Monthly Archives: June 2016

FMS G600 Hand Chuck Glider [RC Conversion]

12 (FILEminimizer)

I had been wanting to fiddle with the famous Multiplex Fox for a while and I had been going though all the build logs I could find on the internet, from gentle 3Ch slope gliders to beastly speed demons, they all exist. Unfortunately, while I was at that, the Fox at the local hobby store was quietly sold out and honestly, I didn’t have much patience to wait for one from outside the country.

In all my despair, the corner of my eye caught the FMS G600 at another local store and I definitely wasn’t letting this one go. The G600 is an EPO hand launch glider with a wingspan of about 500mm, a wee bit bigger than the Fox. The most distinctive difference between the both is the T-tail on the G600 versus the conventional empennage on the Fox. I knew T-tails had a sort of smooth and damped tail moments but I had never flown one before and that was something I was looking forward to. Another observation I could make is the slightly under-cambered aerofoil on the G600 and referring to the pictures on the internet, looks like the Fox has a flat-bottom aerofoil.

The RC conversion of these hand launch gliders isn’t as straight forward as assembling other EPO kits because the placements of components is critical to achieving proper CG at the end, but also it isn’t as painstaking as building a beginner’s balsa kit. One obvious constrain comes from  the small size of the model, I would suggest to keep the wing loading to a minimum which means using lightweight micro electronics. Although, you can always thrown in an immensely powerful motor and overpower your way out of high wing loading, I personally don’t prefer the rocket pig approach for one specific reason that the model’s structure and aerodynamics are more favorable for a lightweight, slow speed setup. Talking about slow speed, I was expecting it to be a nice indoor slow flier but the stall speed is deceptively high, with higher wing loading, stall speed increases further making it impossible for gentle landings. Nothing to complain about, I still happily fly it outdoors even in mild breeze.

My setup:

  1. Hextronic 10g 2000KV brushless outrunner
  2. ZTW Mantis 12A ESC
  3. Hextronic HXT500 5g servos
  4. KS-Servo 4Ch receiver [FrSky compatible]
  5. ThunderPower 2S 325mAh 70C LiPo
  6. 5x5E composite prop

The model flies nice in calm and no-wind conditions and my power setup allows for 8 to 10 mins of flight time depending on how aggressively I fly. I’m not sure about other conversions, but my plane has a less-than-impressive glide slope even though it’s lightly loaded, partly because it has an unpredictable pitching tendency. The plane noticeably tends to pitch up with increase in throttle or in headwind and nose-dive on throttle cut or tailwind. Adjusting thrust angles or adequately trimming the control surfaces will help to a certain extent but does not totally eliminate it simply because the pitching tendency varies through the entire throttle range. The reason I mentioned this is because I spent quite a bit of time playing with different thrust angles and trim settings only to find out it’s the inherent flight characteristics of under-cambered wings. It’s not a big deal though, I got used to it after a couple of flights.

My conversion isn’t nearly perfect, I have identified and mentioned a few flaws and possible corrections based on my assessment of the issue, please do carefully take note of all the mentions if you’re following my build procedure. Suggestions and questions have my attention. Please do share your builds, I’d love to see them!

 

Recommended corrections:

  1. Maintain a wall thickness of at least 5mm around the cockpit cavity and the canopy space, anything more flimsy can start to deform overtime since it’s a belly lander.
  2. I’ve used HXT 500 servos, although they fall into the 5g size category they weigh about 7-9g and are pretty over-sized for this plane , I probably would use something that is actually around 5g overall and a smaller physical profile.
  3. Do not make any cavities or mount servos on the tail boom section, it tends to weaken the section by allowing for stress raisers when you land on the tail. The tail section my plane ripped apart around the rudder servo mount in a hard landing.
  4. It’s a must to add supports to the horizontal stabilizer, a couple of carbons rods on either sides will be adequate.
  5. The rudder authority seems very laggy and not really interactive. I would not cut the rudder and save the unnecessary weight of an additional servo.

 

 

Anjan Babu

anjanbabu05@gmail.com

Arduino Enclosure – TiffinBOX

TiffinBOX (1)

I short my Arduino boards quite often, as unlikely as it seems. Mostly because my desk is littered with solder blobs and steel rulers and other desperate conductors of electricity. Although, the shorts haven’t caused anything more than harmless reboots, I figured I should get a case before my boards are fried. So I get on my usual online marketplaces seeking nifty cases for my Arduino Mega ADK and Uno. In the meanwhile, my boards are seeking shelter in a “tiffin box”. Given my very choosy nature, all the cases I came across on the internet were either utterly bland with no consideration to aesthetics of my liking or simply out of my budget. What do I do? I do what I always do, make my own. Having scrolled through pages of different products offered by a variety of sellers over a range of prices, I set some fundamental design rules based on my observations.

1) Most products use the mounting holes on the Arduino board to secure it to the case using screws and if you ever took a close look at the holes, you can see they are uncomfortably close to exposed solder pads and other active components. Another potential issue I found with screw-mounting the board is that if you ever drop the case accidentally, chances are, the screws might transfer the impact stresses to the board which does not sound very good. In my design, I constrain the board by slotting the protruding female headers through the top plate of the case, nothing “holds” the board, rather it simply “floats” in a tight tolerance space on foam padding. When you do drop the case, the impact stress are likely to travel through the case’s outer structure and not the board itself.

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