Written by Rob Turnbull Tuesday, 20 November 2007 00:00
The equipment that I will be using for the HDX500 build is as follows:
Motor: Medusa 36-50-810
ESC: Kontronic Jazz 80-6-18
Receiver: Spektrum AR6100
Collective / Cyclics 3x Hitec HS-85MG's for eCCPM
Gyro: Futaba GY401 with 9254 Servo
Battery: Kokam 3200 mAh 4S pack
Transmitter: Spektrum DX7
The following is a review of the HDX 500 model helicopter supplied courtesy of www.helidirect.com.
This is a new heli in the 500 class which directly competes with the Hirobo Lepton, and in fact, many parts are interchangeable between the two models. The beauty of that is the HDX 500 parts are somewhat cheaper than the Lepton equivalents, making it a good alternative choice for spares.
The 500 is a little larger than a Trex450 but smaller than a 30 size nitro, or 550 size electric.
Here's a couple of photos of the box and it's carefully wrapped contents.
Taking the contents out of the box and unwrapping them reveals a mostly pre-built helicopter airframe that needs a little assembly to complete it ready for the electrics installation. It all looks pretty good, although at this early stage I'm already thinking about rebuilding the pre-built parts to ensure the relevant areas have been threadlocked. As it turns out, this pre-built kit was very well put together already!
Here's a few more shots of the elements that make up the kit.
The parts missing from the photos above were not missing from the kit, but for the sake of brevity, I decided to select just a few photos for this review.
The box that I received did not contain a manual so I used the few pictures on the box, and some general heli building knowledge to put it together. Since then, the manual has been made available online as a downloadable PDF, the link at the time of writing is: http://www.helidirect.com/upload/HDX500SE-Manual-V1.9.pdf. There may well be a manual included in the shipping boxes now?
The build is very easy, with many parts already pre-built, the task is more akin to fitting the last few pieces of a jigsaw together. The one thing that wasn't pre-built that I really wish had been is the rod linkages. It's one of those loathsome jobs that takes a while and really starts to hurt the fingers!
I started with the tail assembly, fitting the pre-built tail rotor assembly onto the boom, lining up the two holes in the casing with the two in the boom, and then fixing together using two long bolts which pass right through the boom, between the belt, and hold the vertical fin in place. I used my favourite trick to make life easy when threading belts through booms, which is to wrap the end of the belt in tape. This allows it to pass freely through the boom.
Next I fitted the skids to the main frames and installed the main gears and the tail boom assembly into the heli. At a later stage of the build it became apparent that the main gear 'one-way' assembly had been pre-built the wrong way around (upside down) and had to be removed and rebuilt the right way around. This was to allow the main gear to mesh with the motor pinion. The gap between the upper tail drive gear and the lower main gear is reduced (the main gear rising up instead of the tail gear dropping lower), allowing the motor pinion to mesh fully on the main gear.
In the middle two photos of the main gear (above), the left picture shows the incorrect assembly and was how the kit arrived. As you can see in the picture, the gear is sunk in the middle. This allows the main gear to sit higher when correctly assembled in order to mesh with the main motor pinion. The one-way bearing is viewed from the bottom in both images. I removed the one-way housing from the main gear, flipped the gear over and refitted the one-way housing to it, running the bolts through from the bottom, as seen in the picture on the right. This resulted in the correct assembly.
The lower two pictures above show the boom fitted into the frame clamps, viewed from above with the gyro plate removed. Finally, the bottom right picture shows the main shaft which has three holes drilled through it to allow some variation of pitch range when setting up the heli mechanically. Using the lower hole will give the most pitch range availability, and the upper hole the least.
Fitting the boom can be a little fiddly - feeding the belt through to the gears, and then getting it onto the upper tail drive gear - making sure the twist is correct in the belt. The construction of the frames is such that you can push the boom quite a long way into the frames to give yourself some manoeuvring room to get the belt fitted to the tail drive gear.
Head assembly (and final tail assembly positioning)
The head assembly is mounted next, which will hold the main gears firm so you can tension the belt, plus the model starts to really look like a heli! I put the mast locking collar onto the shaft and slide it up higher than it needs to go, then loosely pinch it down. This keeps the swashplate and washout assembly up out of the way while I get the main mast fitted and bolted through the gears (you can just see the bottom of it under the swashplate in the left picture below).
