Get some eyes in the sky!
ASSUMED KNOWLEDGE: The Complete DIY Quadcopter Project This is Part 6 of our massive H4WK project. It is recommended that you read the previous installments before trying to implement the build portion of this installment. However if you have a good knowledge of quadcopters or just want some great reading, you might like to continue anyway. After all, we're not your Mum!
If you are keen to get silky smooth aerial footage or jaw-dropping FPV videos you might want to consider installing a camera gimbal onto your multirotor. Even the most perfectly balanced multirotors will give you some level of shakiness in your video. By using a gimbal, it compensates for the change of roll, pitch and yaw angles (if you are using a three-axis gimbal), producing beautiful, smooth footage.
The two most commonly used types of gimbals are: servo, and brushless motor driven.
Servo gimbals are generally cheaper, lighter and less complicated to get up and running. They do however, give amateur results; jittering still occurs in the video due to overshooting movements from the servo (basically a mechanical limitation of the servo). Response time is also slow. You can improve the performance by using digital metal gear servos, but the cost increases.
Servo gimbals are also supported on a lot of flight controllers, as the servo can be plugged straight in without needing a control board. Servo gimbals are great for any application where video quality is not essential; it also works great for FPV cameras so you can move the camera around while in the air.
As the name states, brushless gimbals are driven by brushless motors. Even though they are more expensive, you will get beautiful and jitter-free videos. The reaction time is fast and the movement is smooth. They are more complicated though, as they do require a control board, and some brands may not work on all flight controllers.
Since we are looking for smooth footage, we will be focusing on brushless motor driven gimbals.
HOW DO THEY WORK?
Interestingly, camera gimbals contain many of the same technologies that are found on your flight board. The gimbal is made up of four key parts:
ANTI-VIBRATION MOUNTS: Used to further reduce jittery footage.
CONTROL UNIT: Processes positioning data from the inertial measurement unit (IMU) and user commands to move the motors to a certain position.
BRUSHLESS MOTORS: Controls each axis of movement.
CAMERA MOUNT: Holds the camera in place. Some gimbals have cameras pre-installed.
Like our flight controller, gimbal controllers contain an IMU. Using a PID controller, data from the IMU is processed and the controller sends out commands to the brushless motors to stabilise and keep the camera level.
SELECTING CAMERAS, VIDEO TRANSMITTERS AND RECEIVERS
Multirotors are a great tool for all sorts of imagery applications such as film, photography, surveying and inspection. All you need to do is pick the right camera or sensor for the job. Following is a rundown of some of the most commonly used types of cameras.
ACTION CAMERAS: Great for general-purpose photography, videography or FPV flying. Getting a gimbal for your action camera is cheap due to them being quite popular.
VIDEO/DSLR/MIRRORLESS/COMPACT CAMERAS: Great for professional photography, videography and surveying. Gimbals are larger for these cameras and more expensive, and you will need a larger multirotor to carry it.
THERMAL CAMERA: Thermal cameras have specialty use cases on drones. They are quite popular for surveying, fire fighting, security, and search and rescue operations where seeing heat signatures are extremely important.
MULTISPECTRAL CAMERA: Multispectral cameras are heavily used in agriculture surveying, as you can get more data about plants while capturing multiple images in different light spectrums. Different spectrums provide further insight into the age of the plant, when it’s ready to harvest, if it’s getting enough water, and much more.
Gimbals are one of those items where the more you spend, the better the quality and more reliable it will be. That said, your gimbal selection will be based on what camera you buy. Gimbals are weight-calibrated and designed for particular camera brands, so you will need to make sure your camera is compatible. Also note that not all cameras have a specific gimbal so a majority of the time you will have to modify what is available or make your own.
VIDEO TRANSMITTERs (VTX) AND VIDEO RECEIVERs (VRX)
We provided some basic points about VTX and VRX in Issue 10 but let’s get a little deeper here.
The frequency you select is one of the most important things to consider, when making a purchase for a VTX and VRX. Most video transmission equipment you can buy runs on 5.8GHz, as it’s legal to use in most parts of the world.
Higher frequencies can carry more bandwidth, which is great; however, the signal will have a harder time penetrating through walls or trees. Lower frequencies like 915MHz will most likely have a more reliable signal as its less susceptible to interference and can pass through objects easier. Keep in mind though, lower frequency equipment usually have larger antennas and modules, and also tend to be more expensive as they’re not as commonly used.
