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TIPS and TRICKS

MOBULA7 UPGRADE: Better Range with the Onboard receiver

26/2/2019

15 Comments

 
PictureThis mobula 7 is getting more and more upgraded
Introduction
The crazybee F3 and F4 series of all in one boards that are the heart of the mobula7, m7hd, eachine trashcan, snapper7, ur65, uk/us65 and even beta75pro2 are an amazing piece of technology that incorporates a flight controller, 4xBL_HeliS ESCs and a receiver. Cramming all of this on one board does mean some compromises though and the biggest one for me is the poor receiver range. This brief article will show how to get a minor improvement with zero investment. Note: this mod is relevant for all the models listed above.

This is the third article in my series of HappyModel Mobula7 upgrades, many of which can be used for the Trashcan too. Also to come are:
  • Swapping to a much more durable frame​
  • Improving the battery connector for more power
  • tuning betaflight filters more specifically for brushless whoops, 
  • converting to run 'props out' 
  • propeller upgrades. 
  • receiver range improvement
  • modding your 1s battery to be a proper 2s
All links will be updated here when completed. Many of these I've completed the work and am testing at present - it's starting to feel like a more complete little quad now. If you're looking for my review including setup it can be found here
Current situation
The mobula7 (and other models listed in the intro) uses an onboard receiver - either frsky, flysky or dsm protocols all of which run on the 2.4GHz wavelength. The have a small antenna soldered to a through hole that is tucked safely underneath the main board and above the battery tray. This is is the most durable solution but not the best option for maximising control signal.
Picture
Tou may be able to see the single black receiver wire underneath the red motor wires
Optimising the range
The easiest way to improve the reception of the control signal without changing anything else is to move the antenna into a better location. This is to receive an unimpeded control signal as clearly as as possible which for me meant pointing the antenna up to clear of the rest of the quad as possible. Obviously the antenna pointing down is not ideal for this so feel free to follow the 5 minute guide below on how to solve this.
Picture
1. Start with a clear bench, included philips screwdriver and a good soldering iron with a fine tip (I highly recommend the TS100).
Picture
2. See this little solder pad the screwdriver is pointing to? This is the back side of the solder pad the rx antenna is soldered to (confirmed with a DMM). Heat this pad to remove the antenna.
Picture
3. Here is the antenna remove. It is simply a piece of silicon insulated wire that is approximately 31mm long which correlates to 1/4 of a wavelength (31.23mm). Rather than using a new piece I've kept this one as acutal antenna length is also determined by internal electronics.
Picture
4. Solder it to that same spot on top of the board. If you melt the post like me it's not the end of the world - this one is redundant for the canopy on all of the happymodel variants.
Picture
5. Re-install the canopy and route the newly exposed antenna how you wish. As you can see here it is more clear of where it was but see below for recommendations for further improvements.
Has it improved?
Yes is has, but only a little. I often fly from my backyard and loop a tree about 50m away from where I stand. I'd always get telemetry lost warnings when I rounded it every time but now only about 20-30% of the time. A minor improvement but given the poor range I'll take what I can get.
Recommendations for further improvement
The next easiest improvement would be to use a piece of insulated wire that is 62.46mm long - 1/2 a wavelength. This is now to much to increase the wavelength as it is to lengthen the active element so that some of it can clear the body of the quadcopter. Credit to KababFPV for this recommendation here. Note if you want to do this I'd recommend using some wire you have lying but if you have none it is available in all gauges cheaply here (I recommend 26AWG for this application)
Picture
The Crazybee F4 and F4 pro boards have a spare UART (TX2, TX2) and an inverted RX for SBUS
If that still isn't good enough you'll need to go with an external receiver. For a Mobula7 that runs the crazybee F3 and only has one UART that means you'll have to give up smart audio to connect the receiver. If you have one of the F4 or newer boards there is a spare UART meaning you can connect any receiver you wish - including crossfire if you really want. With this option the control link won't be in question - it'll be your video or battery life that will define your range.
Thanks for reading, if you found this article useful please feel free to like or share, the facebook links below directly link/like this article. Links are affiliated and help me buy the bits I need to produce this type of content.
15 Comments
Alex
27/2/2019 11:01:49 pm

Great article, had the same experience with my trashcan re RX. I have been trying to figure out how I can use an external RX, I have the FRsky version.

