fmkit's ULink (review/discussion/etc) - RC Groups
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Jun 13, 2012, 10:12 PM
CrashMeUp's Avatar

fmkit's ULink (review/discussion/etc)

I've received fmkit's rx/tx LRS solution a little while ago and I wanted to share my experience. (got it from )

Please note that this is a home made version and you'll be able to tell that. However, solder points, etc, were all well made and it looks reliable.

I had some issue at the beginning with my submicro analog servos, even thus the board supports analog and digital servos, the first channel would jitter a lot for some reason.

I have bought new digital submicro servos for testing due to this, and those work perfectly fine.

Here's a quick demo video:
Sorry, no sound, mic is broken. You can see the 2 control servos and the pan and the tilt servos. You can see the WMP gyro/accelerometers in action.

The movement is (very) quick, smooth and relatively precise. Pan&tilt is done via presets (hit a button), but can also be done via joystick (obviously if you move the camera via the joystick your plane better go straight..)

fmkit ulink (1 min 42 sec)

I'm going to install the new servos in one of my wing and go for a range test, then a flight, and report.
Last edited by CrashMeUp; Jun 14, 2012 at 03:50 AM.
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Jun 14, 2012, 12:35 AM
fmkit's Avatar
1st ch. you mean trottle ? It always has rate faster than analog, every ESC drom China thatI tried works at fast refresh rate.

There is no full description of setup codes used w/Ulink so I'll post most used codes here:

1st you have to set starting frequency of nunchuck and RX
enter 6 digits into RX and same into Nunchuck after clicking "C" 6 times.:
U-Link RX, setting RF channel (1 min 1 sec)

Then set sub-channels on both, RX use codes 1.x and nunchuck as all setup codes the same but starting with 6, that is 6.1.x

Sub-channels are pre-defined groups of frequencies so RX can track multiple transmitters (repeaters and nunchucks) when flying in multimaster mode or when you fly and someone else control your P/T

The RX has beacon function, to enter new frequenc y enter 6digits same as RX frequency set but substituteleading "4" with "1" , if entered 162622 actual frequency stored will be 462.822MHz (CH5 FRS)

single digits codes:
1 click - calibrate gyros (never used, it's easier to push elevator stick while holding Z-btn on nunchuck
2 clicks - reverse both servos(only works if active flying wing mix)
3clicks -reverse pan direction
4clicks - reverse tilt direction
5clicks activates video switcher( if installed) or switches between cormal pan servo and continuoes totation servo

group 2.x used to set gyro gain (normally not needed)

group 3.x used to reverse gyros:
3.1 X gyro reverse
3.2 Y :reverse
3.3 Yaw gyro revers
3.4 swap X and Y axis ( same effect as if rotate RX board 90degree), thus the board can be installed in 8 positions (4 with 90deg. pitch face up and 4 upside down)

4.1 and 4,2 flying wing mixes , 4.3 classic mix, 4.4 - base installation for camera or antenna P/T (not flying mode)

5.x AUX B modes:
5.1 fireworks igniter - connect nichrome wire to high current FET (oboard)
5.2 random LED lights (same FET used to control power LEDs)
5.3 PPM input, incoming PPM is master -overtakes control if 1st 2 channels not centered(1.5ms)
5.4 the same but control signal is ch5
5.5 Power LEDs strobe - double blink every 1.5s

6.X Aux-A codes:
6.1 Fireworks igniter 2nd channel
6.2 3-position switch (PWM 1ms,1.5ms,2ms)
6.3 Rudder PWM out
6.4 PPM out
6.5 LEDs blinks fast

7.x frequency hopping step (0-2MHz)

8. servo reverse, for mixes 4.3 and up:
8.1 reverse Aileron
8.2 reverse Elevator
8.3 rudder

9.1 digital servos 9.2 analog

Beacon starts to transmit only if motor was active atleast 1s,, when you connect power to RX buzzer and beacon won't activate till 1st failsave then timed 2minutes on old receivers and 50seconds on new.
Jun 14, 2012, 12:52 AM
fmkit's Avatar
Nunchuck setup. all codes start with 6, wait for"ready" tone then input codes

6.1x sub-channel
6.2.x used on old nunchucks to switch starting frequencies
6.3.1 if you replaced joystick board calibrate accelerometers just once, hold nunchuck neutral till "stored" tone - have to hold neutral only for this code
6.3.2 sets Nunchuck output PPM
6.3.3 PWM out -servo tester
6.3.4 PPM-in (can mix incoming PPM )
6.3.5 Automatic switch, when powered the nunchuck samples PPM-n for 1/2s, if no input detected switches to PPM-out(use with SIM, or RF hack module)

To activate trottle click Z 2,3 or 4 times - all the same effect, 1click shuts the motor off
to control rudder have to hold Z btn or click Z 3 times

