MOBULA7 UPGRADE: Better Range with the Onboard receiver

This 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.

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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.

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.

1. Start with a clear bench, included philips screwdriver and a good soldering iron with a fine tip (I highly recommend the TS100).

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.

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.

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.

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)

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.