Le FPV 150

I have enough of 250 FPV racers now. So what's next? I've seen the new frames and a few builds of smaller racers with similar performance as the 250 sized quads and been dreaming of one for a while. Imagine the agility and the ease of transport that comes with a smaller size. Now it is time, after pondering, ordering, waiting, ordering more, waiting even more, to put things together.

FPV 150
Diatone ET 150 / FPV150

Parts



The Build

Motors and ESCs

The ESCs comes flashed with the latest BLHeli version and are flashable and configurable through the servo connector (i.e. there's a bootloader as well). Out of the 5 I ordered one was partly a dud. It works, but cannot be configured through the servo lead. This was a common problem with early batches. I won't be using that one. Thanks to the BLHeli software there's no need to pay attention to how the motor wires are soldered. Instead you can change the rotation direction by configuring the ESC.

To solder the motor I peeled back the heat shrink cover to reveal the solder points for the motor wires. I also removed the heat shrink that covers the servo connection, we'll get to that later. I desoldered the motor leads from the ESC, the wires on the motors are more than enough.

Preparing the ESC
ESC with some of the heat shrink removed to reveal solder points.

I had to cut down the motor wires as short as I dared, about 1 cm. I could then easily solder the motor wire to the ESC.

Soldered motor mounted on arm
Motor soldered and mounted on the frame.

The motor keeps everything in place once screwed into place. I tacked down the ESC even more with some insulation tape to protect the solder points of the motor. After that, I actually covered the tape with the DYS sticker.

Once all the ESCs and motors are in place I went through the ESC configuration and switched motor direction where needed.

I attached the ESC leads to the power distribution board. This is the first time I realize how small the frame is and the challenges that lies ahead. I had to complicate things a little to make room for the future battery lead and potentially a capacitor or two.

ESCs soldered
ESCs and motors mounted on the frame.



Receiver and flight controller

Since I have gotten used to, and like, the CC3D series of flight controllers this racer will be no exception. A lot have happened since my last build and there are now more form factors of the classic controller to choose from. I went with the so called Mini CC3D. Its size makes it a hot candidate for a small build like this. I plan to mount the controller in the front, behind the camera and together with the receiver. I picked a cheap and small S-FHSS receiver, the new OrangeRX SF400S. It is a 4-channel/S-BUS receiver, similar to the 6303 and 7003 that I commonly use but wrapped in heat shrink and without diversity antenna.

Even at its size it is still a bit clumsy with the servo connectors. So I removed them. But I messed up. I always mess up when I try to de solder the pin headers. This time I was a bit to violent and lifted the soldering pads of one of the channels. Fortunately it wasn't the S-BUS port that got destroyed (because that's what happens).

Receiver and flight controller
Receiver connected to the flight controller.


I used one of the wires that comes with the flight controller and soldered the leads directly to the receivers S-BUS port. The cable is then connected to the main port of the CC3D. This is possibly the smallest installation I can imagine of the two.

To connect the outputs of the flight controller to the ESC I used the output connector with harness directly. The servo connector with wires was desoldered from the ESCs and then I cut the cables on the connector harness to appropriate lengths. I then soldered the signal wires directly on the ESC solder pad. This is why I prepared the ESC by opening up a part of the heat shrink. I did not solder any ground wires as it is only the signal that is opto-coupled and the ground is shared with the negative lead cable from the battery.


Motor control wires
Signal wires to the ESCs.

I stacked the receiver and the flight controller in the from of the frame. This is the only place I can imagine that they will fit. I paid attention to make the bind/mode button reachable from the bottom while placing the receiver. Both the receiver and the flight controller is attached only by double sided tape. There is not much room for a zip-tie and I think I will need to do without it. In fact, the installation looks quite ugly and the flight controller is not mounted flat, but that will be fixed by the calibration later on.


Receiver position
Receiver installed in the front of the frame.
Receiver and FC with camera
Receiver, flight controller and camera (we'll get to that in a moment).

Camera

Partly, I actually prepared the camera before I did the receiver and flight controller installation. This was mainly to get an idea on how i could attach it and how much space it would occupy.

There is nothing in this frame that prepares you for the attachment of the camera. There is only one spot, and at that spot are the two frame standoffs more or less. So, I had to take my saw out and claim to have carpentering skills. Which I really don't. This is one of this moments when I ask myself why I haven't ordered a 3D-printer yet. When I grab the cheap piece-of-crap fine wood saw and dust off the sheets of plywood to make the few rare wooded pieces I occasionally need to build something. I think 3D-printer must be next in line very soon!

Enough of the ranting. I cut a small plate of plywood to attach the camera. It fits between to two standoffs and I drilled small holes in the corners to be able to attach it using thin steel wires.

Camera mounting plate
Plate to attach the camera.

The camera itself is glued down to the plate using hot glue. I didn't spare the glue and filled the edges to give it some protection from potential moisture coming its way.


Camera glued down
Camera on the camera plate, with top frame plate.



Video transmitter and the top plate

HobbyKing carries a small 5.8GHz video transmitter with an angle antenna connector. This is perfect as I otherwise would need to have used an angled adapter if I wanted to protect the connector from impact, as I experienced earlier. The top plate has a hole in the rearmost area that seems to made for this purpose, except it is a bit small for a antenna connector.

