This post is only a short update for SmartPort inverter for F4 flight controllers. Here is alternative SmartPort inverter circuit using bipolar BC547 instead of unipolar 2N7000. All other aspects of operations are the same like in MOSFET version.
It’s still middle of winter here in northern hemisphere, but I’m slowly preparing for next flying season. One of my goals is to push my DIY HC-12 Telelemetry System to a next level. In both range and quality. For quality I’m planning small hardware LTM decoder with LCD. For range, I want to reach at least 1.5km with 9600bps FU3 mode and 2.5km with 1200bps FU4 mode.
While STM32F4 family processors installed in newest flight controllers are superior to STM32F3 (and F1 of course) in terms of raw speed, they are inferior to F3 family in terms of IO handling capabilities. For example, F4 family is not equipped with UART port inverters. Just take a look at the Omnibus F4 flight controller. There is an S.BUS inverter, but not a SmartPort inverter. That creates a series of problems when it comes to connecting various serial RX receivers and telemetry systems.
The most popular FrSky (Futaba) S.Bus serial RX protocol and FrSky SmartPort telemetry require inverted UART signal. If there is no hardware inverter on hardware UART port, they will not work. While S.Bus requires only one data line, an external inverter is not a big issue. Some time ago I’ve published The Simplest Hardware Inverter. One MOSFET transistor, one resistor and that are all.
In the case of SmartPort, it’s slightly more complicated. Not only signal is inverted, SmartPort also combines TX and RX UART line into a single wire. That means the following:
- The more complicated inverter is required
- The software has to support this case and fallback to unidirectional UART mode
Entry level DLG (Discus Launch Glider) from HobbyKing has a quite important flaw for a “entry” level model: it is not durable. As a matter of fact, it is quite fragile, specially where plastic nose section is attached to composite fuselage tube. It is attached only with 3 small screws, and I can guarantee: every harder landing will result with something broken. During 3 first weekends with my Mini DLG Pro, I had to glue it back together every second flying session.
Those 3 screws are just not stron enough to keep everything together, so I’ve decided to fix it with epoxy glue and I suggest all new owners of this DLG do it at the beginning. Thin layer of epoxy put everywhere where plastic meets fuselage tube is enough. It make glider strong like it should be from the beginning.
There is a penalty of course: nose section no longer can be detached. Since HobbyKing does not sell replacement parts for this model, this is not a big problem after all…
3 weeks after my first post on Project Dualcopter, it's time for small update. The plan was to install servos and control surfaces. Instead, I've done:
- Basic electrical wiring for motors and ESCs. They have power now and are ready to be connected to flight controller
- To level shelf (above propellers) designed to hold flight controller and radio receiver
- Think for a moment about landing gear. Yeap, there will be some sort of shock absorbers
- Think for a moment where battery will be placed: as low as possible to keep center of gravity below center of thrust
- Decide which propeller should run clockwise and which should run counterclockwise: top should go clockwise, bottom should go counterclockwise
Flying season 2016 is slowly coming to an end on northern hemisphere. That means less time spent on an airfield and more time spent behind a desk. For this autumn I've found a very interesting, small project: Dualcopter.
Dualcopter is an UAV with two coaxial contra-rotating propellers and 2 control surfaces driven by servos. Lift and yaw are controlled by propellers, while pitch and roll by ailerons placed below motors. This video illustrates how it looks like:
My Dualcopter will be slightly different. Instead of foam and wood I will use 3D printed parts connected together CA glue and zip ties. Maybe it will not be super strong and probably will not survive any crash, but should be enough to make it fly for a minute or so. Almost all parts would be either 3D printed or taken from spare box. I'm not planning any new purchases.
- Motors: Turnigy MT2213 935KV
- Props: APC 1045 MR
- ESC: Afro 20A
- FC: Flip32 probably with INAV inside
- Battery: 1300mAh 3S
- Weight: around 800g with battery
So far, after 2 evenings I have this:
Two motors mounted on a frame.
Next step would be to build bottom section with ailerons and battery compartment.
For the last few week I’ve been little busy building my next fixed wing UAV: “Marabou Stork” Depron/Carbon/3D Printed airplane with pusher prop build for FPV. It’s improved version of “Red Cruiser” model from last year.
It’s equipped with KFm-2 wing, Turnigy D2826-6 2200KV motor, APC-E 7×4″ propeller, 2700mAh Lipo battery, FPV setup with MinimOSD and RunCam PZ0420H camera. And Flip32 running INAV for stabilization and navigation (no GPS yet).
As you can see on a video above, it flies. Even pretty well. It needs some tuning, but have big potential. Unfortunately elevator malfunction grounded it after few minutes in the air.
Depron is an amazing material. Light, cheap, waterproof, easy to process and quite durable. Almost everything in RC world can be made from Depron. All one needs is imagination, glue and proper knife. Like I mentioned few times before, I’m cheap, so at the beginning of my adventure with Depron, I was choosing cheap modeling knives. Usually no-name. They had one very serious flaw: knife’s blade had to be replaced every few cuts. And even so, cut was far from perfect.
Luckily, I’ve found a perfect, more expensive but cheaper on a long run, solution: Olfa Knives. Especially Olfa SK-9 Knife with SKB-2 Blades. They are sharp, strong and lasts for a long time. When needed, SKB-2 blade can be used without a knife. SK-9 has one disadvantage: there is no lock, so keeping blade extended all the time requires thumb to be used. And that make it hard to switch knife between hands.
But the bottom line is: I love Olfa knives. Not only when working with Depron. They are very useful with dealing with cables, unpacking and so on…
Beitian BN-880 (I’ve bought mine from Banggood) is an excellent, cheap and accurate Ublox NEO-M8N GPS module. I’m using it for last few months and I’m very happy with it. But is has one serious flaw: there are no cases/enclosures for it. So, in most applications it is naked. I’ve decided to fix that and designed 3D printed Beitian BN-880 case.
Case can be dowloaded from Thingverse
Telemetry link between UAV (drone, airplane, boat) and laptop/mobile/ground station device can be very useful. Not only to get current drone position, altitude or battery level, but also, when wireless link provides such a possibility, to update drone parameters in-flight. Some radio links, like OpenLRS provides such a possibility out of the box. They include transparent serial bridge and almost any kind of device can use it to communicate with flight controller. Unfortunately, most RC radio systems lacks this functionality and additional telemetry links have to be used. Like 3DR 433Mhz radio link.
One can buy or one can build something by his own. Some time ago I've chosen the second way and decided to build my own wireless serial link to archive 2 way communication between drone and ground station software. My objectives were:
- 433MHz since it is legal in my country
- has to allow to use my phone with EZ-GUI, since I do not like to carry my notebook to an airfield
- as cheap as possible
To satisfy those objectives I've decided as follows: