Having flew small and large size quadcopters, tricopters and hexacopters, I realized mini quadcopter is still my favorite, especially mini-h quad. Small quadcopters are light weight, agile and tough against crashes. It’s generally quicker and cheaper to build too. With the advanced technology, quadcopter parts and HD cameras are made cheaper and smaller, making the mini quad very fun to fly either indoor or outdoor, and capable of filming decent footage videos.

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Note: For a complete parts list for 250 size quadcopter, check this out!

FPV250 Mini Quad – Latest Video

This is the latest video I took with the mini quadcopter.

20/09/2014

04/09/2014

24/08/2014

Decision on Specification

Having built a mini quad before running on 2S, although it was very easy to control and stable, I was not particularly happy with the power. I cannot fly too fast, neither doing flips and acrobatics. This time I will be using the Hobbyking mini quad frame, with the Cobra 1960KV motors on 4S battery. This will be light weight, yet really powerful. Although the FPV250 Mini Quad Frame is X configuration, by adding a long frame kit (Diatone Cage), it looks similar to a H-quad.

Here is my current Specs:

• Diatone FPV250 Quadcopter Frame with Cage Long Frame Kit
• Cobra 2204 1960KV Brushless Motors
• 12A Blue Series ESCs with SimonK Firmware
• Gemfan 5030 Propellers
• KK2.1.5 Flight Controller with Stevis Firmware Naze32 with Multiwii
• Frsky DJT Transmitter and D8R-XP Receiver Frsky D4R-II Receiver
• Turnigy 9X with er9X Firmware
• SONY SUPER HAD 600TVL CCD Camera – PZ0420 with 2.8mm Lense (FPV)
• Mobius Wide Angle Lense (Recording)
• Hobbyking e-OSD with cl-OSD Firmware Super Simple OSD
• Boscam TS832 5.8GHz Video Transmitter ImmersionRC 600mW VTX
• Turnigy Nano Tech 4S Battery 1300mAh/1800mAh
• Weight ~ 650g
• Flight time ~ 8 minutes with 1300mah, 11 mins with 1800mah.

Motors and Power for Mini Quad

As I mentioned in my Cobra 1960KV motor review, these motors can produce 500g of thrust per motor, I estimate to have a 3:1 or even 4:1 thrust power to weight ratio. This leaves a lot of room for additional FPV gear, and enables me to go crazy on arobatics. I also plan to equip a light weight gimbal and Gopro on this quadcopter in the future, if budget permits.

At first I struggled for a bit whether to go for 3S or 4S battery, I eventually went for 4S because of the power, and better efficiency. Here are Some very popular motors on this size of quadcopter if you want to go for 3S instead.

• Cobra 2204 (2300kv) (very efficient for 3S)
• SunnySky X2204S
• RCX 1804 (heard these aren’t that great)
• Lumenier FX2206-13 (good but more expensive than Sunnysky)
• Tiger MN-1806 (very good motors, but most expensive)
• Turnigy Multistar 1704 (hear mixed reviews on these)

Flight controller For mini-h quadcopter

I am planning to use Naze32 Acro eventually, but at the moment I am using the KK2.1.5 with a custom firmware. It flies absolutely great, feels very locked in. Here are some popular choices of flight controllers for the 250 mini quad, just for my own reference.

• KK2.1.5 (very easy to setup, but not as locked in as the Naze32)
• Naze32 (one of the best performance FC’s for mini quad)
• Flip 32 (clone of Naze32, cheaper, and should function as good)
• OpenPilot CC3D
• DJI Naza (heard it doesn’t work very well on mini quad, very unstable)
• APM (odd shape, very hard to mount one frame, it’s an overkill anyway)
• Crius AIO

Assembiling Quadcopter Frame

It was challenging planning where and how to put all my parts on this quadcopter, because the space is so limited, and it was fun to see how everything coming together.

On this frame, the weakest spot I think would be the the part between the arm and motor mount, so I tied a piece of fibre glass rod to it. It might not help at all, but only time and crashes could tell. It gives me confidence anyway (psychologically :-p).

But there are people suggest we don’t need reinforcement, and it’s best to leave some weak point to “take some of the energy” in the event of crashing. I personally think this might be a good idea for larger and heavier multicopters, but mini quad is generally very light, and the crash impact usually is smaller, so it might not be as effective in this case. Here are some good debate posts, pro reinforcement, against reinforcement.

I made a piece of plastic board to attach to the rear, made two holes to hold the video transmitter antenna plug (from an antenna extension cable), and the power distribution cable plug (XT60 female).

Installing Motors and ESCs

The Cobra motors I bought have 2mm screws, so even with the washers they are too small to fit for the motor mount on the FPV250 frame. So I had to make some bigger washers for them with some plastic pieces. I couldn’t find any bigger washers for 2mm screws any where, so DIY!

Actually there is alternative ways to mount the motors. One is to use additional motor mounts. Another is to use cable tie.

Just in case of motor vibration is bad, I bought some rubber screw washers to stick to the bottom of the motors, which could absorb some of the shakes. Only precautions.

ESCs are flashed with SimonK. Here is how I did it.

FPV Gear

For the camera and video transmitter, both take 12V input, but I am running 4S which could reach as high as 16.8V. With success previously on my tricopter, I could use a voltage regular coupled with a LC power filter, to provide reliable power for my FPV gear.

Given the weight limitation, my previous LC filter and voltage regulator are too heavy, so I made another set of LC power filter and mini voltage regulator. It was 35g, now 18g. (about half of that weight comes from the inductor)

OSD

Although I already have a Frsky Telemetry transmitter and receiver (which means when signal gets too low, the transmitter alarm goes off to warn the pilot), I still want to display the RSSI value on the OSD. I do this by using the second spare voltage input on my super simple e-osd, check out how I did this on e-osd RSSI post.

