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Old Jul 30, 2012, 07:37 PM
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HK DH VAMPIRE 70mm EDF - Build Log

I thought I will throw in my build log of the Hobbyking Durafly 70mm EDF DH-100 Vampire ARF kit version.
On opening the kit and assessing things, I found a number of useful things to do that will "improve" it over the kit as it come stock.
I am making it as a hand-launcher, so there is no Retracts information... though I might go over that anyway, as it is a very simple task to do and I might still do that later at some stage. I just felt like making it a hand-launcher, but maybe I will want retracts later - I usually want retracts!
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Old Jul 31, 2012, 09:22 AM
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Just a look at all the parts supplied in the ARF.
Nothing too exciting, just a typical foamie. Quality is quite good, as per typical Durafly (FMS) production.
The STICKERS are terrible!! They are extremely brittle thin material and crack, split, very easily. So be careful around them! Especially how they cover the main gear bays, and thus with no support under them they can crack and disintegrate in a flash!

There is the stock 5 blade fan, and a CS10 next to that.
I will run a CS10 with 2300kv motor - almost certainly a Freewing 'gold' motor.
Otherwise the HobbyKing L2855-2300kv
The Freewing is an 8-pole and larger, stronger motor than the L2855 6-pole.

The manual has the typical 'half useless' low detail construction information.

...
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Old Jul 31, 2012, 09:27 AM
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Seeing it was well documented on how weak the booms are... and just checking them out makes that plainly obvious anyway(!!)... I decided to use Carbon Fibe tube "skewered" up the centre of the booms, so that it is hidden and probably stronger than the common way people run rod or strip under the boom.

It can be a bit larger diameter, and easily cleaned up to be 'gone'. hidden, unseen.

I was going to run one length all the way from one end, but to hide that best you have to start at the wing end, and then the boom gets narrower and narrower as you try to skewer a straight shot all that way!! Pretty close to impossible to do!!
So then I did 2/3 from the wing end, and used a second piece from the rear end to run inwards and past the other CF tube.
That is not quite as good as doing a one piece job, but still very strong and almost as good.

To make the "hole" for the CF tube, I used 4mm piano wire so that it is strong enough and straight enough to go the way you aim it. So I did a pretty good job of the aiming.... I got to the rear end of the Yellow ID bands. Almost all the way required! So the front ones go to that distance, and the rear ones go forwards until the other ends of the yellow bands. A good overlap.

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Old Jul 31, 2012, 09:31 AM
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Next I altered the battery tray, to the usual way I set up for mounting batteries.
I think the stock strap is too far rearwards, is not even spaced wide enough to hold a battery 'properly', plus it is a clunky contraption too!

I epoxy the strap in so it remains where it should be.... not able to slip around.

...
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Old Jul 31, 2012, 09:36 AM
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I dremelled out the EDF housing bay to be longer by about 8mm, so the CS10 stock housing can fit in properly.
The CS10 has its mounting lugs offset from centre a bit, so when you sit the fan into the upper fuselage its mounts do not get to the foam. This is a GOOD thing as it turns out, because is allowed placement of plywood mounting plates so that the CS10 can be screwed in.

Once they ply plates are epoxied in (on), the EDF cover actually just fits right on correctly anyway. But even if it didn't, it would just need a bit of foam cut out at the CS10 mount points.

The CS10 only needs two screws to hold it in fine.

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Old Jul 31, 2012, 09:40 AM
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For the ESC, I decided to make the ESC end wires very short, and extend the motor wires so they reach that then. This is so the motor wires can be taped to the CS10 housing and make it an easier assembly to get into place (or out again). Not a 'must do' thing but it worked out well.

The ESC is velcroed up front.
An airflow hole is cut in the front bulkhead to allow air to pass over the ESC.
This also needs a hole to be cut into the nose gear cover piece.

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Old Jul 31, 2012, 09:48 AM
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After having looked at the wing(s) and how they are attached, I wasn't happy about that. A butt join only to the fuselage.
So I decided I would use a 6mm Carbon Fibre spar, that runs straight across the fuselage. I have not seen these bother ducting airflow to any degree measurable, plus the Vampire has quite "ugly" ducting anyway! (It is an ugly duckling, err ducting). So it is not going to be any issue at all.

I ran it to give 14cm out into each wing. Mark the fuselage point, via referencing the wing held against it, then use the trusty 4mm piano wire length to "drill" the hole out into the wing - passing through the fuselage first so that it gives you to right guidance. But you still need to be vigilant and careful.... taking time and monitoring exact direction as you go.

The wings don't go on until later. So next was to epoxy the fuselage halves together with 15min epoxy, to have enough time, and then rubber band it together until it is dried.
I planned what things needed to be done inside, and it was a good time to join those halves.

...
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Old Jul 31, 2012, 09:55 AM
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I static balanced the CS10, using my 'special 1867 wooden balancer'. Hmm, some carbon fibre on it.... well, I upgraded the original 1867 assembly.
You can sort of make out the rare earth magnets, that combined with the balancing shafts pointed ends, make for close to zero friction.
The magnets are actually spaced 4mm wider than the shaft so that only one end contacts a magnet and the other end is suspended in mod air by the magnetic force there which means zero friction at that end.

Most CS10's rotors I have had are so close to 'very good' already, they run fine just as they come. But I have had at least one notably imbalanced one, so you have to check them in case. I think on this CS10 rotor I used one piece of fibre tape, like the one stuck up top in the pic.

The motor wires are extended and then taped to the housing so that they will go accurately into the EDF cover's "modified wiring slot" every time.
You can see the Freewing 2300kv in one pic.

Note the CS10 shaft adaptor with FLATS filed onto it, so that you can use two shifters to do up the rotor nut - one on the shaft, one on the nut, for guaranteed tightening ability, and no damaging the shaft with vice-grips or pliers etc.

