fangin.com RC, photos & tech

6Jul/141

Character Set Update – MinimOSD

The problem:

The on screen display (OSD) characters from the Hobbyking Minim OSD v1.1 appear garbled.

video and at seven minutes in he explains that both sides of the board need to be powered for the character update to work. I was thinking "what the hell, how is this not stated on the instructions page!"  Actually it is, right here in black and white. The point is, if your Minim OSD lights don't look like the picture below, the character set update probably ain't going to work.

minim OSD ready for character set update

minim OSD ready for character set update

 

 

 

25Jul/130

2.1mm F:2.0 Turnigy Micro FPV Camera Lens

This image shows the view from the default lens that comes with the 1/3-inch SONY CCD Video Camera (PAL) on the left and from the same camera but with the lens swapped for a 2.1mm F:2.0 Turnigy Micro FPV Camera Lens. On the right I've drawn a green box to show the area of the original lens overlaid on the view from the replacement lens. The original lens has quite a smaller Field of View in comparison.

While the new lens has a much wider FOV, objects appear smaller overall. Compare the size of the fridge in the middle of the frame. I'm going to try the wider FOV lens for now as it should be better in tight spaces.

 

2.1mm F2.0 Turnigy Micro FPV Camera Lense

 


 

1/3-inch SONY CCD Video Camera (PAL)

Greenshot_2013-07-25_21-49-01

 

 

 

 

 

 

 

 

 

 

 

2.1mm F:2.0 Turnigy Micro FPV Camera Lens

Greenshot_2013-07-25_21-02-36

30Apr/130

Testing the Low Pass Filter

Testing the Foxtechfpv 1.4GHz Low Pass Filter

http://www.foxtechfpv.com/1400mhz-low-pass-filter-p-439.html

The aim of this experiment was to quantify the signal attenuation of the low pass filter across various frequecies. Ideally I would have produced a frequency response plot of the LPF from 0 to 3GHz but due to limitations with the equipment, I could only test in the ranges 0 - 1040MHz and 2 to 18GHz with two different signal generators. Being limited by the SigGens to the two different frequency ranges (0 to 1.04 GHz and 2 to 18GHz )was a bit disappointing because the real interesting part is the roll off profile at around 1.4GHz. Below 1.4GHz, the loss should be minimal, above 1.4 GHz, according to the foxtechfpv website the signal should be attenuated by at least 45dB. A really good filter will have a short sharp transition from no loss to high loss.

I chose to test at two specific frequencies. 1) 1040MHz is the highest frequency the first SigGen can go and is closest to 1280MHz of the video transmitter being used. 2) At 2560 MHz which is the second harmonic of 1280MHz. Ideally the result will show 0dB loss at 1040MHz and at least 35dB at 2560. So what did the tests show? First some calibration. The LPF uses male and female SMA connectors. To hook it up to the signal generator and Spectrum analyser, a set of adaptors is used to adapt the SMA connectors to the N-Type used on the equipment. By connecting the signal generator directly to the spectrum analyser and transmitting 0dBM, the SpecAn showed -1.2dBm. The SigGen signal is then upped to +1.2dBm to compensate for the loss and set the SpecAn to 0dBm. At 1040MHz, the loss of the LPF is measured to be 0.6dB (better than the 0.7dB on the website). Then the LPF is connected to a 2560 MHz signal (second harmonic of 1280MHz). The SpecAn shows the signal is attenuated by 63dB. Much better than the conservative 35dB stated on the website.

1. 1040MHz Test Setup. Spectrum Analyser on the left, Signal generator on the right.

01 - 1040MHz Test Setup 

2. Cable & connector & SMA adaptor loss. The LPF filter is removed from inline and the signal generator is set to +1.2dBm which results in 0dBm on the Spectrum Analyser. The loss in the measuring cables, connectors and SMA adaptors is then 1.2dB
02 Cable & connector & SMA adaptor loss

3. 1040MHz reference level 0dBm. Without the LPF inline, the SpecAn shows 0dBm.
03 1040MHz Reference level 0dBm

4. 1040MHz filter only loss 0.6 dB. Compensating for the connector and cable loss, the LPF loss shows 0.6dB at 1040 MHz. Why 1040 MHz? That's the highest frequency possible on this particular signal generator.
04 1040MHz filter only loss 0.6 dB

5. Signal Generator for 2560MHz.
05 Signal Generator for 2560MHz

6. 2560MHz reference level at 0 dBM without the LPF inline.
06 2560MHz reference level

7. 2560MHz with LPF inline at -63 dBM with the LPF inline. The LPF is doing it's job 🙂
07 2560MHz with LPF inline

8. foxtechfpv 1.4GHz LPF
08 foxtechfpv 1.4GHz LPF

7Apr/130

1.3GHz Low Pass Filter – The Case For

 

Today I flew the PVC quad on another shakedown flight (after fiddling with the configuration via the GCS). I was flying over a fairly large oval, not very high but on the far side from where I was sitting when all motors lost power. I believe failsafe on my Futaba kicked in. You can hear in the video that the motors stop and then just before hitting the ground, they briefly start again. I walk over to the quad from the other side of the oval, perform a quick inspection to make sure nothings broken or fallen off and without any other changes or resets, power up the OP CC3D by holding yaw right and away I go.

