UAVs for site tour recording – Part 1 – Theory

Thanks to UAVs there is a growing potential for the provision of high quality visualizations of sites from the air for public consumption; whether as part of the requirement of many archaeology companies as charities, as part of planning policies to interact with the public, or the growing importance of crowdfunding archaeological excavations (DigVentures) which require interaction with their backers. UAVs can provide a means of providing this sort of imagery as part of an overall recording strategy. This includes the recording of site tours which can provide details of a sites which can easily be disseminated to the public.

At its simplest the UAV can provide an aerial element to the video of the site tour by flying past or through elements of the site or flying past or hovering in front of the site tour guide.

The DJI Inspire 1 is one such aerial video platform which can be purchased with two remote controllers; one for controlling the UAV, while the other is used to control the camera gimbal. This allows a pilot to fly the UAV on a set path while someone experienced in film making has complete control of the camera.

DJI Inspire 1

DJI Inspire 1

Although the UAV can provide an excellent platform for aerial video recording as part of site tours, recently developed technologies can make this much more automated and provide a means for one person to both:

  1. The site tour guide.
  2. The UAV pilot recording the site tour.

There are two ways in which this can be done.

1. GPS ‘Follow Me’ technology

'Follow Me' technology (DroneDog using Pixhawk)

‘Follow Me’ technology (DroneDog using Pixhawk)

This functionality is available on many UAVs, including some of the DJI series and those using the open source PX4 and Pixhawk autopilot technologies.

With the PX4/Pixhawk systems the mode can be controlled from a number of base station software solutions including Tower, which can run on Android mobile devices such as smartphones.

The systems uses the GPS of the mobile device as a target for the UAV.

A number of cinematic controls for the UAV are available in the app:

  • Leash – UAV follows actor.
  • Lead – UAV leads actor pointing back at them.
  • Left/Right – UAV keeps pace with actor to the side.
  • Circle – UAV circles actor at specified radius.
'Follow Me' controls (3DR Tower)

‘Follow Me’ controls (3DR Tower)

The following parameters can also be set:

  • Altitude.
  • Radius.
3DR Tower - Altitude and Radius

3DR Tower – Altitude and Radius

The system also controls the camera gimbal, pointing the camera towards the GPS enabled device.

Together these controls can provide various aerial video elements useful for integration in a site tour video which can be controlled directly from the mobile device in the hand of the site tour guide.

2.Computer vision technologies

Computer Vision technologies are an important developing area in robotics and are beginning to be fitted to UAVs.

Some of these technologies use image recognition algorithms to match the subject matter between consecutive video frames allowing the UAV to follow a person or object even when it is rotating and so changing the way it appears.

They come in three forms:

A. Software

Currently in beta testing the Vertical Studio app (available on iOS and Android) uses existing camera hardware on the DJI Phantom 3 or Inspire to provide the imagery for the image recognition algorithms running in the app. A target is chosen in the app which then controls the flight of the UAV.

Vertical Studio App

Vertical Studio App

You can also draw walls in the app that designate no fly areas for the UAV.

Walls in the Vertical Studio App

Walls in the Vertical Studio App

B. Add-on technology

The second is an add-on technology that is fitted to an existing UAV, which connects to the autopilot and controls the flight of the UAV. In the case of the Percepto (funded on the Indiegogo crowdfunding website) the processing is done in a companion computer while the video is taken from an add-on camera, controls are then sent to the autopilot and gimbal to control the movement of them in relation to the subject matter.

Percepto Tracking

Percepto Tracking

Percepto Kit

Percepto Kit

C. Integrated technology

The third is an an integral part a newly built UAV, but is in effect a very similar technology to B.

This is the case with the soon to be released DJI Phantom 4, which is the first commercially available UAV with the technology integrated into it.


The app connects to a companion computer on the UAV which uses the imagery from the camera as a source for the computer vision algorithms. Once again the subject matter is selected in the app and the UAV will follow it.

