FPV: Starting blocks

Posted on January 7th, 2010

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Preface

I have decided to start experimenting with a new kind of remote control planes (RC planes), those ones carrying a camera and video transmitter, which you control from the ground like a drone.

Ideally, with a good HD camera, you can make nice artistic movies of your favorite places (as long as you respect the law) from a point of view you couldn’t have before.

However, FPV, or First Person View remote control require assembling, soldering, and basically building up the whole system by yourself. There are a lot of issues which are very sparsely documented and no real effort has been done to document this half decently.

I’ll just report what I have done, and how, for anyone to reproduce if they wish to.

Basics

There are a few components that you will find in a FPV plane:

- The camera(s)

- The video transmitter(s)

- Various sensors (GPS, current, battery, radio signal, and sometimes more)

- Possible control chip, or video interfacing (OSD – On Screen Display of sensor’s values), usually both are integrated on the same circuit

- Remote control receiver

- Gyroscope

- Possible head-tracker for pan and tilt camera

- Possible auto-pilot or assisted piloting (called fly-by-wire), associated with infra-red horizon sensors usually

Camera

There are various kind of cameras available. Their resolution is expressed in TVL (Television Lines).

Basically, a 380 to 420 TVL camera brings a VHS-like quality video. It’s not very good, but its quite decent.

A 480 to 500 TVL camera is nearer to DVD quality. It’s pretty good. 550 TVL cameras are even better.

There are no better cameras, and they wouldn’t be useful because we are limited by the way we transmit the video: PAL or NTSC, which are only “standard resolution”, and not “HD”.

These camera have “3 wires”, 1 video, 1 power (+), 1 ground (-) and usually using CCD technology (not CMOS, image is usually bad with vibrations). The one listed usually let you watch the sun without destroying the image too much (so you can fly) and work well in low light conditions.

Here are a few I like:

Panasonic CX161

A very good little camera. With the proper (plastic!) lens, its pretty lightweight (10 to 14 grams). Only 380 TVL, but a good one for this low resolution!

I can only recommend the excellent vendor http://www.GolfRaider.com (you can find their 2.9mm lens+ CX161 on eBay, if the link is invalid by the time you read this, make a search). This vendor is not only the nicest but also the cheapest!

A pretty good firt buy in any case.

Sony SuperHAD 480-520 TVL

You will find this camera under various names in various “FPV shops”. Its a little heavier than the Panasonic (24-50 grams), and sometimes fitted with a night-vision mode (e.g. “KX-191″)

Sony SN555

This camera also has a few other names, and is basically a SuperHAD with 550TVL. It usually does not have night-vision mode, but weights only 29 grams. It’s quite expensive also, at least 150 USD, but probably one of the best quality available.

HD Cameras

Usually, you have a regular camera and a HD camera. Simply because the HD camera cannot retransmit the video to the ground, so it is only used as a recording device.

Some cameras however let you do this. Mine is a Toshiba Camileo P10. The standard resolution “3 wires” output is 480 TVL. This is quite decent. The image has black lines on top and bottom due to the 16/9 to 4/3 conversion, and has a white timer in the black line. Not that clean, but it works fine when you don’t want 2 cameras on-board. Note that HD cameras usually don’t work that well when pointed to the sun, so don’t crash

Recommendation: CX 161 for starters or small planes, HD camera otherwise

The video transmitter and receiver

These transmitters have a power restriction and frequency restriction that depend on where you live.

In short:

- 2.4Ghz up to 10mW is ok anywhere

- 5.8Ghz up to 25mW is ok anywhere

- Most 1.2/1.3Ghz are forbidden in USA (Real planes)

- 900Mhz is forbidden in Europe (GSM)

Using a higher power transmitter usually require a HAM (Amateur Radio License – Technician Class). Most however do not have one and operate them illegally without troubles, just make sure you do not use the forbidden frequencies for your country (those will get you in troubles real quick)

The higher the frequency, the more sensible to obstacles. 2.4Ghz does not go well through walls, tree, rain, and 5.8Ghz even less.

900Mhz transmitter chips are old and usually of bad quality thus even at high power they’re not always as good as high frequency ones.
1.3Ghz transmitters operate nearby the GPS frequencies, so can diminish their performance or even plainly jam them.

You may not use a video transmitter with the same range of frequencies as your radio transmitter, or they will jam each other, even at 2.4Ghz, the signal will work but be strongly reduced.

As a result, most people use 2.4ghz video transmitters, either 10mW (few hundred meters), or 500mW (long range, few kilometres).  Some people use 5.8Ghz (less interferences since 2.4Ghz is used by many systems), and some 900mhz, since it works with 2.4Ghz radios.

