|Jul 04, 2011, 06:22 AM|
A HK Kinetic 800 ARF Mod Log.
This will be a running log (lots of edits) of my getting a Kinetic 800 ARF ready for flight.
Here is the PNF K800 (plug and fly version) from the Hobby King website:
The ARF version is all loose parts (EPO, plastic, decals, etc) with the exception of the following which are pre-installed:
Which leaves the following to go:
What I purchased to fill the gaps:
EPO - Properties
This is the first time I have seen or worked with EPO, its an impressive material. It does dent, but very small dents seem to 'relax' out. The most impressive property is its stiffness while still being tough. It is also easily workable with mechanical tools (knife, boring-bits, etc).
Again all good.
I first inspected the components to both familiarise myself with how it all went together and to see if I could make any improvements (I can't help myself )
a) Stabilator clevis. Very loose nut holding the stab control-rod clevis. Tightened and used locktite to keep it tight - all good. While I was in there I lightly lubricated moving-parts with plastics grease.
b) Stabilator halves locking mechanism. Clever but required de-swarfing and freeing up of the unlock key-tab. To unlock this device (take a deep breath)
Edit. The above did not work for me the second time. I have now found I need to prise both ends of the locking tab up at the same time (with knife or jewellers screwdrivers), and then pull halves apart (or push apart with thumb/fingers - see picture below). The tabs lock in two places simultaneously. Of course all a bit different (trickier) doing this when the stabilator halves are mounted through the tail fuse.
c) Control-surface hinges. I felt these were a little stiff so to correct for this I sanded the hinge root until free but still secure.
d) Servo fitting. The Turnigy 1440A's fitted perfectly into the wings. These servo's also fit well into fuselage but I wanted to use HXT500's as in my experience the HXT servos are near bullet-proof, this will require fuse cutting.
To fit the HXT500's I used a small dremel-type tool and with this and a knife removed enough material to fit the 500's. These were then 'glued' in with white silicone sealant (fills gaps well and acts as a low-grab adhesive).
e) Prop. I test-fitted the prop to the purchased C20 motor (after reversing the shaft), Plush ESC & 2S LiPo. First observation is that everything fits mechanically well together. Second observation is that the balance of the folding prop and spinner leaves a lot to be desired! Quite a bit of vibration on runup. I ended up replacing the blades with new ones from my local RC store. Unfortunatley all they had were 7.5x4 blades but they fitted perfectly and vibration is now gone, plus hopefully this size will better suit my motor/lipo combo anyway. To replace the blades a retaining pin needs to be pressed out. It is friction-locked and holds nice and securely, although would not want to remove to often I imagine.
f) Wing mounts. Like others I noticed there is a degree or more of upward flex. This is because there is an amount of free-play before the CF ends bear against the root mounts. I corrected this using servo horns cut-down to fit in the slots. Bonus of using the horns is that the curve of the horn can be used as a guide for the CF ends when slotting the wings together. Free-play is now gone.
g) Receiver. I am using a HK 6-ch set. I looked for a position that would allow relatively simple servo pluging in and out as I wanted to try separate-channel ailerons with flap/spoiler funtionality for the first time - so anticipated some plugging/unplugging. The photo shows the final position I decided on. I cut down the corner of a plastic box and glued this to the Kinetic's plastic wing-coupler as a support for the back of the rxr (top). I also used EPP foam as a cushion in which to glue the rxr. Finally an indent was routed out for the aerial.
h) Battery compartment. Used coroflute (plastic "cardboard" that the real estate agents use) to build a little compartment. Around the inside circumference a piece of mousepad was cut down and glued. This acts as a slide for the battery to bear against. EPP was used to narrow the Kinetic fus depth to 16mm - the thickness of the 2S 850mAH Lipo I'm planning on using. I can also use a 3S 470mAH as this is 15mm but longer. It can't be seen but the coroflute had tabs cut into the edges and these were cut into the fus to key the battery box in.