So I pulled out my drill and started drilling. And wow it was hard to enlarge a hole in a carbon fiber plate. Looks like crap when I was done but it'll do the job. I also filed down a small slot where the channel dip switches will be located to make sure I can change channels without taking everything apart.

Antenna mounting hole
Enlarged hole for the video antenna connector.

I started preparing the OSD for installation. I'm using the super-simple. I only need a voltage reading of the battery and this is the cheapest and smallest I've found. It also allows for the simplest of installation. As usual the pin connectors had to be removed, takes up half the space to use cables like that. Then I soldered the power lead to the video transmitter and a lead that goes down to the PDB. I also soldered the video and ground cables. After that, a new heat shrink tube was added and the new more compact installation was complete.


OSD with heat shrink
Resoldered OSD with heat shrink, connector to video transmitter at the top.


OSD with transmitter on top plate
Video transmitter and OSD mounted on the top plate.

I can now attach the OSD and video transmitter to the top plate using double sided tape. I tried to avoid using zip-ties here as they tend to interfere with velcro for the battery on the top side.

Once this part is complete, it is time for the point of no return when the video system is soldered together. This means that the video leads from the camera and the power leads from the PDB to the OSD is soldered in place. And after that, the top plate will be dragging along whenever I need to open her up again.


Top plate electronics soldered to base
Top plate with video transmitter and OSD soldered to the frame electronics.




Camera power lead and the capacitors

I'm not using a LC filter in this build. This might be stupid but I'm taking my chances as is is too clumsy to install a filter in this frame. Instead I'm adding a few extra caps, both on the 12V and 5V circuits of the PDB. Both circuits get a fast ceramic capacitor and the 12V side also get a little bigger electrolytic cap which might (or might not) help during power surges. Hopefully the two ceramic caps will help keeping any interference with the video system away.

Receiver power supply and caps.
Capacitors on the power distribution board.


At this point I also soldered the 5V leads for the camera (yes, 5V) and the 12V leads up to the OSD and video transmitter. After that I power everything up quickly to check if anything decided to let the smoke out and if the video system worked as it should. And it did!


Lost model alarm

I completely forgot about this while planning the build. A lost model alarm is a must. Almost every time I crash it has been very hard to locate the quad without using the alarm. At this point I was having nightmares about how to get one in there. At first I considered using an output PWM signal on the CC3D, since I knew the receiver is a bit damaged from the desoldering accident. This was the alarm can be set off from the transmitter. It will however not be triggered by a missing signal failsafe , this a S-BUS issue I have had before.

Lost model alarm soldered
Lost model alarm soldered to the receiver.

I managed to lift the flight controller slightly from the receiver to inspect the solder pads. All I really needed was one working signal pad to solve this. Fortunately all three pads on one channel was undamaged. I somehow managed to squeeze in the cables and the soldering iron without melting everything. Turned out really well.

Mounting the alarm itself is a bigger problem. The alarm is essentially the size of the buzzer, this is the smallest alarm I have ever seen. But in this frame it is enormous. I tried mounting it on the PDB, but that didn't fit, I couldn't get the top plate on. In the end I managed to attach it using zip-ties between the standoffs. Looks like crap but at least it fits, with just about zero margin.


Last model alarm placement
Lost model alarm mounted between standoffs.


CC3D setup

Configuring the CC3D is a real pain on this machine. It might look like there's some room to connect the USB cable to the flight controller but once the top plate with the OSD and video transmitter is in place it very hard to impossible to get a USB connector in there. This means I have to unscrew the top plate every time I adjust the CC3D. And we all know it takes a few times to get it right.

I actually started out with a configuration example for a 250 sized frame from the librepilot GCS but from a geometrical perspective I knew it was far away from an optimal setup. I tested it out and it was actually quite fine. A few oscillations during hover in in some turns but otherwise it felt fine.

I did a few adjustments until I got a decent setup. Good enough for now, I can't taking it apart and putting it back together any more. I will probably experiment with getting a bluetooth device permanently on board in the future for more fine tuning and setting up rate and acro+ flight modes.

CC3D settings

Please use my settings as nothing but a baseline! Every build is unique and you will need to do your own fine tuning to get the performance you need.


First test flight

My very first impression with this machine was: Shit, I need to learn to fly again. Well, I calmed down fairly quickly but what my reaction was all about was how nimble this machine is compared to a 250 quad. It is lighter and weight to power ratio is probably better and it has so little momentum to build up and work against. It's nimble. That's all.

Additionally, the camera did not perform very well during the conditions at the time. I hope it will be better during summer with more forgiving light conditions. I recorded the flight with my DVR but that recording is actually quite good with the image processing in the DVR. My visibility in the goggles are not nearly as good.



This recording is from the first flight before I had adjusted the PID in the CC3D. You can clearly hear and sometimes see the oscillations caused by the high PID settings.




5 comments :

  1. This comment has been removed by the author.

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  2. Hi!
    I wait for it very much the cc3d your settings onto this machine !

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    Replies
    1. I'll try to work through the settings during the next few weeks. I started out with a 250 preset in librepilot which works but with some oscillations. Adjusting the PIDs takes some time as I need to unscrew the top plate to access the usb connector of the flight controller.

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    2. I've updated the build page with my first good-enough CC3D PID settings now. Please use them only as a baseline for your own settings. Enjoy!

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  3. Thank you for the help. I got converted meanwhile naze32 because I did not find it cc3d setting. Congratulations the side and to the much useful description.

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