FPV 250

Please note that this machine has been decommissioned for future projects. Please see my latest FPV250 build for more updated information.

The FPV250 is HobbyKing reaction to the up and coming FPV racing. The FPV250 is essentially a very cheap frame compared to other frames like the QAV250, Spanky mini H-Quad and Blackout Mini H-Quad. There is also a similar platform called the ZMR X-Power, which is a more complicated design with integrated ESCs and power distribution, still at an equal price. Once the FPV250 was announced by hobbyking I thought: Why not?

HobbyKing suggested setup for FPV 250



There is also an ARF package available with all the above components, a battery, a pan-tilt camera mount, some bolts and a power distribution cable.

Alternative components


Since HobbyKing doesn't have all parts in stock I've starting looking for optional components. From other peoples experiences shared on forums (mainly rcgroups) I've decided to pick up these parts. It should be noted that the motor mounting holes doesn't fit perfectly on the FPV250, but it works well to remove some plastic to get it in place.


FPV gear



Camera mount


The FatShark camera I'm using comes with a pan-tilt arrangement that looks really good and smart when you take it out of the box. However it requires some fiddling to get it in place correctly on the frame. I decided to mount it underneath the frame to avoid the props. To mount the pan-servo you need to remove it from the camera. Remove the screw from the cable holder and pry it apart to access the screw the mounts the servo.
Once mounted I noticed the signal cable from the mount comes out right where I want to put my battery and might prevent balancing the quad if I need to push the battery further forward.




I fixed this by modifying the camera mount to get the cable to exit on the side of the mount.

Normal signal cable exit

After

I could have made this a bit better by letting the cable exit further back. It would probably have looked nicer but this will work too.

Additional work is required when mounting the camera upside-down. I cannot reverse the image with my goggles which results in some warranty-voiding. The camera isn't really made to be mounted upside down and even when taking the camera a part it requires some craftsmanship (force). Don't make the same mistake as I did and discover this the last thing before flying. It is much easier from the start.

To fix it unscrew the "tilt" servo and remove the servo from the outer part of the camera. Remove the two screws holding the camera together and take out your file to remove the plastic which is preventing the board from mounting the other way around. Then put it together again.

Enlarged connector slots on camera mount. Warranty long gone...


Power distribution


First things first. Buy a power distribution board. I didn't and didn't have the patience to wait for one so I did the ordinary spider-web-mess-soldering. It didn't turn out as good as would like to but it'll work for now. I removed the 2mm plugs that came with the ESCs. The cables will be long enough for all ESCs but one, which needs extending. I then soldered everything together with a EC3 and JST plug for battery and video transmitter, respectively.

Power distribution

I mounted the ESCs on the bottom of the arms as the capacitor fits well into the little slot. However, this is a no-go if you want to solder the battery leads directly to the ESC and still be able to resolder them (in worst case). They must be mounted the other way around to expose the motor lead solder points.


Motors


Mounted motor, ESC and power sensor.
I chose to use the ZMR (RCX) 1804 2400kv motors for two reasons. Firstly the HobbyKing motors were out of stock at the time and secondly because the higher kv of the ZMR motor makes them more suitable for two-bladed props on a 3S setup and thus more efficient. The quality of the ZMR motors seems so-so. A friend of mine has one motor which is noticeably weaker than the others and one of my motors was a bit bumbed, correctable but still...

The ZMR motors won't fit the FPV250 since the mounting holes are too tightly spaced on the motor. This will require some modification of the FPV250 frame. I had plans to drill/cut/heat out the holes and enforce the mounting plate with a sheet of plywood or carbon, but the mounts are so thick and the designed in a way that you won't sacrifice stability IMHO. Since my china-copy of a dremel is too noisy I used the soldering iron to heat the plastic and extend the mounting holes further to the center. Seems to work well.

You can't use the mounting screws that comes with the motors, they're much too short. Instead, use a 6mm 2M screws with a 2M washer for a perfect fit. Anything longer will touch the winding in the motor. I do a lot of 450 builds and I have these screws in abundance from the 450 hardware bags.

You might need to cut away a part of the landing gears to avoid interference with the screw and washer. I used thin CA to attach them. This was a bad choice.

Motor screws and landing gear.

Receiver



I didn't intend to equip this machine with telemetry since it's a bit costly. But I'm getting more and more addicted to it and finally installed it anyway. I use a R7003SB receiver together with the e-fuelgauge from Thomas in Denmark which gives me all I need. I placed the receiver in the "well" in the frame since I can't put the flight controller in there.

Receiver placement.


Flight controller


I will use the CC3D flight controller. It fulfills my fundamental requirement of S.BUS support and many are satisfied with its performance in agile flight. This controller board are much smaller than the KK board and mounting it inside the well on the top would prevent access to the USB port. I will build a shelf to place the flight controller in the classical center tower instead and place the receiver underneath.