Some also use 1.3Ghz and put the GPS far enough that it doesnt get jamed. 1.3 Ghz systems usually offer the best range due to lower frequency and recent chips.

Finally, some use the 900mhz because they live in the USA, and do not want 2.4Ghz video (have a 2.4Ghz transmitter or too much interferences)

Very good 2.4Ghz transmitters are based on either the Airwave or Lawmate chipsets.

Cheapest 5.8Ghz ones are based on the Airwave chipset (others are 10x the price for the same performance)

1.3Ghz comes from China usually and its better to pay a little premium and use ones selected by “FPV shops” instead of getting a bad one. However, these are all coming from the same places thus twice cheaper directly from China/Hong-Kong.

Recommendation:  2.4Ghz, 10mW or 500mW. FatShark 10mW if you plan to stay legal, and get video goggles at the same time (see lower, “Video Goggles”)

Remote control

Most people simply use their 35Mhz, 41Mhz or 72Mhz RC systems. They’re relatively cheap, work well, do not interfere with anything  on the plane and have a long range (1-3km).

Some do use their 2.4Ghz systems, which have shorter range and are “line of sight” (meaning, it doesnt go through walls and so on). They usually have 1 km range with good Spektrum or Futaba receivers. (Full range ones)

Finally, some use so-called “LRS” or Long Range Systems. There are basically 3 “cheap” systems currently available that I would look at:

- using a 400+Mhz radio (CB) converted for PPM (RC control signal) use. Cost approx 50 USD, need a lot of soldering skills. Search for “fmkit” on http://www.rcgroups.com for info. Require a transmitter or Wii Nunchuck.

- Thomas Scherrer LRS, cost approx 300 USD. Uses frequency hopping, very hard to jam (unlike the above 50 USD solution), pretty well tested design. Require a transmitter with trainer port.

- Dragon Link UHF. Cost approx 350 USD. Similar to above system. Less tested. Claims better performance, better jaming resistance, and uses less bandwidth. Less channels on the receiver. (9 vs 12). Require a transmitter with trainer port.

Recommendation:  a 35/41/72Mhz system with a good receiver (eg Corona Synthesised receiver), upgrade to a LRS later if you wish (it will use your 35/41/72 transmitter anyway!)

OSD, Chips, Sensors and friends

There is a huge variety of them. Some provide auto-pilot. Some provide “return-to-home” which basically bring your plane back when you lose radio control. Some let you plot your way on Google Earth on your laptop, real time.

These usually need soldering and technical skills. They are not necessary, but recommended.

I’ll only detail the ones which I found interest into:

- Remzibi “poor man” OSD: very feature complete, light. parts of it are open sourced. Includes GPS.

- SimpleOSD XL: small, quite feature complete. Cheap.

Both are constantly updated. SimpleOSD can relay GPS data to the ground for Google earth plotting and antenna tracking (i’ll detail this elsewhere). They have fairly customizable on screen display.

They do not provide auto-pilot or return to home, but can with a lot of work and an additional module, Ardupilot, and infra-red sensors, which I won’t detail as I have no experience with.

- EagleTree, ezOSD: support nearly every feature you can think of, including return-to-home, F-16 like display, Google earth plotting, antenna tracking, etc. Not quite as cheap, light and elegant as the above, but certainly good as well.

Recommendation: SimpleOSD if you can solder, ezOSD otherwise.

Gyroscope

Video needs to be stable. A stable plane helps, but a gyro on the ailerons helps even more.

Here’s one. Only put it on the ailerons or your plane will act weird. This stabilize the plane when you give no input.

Recommendation: Well, the one listed :p

Video goggles

You’ll be either using a small screen to display what the camera sees either video goggles. In both cases just make sure you can isolate from the sun light easily.

For the screen, anything goes as long as you can plug the video in (TV screens usually).

For goggles, good choices are FatSharks (includes 2.4Ghz video receivers and transmitter usually), Rvision/R520/other name (goggles only, cheaper than FatSharks), or HeadPlay Visors.

The headplay’s have a higher resolution and thus the image is  a lot better. However they’re fragile and expensive.

Recommendation: FatSharks or HeadPlay if you’re rich and careful. But really, FatSharks in most cases.

Head Tracker

Some use a head tracker to move the camera on the plane (pan and tilt). This require additional servos, weight, equipment so many do not use it. It does not especially add a lot to the table and is optional.

