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RD180 - jumping on the 180 train
#1
My current mini quad is a QAV250 with 12A ESCs, running 3S and PPM. I've updated it to Betaflight and BLHeli and it flies well but I want to build a new quad that incorporates all of the "modern" advances of the last year: smaller size, SBus, 4S, LittleBee ESCs, tri-blade props, etc.

I also want to keep it light but powerful, so 4S batteries at 1000mah, 1806 motors, no OSD. Really interested to see what kind of flight times I'll get. Unfortunately I need great video so mounting the Yi will bog it down again.

I live in Thailand so my suppliers are all in Asia. Parts list with links:

RD180 frame
Matek 5-in-1 PDB (with 5V BEC)

FrSky X4R-SB (will use Sbus)
X-Racer F303 Flight Controller (new F3 board from fpvmodel, runs ßflight)
Homemade voltage divider for flight pack telemetry

Dragonfly MC1806 2300KV (note: you need 2x CW and 2x CCW)
FVT Littlebee 20A
HQProp 4x4x3 (not the bullnose 4x4.5x3 ones)

HS1177 mini FPV cam with 2.8mm lens
FT952 Vtx 
Spironet for now, want a stubbier antenna to keep a low profile for proximity flying

Xiaomi Yi (would like to replace with lighter 60fps cam of GoPro form factor if one comes out)

Misc. notes:
  • No OSD (I use audio alerts for flight pack voltage and don't like the visual clutter and extra wiring)
  • The X-Racer FC doesn't have Vbat input but I will attempt to make and use a homemade voltage divider for flight pack telemetry.
  • I'm a bit confused about whether video filtering is necessary or not: I normally use it but see a lot of people going without it. The video system will run directly off 4S power from the PDB. If that causes too much noise I will install a filter, or try to swap it for a Vtx that provides its own power to the FPV cam (such as this but hopefully a lighter 200mw type). Unfortunately the 5V from the BEC is just short of the 6V needed for the FT952 Vtx, although enough for the 1177 cam.
  • The X-Racer FC has 16MB of built-in Blackbox memory for tuning. For Cleanflight/Betaflight, it uses the SPRacing F3 hex.
I'll post the completed copter and a flight video later… might take a while as I have a lot on my plate…
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#2
VTx: I just realized I have the Aomway 200mw Tx laying around. When I bought it I was annoyed that it had two separate cables coming out of it, and preferred the simplicity and built-in 90° SMA connector of the FT952.

Now I understand! The +5V out powers the camera and eliminates the need for a filtered supply to the Vtx. So I will be using the Aomway instead, and keeping the FT952 on my other quad that has an LC filter already.
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#3
Keep us posted, it sounds like a fun build. I love sub 180 builds.
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#4
Thanks for the encouragement Arknabbit… however I didn't exactly document the build well! It's done, and it flies great! Now I know what it's like to have a truly responsive, powerful quad. I'm just running on default PIDs in Betaflight 2.4.1, 2kHz. 

I'm also breaking in new packs, so trying to avoid high throttle. I haven't even approached maximum vertical and I'm getting long air time. This is without HD cam so the quad is pretty light. Smile 

Even on default PIDs, the tune seems so much better than my QAV250. Just so much more locked in. Blackbox doesn't show any P oscillations so I'll try to bump up the P, and turn D down as we're on 2kHz and there is almost no bounceback. However, there is a lot of prop wash shudder.

I didn't want to start direct soldering the FPV connections until I knew the system worked (I did some things I've never done). So I have a very cramped frame full of giant servo connectors. I didn't buy any headers/cases for 2-pin JST, but they're not actually much smaller anyway. We need a new, smaller, crimpable connector format for this stuff!

For the FC/motor connections, I invented a low-profile servo connector which I show pictures of in the gallery. I'm sure someone else has done this but I've never seen it. Basically you crimp servo pins but do not use the plastic case. Put shrink over them instead and, if needed, bend them 90° at the thin point around the middle of the pin. Then you get removable servo connectors but much shorter.

I didn't feel ready to direct solder to the FC for this build but I will probably do it next time. I'm learning that in the end, once you have all the connectors soldered/crimped up, and crammed everything into the frame, it would have been easier just to solder the wire! Same goes with replacing blown components: at the end of the day, it isn't really any harder just to desolder and resolder the new one. 

Issues:

1. I'm annoyed with the Matek 5-in-1 board. I definitely would buy a different one next time, because:
  • The motor pads are not in the corners, so you have longer wires than necessary
  • The built-in buzzer requires a PPM signal, which is available from a spare output on the X4R, but they are channels 1-3! So in order to use my buzzer I need to either upload custom firmware to the X4R or remap the main control channels 1-4 in order to clear those channels for PPM. Which I've never done and makes me nervous.
  • The built-in buzzer is so thick that I had to use thicker spacers between it and the FC, creating space problems.
  • It has no filtering, which I thought would be ok, but later read that Littlebees can cause voltage spikes, so now I have a bulky LC filter. I totally would buy a nice PDB with built-in filtering and just use a normal buzzer off the FC next time.
  • The LED functions are of no use to me and waste pads that could have been used for motors. I don't even have LEDs and when I do install them they will be run directly off the pack voltage.
2. I'm using the "voltage divider" method to get telemetry of pack voltage directly through the X4R… but it's almost useless because the voltage jumps all over the place! I've tried using a logical switch that waits for 3 seconds on the Taranis… but it still goes off prematurely (false positive) sometimes. Now I'm worried that it will give false negatives (not go off when it should). Need to do some more testing and ask for help on this one. VBAT just works, so I'm wishing the X-Racer FC just had that (V2 will almost certainly get it). I do have the voltage divider coming after the LC filter so I'm really surprised this is happening. Maybe I should put the voltage divider outside of the filtered zone??

3. The built-in 16MB for Blackbox on the X-Racer FC is great and all, but takes forever to download! A full 16MB takes 40 minutes, whereas with external Blackbox copying the file from the SD card is instantaneous. So forget about taking a peek at the field with your laptop while tuning. Might just have to solder pins on for the external logger after all.

To do:

1. Get the buzzer working.
2. Get voltage monitoring working properly.
3. Tune, as much as I can (noob tuner)
4. Add GoPro powered from 5V BEC (in progress), and retune as needed.

About the GoPro, I was going to use my Xiaomi Yi, but turns out the Yi is exactly the same weight as the GoPro, but its battery is lighter. So when you remove the battery… the GoPro is lighter! So I'm going with the GoPro after all. It's pretty old so I guess it's ok to risk it a bit Wink

I have 24 photos but I can't seem to find a way to attach more than one at a time, which is going to take forever, so here's a Dropbox gallery instead.


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