In Australia, 5.8GHz, 2.4GHz and 915MHz can be used for video transmission. I would avoid using 2.4GHz as most R/C equipment, and WiFi runs on 2.4GHz so you will run into a lot of interference on this band. It can also cause interference with the on-board R/C receiver and potentially cause a fly away.
915MHz is fine to use in Australia as long as it’s within the EIRP range. Just keep in mind it will be more expensive and has a larger antenna. If you are going down that path, my recommendation would be the RFD900+ or RFD900X radios.
5.8GHz is probably your best option due to the availability, price and choice of equipment available. With a correct standard setup you can get very good range – some pilots achieve up to 2km! Of course that’s further than you ever need as you are limited by CASA’s line of sight rule.
Digital Versus Analogue
Digital VTX and RTX have started popping up in the FPV world, resurrecting another digital vs. analogue argument. With current technology, analogue systems are still king due to their zero-latency signal transmission (latency is seen as perceptable delay between the capture and display of the footage). Currently there are no digital systems that can provide zero-latency, which is fine for regular flyers and filmmakers but a pain for racing pilots.
Digital systems are also quite large, still very expensive, and consume quite a lot of power, so you need to make sure you have sufficient space, and be sure the electronics and power systems on your multirotor can handle it.
For most hobbyists, analogue systems remain the way to go, due to the quality, price and size.
Types Of VRX (Video Receiver)
There are three main styles of VRX that you can purchase:
FPV GOGGLES: These are great for racing or freestyle flying, however, it is illegal to use FPV goggles in Australia while operating an aircraft, unless you are at a flying field with exemptions from CASA. Some goggles do not come with a receiver module or have a battery included so make sure you check before purchasing.
Of course if you have a spectator who would like to use FPV goggles, then they're free to do so.
FPV SCREENS: FPV screens are an LCD screen with a built-in battery, and module in the back. They are great for filmmaking and photography, or spectating, as you can position your shot quite easily and the large screen allows spectators to see the action.
RECEIVER MODULES: If you have a small LCD screen lying around or a VR headset, receiver modules are the way to go. It’s sometimes also cheaper to buy a high quality non-FPV screen, and add a receiver to it. You will just need to find a way to power the system while you are out in the field.
Many receivers are also compatible with a smartphone or tablet, to utilise the screen you may already have in your pocket!
When looking for VRX you will notice that there are diversity and non-diversity receivers. The most noticeable difference is that diversity receivers have two antennas, while non-diversity receivers have one. The term “diversity” refers to when two or more radio signals are received from a source (in our case, our multirotor). These opposing sources are compared and the best overall signal is chosen. In diversity receivers, there are two receiving modules inside the device, which are compared and the best signal is displayed.
There are two common methods of comparison: the first one is to compare the receiver signal strength indication (RSSI) voltage of both sources; and the second is picture comparison, where the diversity controller compares the pictures and also analyses the noise in each signal.
Selecting the right antenna can make or break your FPV system, as well as your telemetry system.
Note: we will be focusing on the FPV system but all the information can be transferred to the telemetry system.
Antennas are tuned to a specific frequency so you can’t use a 2.4GHz antenna with a 5.8GHz receiver or transmitter. As mentioned earlier, lower frequency antennas tend to be larger than higher frequency ones, so you need to take that into consideration with your design.
Here are some examples of antennas you can use for your FPV system. Don’t worry about the terms, we will break it down below.
NAME: RUBBER DUCKY
NAME: SKEW PLANAR
POLARISATION: Linear or Circular
Okay, let’s get into some antenna theory!
“Antenna polarisation” describes the way the radio signal travels in space. There are two main categories of antenna: linear polarised and circular polarised.
For linear polarisation, the signal oscillates horizontally or vertically in one plane while travelling. Majority of basic antennas are linearly polarised as it’s cheap to manufacture.
- Antennas are cheaper and easier to repair.
- Generally linear polarisation is great for long distance, as all the energy is focused on a single plane; but there are issues with multipath interference.
- In order to maximise signal strength, the transmitting and receiving antenna have to be aligned to ensure maximum rotation overlap. Also our multirotor constantly moves through the air.