i) Joining the fus halves. I decided to use double-sided tape as the primary method of joining the two halves. I do however use UHU-POR on the plastic to foam parts (wing-joiner & hatch). Plus a light smear of silicone was wiped onto the servos. After getting everything ready the halves were brought together and taped tight with vinyl tape (electricians tape). Its a week on and the halves are staying together well. If they do start to separate I'll just use a line of UHU-POR to bring them together again.
j) Changing out the 1440A servo wires. As the delivered 1440A servo wires were to short I removed the bottom of the servo (just pull and angle and the bottom pulls away) and soldered new cables ordered from HK. Rather tricky soldering (tiny connections) but got there in the end. Obviously tested for correct operation before seating the servos in the wing! I took a photo of the old wires (in case I forgot what goes where) but forgot to take a photo after - sorry! The new wires are quite a bit thicker than those in the photo so I filed the exit in the servo to accomodate. It all worked out nicely.
I used the second hole on the servo arm that came with the 1440A's and cut the third (outermost) hole part off. This gave a max throw of +13/-14mm measure at the aileron trailing-edge.
NOTE: Screw the arm holding-screw into the servo before glueing servos into wing!!! Its painful trying to drive the screw when the servo is recessed. I forgot and had to use long-nosed pliers on the head of the screw to screw it in.
k) Decal fixing. I used 3M/Scotch Super 77 as a bond between the decal and foam. Definitely harder than just sticking down to the foam but hopefully will ensure they stay on. Procedure is place decal on foam, roughly mask with tape and paper, spray lightly with S77, remove masking, place decal & finally clean up with a rag and mineral turps (rag needs to be quite wet with turps or bits of the rag stick to the S77).
UPDATE: I tried spraying the S77 directly on to signwriters vinyl (as I don't have a decal to test), rather than spraying onto the foam of the plane. I then stuck the vinyl with S77 straight onto the foam - works great and needs very little cleanup. If you are quick to place after spraying, the vinyl/decal can still be moved around gently before the S77 cures.
l) Nose attachment. Using an old plastic 'credit card' I cut triangles for each side for a screw fastener. As the plastic card is thin I glued a circle piece of card underneath to give the screw more material to bite into.
m) Motor mounted. I pulled the ESC wires forward from the electronic compartment and then soldered/heatshrinked them to the motor wires. I glued the ESC lightly with UHO-POR, between the ESC heatshrink and fus foam. The ESC wires were then given a pig's-tail twist to pull the wire' slack back out of the motor area to ensure the wires did not rub on the spinning motor bell-housing.
n) Stabilator install. Lub'd the plastic parts that bear against each other in stab operation and slid the right-hand piece in, then the left-hand piece which all clicked together nicely. I am a little disappointed however as the stabilator is not truely at right-angles to the vertical stabiliser. There can be only one reason, the plastic mounting piece was not installed/glued true to the fus at the factory. Shame but hopefully will not affect flight performance.
Updated: I decided to correct the non-parallelism of Stab to Wing. Below are some photos of my surgery. I removed the stabilator halves before taking knife to foam but on reflection that's not absolutely necessary.
Process:o) And that's pretty much it! Just waiting for 850mA Lipos to arrive before final CG & flying. Using smaller Lipo for configuring electronics and rough balancing, looks like I will need to add ~4gms to the nose. Photos below (labelled 'O') are of finished plane.
p) Calibrate HK-T6A V2 Transmitter.
The photos show the settings I settled on. These gave throws of (in mm):MAIDEN FRIGHT
Brilliant maiden flight for argo, disasterous second flight!
The time had come to maiden K800 in the afternoon, finally the rain had stopped and wind dropped to ~16km/hr. Bright/low winter sun with the wind coming "from" the sun (a problem in the making). So first time aileron pilot launches into the wind and wow!! Had me reaching for the throttle before she rocketed out of sight!! My gawd compared to my wing-hangers this thing was fast. So blasted around until 1st battery was getting soft. Landed pretty well in grass but still had a wing pull out (it was not a bad landing).
