FMS G600 Hand Chuck Glider [RC Conversion]

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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

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DIY- Mini Quad Fiberglass Frame

Last year this time, a five-man team including me were working on a mini tricopter for a competition which later got replaced by the mini quadcopter for unexpected reasons. In the span of less than two months (Dec 2013-Jan 2014), a bunch of guys who had never before been around a multirotor and watched months of partial failure with the tricopter which barely lifted a foot off the ground and turned into a three bladed weapon of mass destruction, actually pulled off a working quadcopter that complied with the competition rules.
Honestly, trying to build a mini FPV multirotor with a flight time of 15 minutes is quite a challenge for any beginner. To build a mini quad that weighs in close to a kilogram to do 15 minute flights is out of question. But, we did manage to build a 330mm FPV quad that flew 10 minutes+ on a 3S 1Ah LiPo which is not really bad.
How we did it is not complicated as it is, but it took a lot of prototyping and design optimizations before we saw any real exciting number like 400g AUW and 10 minute flight times. I’m sure there are better contraptions than what we managed, but I’m going to share one crucial thing about our quadcopter, its frame, just in case someone out there is trying to build something quick & dirty similar.
The quadcopter’s frame was the centerpiece of this puzzle, it needed to be very light and very strong — classic engineering paradox — and the final product was a light 28g and about 50 crashes strong fiberglass frame. We improvised on most parts of the glassing process, but you don’t necessarily have to.

Continue reading “DIY- Mini Quad Fiberglass Frame”

DIY – xESC Adapter [Ver2.0 w/ATtiny45]

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Back in October 2013, I made an Arduino based adapter that allows unidirectional aeroplane ESCs to work with surface/pistol radios for RC cars and boats. I used a ATmega8 microcontroller in that adapter and honestly, that by itself was the size of an average ESC, I couldn’t really put it anywhere conveniently on my car due to space constraints and weight concerns (If I can cut down on 5g, believe me, I will).

Even back then, I was trying to make the code work on an ATtiny45 and I wasn’t sure what was going wrong until, Justblair pointed out in the comments that the Tiny45  doesn’t have 16-bit timers, only 8-bit ones and my code was based on the Arduino servo library which utilized 16-bit timers. He also suggested a solution to get my code working on a Tiny45 and that fix is the Servo8Bit library.

Continue reading “DIY – xESC Adapter [Ver2.0 w/ATtiny45]”

G3 “Sinister Saint” — The RC Car From My Dreams [UPDATE]

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Its about 6 years now since I fell in love with contraptions rolling on three wheeled under the influence of instantaneous torque from an electric motor working its magnetic magic inside a metal can held against sintered magnets.

Continue reading “G3 “Sinister Saint” — The RC Car From My Dreams [UPDATE]”

DIY- gForce meter 1.0 [UPDATE]

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So this time around, it’s another fun and functional microcontroller based DIY, a g-force measurement system with data logging to SD card.

HARDWARE USED:

1) Arduino UNO w/ATmega328P
2) 3-axis accelerometer breakout
3) SD card
4) SD card breakout w/level shifting circuit
5) LED Continue reading “DIY- gForce meter 1.0 [UPDATE]”

DIY- xESC Adapter [Ver1.0 w/ATmega8]

This Arduino based DIY is for everyone who would wants to run aeroplane ESCs with a surface radios. It goes in between the ESC and Rx. Although, there is already an adapter called Pistix available in the market for the same purpose, I couldn’t find any schematics or instructions about it to build one myself. With some help, I came up with something similar. How the adapter works: An aeroplane ESC needs 0% throttle indication at startup, but since a surface radio throttle is set at about 25% by default, it makes the ESC beep as a warning to set the throttle to 0%. For the aeroplane ESC to work, you can either mechanically modify the Tx by setting the default position of the throttle to 0% or if that is not possible, you can do it the software way; the adapter takes the 25% signal coming from the Rx and remaps it to 0%, as an indication of ‘no throttle’ to the ESC. Materials required: 1) ATmega8 or equivalent microcontroller- 1 nos 2) 16MHz crystal- 1 nos 3) 22pF ceramic capacitors- 2 nos 4) Servo extender- 1 nos 5) PCB Additionally, you’ll need a programmer to burn the code on to the ATmega8. I used an Arduino UNO board for the same. The Arduino code and the schematic can be downloaded from here– https://www.dropbox.com/sh/anvf4ibo4hesyj1/0zflxkuvDT?m Tested the adapter on my air boat, works flawlessly! I used an ATmega8-16PU microcontroller for this project, couldn’t get the code to run on an surface-mount ATtiny45-20PU, if some electronics genius on here can do that, it can physically reduce the size of the adapter to less than half. I couldn’t have done this project without help from Trishit Ghatak and PeterH (Arduino forum)

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