Would I just be able to buy an FRX receiver, solder to appropriate pins on board, create a new port and then use it for SBUS whilst turning the onboard receiver off?

Im also curious as to whether using an external receiver would mean losing the OSD.

Really appreciate the work you are doing to help people like myself get the best out of their quads, thanks for the great content.

Reply
QUadifyRC
2/3/2019 11:47:59 pm

Thanks Alex. Yes you can use an external receiver, Happymodel themselves use this as a workaround from the factory for the EU. Losing an external receiver has no impact on OSD. I'd recommend a fullspeed nano or xm receiver to keep it light if you go down that path

Reply
Matthew Brulla
14/3/2019 06:27:13 pm

Be aware that the Crazybee F3 in the Mobula7 does not have enough UARTs to have an external receiver and smart audio - which is why the EU version doesn't have SA. The F4, which is in the Trashcan and the Mobula7 HD, does.

Matthew Brulla
14/3/2019 06:31:00 pm

Next time I should read completely...the SA issue was mentioned in the article. My apologies.

Derek Moore
12/6/2019 03:22:20 pm

So if I wanted to connect my xm+ I would just solder it to the grnd, 5v, and the IRX1 pins.

Mrpurple
2/6/2019 03:06:22 am

I thought about using one old "real" shielded antenna from a frsky receiver. I would solder the shield to one of the ground pins. This would enable to position the antenna completly out of the canopy. Has someone tried this yet?

Reply
Quadify RC
4/6/2019 11:55:59 am

You could do that but unless the ground is very close to the antenna solder point then I vaguely remember it can mess with the signal wavelength.

That said if it worked, the outcome would be ideal. I might try later down the track or let me know how you get on if you give it a go?

Reply
STEVE
4/6/2019 05:06:29 am

I saw a youtube video back then and the guy probably from China added new 1/2 wave antenna at the top and without cutting the orginal one. I don't understand what he said in Chinese though. Do you see if it actually hurts the range having two antennas?

Reply
Quadify RC
4/6/2019 11:57:39 am

From the little I've read about trying to use 2 video receiver antennas without diversity it can actually interfere with the signal. It think emperical testing would not be hard through - maybe worth giving it a crack and see if you notice any realy difference?

Reply
Criss Carter
29/6/2019 02:06:59 pm

I run a q100, a China whoop, with the antenna intentionally soldered and pointing down. (Thnz Bobnova of MMC for this tidbit.) I now can fly 200+ meters away. Had to switch vtx cause it lost range before TX does. Pointing up or down doesn't make a difference brother. As long as your tx and rx antennas are matching vertically or horizontal you'll get reception.
Ps using flysky fsi6 with horizontal 5db antenna mod. And Left the horizontal antenna stock. Switched antennas to bottom after nodding fsi6. Yes it helps with range but no more than 50 meters. Which leaves 50+ meters range added by up side down antenna.

Reply
Quadify RC
4/7/2019 02:58:09 pm

Bobnova is a great helper in the community, MMC especially. Haven't been there for a while but it's a great technical forum.

Agree on the vertical vs horizonal, plan was to get more space free from the battery rather than up or down being better.

Reply
jacopo
24/8/2020 04:38:08 am

Hi, thank for your guides about mobula7, they helped me a lot customizing and choosing parts for my quad. During last flight i crashed my Mobula and the little antenna ripped off from the pad. I followed your guide to solder it back on the board. It seems pretty well soldered but my mobula will not communicate with the transmitter anymore. I tried also to do the bind process again but without results. Do you have any advice? thank you

Reply
Quadify RC
24/8/2020 09:07:24 am

Hi there

My pleasure. Bummer about the antenna but you have 2 options which can also be considered an upgrade. First is to install a new discrete receiver. If you are FRSKY I'd recommend the XM receiver which will improve your range but you will need to free up a UART and lose smart audio in the process (assuming you are on the V1 F3 board). Second option is to get a new main board - lots more options with more UARTs and faster processors etc. If it was me, I'd get the receiver and forgo the smart audio VTX control

Reply
Sami
31/12/2020 04:06:57 pm

I am bad at soldering and ripped the RX3 and LED ports and I want to use a XM+ receiver with F3 board. Can I change TX3 port to RX3 and connect a XM+ receiver. Please help.

Reply
Matthew Brulla
1/1/2021 03:07:31 am

You can remap any pins using CLI in Betaflight.

Practice your soldering a bit before attempting again.

Reply



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