With the main shaft bolt secured in place (don't over tighten the bolt through the one way hub or you could deform the hub!) pull up the head and slide the locking collar down into place and fix tightly with threadlock.
Once the head is fitted, the main gears will not move so the tail belt can be tensioned. Pulling the boom out and tightening the boom clamp bolts sorts this out - don't forget the two clamp bolts underneath the boom!
There is also a neat hole in the sideframes which you can poke a blunt tool through to check the belt tension with.
The boom stays don't use mounting bolts, instead they make use of sturdy rocket links, with balls at either end on the side frames and on the horizontal fin mount. Easy to snap on and off should you need to - but no worries of them coming off in flight!
The items that need to be attached to the boom do not have to be fitted prior to the boom being fittted into the main frames. The pushrod guides and the horizontal fin mount can be slid around the boom, or fitted onto it. Once the boom stays are fitted to the side frames, you can fit the horizontal fin mount in the correct place. Apart from fitting the tail blades, the back end is now complete!
The servos are mounted to the two neat little servo mounting bars (one above the other) at the rear of the heli main frames, which keeps the three servos neatly together and in a compact unit.
It becomes quite obvious why there are double bell-cranks on the left side of the helicopter once the servos are in, as they line up perfectly with the relevant servo horns. It's a very well thought out part of the helicopter.
The Hitec HS85 servos fit nicely in there, but you will need to use a large washer to grip each mounting lug when fitting to the heli as the holes in the servo lugs are quite large, meaning the mounting screws will not hold them in place without some help.
The tail servo sits below and behind the cyclic servos in the frames. The mounting hole provided will cater for a vareity of tail servos, which is another nice design thought. The review heli was fitted with a GY401 gyro and matching S9254 servo.
The last part of the frame assembly to fit is the anti-rotation bracket which sits behind the main mast and is fitted to the upper servo mounting plate. Fitting it is quite straightforward, threadlock the two bolts through the anti-rotation guide and fasten down tight.
One of my least favourite jobs of building a heli is making up the rod links, but it has to be done! The manual is quite clear in it's description of which rod to use with which links for a particular use. The six rods used on the head assembly are described on page 5 - make sure you use the correct rocket links in this step - all the others are the same type - the ones attached to the blades (pitch links) use short rocket links, and the upper mixing arms have a mix of mid and short rocket links. Again, the manual is very clear on this.
The links from the swashplate down to the bell cranks are shown on page 7 and the links from the servos to the bell cranks are shown on page 8.
Once the links are fitted to the head, the flybar can be fixed in place to complete the mechanical setup. The head assembly arrives pre-built, and to keep it in one piece, the flybar cradle is temporarily screwed to the flybar seesaw. Those two screws need to be removed before the flybar can be fitted.
Also, note the paddle metal inserts are threaded and countersunk on one side more than the other, so be sure to fit the larger countersunk hole so that it meets the flybar first when inserting the flybar into the paddle.
Once the flybar has been fitted to the head and both paddles have been fitted to it, it must be centred to ensure the heli flies properly. The flybar has a step down from 4mm to 3mm - 4mm runs through the head assembly and half way to the paddle, where it steps down to 3mm and then goes into the paddle. The measurement from the edge of the flybar cradle to the step down to 3mm when the flybar is centred for me was approximately 55mm (just under to be precise - as per the picture). With the paddles wound on and secured exactly the same on both sides, the fly bar will not cause any problems due to imbalance.
Fitting the motor
The motor is fitted to the mounting plate in front of the main mast on top of the heli, with the pinion underneath in order to drive the main gear.
There are two ways to make the task of mounting the motor easier. You could remove the motor mounting plate, fit the motor to it, then re-mount it into position, or you can remove one of the bottom trays and attach the motor to the mounting plate in-situ. Removing the motor mounting plate would have been a better option overall as it slides forward and backward to get the mesh with the main gear right (and I had to undo the stubborn bolts in the motor mount in the end anyway), however, I chose the latter route as the prebuilt frames gave me a hard time undoing the mounting plate bolts initially - the kit really was very well put together with threadlock used in all the right places - I was very pleasantly suprised to see a mostly prebuilt kit so well put together, and in this instance, it actually caused a bit of a hinderance!
According to the manual, there are three plates in the bottom of the frames - the one I removed would be the middle one, which gives you access to the underside of the motor mount. The kit I received only had two plates counting from the front backwards.