So put wing back in, control checks and off again, honest it would have taken surgery to remove my grin. about 30 seconds in, suns real low and wind picks up and I lose orientation!!!! !!!!. Dumbness sets in and I forget to pull the thottle back as I 90degree into the ground! Buggar !! Incredibly tough I must say but not tough enough. Both wings pulled out (but are fine otherwise), C20 motor good, prop good, nose-cone good but full of dirt - just the nose mount cracked in two. Modified stabilator/tail fine but fus just forward of tail very bent! Rudder push rod has a 45 degree bend in it. My battery box and electronics worked great as they were all ok (goodness knows what sort of inertia force the 50gm battery put on the battery box).
So smitten with performance but need new red nose-mount (got off remarkably lightly). The C20 2050kv 2S 850maH combo is great, I could pull vertical and on my maiden was doing did loops and rolls very easily (almost to easily!).
Photos below (amazing how far the dirt was driven into nose cone).
Flew this evening about half an hour before dusk. All good! I did some tweaking of the dings 'n dents by power-off glides and trims. Then launched at half power - had an excellent flight and only landed due to failing visibility as dusk came on. Unlike my maiden I kept the power way back (third to half throttle) and this of course gave me far more reaction time.
Only thing that did annoy the hell out of me was the wing/s pulling out on landing. Guess they are loosened up from the crash. Tonight I'm glueing them in solid!
So great plane, ok for aileron-beginner if throttle is kept back. As others have noted she's a great glider!
WHAT WOULD I DO DIFFERENTLY FROM WHAT I HAVE LEARNED:
1) Probably just use
UPDATE: The D05010MG looks like a stronger servo of same dimensions. See below.
2) Given I had to add 4gms of lead weight to the nose (so keeping the nose light is not a problem) I would build the battery box fully from coroflut and not key it into the EPO foam, just UHU-POR it to the fus. That way it could easily be transferred to another fus.
3) Forget the Hobby King decals, probably just S77 glue some signwriter vinyl shapes on. Just to much trouble either fixing them well on keeping them on.
4) Use Hole#2 on fus servos rather than Hole#3, not a lot of throw is needed with this bird.
5) Use rare-earth magnets as well as clips to hold the wings in, they pull out very easily. UPDATE: OR just glue the wings in.
THINGS THAT WORKED SUPRISINGLY WELL:
1) C20 2050kv motor, 2S Lipo, 7.5x4 prop & Mystery 12Amp ESC combo. Lightweight power.
2) Double-sided tape to hold fus halves together - didn't part in the crash!
3) Turnigy 1440A Servos - survived the crash. UPDATE1: Actually one of them stripped a tooth in the crash.
UPDATE2: These look better: http://www.hobbyking.com/hobbyking/s...dproduct=10965
5) Liquid silicone rubber servo mounting - also survived the crash. Later I found I had to replace one of the wing servos, on levering the servo up the silicone held, held and then released smoothly - perfect.
6) Battery box - kept everything perfectly in place.
7) The modified stab angulation - also stayed put.
ImagesView all Images in thread
|Jul 12, 2011, 09:53 AM|
you might want to trying re-programming your 10A Plush ESC. There is a programming option for the level of current limiting. I believe low medium and high. I bet that it is set on low. Might fix your issues.
|Jul 13, 2011, 03:45 AM|
Thanks for the tip I'll look into that. Although I thought that was timing not current limiting? Or is there a setting for current as well? Cheers.
|Jul 13, 2011, 08:29 AM|
should be a setting for both timing and current limiting.. usually one of 3 settings the stock setting is right in the middle. Looks like on the manual it shows timing and you might want to reset that to medium too.
Google works great to find the manual..
|Jul 13, 2011, 04:38 PM|
No problem accessing the manual - it came with the ESC
So (not for the first time) I read it right through - there is no setting for current. In fact the author avoids the term current limiting completely, referring instead to "thermal protection". So at a guess I imagine they build in a thermal sensor device into one or more of the IC's (NTC resistor perhaps). This would be much cheaper than measuring the voltage drop over a high-current measuring resistor (as these components are relatively expensive and bulky). Of course this is all supposition!
