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Sbach 342 FPV

There we go for the fun part. Not that flying that nice little one isn't fun, but doing it from the inside will be even more fun. After some guesswork, I aim for a max weight of about 7gr for the video equipment. This should include the camera, video transmitter, and a pan servo. The servo should have 180° throw, which won't be easy as there's no known servo that does it out of the box and is light enough.

The video transmitter is easy to choose. As the R/C system is Spektrum 2.4GHz, there's no way to use the good old 2.4GHz / 10mW transmitters anymore. In fact, those have mostly been collecting the dust lately. The obvious choice is thus my current 5.8GHz/20mW version.

About the camera, there was a new camera around that was advertised as weighing approx. 1gr that seemed appropriate for the purpose, apart from one detail, the only version available at this time had a lens with a very narrow FOV (60°) that would not be enough to give the intended result... I ordered one anyway, and later noticed that I had an old awful camera that had a more suitable lens with a thread that turns out to be just a little too small to fit. I had to to some rather creative hacking to dismount the 1gr cam's original lens, take the lens elements out, and drill/sand the lens body's interior so that I could use it as a reduction ring. Its thread could thus be screwed in the mount as normal, but I could then screw the new lens in that plastic part. It had to be brought down to approx. 0.5mm thick to allow that, which was rather long, tedious and risky, but in the end gave perfect results.

The power requirements of both the transmitter and camera are 3-5V. I really wanted to avoid having to use a second battery just for the video system, so I tried to simply install a 5V linear regulator fed with the plane's 2s main battery. This isn't always easy, because the model's components (ESC, servos) generate noise on the power supply that can be bad or not depending on the actual components, and video equipment can be more or less sensitive to it. I had to try 3 different voltage regulators, but fortunately one of those I had managed to eliminate the noise without the need for heavy external filtering components.

Now getting that camera to pan was another fun part. I found a nice 1.7gr servo, but it is unfortunately digital, so no way to use an external servo stretcher to get 180° movement. Fine surgery ahead. I ordered a few, and after testing it worked correctly with the receiver's CH5 output, I went on to take one apart hoping to do the common "resistor mod", where the servo's feedback circuit is fooled into thinking the potentiometer moves less than it does by putting a resistor in series with each end connection. First observation: The pot's axle is plastic, and it will break easily if you apply too much force on it when taking the output gear off. One servo in the trash. The second one went OK. It's REALLY small inside, so it wasn't so easy to solder the 2 tiny 0805 SMD resistors between the pot leads that are deep inside the case and the wires going to the controller board. I added 2.5k resistors, which should approximately double the travel. After sanding down the mechanical end stop on the output gear I reassembled the servo, and time for the test, which fortunately was... successful! A nice 1.7gr, 180° servo. There is quite a bit of play in the gears, but it shouldn't be too bad given the weight of the camera.

So there we go, after a bit of soldering and gluing the whole FPV equipment set is ready for final mounting.

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I initially decided to keep the plastic canopy in place as it seemed to look quite good on the bench, and would have kept the model's look intact:

But that was shortlived, on the first flight it was evident that the sun reflections and blurriness were really unpleasant.

As expected, this model is mainly good for calm conditions. Although it's perfectly flyable with some wind the flight is shaky enough to be annoying. When it's calm however, it is impressive how similar the flight characteristics are to my 1.2m Edge 540. Very stable, neutral, a pleasure to taxi and land, and with smooth head panning action. Flight time is about 8 minutes with a stock 2s/180mAh LiPo in good condition, but those quickly went down to about 6min after a few months. A good replacement is the Nanotech 260mAh, especially since the camera equipment makes the model a bit tail heavy and a compensation is needed to keep it properly balanced anyway. Battery weight is always preferable to dead weight.

This has interestingly been the model I flew the most in 2012... but I still haven't been able to make a decent video of it!

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