To let other pilot controlyour plane withhis nunchuck enter multimaster mode wih 6 fast clicks (Z ) then whenever you're in Z-3 position and stick is centered others can fly your plane.
Jun 14, 2012, 12:58 AM
fmkit's Avatar
Most recent video with Ulink in action, not FPV but RX tracks two nunchucks, friend of mine was controlling P/T while I was controlling the wing.
Rosh HaNikra beach flying low and slow (3 min 14 sec)

Ulink was stable while next to noisy car dvr (simiar as HoryzonHD), normal UHF LRS would crash past 300m, Ulink used 2 repeaters by the time
Jun 14, 2012, 01:32 AM
fmkit's Avatar
plenty of stock:

Jun 14, 2012, 02:11 AM
CrashMeUp's Avatar
1st channel i mean the first servo channel (or maybe its channel 3 for you)
Jun 14, 2012, 02:18 AM
I Like Popcorn
flylite's Avatar
All looks very interesting but could you give us an overview!
Jun 14, 2012, 02:59 AM
Outta Sight
More info please.
Jun 14, 2012, 03:00 AM
Registered User
Originally Posted by fmkit
plenty of stock:
Any information on how to order?
Jun 14, 2012, 03:49 AM
CrashMeUp's Avatar
Here's the ulink on my wing now that I swapped the servos and set it up:

ulink 2 (1 min 54 sec)

I ordered it from
Remember that it's not from a shop but just a person doing this for us so shipping can take a little while, it's home made and so on. On the plus side support is good and as you can see it seems to work quite well

I'm not sure if the video shows how bright the led beacon is. It would blind me at this distance and this is on 2S
Jun 14, 2012, 04:05 AM
fmkit's Avatar
CrashMeUp, when you're in Z1(motor off) or Z3 position rates look very high but that how it suposed to be - this is "hyper" mix when elevones use all available travel, say you about to catch the plane and just turned motor off, now in Z1 mode elevator can go uo and down 100% (normal wings or Z2 only 50%) only while aileron not used and vice versa,
also when you showed gyro response it looked like very high only because the plane was relaxed in your hands, while up and flying the gyros will adjust automatically /set gain per conditions, next time you're in front of camera try to shake the plane hard to imitate oscillation and you'll notice the gyros give up shortly to stop oscillation, the gyros wil reduce gain to zero if needed.,
with stick in extreme position there is no gyro effect so you can loop and roll as you wish.
Jun 14, 2012, 05:07 AM
Formerly bUd~Fokker
vvV FANG Vvv's Avatar
I have had a firm belief for a long while that mr fmkit is perhaps the most innovative thinker and designer/manufacturer that the fpv world and perhaps the wider rc world has had for a long while. What he may lack in fancy websites and presentation he makes up for in innovation..... to me he is one of those rare gifted elecronics people who has solder in his veins.

To me something gets lost in translation and what he says may seem complicated but im sure its not.

If his stuff had fancy packaging and was on hobbyking im sure there would be big threads on it.

I dont know him nor was i paid to say this, and I've only brought the rf beacon which is amazing and every long range flier should have one!

fmkit, could u tell us all in point form what this ULINK does?

Perhaps i (or maybe someone who understands it ) could help write it up for you?
Last edited by vvV FANG Vvv; Jun 14, 2012 at 05:29 AM.
Jun 14, 2012, 05:19 AM
Formerly bUd~Fokker
vvV FANG Vvv's Avatar
Here is the original thread i got lost in the first post

Fpvkiwi who i think is another gifted electronics guru seems to have a good handle on it?
Jun 14, 2012, 05:39 AM
Registered User
Jack_LaLanne's Avatar
I am looking forward to the range test results very much.
Jun 14, 2012, 06:36 AM
fmkit's Avatar
Ulink is an UHF LRS designed for FPV so pilot and spotter can control one plane as a team even if while miles apart. Single RX tracking pilot's nunchak and his repeaters and the same time spotters nunchack and his repeaters
The RX sends telemetry in two separate channels simultaneously. regular digital telemetry refreshed every 0.25s (4Hz), it sends voltage, amperage, signal quality, packets received,flight time, FS log,mAh used, all tx controls status and more.
2nd channnel is pure analog one, low battery, FS and beacon tones all heard using walkie-talkie, analog telemetry has 10x greater range, whenever digital link breaks you'll instantly know real time status by listening tones
The system has built-in P/T servo stretchers, some RXs have video switcher, all RXs have two high-amp switches for use with LEDs or igniters
Gyro stabilization is buil-inbut can be turned off if you got more advanced IMU.
Giros are very easy to use, beside revrsing there is basically no setup - no PIDs to tune, no gain/delays , When powered up the system calibrates itself and you can take off almost instantly.
Stabilization is very useful if flying small unstable planes such as wings without winglets and almost no sweep. Ugliest palne that looks unfliable behaves differently with gyros
The system is not new - it was evolving for over 2 yearsand still refined, we test updated FW atleast every week.

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