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Mr.RC-Cam

FPV Q250 Racer Build Log

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I finally finished building a 250 sized racing Quadcopter. It flies well on the default PID settings but the Altitude-Hold function needs some work.

Edit: Revised the PID settings and the Altitude-Hold feature works awesome now.

I thought I'd share some details. Please keep in mind that these are not assembly instructions -- they're just brief comments about what went into mine. Of course your 250 Quad can be completely different so don't be bashful about personalizing yours.

First, a "beauty shot" taken after this morning's run:

post-2-0-75813100-1415045706_thumb.jpg

Edited by Mr.RC-Cam
Alt-hold update.

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I selected the RCX H250CF Quad frame kit because it looked like it would have enough room for all the components I intended to install. It's a "Full House" FPV installation with OSD, HD camera, telemetry, LED lights, and the kitchen sink. Looking back, the frame kit was a good choice because everything squeezed in.

I installed RCX H1806-6 2400KV motors with the RCX 12A Sky ESC.

The frame has three main tiers. The lowest tier holds the power distribution board, ESC's, and motors. As follows:

post-2-0-42976200-1415051866_thumb.jpg

All the high current ESC wiring is managed by the power distribution board. It also has two DC-DC supplies integrated into it. One is variable and the other is a fixed 12V. They are step down designs so with 3S LiPO power the 12V regulator is essentially pass-thru and does not provide any regulation. I ended up modifying the 12V section to be 10V so that it would be a regulated source. I used this voltage to power some 3 Watt Luxeon Star type LED's. I could have used the variable output for this but I thought I would keep the variable supply free for other uses. Here's the regulator Mod:

post-2-0-43660700-1415053052_thumb.jpg

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The chosen flight controller is a Flip32+ which is a variant of the popular Naze32 flight controller. I loaded the latest version of the Naze32 Baseflight firmware into it. Baseflight is a forked 32-bit port of the MultiWiiCopter open source code. I had to add some cables & connectors to the Flip32+ for the minimOSD, FrSky telemetry, voltage monitor, Beeper, LED control, and current sensor. As follows:

Top side:

post-2-0-64582700-1415053443_thumb.jpg

Bottom side:

post-2-0-08212800-1415079564_thumb.jpg

The Flip32+'s voltage monitor already has the required attenuator resistors and can directly connect to the 3S battery. The high amperage shunt current sensor is a DiY solution based on a INA139 current sensing IC that is configured for approximately 70mV/Amp scaling. The sensor's hardware scaling is set by the 68K resistor that was mounted on the bottom of the Flip32+ (at the CH2 input location). The Baseflight software has a calibration feature to accommodate a variety of current sensors.

post-2-0-57130200-1415054157_thumb.jpg

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There are three 3-Watt rated LED's wired in series. They are powered by the 10V DC-DC supply and current limited to 350mA with some resistors (two 22 ohm in parallel).

At the rear are two adjacent red "afterburner" lights.

post-2-0-64068300-1415060637_thumb.jpg

The LED's turn on when the model is Armed. There's a VO14642A Solid State Relay (SSR) that is connected via a 470 ohm resistor to the Flip32+ port pin that powers the on-board ARM led. The SSR is an optically isolated MOSFET transistor which is a fantastic way to control the LED power without inducing noise into the flight controller. Keep in mind that the port pin can only supply a couple mA's of current, so some kind of transistor switch is needed. The SSR method works well.

The SSR chip is mounted on the front LED, which is a bright white "headlight." The other two LEDs (at the rear) are in series with this.

post-2-0-32687200-1415060920_thumb.jpg

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The second tier holds the Flip32+ flight controller, R/C Rx and video gear. Here's a view before the Flip32+ was mounted.

post-2-0-63054300-1415059652_thumb.jpg

The R/C system is a 9x running OpenTx. The receiver choice was a FrSky DFR4-II. This receiver has CPPM (PPM-Sum), RSSI and telemetry.

The OSD is a minimOSD (KV Team Mod 1.0). All of the OSD's realtime data, including the artificial horizon, is provided by a RS232 TTL serial communication from the Flip32+. The only exception is that the R/C receiver's RSSI is directly connected to the minimOSD. I updated the minimOSD with the latest V2.3 firmware from Team KV. BTW, it is powered by 5V (its 12V input was NOT used due to the bad things I read about using it).

The FrSky DFR4-II's RSSI feature is not an analog voltage. Instead it is a PWM waveform. I could not get it to work (RSSI value on the OSD never changed). After some head scratching I discovered that my DFR4-II's RSSI output was broken. My o-scope showed that it had the correct PWM waveform, but it never varied regardless of signal strength. That issue was solved with a new DFR4-II.

