibration. I see a CNC center hub in my future not only to eliminate this vibration, but also so I can crank up the headspeed with some nice carbon blades.

Next up is the tail. If you choose to install a Futabal 9650 servo for the tail, you'll either need to purchase the optional 9650 basemount, or the excellent CNC tailboom mounts available from RC-Tek as the frame mounts are too small to accommodate the 9650. Since the basemount was on back order at the time we were collecting bits for this review, I chose to order the RC-Tek mounts. They are very nice!

The stock motor seems to be powerful and smooth. One thing I do want to mention is the pinion gear suggestions from the small leaflet included with the motor. In it they say "suitable pinions are 14T with 3 cell battery as the initial use for smooth yet very powerful combination for 3D flying. A 15T pinion can be used for very high rpm." Well, let me just say you do not want to use a 14T or 15T pinion for sport flying with the stock wood blades. Even with a 13T pinion, I tached 3200 rpm at 85% throttle! IMO, this is too fast for wood blades and plastic head parts. For the initial test flights I dialed back the throttle curve to 2600 rpm. Speaking of blades, the stock blades are beautiful, and seem to track and fly nicely. My blades were .3g out of balance, but the CG of both blades was identical. One wrap of clear packing tape on the CG of the light blade brought them into balance. A bit of "bling" was added in the form of dayglo orange trim Monokote and some holographic flash tape from HiLaunch.com

The rest of the setup went very smoothly. Wires were tidied up using waxed dental floss, and a hook-and-loop strap was glued to the front of the frame using GOOP adhesive to retain the battery. Programming the Jeti Spin 33 is a piece of cake when using the Spin Box unit. At the time of this review I have not yet enabled governor mode (as you'll be able to hear in the flight video below), but I do plan to try it. The Jeti Spin 33 has a wonderful soft start and slow spoolup, and (very important for Spektrum) it has a switch-mode BEC capable of driving 7 servos! This eliminates the need to use a separate BEC, and is something I wish other ESC manufacturers would start doing. It's worth the extra cost to avoid the hassle of a separate BEC.Look for a more in-depth review of the Spin 33 and Spin Box at a future date.

Flying

For the initial setup, I chose to configure the Bell-Hiller ratio for "beginner" level. Even with this setting, the cyclic is quick! If you are a beginner, you'll probably want to add some flybar weights and / or use some expo on your cyclic until you get accustomed to the quick response. My trim settings were spot on, and tracking was excellent as well. Despite the cyclic being really quick, the Dragonus is also remarkably stable for a mini. I suspect with flybar weights and / or longer and heavier blades, it would remain locked in during hover like my Swift. Collective response is smooth and powerful, and as you can see from the video it has plenty of "pop" even with wood blades and 2600 rpm headspeed. Average current draw for the first flight was 13.2 amps, based on recharge data. This will allow safe 7+ minute flights without pushing the pack beyond 80% of its capacity.

Conclusion

I'm impressed! While there were a few "out of the box" issues with this early release ARF, the problems were minor and quickly addressed by Hobby-Lobby. The flying performance is excellent, and will only get better as I become more acquainted with it's characteristics. If you are looking for something that's slightly off the beaten path, rather than "just buying a T-Rex", then give the Dragonus a close look. I think you'll like what you see.

Videos

Walk-Around


Flying


If you'd like, you may download higher resolution versions of the walk around and flying videos from JustPlaneChris' website.