It’s hard to keep antennas aligned at all times so there will be signal degradation. You can avoid this by using a diversity receiver and have each antenna angle in each plane to maximise overlap. We can also solve the signal degradation by using circular polarisation antennas.
For circular polarisation, signals are transmitted on both the horizontal and vertical planes with a 90-degree phase shift (basically looks like a spinning corkscrew).
- Circular polarised signals always overlap no matter the orientation or angle of the multirotor relative to your receiving antenna.
- They are more expensive than linear antennas and a lot more susceptible to damage as they are larger.
- Circular polarised antennas are great for their ability to reject multipath interference. Multipath interference occurs when radio signals from two or more paths reach the receiving antennas. It usually happens when your transmitting signal is reflected off the Earth’s surface, objects or bodies of water, which causes multiple paths of the same signal.
RHCP and LHCP
Within circular polarisation, we also categorise the direction of the polarisation. There are two types: left-hand (LHCP) and right-hand (RHCP).
The transmitter and receiver need to have matching directions or else it will result in significant signal loss, and the planes will not be aligned. The direction helps with reducing cross polarisation, as an LHCP antenna will reject with RHCP signals, and visa versa.
Use circular polarisation when:
- Acrobatic flying where the angle of the aircraft is constantly changing.
- Flying close to large objects, such as buildings, trees, or enclosed environments like a stadium.
Use linear polarisation when:
- Long distance flying where your line of sight is clear.
- Stabilised flying where the angle of the aircraft is not changing much.
- Size of a circular polarised antenna is an issue.
For telemetry, there is some debate regarding whether you should use a circular or linear antenna. In my opinion, circular antennas don’t provide you with additional benefits beyond linear antennas, as the low frequency will penetrate objects better, and have less reflection. Also, the circular polarised antenna is quite large for 915MHz, so you will add more mass to your aircraft; and telemetry doesn’t have to be 100% reliable, compared to video because you will get the missed packet in the next broadcast.
Directional and Omnidirectional
The next classification of antennas is “directional” and “omnidirectional”. These characteristics apply to both circular and linear antennas. A good way to describe the energy of your radio system is to consider it to behave like a water balloon. Essentially, different antennas alter the shape of the balloon, but the overall amount of water remains fixed.
In order to get more range, we can stretch the water balloon out to make it longer/thinner (at the cost of reducing its width or coverage). Alternatively, if we squash the water balloon, it will become short and fat, which means we can get more coverage (larger beam width) at the cost of reduced range.
Directional antennas are designed to get more range, as they increase the range by reducing coverage. This focuses the signal into a long but narrow beam (essentially stretching the water balloon).
Omnidirectional antennas, on the other hand, increase the coverage by reducing range (essentially squashing the balloon). This spreads the beam wide and short.
Antenna gain is like a garden hose; focusing the stream into one direction appears to provide more power, but in a confined direction. A gain in one direction is a result of a loss in other directions. This gain is measured in deciBells (dB). A perfectly Isotropic Antenna, transmits energy equally in all spherical directions, but there are no practical Isotropic Antennas. The radiation patterns of all real antennas will have both gains and losses.
However, in real life that is not usually possible. So antennas, such as rubber ducky antennas, which claim to have a gain of about 3dB, will compress the pattern down to gain extra horizontal range.
This image will help with visualising the antenna radiation pattern.
As we increase gain even more, with directional antennas, not only is the pattern compressed more vertically, but it also becomes more stretched in a horizontal direction.
As our gain increases, the antenna essentially stretches the radiation pattern out further, in a specific direction, in order to gain extra range. Typically, for long range flying you will always use an omnidirectional antenna on your aircraft, since it’s always moving at various angles and uses a directional antenna on the ground that will need to always point at your aircraft, to increase the quality of the signal and range.
WHICH ANTENNA SHOULD YOU USE?
Omnidirectional antennas are great for everyday flying, as they have a wide coverage, so you don’t need to keep them pointed at your aircraft to ensure you retain signal. Directional antennas allow you to fly longer distances and still receive a good signal, but since the beam is narrow, you always need to ensure it is pointing at your drone.
The basic rubber ducky antennas included in the box of most hardware will cover you for most short distance flights, but you will notice issues with the quality of the signal. I’d recommend upgrading your transmitter antenna to a skew planar antenna, and the receiver antenna to a cloverleaf antenna. These antennas are omnidirectional and circular polarised so will work well for general flying.
