Marabou Stork reborn

It took me quite some time, but I've finally rebuilt my Depron FPV airplane Marabout Stork after last year's crash.

In theory, all I had to do, was to replace nose section. At the end, it turned out, that I should also reinforce wing mount, redo FPV system and replace flight controller. So, full list of changes:

  • Rebuilt nose section that is longer than original by 30mm
  • Full sized MinimOSD was replaced with Micro MinimOSD to save some space
  • Flip32 flight controller was replaced by SP Racing F3 and external BMP280 barometer
  • INAV 1.7 baby!
  • Various reinforcements, mainly around wing mount

Weather conditions in above video were far from perfect. Wind speed around 50km/h made everything hard.

It still awaits for new GPS module, since Ublox Neo-6M is really, really, really crappy solution…

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3D Printed Faceplate for SkyZone SKY-01 FPV goggles

While SkyZone SKY-01 are pretty good FPV goggles, they are not very comfortable. Instead big faceplate, they only have rubber eyecups. This approach works, but well…

Like always, there is a solution: 3D printed faceplate for SkyZone SKY-01. Thingieverse has at least few different designs, but I’ve chose the one from the link above. They fit right and do not have fan adapter which I do not use.

Foam pads for faceplate are a second problem. In first iteration I just uses gray sponge I had at home and white, dense, closed foam from Emax motors and glued everything together with Uhu Por. Continue reading “3D Printed Faceplate for SkyZone SKY-01 FPV goggles” »

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Relaxing Winter FPV Session

Winter is not the best time for FPV. Day is short, it is cold, it snows or rains most of the time. But sometimes, when sun is shining, there is a slim window ofopportunity to just go outside and fly. You will get cold, batteries will last shorter, but it will be worth it.

Some people will say it is boring. For me it's not boring. It's 100% relaxing…

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Marabou Stork: fixed wing FPV platform

Marabou Stork, my Depron/Carbon/3D Printed FPV airplane is officially done. Although it had first flight a week ago, some technical problems postponed full feature trials until yesterday. I would not call it a "huge success", but it was fine.

Here is a video from some FPV flying:

After around 1 hour in the air, here are some conclusions:

  • Wing is closing to it's limits. Originally it was designed for an airplane that weights around 500g. Marabou Stork weights 900g. Do not get me wrong, it still flies good, I really love KFm-2 profile on it, but you have to start to remember about things like air speed, specially during turns: too much yaw, not enough speed and bam, you have stall. It's easy to recover, no problems there, but last years model (the same wing, less weight) was free of it
  • Neo-6m GPS is, hmm.., crap… I have to update to Ublox Neo-M8 as soon as possible
  • INAV is unable to process GPS altitude and barometer altitude simultaneously: altitude jumps up and down like crazy. For now, the only solution is to disable either baro or GPS altitude component from computations. It's simple and I will try to write few words about it next week
  • Did not tested fixed wing navigation features of INAV yet. Reasons: two points from above
  • Boscam TS-351 200mW 5.8GHz transmitter with crappy clover-leaf antenna behaves much better than expected. I had excellent reception on my Skyzone Sky-01 at 1km and had to return due to RC link RSSI warnings
  • I'm disappointed with FrSky X4R range. Looks like 1km is a safe side limit here. RSSI was dropping to 40 and did not wanted to push it further. Probably it's because crappy antennas. They are equipped with simple whips, not dipoles like X8R for example. Next week I will try connecting 2.4GHz dipole to X4R and will give it another try

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Antennas: power loss on polarization mismatch

Most people in RC hobby knows that receiver and transmitter antennas should match polarization. But what would happen if there was a mismatch? For example when transmitter uses linear vertical and receiver circular left hand? There would be a loss of power, attenuation. How much? Look at table below. Remember: -3dBi means half of power is lost during polarization change and you need +6dBi power (4 times more) to increase range by factor of two.

 

Vertical Horizontal LHCP RHCP
Vertcal 0dBi -20dBi -3dBi -3dBi
Horizontal -20dBi 0dBi -3dBi -3dBi
LHCP -3dBi -3dBi 0dBi -20dBi
LHCP -3dBi -3dBi -20dBi 0dBi
  • -20dBi is practical value. In theory, all power should be lost during this conversion. But we are living in not perfect world and always some power will go though
  • Vertical – Linear Vertical Polarization
  • Horizontal – Linear Horizontal Polarization
  • LHCP – Left Hand Circular Polarized
  • RHCP – Right Hand Circular Polarized

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Improve Boscam BOS 600 cooling with thermopad

Boscam BOS 600 is a 5.8GHz 600mW 32 channel video transmitter well suited for long range (> 1km) FPV flights. Its design makes the whole casing a radiator. This is good, since 600mW of RF means a lot of heat. Unfortunately, Boscams BOS 600 design has a serious bug there: so what if whole casing can act as a radiator, since connection between RF module and casing is poor? Just look at picture below.

Boscam BOS 600 poor cooling

RF chip is not even touching casing, gap is filled with a blob of thermal compound. Add far from perfect quality control and you will have overheating transmitter that will loose output power or even burn. But it can be fixed with a small piece of 2mm thick thermopad.

  1. Open casing by removing 4 screws on the sides of transmitter
  2. Clean RF chip and casing from existing thermal compound
  3. Cut a pice of thermopad similar in size to metal block screwed to bottom part of casingThermopad cut
  4. Remove protective film from thermopad and put it in metal blockThermopad BOS 600
  5. Assemble whole unit and screw both parts together. Thermopad will tightly fit the gap between RF chip and casing, making heat transfer easier
  6. As a final touch I have added an additional aluminium radiator that I’ve bought for my Rasperry Pis. But this is not needed, and can be skippedBOS600 radiator

Final note of thermopads. They come in different thicknesses. 1mm and 2mm should be fine for DIY projects, and can be bought cheap from eBay or any other internet store. Strip big enough to improve dozen of BOS 600 transmitters should cost not more than few dollars or euros.

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DIY FPV LC power noise filter

Both electrical motor and ESC are source of electrical noise that influences all devices connected to the same battery. This is why, very often, on airplanes or big multirotors FPV circuit is powered from separate battery. On small or medium drones this can be hard to archive: additional weight will influence both flight performance and flight time. So, when your setup is suffering from a power noise manifesting itself as vertical bars or other image distortions on goggles/monitor, you can do 3 things:

  • use separate battery to power camera and video TX,
  • cut the noise using LC low-pass power filter.

I would choose low-pass filter. Cheaper and lighter. You can buy one for a few dollars/euros or make 10 by yourself for the same price.

LC power noise filter for FPV

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