I have been browsing the mini multi rotor thread on RC Groups and watching online videos of people flying 250mm high powered quads FPV and it looks like a lot of fun…!
One that seems to have a lot of fans is the Blackout mini. However, it never seems to be in stock!
After a bit of online research, I bought one from fpv-reconn.com
Finding parts for this class of quad is not easy, as I am sure anyone who has tried, knows how frustrating it can be to wait for parts to come back into stock. Motors (good quality ones) are the hardest to find.
I particularly liked the RD230 as it comes with options for both 5” and 6” arms/props. The clean plate seems well isolated so I thought it would suit APM better from a vibration point of view. Most folks seem to like the Naze32 (acro or full) board but I wanted to try the HobbyKing APM mini as I have some experience with the APM and Pixhawk platforms.
I am not a great LoS pilot (need a LOT more practice!!) let alone flying FPV with goggles..!! But I am keen to learn and improve. Living in a large city, I don’t have access to “safe” wide open spaces to fly my larger quads (650mm class with Pixahwk) so a mini quad is better option for park flying. I still observe all safety rules and ensure I am a safe distance from people or pets
RD230 with 3mm thick 6” arms –fpv-reconn.com
Cobra 2204-28 2300Kv motors – 6030 props
HK Blue series ESC’s flashed with latest SimonK
HK mini APM 2.5 (on-board compass) with ublox LEA-6H GPS and power module
APM telemetry Tx/Rx (433Mhz)
FrSky 8XR Rx – Taranis Tx
Various 3s batteries ranging from 1300 to 1800mah
Mobius action cam – lens B
I did a quick & dirty build just to get it up in the air and see if this setup flies ok. I was not sure what layout to use (H or X) on mission planner, I went with H. I plan to rebuild and clean up later. Still not certain if it is better to stick with a PDB or make a wiring harness for the power.
Once I am happy with the flight setup; I plan to install the FPV gear. A 600-800 Tvl board camera and a Boscam 400mw 5.8Ghz video Tx and Boscam 32Ch Rx. I have the Pirate Eye monocular glasses which has a VGA display on one eye. I am not sure if I can handle full FPV goggles and the sensory deprivation... Perhaps when I have more skills and confidence..!
There is a LOT of wire shortening and soldering required. The mini APM does not use the same connectors as its bigger brother and the colours / pin assignments are not the same nor are they well documented. Thankfully there is a user created document online to help out.
I tried a few indoor hops (without GPS) in stabilise mode. The stock PID’s were WAY TOO HIGH and set roll/pitch sensitivity to 0.0930 and hover throttle to 410 to get it to hover without trying to flip over. This was to be expected as these quads are generally overpowered (by design). But even with these parameters it seemed a bit twitchy and I should have gone lower still. However indoors I had no chance to open up the throttle so it did not look too bad but once outside, it became obvious how twitchy it gets with a bit of high throttle. It was flyable but really rocking side to side; horrible to watch on my video! Indoor hovering vibes were very impressive indeed, between 3-4 points on the all axis (X, Y, Z) according to the logs. The props were not balanced.
I did not do compass MOT; so was not sure how bad the mag interference might be, given how closely everything is located on this frame. When I switched to loiter, I was very pleasantly surprised by the solid position hold. The third clip shows it loitering – if you look at the shadows (5 minutes 52 seconds) you can see me pull the quad out of position and it recovering its position in loiter.
I think the battery is making a difference in the sensitivity. In the first and second clip, I am using a 1800mah A-Spec battery. According to the HK spec these have a 65~130c rating. In the third clip I use a 1300mah rated at 45~90c. The third clip is less twitchy, or at least it looks that way to me.
I am going to experiment with lower PID’s and lowering the rate of climb. I am not sure if auto tune might work on a quad of this power to weight ratio, but might give that a try too. The thing that worries me is that if I reduce the values way down, I might get rid of the twitching but may also end up with a sluggish unresponsive quad.
Could the twitchy behaviour in flight caused by bad motor timing due to the flashed firmware in the ESC’s? I have read some posts claiming the latest version of SimonK has some timing issues with the Sunny Sky 2300Kv motors, hence people are using the 2103 version of the firmware. The oscillations are very pronounced when pushing the throttle hard in climb or forward/backward flight. Any ideas?
I also plan to try out 5” props (both bi and tri blade) to see how that works out. Lots of different things to try…. And a lot more to learn…
Clearly the clips I have posted are horrible examples of AP, but I am hoping the more experienced pilots might be kind enough to offer some advice on tuning and performance improvement after seeing them.