Generally, the price gives a good indication on the quality and precision of the antenna. More expensive antennas tend to deliver better range, as they are made using better materials, and with higher precision. It’s not always the case though, so it’s up to you if you think it’s worth paying double the price, to get a 10% increase in range. Reading through reviews will help you make a more informed decision.
Let’s now install a gimbal on H4WK!
Mounting rails are a common feature on most commercial drones as it makes it easy to add or remove equipment. Our gimbal is equipped with a mounting rail attachment, so we are going to make use of that and install a small mounting rail onto H4WK.
|ELECTRONICS Parts Required:|
|1 × Tarot TL3T01 ZYX-T3D-III Pi 3|
|1 × Boscam TS832|
|1 × GoPro Hero 3/4 or Compatible Camera|
|2 × M3x35mm Cap Head Screw|
|4 × M3 Washers|
|2 × M3 Nuts|
|8 × M2.5x6mm Cap Head Screw|
|2 × 10mm O.D. 100mm Length Aluminium Tube or Carbon Fibre Tube|
|4 × M10 Damper Mount|
|1 × 3-Pin Male Header|
|1 × 10cm M-F Servo Lead Extender|
|VHB Double-Sided Tape|
|2cm of 10mm Heat Shrink|
|Allen Key Set|
|Needle Nose Pliers|
|Micro USB Cable|
Note: We have provided an "Add On" bracket, as well as an updated chassis which integrates the mount. If you're using the integrated mount, you won't need the 2 x 35mm screws, as well as 2 x nuts and 2 x washers, as these are used to hold the mount in place.
Before we begin, I wanted to note we made a slight modification to H4WK, whereby we’ve removed the old PDB and added in the Matek 5 in 1 Power Distribution Board (PDB).
If you’ve already printed out the H4WK body, you can print out the removable gimbal mount, or you can print the new H4WK top base, which will have the gimbal mount integrated.
Infill of 15% is more than enough, as we need to keep the weight down.
ASSEMBLING THE MOUNT
Add thread lock to the M2.5 cap head screws, and screw on the 4 x M10 damper mounts to the gimbal mount.
ATTACHING THE MOUNT TO H4WK
Note: this step does not apply if you have printed the new H4WK top base.
The mount sits on the top, at the front of the H4WK and is bolted through the two angled slots. Place one washer on the screw, then thread it through the mount, top and bottom base of H4WK. Add thread lock to the nut, add another washer to the screw, and then finally tighten the nut to the screw.
INSTALLING MOUNTING RAILS
For the rails, we’re using 10mm aluminium round tubes. Alternatively, you could use 10mm carbon fibre round tubes to reduce the weight. Push the tubes into the damper mounts. Be careful as it does require some force to push them in.
The end of the tube should be in line with the centreline of the M3 screws; roughly 10mm from the face of the last damper mount.
ATTACH THE GIMBAL
Loosen the gimbal rail clamps by unscrewing the thumb screw, and slide it onto the rail until there’s a small gap between the gimbal base plate and the 3D printed mount.
Take the VTX wire harness and remove the red cable from the 3-pin servo lead and 5-pin.
Next, take the 3-pin header and using needle-nose pliers to move the plastic insulation so that the copper pins are even on both sides.
Take the gimbal control and video wire harness, and plug in the 3-pin header into the servo connector of the black and white cable. Then plug the servo connector from the VTX harness to that.
Place the 2cm piece of 10mm heat-shrink tubing over the connection and shrink it. This will help ensure a quality connection.
Plug in the gimbal harness to the gimbal breakout board, and plug the 5-pin connector to the VTX.
Next, take the second servo connector on the gimbal wire harness (the one with three cables coming out of it), and plug it into the servo extender.
MOUNT GIMBAL BREAKOUT BOARD TO THE UNDERSIDE OF H4WK
Use VHB double-sided tape to mount the cable breakout board on the underside of H4WK.
Screw the VTX antenna on and cable-tie the VTX onto the back right boom (actual position isn't critical, but it helps keep it balanced)
Next, plug in the servo extender lead to pin 6 of the flight controller (that should leave a gap between the 4 which go to the rotor motors). You'll notice in the image we have taped our rotor connectors together. This is purely to help avoid any mixups should they become disconnected.
