I wrote a blog on RCGroups about my micro sized FPV Quad project, which became very popular, so I thought I'll post it on flitetest. I wanted to have a small FPV Quadcopter, so I can also fly indoors. My goals were small size, some crash resistance, reasonable flight times and performance, good video quality, good flight characteristics, reasonable range, and I wanted to use my existing transmitter which is a Taranis with a FlySky (same protocol as the Turnigy 9X) module in the back.
Small size & crash resistance: There are some frames out there, but I chose one of the 100 sized platform frames from picnicquads.com. It is made out of a sandwich composite material, so it is tough, yet very lightweight. You can also choose from different motor sizes, because the motor mounts are separate.
Flight times & performance: To accomplish these I did some research on RCGroups about the best motor/prop combo. Next I calculated the MTOM to be about 50g with a bigger (750mAh 1S LiPo) battery, which meant I need to have 100g+ thrust. RCG member woodsturning did a lot of micro quad equipment testing and for my needs the Chaoli CL-0720 motors with the Hubsan propellers seemed to be the best.
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Video quality: After watching some DVR videos of small cameras I decided to use a 520TVL MC900 with a wide angle lens from FPVHobby. It has a really nice image and also works in low light conditions. I have a Fatshark Base with a built in receiver, which is fixed on 5705Mhz, so the VTX also had to have this frequency. The TX5810-100 also from FPVHobby has this Frequency, so I bought it despite the unreasonably high price. It also turned out, that the channel memory doesn't really work. It only works if I disconnect the battery for a few seconds. Otherwise I always have to cycle through all 8 channels to see a picture in my goggles. I also had to use a Pololu 5V step up voltage regulator to get rid of the noise from the motors.
Flight characteristics & range: This was the complicated part. Because of the size and weight limitations a separate RX and FC was out of the question. Since there is no available Frsky or FlySky micro FC on the market I had to build my own. RCG member midelic already had an ongoing project to build a Multiwii board with integrated brushed controllers and FlySky RX. He wouldn't build me one, so I built my own. Since 1 piece would have cost me a fortune I ordered parts for 18 pieces and decided to sell the rest later. I built my own and did some testing. There were some bugs in the code first, but midelic fixed them for me and now it works flawlessly.
Conclusion: All together the quad cost me $175. Despite the problematic and expensive VideoTX it all came out working very nicely. Range is very good. Indoors I flew about 50m with several walls between me and the quad while maintaining good control and adequate image quality. Currently I am using 500mAh 1S LiPos, because I already had them. I get flight times of about 8 minutes, so there is really no need for the bigger battery. T/O weight including the battery is 45g, which is lower, than calculated. The performance is very nice and the control is very precise. I can fly through holes that are twice as bis as the quad.
Ad: If you ever have the same problem like me with the small FC, contact me and I will sell you one of the boards. I build and test each one myself. The dimensions are 43x25mm (including PCB antenna) and it weighs only 2.7g. I sell them for $30 including worldwide shipping. I of course have midelic's permission.
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