The Flip32+ has a "soft-serial" port (on the CH6 location) that was connected to the FrSky DFR4-II's telemetry data input. This conveniently sends the 3S LiPO voltage and current sensor measurements back to my 9X transmitter. It's a single wire connection. I also connected the 3S voltage (with a DiY attenuator resistor) to the A2 input of the FrSky R/C receiver. This duplication of the 3S voltage monitoring might not have been necessary, but it seems to allow more flexibility with the 9X's telemetry alarms.

I blew an entire day trying to get the current sensor to work. There are two supported configurations, one uses the Flip32's "CH8" ADC input and the other uses the "CH2" ADC input. I selected CH8 which turned out to be a bad idea. After much hair pulling I discovered by a process of elimination that CH8 ADC input was being disabled when the FrSky telemetry soft serial feature was enabled. The solution was to move the current sensor over to the CH2 ADC input.

However, my original scaling resistor value was too sensitive and Baseflight was not able to calibrate the current. I pulled out the Flip32+ and swapped out the resistor soldered on CH2. That little detour was all it took to get the OSD and R/C Tx to report correct current values.

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The video transmitter is a Flysight 5.8GHz (ImmersionRC/Fatshark compatible version). Not much to say other than I really like 5.8GHz wireless video for multirotor installations; Plays nice with the nearby electronics and video quality is fantastic.

But you know how they say trouble comes in three's. Well that came true during this build. When I powered up the minimOSD without the camera I correctly saw all the realtime telemetry data (which comes from BaseFlight) on a black background. But whenever the video camera was connected the telemetry data would be missing (but the camera's view was always fine).

So more hair pulling.

Google found an endless number of victims that experienced this issue. Their solutions were unusual: For example, some said changing power supply connections solved it, some said twisting wires solved it, some had to change the camera, and some said pressing the minimOSD reset button after power-up made things come alive. Some gave up.

A few hours with an o-scope, followed by a source code review, resulted in identifying the cause of the missing OSD image. The issue is caused by cameras with marginal sync amplitudes. The minimOSD performs all screen updates at the start of a vertical sync period (during the blanking period). The sync detection is done by the MAX7456 video processor on the mimimOSD board. Because the MAX7456 cannot detect low amplitude vertical syncs the OSD firmware is forever held in a wait state and never paints the screen. The OSD worked without the camera because the MAX7456 will self-generate the sync signals when a camera is not installed.

My temporary solution was to measure the video signals from several different camera models until I found one with proper sync levels. Luckily I struck gold. I believe the reason there are so many cameras with incorrect sync levels is because the Chinese camera makers simply copy each other's circuit designs and problems like this are perpetuated.

I suspect this issue can be resolved with a minimOSD firmware tweak. It is an open source Arduino project, so modifying the code is not a problem. I'll try to find a solution when I have more free time. In the meantime I'm going to fly this bad boy!

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The top tier holds the Mobius HD Action camera and battery pack. No extra room to spare and so it was nice to find that everything fit. The three tiers quickly come apart for service/repairs without too much fuss.

post-2-0-41082700-1415068755_thumb.jpg

I think that sums up my Quad 250 assembly adventure. These tiny things are fast, nimble, and surprisingly noisy. In other words, pure perfection. :)

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Great write up as usual, do you get any signal blocking with that big chunk of electronics and boards?

What is the flight time?

Terry

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do you get any signal blocking with that big chunk of electronics and boards?

I haven't had any RF fading or multipath issues despite the BlueBeam Omni's antenna location and the nearby structures at my flying area. 100% picture perfect so far. Mostly because the flight distances have been under 100 feet (backyard flying course). BTW, there's a +5dBi CP Patch on the vRx. The RF force is strong with this one.

What is the flight time?

Motor current during forward flight is about 10A. Flight time with a freshly charged 3S 1300mAH is about 6 minutes. The 9x's telemetry and the OSD both report mAH consumption. I end flights with about 200mAH remaining.

The Quad has developed a twitch that randomly occurs about twice a minute during flight. I'll troubleshoot it after I upgrade the cheap 5030 props that are being used (they came with the motors).

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Not much flight time there. Is it possible to fly with a bigger battery or is the weight getting critical?

Terry

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Sure, you can use a higher capacity pack for longer times. With better props and 1500mAH packs I would expect mine would get 8+ minute flights.Some pilots haul 2200mAH packs on their 250 for much longer run times.

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That sounds more like it :)

6 minutes takes me back to my first steps into AP...

Terry

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Keep in mind that flight times will depend on how you fly. Someone that likes to hover around and loiter will certainly get longer times.

I rarely post videos since FPV on youtube is as common as dirt. But I've been told that if there's no video then it didn't happen. So here's a backyard test flight from today.

After I get more time on the sticks I plan on running a fast action course that goes along the fenced property. I'll include some obstacles in the course to add more thrills to the ride.

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I've run through a couple dozen packs so far and only messed up four props. Either I'm not trying hard enough or I've been lucky. I've ordered some better props and it will be interesting to see if they help the flight times.

Flying in full acrobat mode is still too much for me to handle at high speeds. But Horizon mode is perfect for my skills. It switches to acrobat mode when the sticks are off-center, but centered sticks revert back to level/stable mode. So best of both worlds for old dudes like me.

As mentioned earlier, the minimOSD does not work with some cameras because they have incorrect sync levels. Since the problem has frustrated many users it seemed like something that needed to be fixed. Fortunately I was able to patch the minimOSD code and this issue has been solved. I'll start a new topic and post the patched Arduino code soon.

EDIT: The patched minimOSD code is available here:

http://www.rc-cam.com/forum/index.php?/topic/4003-minimosd-software-fix-for-chinese-cameras/

Edited by Mr.RC-Cam
Added link to patched code.

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Now flying with Gemfan 8040 props. With a 1600mAH 3S pack the flight time is about 7.5 minutes (200mAH remaining). 8 minutes is possible if the Mobius HD camera is removed.

I suppose I would beat the 10 min mark if I stripped off all the FPV hardware. I'd have something that flies nearly twice as long but is half the fun. :)

I'm still experiencing the random glitch during flight. Some flights are worse than others and I have not found the cause yet.

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Mr.RC-CAM, can you share your Flip32+ CLI settings (cleanflight/baseflight) for getting the D4R-II telem working on R/C channel 2/6?

I have an almost identical setup and want to have minimosd off the serial port TX/RX/V/G + hook up Telem on channel 2 or 6. I don't know enough to wing it, as my attempts have not worked so far.

Are you directly hooked from the receiver to the FC on CH6? if so what did you do to set that channel to rcv telem?

Thanks!

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This is my Baseflight backup file:

baseflight_backup_11.5.2014.13.6.txt

These are the CLI entries for soft-serial FrSky Telemetry on Flip32's CH6 (I use CH2 for current sensor):

feature SOFTSERIAL

feature TELEMETRY

set softserial_baudrate=9600
set softserial_1_inverted=1
set telemetry_port=1
set telemetry_provider=0

The FrSky Rx's Telemetry output is directly connected to the Flip32 (no other hardware needed).

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This is my Baseflight backup file:

attachicon.gifbaseflight_backup_11.5.2014.13.6.txt

These are the CLI entries for soft-serial FrSky Telemetry on Flip32's CH6 (I use CH2 for current sensor):

feature SOFTSERIAL

feature TELEMETRY

set softserial_baudrate=9600
set softserial_1_inverted=1
set telemetry_port=1
set telemetry_provider=0

would I set rssi_channel = 2? or should I just stick with CH6 with only signal coming off the receiver (no ground)?

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My FrSky Rx's RSSI output is directly connected to the minimOSD (it is not wired to the Flip32+). So I can't offer any proven advice on connecting it directly to the Flip32+.

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My FrSky Rx's RSSI output is directly connected to the minimOSD (it is not wired to the Flip32+). So I can't offer any proven advice on connecting it directly to the Flip32+.

Wait... so what am I confusing? The Yellow wire in your photo, is that the RX? Or TX off the receiver? I was assuming the RX connected to CH6, gets you telem -> taranis? Then what... RSSI is the TX? and you wired that to your minimosd for visual? Do i have that right? The FC won't know the RSSI in the end.

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I was assuming the RX connected to CH6, gets you telem -> taranis?

That is correct.

RSSI is the TX? and you wired that to your minimosd for visual?

That is correct. It is displayed as a 0-100% value on the monitor.

The FC won't know the RSSI in the end.

That is correct. My FC does not need to know RSSI. It's a parameter for my eyes only. :)

Edit: Keep in mind that your Taranis (like my hacked 9X) already reports RSSI of the R/C link. So there is no need to involve the FC to communicate the FrSky RSSI data.

Edited by Mr.RC-Cam
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That is correct.

That is correct. It is displayed as a 0-100% value on the monitor.

That is correct. My FC does not need to know RSSI. It's a parameter for my eyes only. :)

Edit: Keep in mind that your Taranis (like my hacked 9X) already reports RSSI of the R/C link. So there is no need to involve the FC to communicate the FrSky RSSI data.

Understood, I ended up running the RX to RC6, enabling telem, mucking about with the cleanflight (changed) cli settings, and got it working via help from the cleanflight IRC channel. I left RSSI alone as I have it setup for a voice feedback toggle on my Taranis, one less thing in my view.

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FYI for anyone that is using CleanFlight and wants the commands to accomplish this:

feature TELEMETRY
feature SOFTSERIAL (need to have PPM enabled)
set serial_port_3_scenario = 4
set telemetry_inversion=1
Edited by kubzzz

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