CC3D Flight controller, for size reference

I cut a shelf from plywood to place over the "well" with the receiver and mounted the CC3D with gyro tape directly upon it. The shelf has been cut to provide access to the USB-port which is located on the lower side of the board. The picture below is taken with 3-bladed props since I don't have the 2-bladed at this point. I will switch to those later on.

Shelf with CC3D.

I will probably build another story to the center tower to cover the CC3D and make it easier to attach cables. The additional plate will also serve well for attaching a Mobius.


Video transmitter


I wasn't satisfied with how the video transmitter fits on the back plate, which is supposedly made for that purpose. It will be mounted rather far back and prevent easy access to the USB port of the flight controller.

This leaves two options (that I can think of). Either a vertical mount, which would have been really nice, using a short stemmed antenna or building a tower with a level for the transmitter. I picked the latter since I have no short stemmed antennas "in stock" and to provide some protection to the controller. I built it using plywood pieces and nylon standoffs and screws. Turned out quite nice. I think you could probably use rotor bits plates for this tower build and it would have looked more "pro".

Video transmitter tower.

Final result with cables tucked in and two bladed props.


Note: This simple placement of the video transmitter in combination with the new heavier ImmersionRC SpiroNet antennas seems to come with some consequences. In the event of even a lighter crash the connector on the video transmitter board will not survive. I repaired mine once but then it started breaking off in-flight. I will post an update once I have a better solution.
Video transmitter with almost broken off connector.



CC3D Settings

These are my settings. I've spent a lot of time trying to find "optimal" settings that makes the quad responsive, stable and gives somewhat stable footage.


CC3D Stabilization settings


Flight results


Initial flight after making the basic setup of the CC3D board. This flight was made with 3-bladed props. I had slight oscillations in the ground effect but I'm so far impressed by the stability of the CC3D. Video and flight data.

First FPV (first for me and the machine) flight after several adjustments. It feels very reliable now and stabilizes well but I still have the impression I'm having oscillations. Check out the video to see for yourself.

After spending a lot of time setting up the CC3D and some 20 flights I think the quad is now flying as good as it can and performs good enough for my skill.


Changes for the next version

  • Don't use the Multistar ESCs. They do not come with SimonK and are difficult to flash. If HobbyKing is the preferred source of stuff then Afro is probably the way to go. But there are other options out there as well.
  • Don't use the Fatshark pan-tilt camera. The camera isn't very good and the servos seems of lesser quality. Mine tends to draw excessive current when idling. Also, getting used to flying without the pan-tilt makes you get rid of some weight and power consumtion.
  • Maybe use the long frame upgrade for the FPV250 frame. This way it is easier to build, no additional carpentry needed, and with the battery mounted top-side you can loose the landing pins and belly land instead.


More stuff


8 comments :

  1. go on.. i may buy one for my fpv flights.. pls finish yours.

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    Replies
    1. I'm just as impatient as you but still waiting for parts from Hong Kong and Malaysia. It might take up to two more weeks before I can continue...

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    2. I case you haven't noticed my build is finished and flying. It suits me well as an FPV beginner but will it fit the experience pilot? Do check out Bruce's review for useful comments on the kit and setup. https://www.youtube.com/watch?v=_P6tQaPEL28

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  2. Nice build log, Thanks! I was not sure how to fix the motors and now i will follow your tip. Thank you! Happy flights!

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  3. Just started following your blog!
    I want to build my own FPV250 and looking at HK Clean&Dirty model cause of the vibration dampeners. As far as controller; have you thought of using Naze32? I have KK2 now but wanted to try Naze32(seems popular). Do you use OSD when using FPV250? The motors (Multistar 2206-2150KV) is not available at HK; from your experience which motor do you recommend for FPV250? I thought of using 20amp ESC instead of 12a; can I use existing 30a esc?

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    Replies
    1. Yes, I have considered the Naze32 but it has been hard to come by at times and I decided to go with the CC3D instead. I have used the KK2 board on a tricopter but I'm not that satisfied with it and I wanted to move up a notch.

      I don't use OSD since I have telemetry in my remote and use that for monitoring the battery voltage and capacity. I would recommend using either that or a simple OSD to avoid damaging your battery or falling down in the "wrong" place.

      In terms of motor I use the RCX/ZMR 1804 which I like, but will use the slightly bigger 1806 on the next build. RCTimer also has a good 1806 motor.

      There's no need to use an ESC bigger than 10A. The FPV250 averages at 10A and maxes out at about 20A, which is still only 5A per ESC. Anything bigger than that is just carrying extra weight.

      Instead of ordering from HK you could order the frame, motors and ESCs from banggood, which carries an updated version of the Clean&Dirty frame.

      Diatone 17# v3 frame
      ZMR 1804 + 10AESC combo

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    2. Well look at that, HobbyKing just started selling the Naze32 Acro. Suppose it will be easier to come by from now on. Check it out!

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