Sailfly-X Upgrade: Improving Range

The Happymodel Sailfly X is my favourite quad I've reviewed so fat this year (review is here) but as with any product, there are shortcomings especially when is it built to a price. Like I did with the Mobula7 I'm starting a new series of articles on upgrading and customising the Sailfly-x.

Current State

The Sailfly-X is based around a Crazybee board like many other models, in this case it is the latest revision CrazybeeF4 pro V2.1. It uses a SPI-connected receiver that offers full telemmetry and D16 or D8 modes for FRSKY. There is some very cool technology here (I think SPI connected receivers will be the future) but the implementation here is not great on the key measure - range performance. In this article I'll document how to improve range from minor tweaks to full on long range and will be relevant for FRSK, Flysky and DSM

Step 1: Software only
The most simple mod to do is ensure the onboard receiver is given an armchair ride from a software standpoint. This means changing D16 to D8 mode in betaflight and turning off telemetry which has been known to lock up the flight controller. This can be done as below. 

Next you'll need to rebind with your trasnmitter set to D8 if you were previously bound in D16 mode. Same binding procedure as previously applies (here). Update: you don't actually need to rebind! The bind settings stored in betaflight are the same regardless of D16/D8

Lastly for this step use a small plastic too to fish the recevier antenna (single black wire) out from underneath the canopy to pop out in the opening by the VTX button per second image below circled in white. This took minimum effort but gave me a small but repeatable improvement in signal quality at a fixed range.

Step 2: Lengthen the stock antenna
If you find you want more range (and you probably do) the next step is to increase the receiver wire length from a 1/4 wavelength (31.23mm) to a half wavelength (62.46mm). This will allow you to pop it out of the canopy further and increase the size of the active element. You'll obviously need to solder and measure accurately but you can use any small light guage wire you have lying around. See below for how I did this:

1. Remove the nylon nuts holding the canopy on

2. Gently lift the canopy out of the way. I recommend leaving the camera plugged in as people have had issues with the pug breaking off

3. Locate the stock 1/4 wavelength antenna to the right and desolder

4. Cut a new piece of scrap wire as close as possible to 62.46mm. See above compared to stock 31.23mm

5. Solder the new, longer antenna in the same spot

6. reinstall the canopy and poke the new antenna out of the vtx button hole in the canopy

7. I used the ol' ziptie-heatshink trick to keep the longer antenna away from harm. You may want to figure out a more aesthetically pleasing solution but this is robust, works well and I can't see it in my goggles :)

Step 3: Add a discrete receiver
This is where you start spending money but not a lot. I recommend purchasing a XM or XM+ receiver at 1.0 or 1.5g respectively. The XM is smaller and lighter but the XM+ adds diversity. You could also use the r-xsr which has the weight of the XM with diversity AND telemmetry but is about twice the price. Personally I think the cheaper, lighter XM is best suited to this application because even this receiver will outstrip the performance of the 25mW VTX. 

The FRSKY XM is about $12

The FRSKY XM+ is about $14

The FRSKY R-XSR is about $25

Adding a discrete recevier is a much better option on the F4 boards like the sailfly-x compared to the original F3 mobula7 boards because they have a spare full UART meaning you can add a receiver with full telemmetry without compromising the ability to use smart audio for VTX control. Software and wiring as below:​

Step 4: 900MHz (Crossfire or R9m)
If you want to go for ultimate range or you use only these systems you can go for Crossfire or R9m. If you've got these then likely you have the knowledge to wire yourself but for completeness see below for wiring and software setup:

So there you go, options to upgrade your reception range from free to expensive. I'm currently using the 1/2 wavelength antenna (step 2) and it is fine given the VTX output but have a FRSKY XM receiver in waiting.

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