Once the pinion is securely fitted to the motor, it can be mounted to the plate. You will need to be able to slide the plate towards the main gear to mesh it correctly with the main gear. The bolts holding the plate in place need to be loosened to allow this meshing and, as mentioned, the bolts on the review heli were loctited in and tightened up extremely tightly (I had to carefully use heat on the plate to get them to come loose - prior to fitting the motor, of course!)
With the gear mesh set correctly, threadlock and tighten the motor mounting plate bolts to secure it in place.
The Kontronic Jazz 80-6-18 ESC I have used fits neatly into the top of the frames at the front of the heli and the motor wires reach it comfortably. The battery pack (half wrapped in Impad protection foam) fits in between the lower frames below the ESC, and the receiver is mounted in the lower frames behind the battery pack (ordinarily, this would be on the third tray back, but that is missing from the review heli so I tie-wrapped my Spektrum AR6100 receiver to the side frame in roughly the same location instead).
With the electrics fitted and plugged in correctly, it was time to set it up and go fly it!
The first spool up of the heli was quite impressive. I wasn't really sure what to expect from it, but it sounded very powerful, and it was certainly humming nicely once the ESC had settled at the 80% headspeed I had initially set. Everything ran smooth, no twitches or wierd noises - nothing wrong at all.
The first thing I have to say about this heli is that it's hovering stability is astounding. This is mainly down to a lack of cyclic throws making the heli generally very stable. With better cyclic throws, I still think the heli would be very stable, but would be able to move around in a hover faster (a little less stable).
On a 4S Kokam 3200 pack, the power being delivered to the rotor head sounds impressive, and it is, to a degree. This heli can't be upgraded, it's as upgraded as it gets - metal head, metal tail, G10 frames, the works, but at a price - and that price is the weight. The heli is heavy, adding to the stability factor, but this detracts from the 3D side of things to a fairly large degree. It is certainly possible to perform some gentle 3D manoeuvres, but with the cyclic rate being as slow as it is, it makes tic tocs all but impossible, and flips and rolls very slow.
The kit usually comes supplied with motor and ESC, and I would presume the pinion to be with the motor. These items were not part of the review kit so I had to source a pinion for it, which initially proved difficult, but eventually, I found the right 24 tooth pinion. The first pinion I tried was a 22 tooth and this left the heli feeling underpowered in flight, capable of nothing more than basic hovering and forward flight. Too much pitch would bog the head badly - so the right pinion was definitely required!
Having fitted the correct 24 tooth pinion and tested the heli again, I then found it to be a little more lively in terms of power. That said, the power holding capabilities are not fantastic - the head can be loaded up quite easily, dragging the headspeed down fairly quickly, and then you have to wait for it to build up again.If you're not looking to fly 3D, but simply want to fly around the sky with a heli that can utilise existing 3S and 4S packs (when joining similar packs together, i.e. 2 x 3S packs in series or 2x 4S packs in parallel) then this could well be the right heli for you.
Build quality is excellent (even pre-built parts were put together properly)
Easy to work on
The layout is well thought out
Extremely stable in a hover and great in forward flight
No mechanical upgrades required
Good value for money
It's quite heavy when fully kitted out
It's not a 3D machine (if thats what you're looking for)
Using longer rudder servo horns might be a problem due to the boom clamp being in the way
The tail pushrod was not long enough - longer rocket links were needed on both ends
The bundled main rotor blades are pretty flexible, which is quite likely to be a factor in the lower 3D performance capabilities of this heli - upgrading these to some better, stiffer blades could be a big help.
The build was quite enjoyable and very easy, to the point that I didn't need the manual to do it (although beginners may well need it!), and the high quality of the helicopter overall is pretty obvious throughout.
It's been well thought out when it comes to CCPM servo layout, I found the servo mounting brackets to be a great idea that really works well.
The frames are robust, while also being quite light and cheap to replace if required - being G10.
Overall, I'm very impressed with the helicopter, but I felt a bit let down with it's 3D performance as I was expecting a lot more from it due to the name of the helicopter.
If you're looking for outstanding stabillity in an electric helicopter, this is definitely a contender for the crown. If you want to be running a 500 size electric heli for anything more than sedate 3D flying, you need to look elsewhere.
( 11 Votes )