The GEP RC MX-3 Sparrow was an awesome 3" quadcopter that sadly had little uptake because of it's high price ($249 retail). As at 28 June 2018 Gearbest is clearing them for $149 here which represents great value for money. I've chosen to convert this to a competitive lightweight 4" racer.
I haven't done a formal review on the quad but key features of the MX-3 sparrow but key features were:
The change was simple, I purchased a lightweight Toothfairy 4" frame from piroflip, some HQ 4x4.3x3 v1s props and transferred. While I was at it I also switched the camera for a Caddx F1 and the stock TX20 vtx for and AKK FX3 with smart audio and up to 600mW power. Since dipoles are frowned upon at my club I've also used a UXII mmcx RHCP antenna. A full list of all components and links are at the bottom of this page.
Assembly pictures are below. I'll mention here that it was not until I disassembled the MX-3 sparrow that I realised the design and finish the GEPRC put in are second to none right down to the smallest detail. I was thoroughly impressed and can now see where the cost started to come in. Moving on, build pictures below, this was pretty straightforward.
I was really pleased with the finished build but was what was even more pleasing was that the final weight (ready to fly except battery) was pretty much identical to the MX3 sparrow - 150g, even with heavier components like the new VTX and CP antenna. Given this is swinging an inch larger prop I'd expect (and got) much better performance and efficiency.
This is now one of my mainstay racers where I can be competive on all but the most open tracks. It can give me a distinct advantage on small to medium size tracks as well where I'm well over 100g lighter than even the lightest 5" racers. I feel the 1408 motors are a much better match for the 4" props and feel like they could manage even more pitch than the 4.3 I'm currently using - I believe HQ are due to release a 5.0 pitch model I'm looking forward to trying soon.
If you are like the look of this build you can either strip down the GEP Sparrow like I did (currently on special for $149 at Gearbest or try your luck at Banggood). All other parts below: