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

Parts list:
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.

Views: 5316

Comment by Keyvan R on June 9, 2014 at 6:11am

These are the current values on mission planner.

Comment by Cronselaar on June 9, 2014 at 6:52am

In a months time i'll join in the fun... Cutting my own frames and will be using the AOIP... Waiting for motors are a pain...

Comment by Raph on June 9, 2014 at 7:04am

thank you for sharing - I am waiting for the blackout, my plan is to try the APM on it.. I hope it's not too heavy!

I would suggest doing the nob tuning option - just seems like your PID's are too high. If that is not possible, try to ~half them from 0.0901 to something like 0.0500 and i bet you will be much happier. Also, post  logs if you want more help - could easily tell if a motor is not performing as it should.

Cronselaar - you can buy the luminier motors http://www.getfpv.com/fxc1806-14-2300kv.html

Comment by Euan Ramsay on June 9, 2014 at 11:28am

Comment by Hugues on June 9, 2014 at 12:42pm

The links to the clip do not work, can you repost pls?

Comment by Keyvan R on June 9, 2014 at 2:39pm

Apologies about the broken links. It's my first blog post and I did try to embed the code from vimeo and youtube but it just showed up as yellow boxes. I shall try again

Comment by Hugues on June 9, 2014 at 11:38pm

Thx for reposting your vids. Your gains are way too high as seen from the roll oscillations.

You do not have jello on your video which is really nice!

Comment by Alberto Luján on June 10, 2014 at 9:21am

Lower your gains and do the autotunning. That worked for me all the times in differents sizes. My smallest size is a 330mm though. If autotunning doesn't do the job, clear your D gains and tune P and I for smoth flight, and when it becomes flightable, start rising D by small steps to make ir rock solid. I must confess that now I do autotuning always, so my manual tuning skills are not very trusty  

Comment by Raph on June 19, 2014 at 9:53am

finally got my 250 quad. this thing is so much fun! managed to get a full sized apm 2.6 + GPS, getting 10 minutes of flight with a 2200 3s battery. Here's a quick test flight:

Comment by Rick Swanson on August 14, 2014 at 11:06am

Thanks for those PID's.  They'll become famous when the onslaught of 250 builders that is coming start looking for how to get the multirotor version of a hoped up porsche to fly right.  Do you guys recommend a better esc for apm than any simon-k.  I've seen the stalling issues with both of my copters, and it kinda stinks.  I cant get even a little agressive with either or I lose a motor.  That stinks when you're 50 feet in the air.


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