November 25, 2014

Mini-quad headlights for FPV

Now that winter is coming (pun intended) we only have a few hours of sunlight during the day. This means that flying during weekdays are impossible. Even during weekends the time frame is limited.

What if you could put headlights configured correctly to be able to fly FPV during dark hours?

There are a lot of things to think about to get this right and I have no idea where to start.

  • Reflector angle, how to find one that is suitable for the camera I use
  • Light wavelength, what is best for the camera
  • Luminous flux, higher often means heavier gear and more expensive drivers
Since I have no idea where to start I'm going to build a first one just to see what happens. I started out with a headlight LED kit from HobbyKing. It's a bit short on specs but since I wanted to re-solder the wires I had to take it apart and found out a few interesting things.

Voltage step down diodes
PWM switch with voltage step down diodes for headlight system

The setup is specified to run at 6.5-8.4 V. Essentially it is made for 2S since it comes with a 2S connector. To achieve the voltage range they have placed the two LEDs in series and added two diodes to "step down" the voltage by about 1.4V. This is the very cheapest and ineffective way of doing this. As a result each LED run at 2.5-3.5 V. The setup is said to consume 500mA. This would give a per-LED power of about 1.2-1.5W. It's hard to guess but we can maybe expect 100lm to come out of each diode. But thats when the battery is fully charged and unloaded, it will probably be much less when we get close to 6.5V.

When re-soldering the LED wires I tugged one of them a bit hard and decided to the the reflector apart to check internal wiring. It's essentially a plastic reflector assembly with a LED emitter glued to it with a simple heat sink glued to the module. The emitter is a very typical 20mm star device like this one and can be found in a multitude of configurations, prices and qualities from Chinese vendors. If the emitter is not powerful enough it can easily be replaced by a more powerful one.

I have no intentions of using 2S to power the LED. In fact, I have no machines with 2S power systems. Instead I'll be using a cheap voltage regulator to provide the required voltage to the device. I will remove the two diodes and power the headlights using the switch. The switch itself is a quite useful device, it can be bought at hobbyking at almost the same price as the headlight kit. Anyone know where I can get one cheaper?

I'm building the headlight setup like a "module" that I can mount wherever I usually put the mobius. The mobius is useless in low light conditions and obviously will be of no use when I use the head lights. I'm using a glass fiber piece from the rotorbits series, very useful for prototyping.

Headlight LEDs mounted on a piece from the rotorbits

I will use a very cheap voltage regulator to drive the LED. Besides from cheap it is also very light and not current regulating. This is not recommended but I will give it a try to see how bad it can get. The regulator has a dial for setting the output voltage. I adjusted it to 6V to start with and will probably increase it to about 6.6V which is likely to be a suitable voltage for the LEDs.

Voltage regulator and electronic PWM switch
 Those cheap regulators are known to cause some noise which can effect the FPV equipment. This is often due to undersized capacitors. I added additional ceramic capacitors to both the input and output (output should be useless actually) to counter this right away.

Additional capacitors on the voltage regulator.

Once everything was put together I attached the to the plate with the LEDs. I tested the setup on the bench with ESC/Battery/receiver I could live without in case the non-current-regulatory property of the driver would cause imminent death of anything. But nothing happend, the LEDs worked and I increased the voltage a little bit as expected.

I attached a JST connector to source 3S from the power distribution and used the ReceiverPort in PPM+Outputs mode on the CC3D to connect channel 7 to the PWM switch. It took some fiddling with the transmitter and even more with the CC3D to get it working properly. But I now have the headlights on a switch on the transmitter.

Headlights mounted on the 250 mini-quad

Headlights in action (impossible to take a good photo of this)

I ran out of time but got to try them out flying line of sight. I recorded the results of course with a DVR to get the actual FPV view. It turns out the camera handles the low light conditions better than I expected and the headlights does a great job at lighting up branches that you wouldn't see otherwise.

November 9, 2014

Flight controller mounts

Flight controllers are getting smaller and smaller. OpenPilot launched the CC3D Atom a while back which takes another step for the compact builder. But, despite the development, some frames are still made with the old 50x50mm size in mind. They might not even have the common diagonal slots to make mounting a bit more general. Yes, I'm talking about my favorite, the Diatone FPV250.

Both HobbyKing and Banggood (other vendors too) have a few mounts and adapters for the 36mm boards. I ordered a few just to get a feel of how good they are and how well they can be used.

FC Mounts
Flight controller board mounts, top left, top right, bottom left, bottom right.

As seen in the picture you can pick and choose between pure mounts, adapters and adapters with dampers.