 
 
 
 
I've used this Futaba Tx and Rx pair in nitro fixed wing models at much further range and never had an issue. The main difference is now I have a 150mW 1.3GHz video transmitter (http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_30_38&products_id=1018) about 20cm away from my 7 channel 2.4GHz receiver. I've read about guys using low pass filters on the vTx so I thought it might be worth checking the interaction between the 1.3Ghz vTx and the 2.4GHz Rx. Fortunately a guy from work that came out to watch carries a spectrum analyser around in his car so we set about looking at how "dirty" is the 1.3GHz vTx.
 
The screenshots of the specan show a 2GHz wide band centred at 2GHz (so it's showing from 1 - 3 GHz). The first screenshot is using the "Max Hold" function on the specan which is effectively a cumulative trace that shows the max detected levels across the band and holds it. This screenshot shows my 2.4GHz Tx as well as the in building wifi and a few other small peaks. At this point, my video transmitter is powered down.
 
 
The second screenshot on the same scale (1 to 3GHz) after the vTx has been powered up for a few seconds. You can see a peak at 1280MHz (vTx frequency) but disturbingly, across the whole band are is a whole lot of noise coming from the vTx. The second harmonic at 2560MHz appears to be right where we see the Futaba Tx.
 
 
The effect of this noisy little transmitter means it's desensitising my 2.4GHz receiver. It's like someone talking really loud (1.3GHzvTx) standing right next to you (2.4GHz Rx) when you're trying to listen to instructions from someone talking in a normal voice on the other side of the room (the 2.4GHz Tx). 
 
To address the problem a 1.3GHz low pass filter can be fitted in-line on the vTx between the output and the antenna. The low pass filter allows the video signal to be transmitted down in the 1.3GHz band but anything above roughly that frequency is heavily attenuated. The noise coming from the vTx is no longer shouting in the ear of the 2.4GHz receiver so I can hear the instructions from the transmitter much easier and at a further distance. I've ordered this low pass filter (http://www.foxtechfpv.com/1400mhz-low-pass-filter-p-439.html) from foxtechfpv to hopefully solve the problem.
 
I forgot to mention why 1.3Ghz and 2.4GHz interfere with each other - harmonics. Check it out on wikipedia http://en.wikipedia.org/wiki/Harmonic
 
What I found most useful today was being able to see the problem right there on the spectrum analyser. Being able to see the video transmitter peak at 1280MHz and then all the  smaller peaks across the rest of the band including the 2.4GHz area right where my Futaba Tx is.
 
What will be interesting to look at next is after I fit the low pass filter, how does it look on the spectrum analyser. I expect it should look much cleaner. Something else I also want to look at on the specan is the 1 watt 1.3GHz vTx  fitted to my DJI F450. I've flown that at much further range without issue. Is the vTx a much better one where it transmits only on the frequency its supposed to? I'll hook it up and find out.
 
--------------------------------------------------------------------------------------------------
 
Without the "Max Hold" function on the specan, this is how it looks.;
 
First with the 1.3GHz vTx off
 
Then with the vTx on
Filed under: CC3D, FPV, RC No Comments
8Aug/120

Flips & Rolls with the Naza F450 Quad

This video shows my first loops and rolls with the DJI Naza F450 Quad. I did at least one in every direction (left, right, forwards and backwards). The entire flight was flown via FPV which I found much easier for these moves. Flying line of sight at this height and distance makes it hard to maintain orientation.

A guy that started flying the F450 about the same time as me told me how he tried to roll it, it got half way and dived into the ground. Broke an arm or two and some props. Thanks to the well thought out F450 frame, he was back up and running in no time but after hearing such a tale I was a bit apprehensive to try it myself..... until now. With my FPV gear up and running it's much easier to gain a lot of height and maintain orientation. 

The setup is a stock F450 quad with 8" props and 4S battery (4000mAh on this flight). Other than the gain settings as described here (http://fangin.com/blog/2012/08/07/dji-naza-f450-gain-settings-flips-and-rolls/), there's not much to it. Gain plenty of height and bang the stick over. I can see how if the gains were set too low, the roll rate might not be quick enough to complete the roll without losing too much height.