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Thread: LKTR250 - Mini FPV Quad - scratch build CNC frame - build log

  1. #1
    Navigator LKTRSMG's Avatar
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    LKTR250 - Mini FPV Quad - scratch build CNC frame - build log

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    Hi guys,

    with all the cool 250 size FPV quads out there I decided I needed one (or two) as well. I like to design and build my own stuff so I drew up a little frame and had it CNC cut by a friend.

    This is no commercial project, I'm not going to sell any frames.

    The dxf file for your non-commercial use is at the bottom of the post.

    Concept:
    - 250mm diagonal
    - symmetrical, square motor geometry
    - G10 1.5mm frame
    - aluminum or carbon 10x10mm square arms
    - vibration dampening system, dirty/clean frame separation
    - full range FPV capable
    - under 500g / 1.1 lbs
    - free FOV for HD and fpv cam (no props in view)
    - Mobius cam for HD recording
    - LKTR250 (pronounced electro-two-fifty)


    Setup:
    - 3S NanoTech 1300mAh 45-90C
    - Naze32
    - BlueSeries 12A ESC, SimonK flashed
    - Motors:
    - RCX 1804 2400 KV
    - Tiger MN1806 2300 KV
    - RCTimer 5x3 Carbon Props
    - EzUHF 4Ch Lite (PPM)
    - Sony 600 TVL Cam PZ0420
    - E-OSD
    - DPCAV filter
    - 2.4 or 1.2 vtx

    Before I started I did some motor/prop testing with 5x3 plastic props from HK - the most unbalanced props ever, and 5x3 carbon from rctimer. The rctimer props are very stiff, some are very unbalanced, some are ok. Balanced all props for the testing and later flying of course.
    Tested on the RCX1804 2400 and the Tiger MN1806 2300.

    RCX1804, plastic 5x3: max thrust 280g
    RCX1804, carbon 5x3: max thrust 335g @ 8 amps
    NM1806, carbon 5x3: max thrust 480g @ 14 amps - overamping the ESC here but thats only max...

    both motors run at about 2 amps for hover thrust (125g) so I figure hover-only flight time will be 6-7 minutes on a 3S 1300

    After the tests I was pretty sure I will get some decent acro performace with the 5x3 carbons props from both motors.
    I would like to get a flighttime of 5 min acro, from the test I think thats realistic.


    The stuff:
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    CNCing:
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    Frame parts done:
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    It will look something like this:
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    BR
    LKTRSMG
    Attached Files Attached Files
    Last edited by LKTRSMG; 16th March 2014 at 06:54 PM. Reason: added the dxf file

  2. #2
    Navigator LKTRSMG's Avatar
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    Empty frame with nylon M2.5 standoffs and screws. Dirty frame uses 10mm standoffs, clean frame 25 or 30mm (depending on Lipo). 25mm is minimum because of the board cam.
    Click image for larger version. 

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    Preparing the Naze - it will be mounted under the clean frame bottom plate in order to have more room / space to move for the battery. So I need the naze with connectors to be below 10mm thick.
    Soldered pin headers. From left are ESCs signal 1-4, then 5V and GND. I will be using one ESCs BEC.
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    To the RC rx ... sum PPM. Naze will be mounted 90 so i can access the USB from the side. Already figured out the ALIGN_... parameters
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    Dirty frame - 10mm M2.5 standoffs, double sided foam tape for ESC mounting:
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    lower plate (left), upper plate with 6x10mm rubber dampers. EDIT: I found 6x13mm are softer and much better suited for jello elimination and fc vibrations issues.
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    Power distribution is a 2mm double sided pcb, mounted with nylon M3 screw.
    ESC power wires are cut to length and soldered to the distro board.
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    One ESC after the other, working on the GND side first.
    ESCs have been flashed, heatshrinked and labeled before... heard lot of bad things (cogging issues) about SimonK and the RCX Motors but the 05-15 firmware (the first version I tried) works flawlessly for me, so I kept it.
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    Last edited by LKTRSMG; 8th February 2014 at 06:22 PM.

  3. #3
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    Last edited by LKTRSMG; 15th March 2014 at 10:15 AM.

  4. #4
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    more build...

  5. #5
    Pilot Pixturethis's Avatar
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    Looks great. I would use it without the Fpv camera & just use the mobius camera as Fpv & HD. Also would use 2.4 Rc receiver & no OSD. But that's me.

  6. #6
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    mobius has way too much lag/latency for my kind of flying. 2.4 RC would be an option for sure, but I had the ezuhf laying around anyways

  7. #7
    Pilot Pixturethis's Avatar
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    Funny, it's what I use on my 350qx. Never had any trouble with it lagging.

  8. #8
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    Dirty frame / ESCs / power distro

    Working on the power distro board, GND side is ready. Distro board is 2mm PCB double sided copper, mounted with M3 nylon screw/nut. I wanted to go as light and small as possible for the power distro. Also very cheap...
    ESCs are already numbered according to the naze firmware - #4 and #2 are the front motors/escs.
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    Flipping the power distro and ESCs over to solder the +12V side:
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    Solderd 16AWG power wires, will add XT60 connector later. On the left side you see the power line for the video system.
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    sticking the ESCs to the frame with double sided foam tape:
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    the dirty frame sandwich, video system power, battery leads, 4 ESC signal and 1 pair of ESC BEC wires. ESC wires will be crimped with servo connectors, housing will be a 6-pin female housing that will connect to the naze (see pics in first post).
    Four M2.5 6mm ISO 7380 hex screws to fix the upper dirty frame piece:
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    10mm height, ESC fit in easily - 8mm would also be an option, I might use 8mm square carbon arms for an even lighter build.
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    dirty frame done:
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    Last edited by LKTRSMG; 27th January 2014 at 05:32 AM.