Starting from the top left; this is a simple build with two carbon/glass fiber plates, a few holes in them and damper rubbers to hold them together. It's actually an adapter with a wider base. I really like this one, it's compact and has the right "feel" to the dampers. Also, it comes with an seemingly random set of nylon standoffs and screws. The screws are too long and does not fit in the standoffs. I might try this out on the next mini-quad build, maybe in the configuration below.

CC3D mounted on power distribution board and FC mount

To the top right is a 3D-printed adapter-damper mount. It has the right feel to it but looks kind of crappy being 3D-printed. It also has an enormous base and mounting it requires a lot of space. It does not fit inside the pit of the FPV250.

FC mount "on" the FPV250

The two bottom mounts are from HobbyKing. One adapter and one mount. The adapter is really simple and could be used in the FPV250 for a small flight controller. Thanks to the big hole in the middle it leaves a lot of room for the cables.

The last one to the right is the simplest of mounts. I don't really know what this is for since a set of standoffs would probably do the same job. One could imagine using this on the top of the flight controller as a protection. I'm unsure if even an angled set of servo headers would fit. Personally I always solder the signal wires and it would probably work for me.

November 4, 2014

Tri-copter fixes

I finally got around to do some of the adjustments I've been planning for such a long time on the tri-copter. I've had numerous issues with this machine like vibrations, video jello, video interference, bad flight characteristics. Those issues was dealt with today. First off, an image before the remake.

The cable mess

I made three major adjustments today (and a handful small ones):

  • Replace the KK board with a CC3D
  • Improved wiring and mounting of the Mobius
  • Replaced a motor shaft

First off the most invasive one, the controller board. I never had any success with the KK board. I know many come a long way with the board and love it because of its price and the LCD display. But not me, and the CC3D has never let me down before. Everything started with ripping out a lot of connectors and removing the KK.

While replacing the flight controller I also installed a power distribution board for the 5V system. I need to source the LEDs, receiver, flight controller and mobius from the 5V BEC and I want to avoid using the flight controller connectors for power distribution.

LV power distribution
Mini power distribution for 5V
I cut all the ESC and servo wires and soldered them directly. Since I sources ground and 5V from the power distribution to the receiver I only needed one wire for the S-BUS to the flight controller. I made a "special cable" for that.

CC3D mounted
Single wire CC3D connection

I made a new "pad" for the mobius to sit on. Place in a better connection with respect to the video cable, I had a lot of trouble keeping it in place before. I used some left over semi rigid foam and stacked a few pieces to build up the platform.

Mobius mounted
Mobius foamy platform

Then I took a look at the bad motor. I had noticed before that there was probably an issue with the motor, mount or prop. Forums had told me that the prop mounts for the NTM Prop drive motors can be of lesser quality. And it was true. Once I spun it up without the propeller on you could clearly see that the shaft/mount was crocked. I replaced it with a new mount (I ordered three extra just in case) and the issue was resolved.

I tested spinning it up and giving it a short flight indoors and everything worked as it should. The CC3D is still on "factory" defaults but it flew anyway, I did not dare take it out of the ground effect as the space was kind of tight.

I had issues with interference in the FPV gear before and I made an LC filter to counter that. It helped somewhat but apparently not completely. I'm unsure if my filter is insufficient or if I need to add another one to the 5V powering the mobius to prevent the mobius from bridging the interference to the transmitter. I caught the interference issue on video, skip to about 50 seconds to see the liftoff and the black lines it comes with.

November 3, 2014

Crappy chinese CC3D clone from banggood

Since I had gotten two CC3Ds from banggood that where really good, as good as the original ones, I had a third one come in a few weeks back. Today was the day that it was supposed to come into use. It didn't.

Turns out a got a bad one. I already started having suspicions when I took it out of the bag. The PCB on this one was much thinner than my previous ones. And with no greater surprise it turns out that it doesn't have a boot loader on it. Just as many have reported before on various forums.

What to do now? If you consult the forums most will tell you to chuck it and order the good stuff from drotek or similar. But can it be that hard to flash your own bootloader? I'll soon find out. Googling for a few seconds pointed me to a detailed description of the process. I only need to get a FTDI, but they aren't that many euros. I have already ordered one from Hong Kong. Hopefully I'll get it within a few weeks we'll see how well the flashing goes.

It seems not to have been as bad as I suspected. Since I considered the board to need some work to get it working if it would ever I started fiddling with it follow the guide on the openpilot wiki. Turns out I could actually flash a new bootloader onto the device using the rescue method. This means there is actually a bootloader on it but the device failed to boot for some reason, maybe the firmware was missing or corrupted.

Anyway. It seems to be working now. But since the "feel" of the device is not fantastic, I must build another small and cheap machine to put it in. :)