Feed the power cable from the gimbal breakout board through the gap. We always want our wiring as tidy as possible.
Unscrew your flight controller to expose the PDB, and locate the 5V and 12V pads. Snip off the red connector on the VTX power cable.
Solder the VTX power cable onto the 5V pad.
Solder the gimbal power cable to the 12V pad on the power distribution board.
Double-check your wiring, screw the flight board back on, mount your action camera onto the gimbal, and plug in the battery. If everything is correct the gimbal will self-level and react when you move H4WK around.
To install the required software for your gimbal, you can download the Tarot TL3T01 ZYX-T3D-III Gimbal Software and Tarot USB Driver from this link: http://www.tarotrc.com/Download/Detail.aspx?Lang=en&Id=f21846f6-6580-460a-ba50-48b7b45bb1af
Install the USB driver and then install the gimbal software.
Note: The software is only available for Windows.
SETTING UP THE GIMBAL
Plug in the gimbal USB adapter to the gimbal breakout board.
Then plug in the battery to H4WK, and let the gimbal and flight controller initialise.
Launch the gimbal software and then insert a micro USB cable into the USB adapter and plug it into your computer.
Press the refresh button then select the “COM” port for your gimbal. Then press “Connect”.
The settings you want to change are as followed:
- Receiver type: Convention
- Default mode: Pan Follow
- RC Mapping:
- Tilt: Channel 1
- Mode: Unmapping
- Pan: Unmapping
- Control Mode: Angle Control
Once completed, press “Run Gimbal”. Your gimbal will start up, when you move H4WK around to check that the gimbal is moving and reacting. Then press “Write Flash”. Press the “Disconnect” button once the parameters have been saved. The notification appears in the bottom left hand corner.
SET CHANNEL 6 ON RC REMOTE
Since we are using a six-channel receiver, we can only control tilt on our gimbal, as channel 5 is used for our flight mode selection.
On the Fly Sky FS-i6, go to “Aux. channels” and set Channel 6 to “Source Vrb”, which is the right hand side turn knob. Hold cancel for three seconds to save the setting.
SETTING UP ON MISSION PLANNER
We will now connect to the flight controller via the telemetry module or USB. Before we go into the gimbal settings, we first need to recalibrate our remote, as we have set up a new switch. Refer back to Issue 10 for instructions regarding the remote calibration.
Click “Optional Hardware” and then “Camera Gimbal”. Now change the following settings:
|Servo Limits:||From the remote calibration screen, insert the MAX and MIN PWM values for the channel 6 switch|
|Angle Limits:||Min: -90|
|Input Ch: RC6|
Once complete, disconnect the flight controller and restart H4WK.
After H4WK has finished initialising, rotate the dial clockwise and counter-clockwise on your remote; the gimbal should tilt up and down as you rotate.
CONNECTING YOUR CAMERA AND RECEIVER
Plug in the micro USB connector to the gimbal, and plug that into your action camera. You should now be charging your camera as well as transmitting your video feed.
On your receiver, search through the channels until you pick up the signal from your VTX. If you are noticing some interference you can change the channel on the VTX by pressing the CH button. If the interference persists, you can change to another frequency band by pressing the FR button.
Depending on the receiver being used, you'll probably need to download an app for your device to make it work. Once that's done, you really just need to plug the unit in to your phone or tablet, generally with your usual charge / sync cable, and presto! We have used the Eachine R051 with iOS. It can be a little clunky in the app, but it works well overall.
It's worth noting that some receivers have an internal battery, so may require charging before you try and connect to your phone. It's one of those quirks that can easily catch you out. You may have assumed that by connecting it to your phone, it will be powered by the phone. However not everything will work that way, hence the internal battery. The same micro USB port you use to connect to your phone is often also the charging port for the internal battery.
Video quality on the transmitter and receiver is usually not high-definition, as your camera might be. This is due to the analogue video output from the camera. This is an industry standard format that is exceptionally easy to interface with.
Most cameras will also have some type of HDMI connector which does indeed provide a live HD video feed. In reality, the cost of better hardware feeding the HDMI output to the transmitter and receiver is rarely worth it. The screen is really just so you can see what your drone sees in the camera, after all. The high-definition video on the MicroSD card when the drone returns is what you really want!.