So anyway tried all three timings and results are identical - runs up to 11Amps and then ramps down to a max of 6.5Amps. My guess is its thermal limiting prematurely (switching elements are only getting luke warm).
I'll know for sure its an ESC problem as soon as my Mystery 12Amp arrives - should be here in a couple of days. I'll duplicate the test with only the ESC being changed.
|Jul 15, 2011, 09:48 PM|
Change prop blades.
I was at my local RC store buying connectors and saw these: http://www.hobbycity.co.nz/shop/RC+P...4-FOLDING.html, (closest they had to the Kinetic's 8x5) on a bit of an impulse I bought them to try out.
After driving the retaining pins out of the current folding prop (they are suprisingly tight and secure) these new blades fitted perfectly.
Just waiting for my larger 2S to charge but running this 'new' prop up on a small battery showed two things - vibration is gone (so I had badly balanced Kinetic blades) and the thrust sound of the prop with this new combination is much 'nicer'. By which I mean, it just seems to sound more smooth and less 'thrashy'. The Kinetic blades have a relatively large pitch (5") so going to 4" is going to change the sound but it even so it still sounded 'better'.
I'll add this into the main blog post as well.
|Jul 16, 2011, 11:06 AM|
^^ i got some of these with the complete stock motor/ESC and its pretty nice. The stock blades on my broke on the first flight it was sad. I use 3S 500 packs btw. I have used very small 2s 360 and 2s 500s as well and 3s 800s and of them all the 3s 500 is the best I like for duration (10mins) weight and power.
|Jul 17, 2011, 03:57 PM|
Nice, blades. I like the Aero~naut props, unfortunatly my local store didn't have the right size. Wow you went for 6" pitch - once your Kinetic gets up to speed it must rocket!
|Jul 17, 2011, 04:11 PM|
ESC problem solved.
The problem actually was the battery packs I was using: http://www.hobbyking.com/hobbyking/s...dproduct=11894 were voltage sagging (both of the ones I have).
I thought I would be ok as per:
0.37AH x 25C (constant) = 9.25Amps.
Don't beleive the labels! At ~10Amps load the voltage started at 7.8V and in the space of 1 or 2 seconds went to 5.8 which is where the ESC LVC (low voltage cutoff) kicked in!!!
No wonder my ESC was not delivering 10Amps, the battery could not supply the amperage.
I had the same battery as a 460mA and this time much less sag.
0.46AH x 25C (constant) = 11.5Amps.
Never mind the claimed 40C Burst draw capability . Even putting aside the 20AWG wiring that comes with these batterys (I2*R losses).
Due to the weight I need to CG this bird I'll use a 850mAH battery for the final config. So no battery V-sag problems I should think.
My apologies for slagging the Turnigy Plush! Kinda ironic given Turnigy also make the battery I was challenged by
|Jul 18, 2011, 05:38 AM|
Woops didn't mean to slag Turnigy batterys. I had Rhino's before the Turnigy's and also another brand I can't remember. I'm pretty sure they all fairly much perform the same despite all the techo marketing etc. However to compete in the marketplace I imagine its pretty much standard to quote max ratings as Constant Capability. Not a problem though - just don't try riding the edge of the specification envelope with your combos, as I unthinkingly did in the example above.
|Jul 29, 2011, 12:35 AM|
I'm following your build, and I must admit the Kinetic looks fantastic doesn't it. Can't wait to see it flying, hopefully avoiding all the lamp posts at the park...
all the best mate
|Jul 29, 2011, 07:09 AM|
Cheers Andy. Batterys arrived today and everything calibrated. Hopefully maiden flight tomorrow if weather is accomodating.
The lamp posts will have to wait awhile as I always (all three times) maiden my planes at a farm-park a short drive away!
|Jul 29, 2011, 12:06 PM|
|Jul 29, 2011, 05:14 PM|
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