...
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Old Jul 31, 2012, 09:59 AM
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Next was a bit of "cockpit improving".....
Adding about 10mm of foam under the pilot, cutting it to match him and epoxying it to him underneath. Then brush painting it in 'Brunswick Green' acrylic, which was a perfect match for his attire. Then dabs of epoxy to stick him into the cockpit.

I printed out a black and white instrument panel (seeing I don't have a colour printer) to help make the cockpit look at least a BIT nicer.....

I CA'ed the canopy on... which showed me for the 100th time why I HATE CA!!!
It works on some things... not many, in a truly useful way.
I should have used epoxy as usual.....

...
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Old Jul 31, 2012, 10:06 AM
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I epoxied the wings on, even though I had read the manual and it said to do the servo wiring FIRST.
I actually forgot... DOH!!
But it didn't matter because the servo wires need lengthening anyway (all three sets) so you could easily feed the 'blank' extension wiring end out through the holes anyway seeing they have no connector on them yet.

I soldered and heat-shrunk the joins and they still fit into the wire slots fine.

The servos are a tight fit into the servo bays even when just pressed in, but you stlll need to glue them. So I used a drop of CA on 4 points they touch the foam on the servo SIDES... not under. This allows you to use a knife to cut the glue joins and easily get a servo out again.

The wiring is all covered with strips of plain old celophane tape, which will allow painting over it so you can match up and cover the wiring slots. IF you want to do that. I mights... or might not (paint it).
But it will be WBPU'ed totally, so using the tape is still good for that.

The battery bay pic is just before adding the velcro strips to the baseplate. They hold the battery some amount, but are really to prevent it moving fore/aft or sideways. The strap is the real "clamp" of the battery, which the velcro underneath also works with to make for a rock solid battery hold.
The RX and separate SBEC will each mount to on one side of the nose area, where it has a step and thus good space to have those. RX to the nose left side, SBEC to the nose right side.

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Old Jul 31, 2012, 10:12 AM
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The nose gear bay rear bulkhead has a cutout to let airflow in over the ESC, and the nose gear bay cover piece also needs a hole cut ino that of course.
The cover is then pressed in and two small pieces of tape, fore and aft, keep it there fine.

The main gear bays have solid foam pieces to go into them too, so I cut a bevelled edge onto them, which allows it to get under the fragile stickers totally fine then. They are a tight fit and they won't need any tape or anything to keep them in.
(I probably should have cut an ARC into them, not an angled edge - for it to be even easier to fit them.)
Another idea I thought of AFTER was that you should cover the yellow sticker area that is over the wheel/retract bays (like where the '92' is) with celophane tape to make them much stronger before you try to feed the foam blanks in under those areas!

...
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Old Jul 31, 2012, 10:18 AM
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I actually stuffed up my ESC power connector, as all the batteries I have for this use are HXT 4mm bullets! Sheesh....
So a bit more de-soldering and soldering to correct that.

Note the extra wires from the connector, with a JST plug on it. That is the power take-off for the SBEC, so that you can unplug it if you want to. 1) To change it if required. 2) You can run the RX from a small 3S battery when testing stuff (no motor power then).

The control surface travels are HUGE!! I used the outermost holes on control horns. And second hole in on the servos, so that it has less 'drive' than its outermost hole. But it is still very large movement - too much. But that is ok, I will endpoint limit it, plus have dual rates anyway.
It could be FUN using the full travels, SOME times. hehe
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Old Jul 31, 2012, 10:27 AM
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Thew Vampire does not have enough inlet ducting airflow to get full power from a fan. Even the stock fan on only 4S. And will be even worse on a CS10 using 5S.
People generally cut open the underneath existing "gills" into larger openings, to get more airflow capability.
I don't like that idea too much.....

For a landing gear version, it means more FOD chances. Plus could (should?) affect flight in some speed/power situations, like causing "ballooning" (or the opposite). Though no one really says that happens to them... so maybe it doesn't happen.

I will test the thrust in its stock form - which for sure will be stunted due to the poor ducting. And my first preference, to solve the airflow problem, is to add "Cheater Doors" to the TOP of the Vampire. Where there are two 'panels' marked out already.
You just cut those out and make plastic 'doors' for them instead, hinged with modified control surface hinges that are spring loaded. This means they remain closed UNLESS the EDF needs more air and it will drag them open more - the springs are WEAK, so the doors open with almost zero resistance. But it is enough that they close fully when the plane is stationary, or anytime it doesn't need more air than the stock ducting path can feed it.

At worst, they can be replaced and not used.....

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Old Jul 31, 2012, 10:38 AM
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If its any help to you, my friend has the RTF version with the retracts. Retracts work well and have held up well on our grass strip, but he did have a bit of an issue with the model pitching down when the throttle was opened, preventing a rise off ground. He solved this by glueing a ring from a drinks can in the rear of the fuselage pod, angled upwards to reduce the downthrust from the fan. The model is also C of G sensitive, so he advises not to go rearward of the recommended position.

Mike
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Old Jul 31, 2012, 05:43 PM
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Tell him to raise the nose gear length a bit. That would be better. A few degrees AoA makes a lot of difference to a plane taking off.

I bought the ARF so I could make it a hand launcher, but I would still buy ARF even if I was doing retracts because of all the other 'own choices' you can make, but also to use decent retracts. There are a lot of stories of how lousy the stock retracts are - unreliable - and I have seen a PNF in the flesh myself doing that right from new. First few cycles on the bench and one main didn't operate reliably. And almost every flight - and if down it would collapse anyway. And as mentioned, lots of people having that issue. Cheap metal trunion PZ's are fantastic ($10 ea) and it seems Durafly/FMS chose a very budget version of those to use.
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