Unfortunately, the information I was given by people commented on the Hobbyking website was wrong. This OSD cannot handle 4S battery, it got fried when connected the first time. Now I need to get the Super Simple mini OSD instead, and another 10 days before it gets here.

Done!

All put together nicely, the mini quad is a little heavier than I expected, overall around 650 grams, but I still get around 9 mins flight time out of the 4S 1300mah Battery (hovering).

Battery

I am using 4S battery, the With battery, I tested 3 different capacity batteries, 1300mah, 1800mah and 2200mah. Flight times are approximately:

• 1300 – 8 mins – hovers at 50% throttle
• 1800 – 11 mins – hovers at 54% throttle
• 2200 – 12.5 mins – hovers at 59% throttle

With the larger batteries, it gets heavier too, so it becomes less agile. But it seems to help removing some of the vibrations and jello from the video, so if I want to go casual FPV, larger batteries would be nice. But I would probably stick with the 1300mah batteries for now due to better power efficiency.

I also tried 1300mah Zippy, but the Turnigy Nano tech ones just runs better and longer. Maybe it’s the Zippy battery I have is getting old.

First test flight with KK2! Wobble problem (update 06/06/2014)

Once you have tuned your PI gains for the quadcopter indoor, or in a wind less environment, I found it is important to always lower your PI gains by at least 10%, and test it again in mild wind to further adjust them. Although it might seem perfectly tuned, a little bit of wind could unstabilize the aircraft. With mini quad the arms are so short, it’s difficult to notice tiny oscillations LOS, which is obvious only in FPV video footage.

I found this PI settings gave me the best result:

• Pitch/Roll
  • P: 65
  • I: 35
• Yaw
  • P: 100
  • I: 100
• Auto Level
  • P: 55

But you can see it’s getting better later on. It still wobbles a little, probably because of the high wind. But also balancing the props helps too. I guess it’s just how auto level is.

Vibration Dampening and Camera Mounting (update 11/06/2014)

When having jello in your footage, or shaking videos, would adding vibration dampening foam, or other material help? In my opinion, not really. Probably because the mobius camera is so light, the foam just didn’t work for me, instead of reducing jello it became worse.

I found attaching the camera directly on the frame worked the best. I mount the camera on the top of the frame with velcro, and it’s further secured by a plastic bend, and a velcro strap to hold it in place. It’s important to make sure the camera is not movable, even when the quadcopter is shaking very hard.

Another thing is the props showing up in the video. You can see the spining props in the above video, because I deliberately moved the camera back from the front of the frame, just in case of crash, I might damage the camera lens. To avoid having props showing up in the video, the camera would have to be moved forward a little, and the lens of the camera will stick out of the frame front edge. That means in crash, the first thing that takes impact would be the camera lens but not the frame. For this, I strap some foam like I did in the picture, which will take some of the impact.

With the KK2 flight controller, I found it flies much better in acro mode, at least not affected by the wind as badly in self-level mode.

A friend on Youtube (jamesb72) suggests using multiple layers of velcro helps reducing vibration too. I tried that and it seems working pretty well. But make sure the camera is secured using rubber bends, straps, or whatever.

Carrying Case for Mini Quad (update 15/06/2014)

Found this water proof carrying case (plastic tool box) for my mini quad. The internal dimension is JUST right. I used to put the mini quad in my backpack when travelling, but the propellers can be easily bent and bring jello to the video. Having a protective carrying case not only keeps everything nice and tidy, it just looks so much more professional. :-D

The case I bought came with foam that is pick and pluck, which means you can remove the correct amount at the desire places, to fit your quad and additional equipment in perfectly.

Training in the forest (Update 29/06/2014)

The best fun of this mini quad is probably flying though tight spaces, something that a large multicopter is unable to do. I am not very good at flying through trees, and I probably crash every 2 minutes. But hey, it’s so much fun and I just cannot stop!

I seem to have a tendency of turning right, whenever I am about to crash into something. That’s why I always break the bottom left prop. Now I have a bunch of CW props, and no CCW props left!

And then I told myself, I need to turn left this time, and I did it! I crashed the other side finally! haha… I am still working on this, although I crash many times, I still enjoy it, a lot!

I crashed so many times in a day, broke many props, but the frame is still standing! Very tough indeed.

Trying out Naze32 on FPV250 Mini Quad (07/07/2014)

I have been hearing a lot of good thing about Naze32 on micro size multicopters, but because the FPV250 frame is not compatible with small size flight controller like the Naze32, so I had to use the KK2.1.5. However, I figured out how to mount the little FC on the mini quad frame finally.

I will start a new post to document my experience with this tiny flight controller – Naze32 on mini quad. I also started a post focus on PID tuning on the Naze32.

Quick video showing the performance (using default PID)

Burnt ESC – Update 29/07/2014

I had quite a big crash when practising flips. After that the mini quad just kept turning right although it takes off fine.

Spent a whole day trying to figure out what is wrong: swapped out FC, then motors, finally tracked down it’s one of the ESCs that is not outputting the correct power. Took off the headshrinks, found one of the FETs under the heatsink is burnt!

No wonder I could smell smoke right after the crash, but I could never guess it’s the ESC.

Rebuild! ( update 13/08/2014)

It’s been great fun, but after countless crashes, I feel like it’s time to swap out the old motors and ESCs, and clear the dirt off the components. I have also just received a new vTX, radio receiver, and the new FPV250LH frame.

This would be the last update on this post, check out my new mini quad build log!