A good one is the Flytron DT-3K. I do not use any head tracker. Once again, FatSharks have an option including pan&tilt camera and servos (attention: its a CMOS 420TVL camera. It’s good enough to fly and have fun, but not very good compared to other cameras listed!)

Power supply, voltages, current, linking it together

Well, this is an important one. Are you gonna use a separate battery? Which capacity? What is compatible with what?

These are the questions I will try to answer.

Voltage:

A simple way of doing things, is having the OSD/boards, camera, and video transmitters having the same voltage. This way, all 3 can use the same power supply. Usually its 5.5 volts or 12 volts. So make sure your equipment accept the same voltage.

Current:

Once you have selected the equipement, check their average current consumption (in mA) and add it up. A typical system might consume between 250 mA and 1A (sometimes more).

Battery capacity and voltage:

If your system is 5.5 volts, on a super light plane, you might consider a 1 cell Lipo battery. They deliver only 3.7 volts, so you will need a “booster” or regulator. A good idea is to use a LED driver that deliver a stable filtered current. You need soldering skills once again.  Another possibility is to use a regulator, like the Dimension Engineering micro regulator any-volt. Careful tho, any-volt provides 500mA max output current. LED drivers provide usually up to 1A and are cheap.

Another solution, is to do… exactly the same, with a 2 cells Lipo (7.4 volts). This time, the voltage will be reduced.

Finally, for 12 volts systems, you may use a 3 cells or 4 cells lipo battery (11.1 volts and 14.8 volts), sometimes even directly without regulator (for the 4 cells especially since when voltage is low it will still be above 12 volts). Just make sure this wont burn your equipement.

Otherwise, once again, you’ve to add your voltage regulator.

Let’s say your equipment uses 500mA. Battery capacity is measured in mAh (milli-amperes per hour), so a 500 mAh battery will last 1 hour in this case. a 250 mAh battery will last 30mins. And so on. Just make sure your battery lasts more than a complete flight, by at least 25%.

Grounding:

You might get nasty lines or stripes in the video output. This is often due to bad grounding. Usually, you must “star ground” your equipment, and at least the camera. Basically, each ground (-) goes to a single, unique soldering location directly (without going through any other wire).

In other cases, you might have to shield your equipment a bit, by twisting wires or adding ferrites (small metal rings, you twist the wires around them to eliminate noise)

Linking and location of the various elements:

Use shielded, but thin wires. Replace plugs by servo plugs, or dean plugs. This will make your equipment lighter and easier to deal with. (All this require soldering skills).

Put the RC receiver far from the video transmitter. Put the OSD and GPS, far from the video transmitter as well. Put the electric motor’s electronic speed control (ESC) far from everything

Make sure your antennas extend properly. Range check on the ground. Change the placement if its not good enough. Repeat as many times as necessary, if you don’t want to crash your plane at first flight

Using a single battery:

It’s tempting to use the same battery for the motor RC control, and the video.

If thats the case, use a large enough battery to supply the motor in addition to the other elements. Make sure you have an OSD informing you of the voltage, so that you dont lose motor, RC control and video at the same time. Having a low voltage cut-off (LVC) on the speed controller (ESC) helps, as you will keep the video and control. Make sure its set to a high enough voltage! Once again, test on the ground first.

When you apply power on the motor, it will draw a lot of current, and your video will have stripes or display un-properly. To avoid this, buy a RL filter, or a LED driver that you put between your FPV equipment and the battery (or at least, behind the camera)

Conclusion

I hope these infos can help someone to get started. I’ll post in more details, my “micro FPV” system and “regular HD FPV” system in future posts, if all goes well

Ideally, one could make a computer controlled with “via Internet” user control aicraft. A similar system exists and has been presented recently, the AR.Drone. Basically, this thing flies itself using infra-red sensors, and a user can tell it to go left or right or up or down. But this is no direct control, it’s really just being flown by the on board computer

A mix of computer controlled and user controlled aircraft would ensure stability and security (of both the model and the people or environment around it). This is partially implemented in the OSD including  “fly-by-wire” and “return-to-home” functionality.

Other links:

http://www.dpcav.com/ (Video RX/TX)

http://www.futurehobbies.com/ (Not really recommended due to poor communication an delays, but only place to get Headplays outside Europe)

http://www.nghobbies.com/ (various)

http://www.rangevideo.com/ (various)

http://www.flytron.com/ (various electronics)

http://alai.h3m.com/~s0350672/catalogo/ (various, located in Europe)

http://www.fpv-community.com/ (forum)

http://www.rcgroups.com/ (forum)

there’s probably many others.