[jdl]

Hi,

Latest "next" build, r878.

I'm using OPLINK Mini for telemetry and PPM control together with Revolution board on ZMR250 clone. Decided to get rid of 2.4GHz Receiver on that particular frame. The only signifficant drawback I've found so far is that I can only use 8 channels with Type: OpLink in Remote Control Input settings.

With RadioLink R9D receiver in PPM or SBUS mode I used 9 channels: Accessories 0-3 for: camera switcher, LEDs control, OSD modes control, Arming via switch.

Any reason channels over 8 to be unavailable in OPLINK PPM? I think I've read somewhere that this limitation is planned to be removed...

[f5soh]

Right now the OPLM PPM input accept only 8 channels, this limitation is removed to allow receiving all PPM streams from various RC Radio. (like Aurora that send 9ch PPM stream)

OPLM still use/transmit only 8 channels in radio link, this means all channels send by the radio and above the ch8 are ignored.
The reason of limiting to 8ch is avoid too much latency.

[jdl]

I got it. 10x!

Indeed, I think I feel some luggishness in control when using OPLINK PPM vs Radiolink R9D SBUS or PPM but I'm ok with it - a little tradeoff for bigger reliable range and full telemetry. I'm using this craft for video shooting and not for racing. So the little delays in control are not critical.

I've managed to fly up to 3300m straight line distance on 2.4GHz and up to 3500m on 433MHz at about 150m height over ground but OPLINK link is much more reliable when flying low over ground at distances over 600m.

Still, it would be nice to have an option to use channel 9, maybe 10, despite of bigger delay.

[f5soh]

Bigger delay is really not wanted despite you have no issues about that.
If i remember right the 8 channels are in one packet frame and add ch9 is not doable without bigger changes.

[chromvis]

Just warning about reliability of OPLINK connection. I made the same (PPM+telemetry) but ten read this thread: https://forum.librepilot.org/index.php?topic=1332.msg13036#msg13036 and decided to do simple walking test. I lost control in mere 30 meters. So, be aware.

[jdl]

Well, till now I have flown maybe more than hundred kilometers overall path with OpLink PPM control at distances from 1 to 3.5km from ground station without single failure. I used "next" r616 build till yesterday with M8N GPS and I2C External Mag, and failsafe set to RTB. In rare cases the link breaks, for instance flying a meter high over ground 800+ meters away, but that is expected and normal, and RSSI indicator warnes me what's going to happen. When failsafe triggers, copter attempts to jump 10 meters up as a part of RTB sequence and immediately regains control.

Maybe your problems are due to bad hardware or antennas. Stock antennas don't give much range but are still ok for some hundred meters. Another reason for link failure may be strong RF interference in your test area, 433MHz  band is rather crowded. I usually don't fly in urban areas so I rarely notice noise in 433MHz band.

My build uses following components:
Revolution Board and OpLink Mini from Banggood, 433MHz Sander Whip Antenna (Monopole) on copter and HobbyKing RMILEC 433MHz SRC771 1/2 Wave Length UHF Antenna on transmitter (Oplink Mini).

Almost identical transmitter setup: Radiolink AT9, OpLink powered through trainer port via LC filtered!!! (this may be or may not be important) switching 5V regulator and HC-05 bluetooth module. PPM to OpLink from trainer port.

Today I tested "next" r878, flown to 1+km and back, no time for longer tests, no problems, on return went to 2-3 meters over ground at distance of 700+ meters away and RSSI was all the time in the range -63-83dB. Of course, this is on the field, large open area without (almost any) obstacles.

Still, thanks for the warning, I'll do a walk test too, just out of curiosity, and will share the result.

[jdl]

Bigger delay is really not wanted despite you have no issues about that.
If i remember right the 8 channels are in one packet frame and add ch9 is not doable without bigger changes.

I understand. Thanks for explanation!

[f5soh]

Just warning about reliability of OPLINK connection. I made the same (PPM+telemetry) but ten read this thread: https://forum.librepilot.org/index.php?topic=1332.msg13036#msg13036 and decided to do simple walking test. I lost control in mere 30 meters. So, be aware.

If you need some numbers, last walking test i did using random Oplm pair resulted in link lost at 80m using lowest power (1.25mW) in both sides.

[chromvis]

OK. I tested it again, and, apparently, it is not OPLINK it is HC-05 bluetooth module problem. OPLINK connected through USB to computer gave me -80db signal loss in 100 m behind the big house in dense woods (did not dare to walk further). It did not matter which unit was coordinator and I tested with original whip 1/4lambda (17 cm) dipole antenna and with regular short one - almost no difference.
Set up was: sparkey2 with new helical antenna (as it came from Banggood) and RadioLink transmitter (radio OFF) trainer socket used for power (and ppm) with 5V BEC (I believe it has LC filter) connected to OPLINK flexi port, Bluetooth connected to Main port.
When using bluetooth connection lost within 10 m. (Transmitter with bluetooth was always close to laptop). Not sure if it is bad bluetooth  Will try another unit.
I was using only telemetry, did not activate PPM transmission this time.
Any ideas why it happened?

[chromvis]

This problem with OPLINK when people reporting over 1 km working distance and I could not get even 10 meters was bothering me for a while.
As I wrote in previous post, if it is just telemetry transmission to OPLINK and USB connection to laptop everything seems to be OK.
If I am using OPLINK with Bluetooth transmission of telemetry to laptop - I am getting 10 meters working distance. Walking with Laptop and TX with connected OPLINK and Bluetooth away from copter shows lost connection in 10 - 15 m.
I thought, it may be bad HC-05 unit, so I programmed 3 HC-05 and one HC-06 for 57600 (one HC-05 I tried with 115200 - unsuccessfully with OPlink and Revo set for 115200 telemetry Bluetooth unit does not want to go to pairing mode at all (only if TX and RX wires from oplink are disconnected it could be paired).
I tested all each Bluetooth unit with two different OPLINKs (one actually arrived today) and with Sparkey2 and Revolution FCs.
All results are the same - At 100 mW output energy I am getting intermittent connection within 10 - 15 meters from copter. I even did not activate PPM function on Flexi port.
May be PPM only will work for greater distance, but I am afraid that OPLINK copter control together with Bluetooth telemetry is practically impossible!!!

[hwh]

Why are you using the short range 115200 setting instead of the default 38400?  I'm not surprised you can't get much range at that speed.  38400 is the standard speed and people getting 1km range are probably using it.  When you increase the link speed you shorten the usable distance.

What do your oplinks do at 38400 without the bluetooth transmitter?  If they're still short range they're probably either off frequency or have bad antenna connectors.

Of 8 Chinese oplinks I have two work great, the ones that have SMA connectors instead of MMCX.  Of the others 4 work normally and 3 put out less power at 100mW than the others do at 12.6mW.  I think it's the antenna connectors but don't have replacements on hand to make sure.  The next time I order parts (probably in a week or two) I'll order a couple of good Amphenol brand MMCX connectors and test it.

[chromvis]

I am using 57600 primarily. I just tried one with 115200 for testing sake.
Without Bluetooth all worked great. I got big distance. It is when I hook up Bluetooth everything falls apart.
Oplinks itself work normal for telemetry transmission while hooked through USB to computer.
4 different Bluetooth units work OK too (tested with arduino).
It is only when I connect Bluetooth to OPLINK I get problems.
Within 1 to 10 meters everything is OK. With distance greater than 10 meters - abrupt fail of signal strength. GSC reports lost connection.
I did not dare to check actual copter control with this setup, but in other thread here lost of actual control was reported here https://forum.librepilot.org/index.php?topic=1332.60