  9. #9
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    Booms and motors

    for the booms i made some prototypes from 10mm square aluminum and 10mm square carbon tubes.
    Boom length is 104 mm
    aluminum boom weight: about 10g (per arm)
    carbon: about 6g

    So I decided to go for carbonfibre.
    drilling the carbon fibre is a bit tricky - Ive found it works best when inserting a fitting piece of scrap wood into the tube so the drill bit has somthing to work against on the other side.
    Drilling template for the arms. Motor hole spacing is 12.5mm, 2.5mm holes so will fit both the RCX (12.4mm) and the Tiger (12mm).
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    Next thing was to decide how to mount the motors to the booms. For the Tigers I decided to go as strong as possible by using standoff in the arms (8mm inner space). The M2 motor screws go all the way from the bottom of the boom into the motor:


    The tigers look so sexy
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    Mounting the arms to the frame. M2.5 16mm screws, nyloc nuts:
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    How the motor is mounted to the arm. Only 2 screws - I used only 2 screws on larger quads with good results so I'm sure this will be enough.
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    done. ESC-Motor wires will be soldered later.
    I'm using aluminum nyloc nuts instead of the original tiger motor spinners.
    Tiger spinner: 1 g
    aluminum nut: 0.5 g - easy decision
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    Frame is very rigid. There is almost no flex motor-to-motor (short distance), a little bit of torsional / diagonal flex.
    So rigidity should be more than ok for acro flying.
    Tiger prop adapters are 4mm / M4 - my props are all 5mm ... so 2 layers of heatshrink and I'm at 5mm

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    Short motor-to-motor: 180mm
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    180mm as well...:
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    diagonal motor-to-motor: little more than 250mm. SQRT(2)*180mm = 255.6 - Close enough to call it a two-fifty.
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    Last edited by LKTRSMG; 29th January 2014 at 08:37 AM.

  10. #10
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    Clean frame and electronics

    E-OSD and L-C-filter have been combined and heatshrinked together as seen in the pic below next to the board cam:
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    Clean frame parts on the left in pic below. Mounting holes for velcro and cable ties are already in the design. 30,5mm FC mounting on the lower (long) part.
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    Nylon spacers M2.5 on the clean frame:
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    FPV cam install. PZ0420, clipped the board to the smaller footprint of 33x33mm, then plastidip-ed.
    Cam is fixed by one cable tie, foam tape between cam and frame.
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    Cam board goes through the clean frame bottom in order to keep the clean frame height at 25mm, also this way its easier to securely mount the cam with only one zip tie. Saving weight wherever I can.
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    M3 nylon screws for the FC mounting below the clean frame. I will be using 4 screws of course
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    For making the E-OSD / LC-Filter pack see http://fpvlab.com/forums/showthread....l=1#post427276

    For the FC and RC RX install see http://fpvlab.com/forums/showthread....l=1#post427790


    Here is the finished clean frame.
    4Ch ez rx on the left, sitting underneath the clean frame, attached by two cable ties. Clean frame was designed specifically for the 4Ch. The antenna goes through the frame to save the sma/rx pcb from breaking in case of crash (or to offer some protection atleast). This way I achieve maximum separation of the uhf rx antenna from the Mobius (433 mhz noise in close vicinity) and other possibly rf-noisy components.
    Below the frame in the center hangs the naze fc.
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    Another angle. Velcro straps are scorpion size small. Best velcro ever
    on the right side you see the cam, behind the cam is the filter/e-osd package.
    Why use an osd? Because I like to monitor my voltage when flying, thats all.
    In the center on top of the clean frame is the vtx, boscam 2.4. I removed the bulky heatsink - been doing this forever with the boscam vtx's with no negative consequences.
    Velcro on top will hold the Mobius. Buttons on the Mobius are reachable with the velcro on. To avoid slipping of the Mobius I'm using selfadhesive rubber foam 2mm.
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    Joining clean and dirty frame. On the FC is the custom 6-pin connector. Labeled to avoid reverse polarity. This is necessary because among other things I am a master magician and work with magic smoke regularly. As you might know, magic smoke is costly so I try to limit my use of it.
    Video system power is connected through a JST connector.
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    Naze mounted 90 (sideways) so I can plug in a USB connector from the side.

    Edit - this is what I did first, but not needed:
    CLI parameters:
    set align_gyro_x = -2
    set align_gyro_y = 1
    set align_gyro_z = -3
    set align_acc_x = -1
    set align_acc_y = -2
    set align_acc_z = 3
    easier way with current firmware:
    set align_board_yaw = 90


    the spacer above the USB needed a countersunk screw, drilled the hole to the countersunk screw in order to safe 2mm and have the screw flush with the frame bottom.
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    Last edited by LKTRSMG; 5th February 2014 at 05:46 PM.

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