Phantom 4 App

Phantom 4 App

 

Sources
https://3dr.com/kb/follow-instructions/

http://www.dji.com/product/phantom-4

http://www.dji.com/product/intelligent-flight-modes

http://vertical.ai/features/

http://www.percepto.co/

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Chris Anderson – InterDrone Keynote – The future of Drones

On the 9th of September Chris Anderson, the CEO of the 3DRobotics (3DR) Drone company, gave the keynote speech at the International Drone Conference and Exposition (InterDrone) Conference in Las Vegas on the future of drones.

Mapping
He discussed the previous democratizing of technologies such as the personal computer and the internet which put powerful tools in the hands of normal people empowering them; and that thanks to drone development remote sensing will develop in the same direction.

With improvement satellites have the potential to reduce their costs in remote sensing by a factor of 1 in 10, while drones have the potential to reduce the costs by a factor of 4 in 10.

The reason that the mobile phone network beat satellite phones is the same reason that drones will beat satellites in recording. Drones have the ability to scale in a way that satellites cannot.

He compared the pros and cons between Satellite, manned aircraft and drones in a hypothetical recording of the American State of Kansas. His model suggested that satellites and drones would have the same setup costs; with 100 satellites costing 100 million dollars and 200,000 drones costing the same amount to capture Kansas on a daily basis.

The satellites have high maintenance costs as they are located in space, while drones have much lower costs while piloted and less when un-piloted.

Satellite Drone
Data Resolution 300 cm per pixel 3 cm per pixel
Data Received Hours Minutes

The drones have the potential to record a site on the hour every hour.
Also at any one times 2/3 of the planet is under cloud cover making the drones the much better option as they generally fly under the clouds.

He concluded that for mapping 50 hectares the satellites would be the much cheaper option, but for mapping 5 hectares the manned drone is the cheaper option, while the manned aircraft was the worst option in all cases. But autonomous drones operating as a fleet would be the better option all the way up to 500 hectares.

Autonomous Drones
With the development of autonomy drones, rather than doing things in the same way as manned aircraft they could do things in whole new innovative ways.
They could:

  • Act as unmanned sensors.
  • Record every hour on the hour.
  • Charge themselves on charging pads.
  • Be based in weatherproof boxes.

These technologies are possible now and 3DR support both swarming and fleets.

It could be possible to control 200,000 drones from a web browser a thousand miles away. Both 3DR and DJI are migrating all of their control functions to mobile devices meaning that the platforms can act as connected devices from the start.

The development of the drone can be linked with sales:

  • Drones as vehicles – 500 thousand.
  • Drones as cameras – 1 million.
  • Drones as something bigger – 10-100 million potential.

The drones have the potential to act as sensors connected to the internet almost forgetting about the device, with its data being passed to the cloud.

Potential drone uses
He discussed the potential of drones taking part in a number of the popular modern technological buzzwords:

  • Internet of things.
  • Big data.
  • Reality capture.
  • Personal storytelling.
  • The democratisation of Hollywood.
  • Video age.
  • Personal robotics.
  • Automation.
  • The new near-space race.

He also discussed how drones came about thanks to mobile phone technology and its significant investment in the research and design of the technologies which enable phones to work including GPS, accelerometers as well as their computing technology. The mobile phone industry developed these technologies which allowed the drone industry to begin. The drone is basically a smartphone with propellers.

Technological/Future Developments
With improvements in the on-board computing processing power drones now have the ability to us the Robotic Operating System (ROS) allowing the drone industry to draw on the extensive academic developments in AI (Artificial Intelligence), Computer Vision, path-finding and other technologies. With ideas from a number of different industries converging.

The Dronecode project has already brought together a number of open source drone projects under the governance of The Linux Foundation.
These include:

  • Ardupilot, PX4 and Pixhawk autopilot systems.
  • MAVLink (Micro Aerial Vehicle Communication Protocol).
  • UAVCAN is a lightweight protocol designed for reliable communication in aerospace and robotic applications via CAN bus.
  • ROS – The Robot Operating System (ROS) is a set of software libraries and tools that help you build robot applications.

Cloud based systems such as droneshare and dronedeploy allow both the control and processing of drone data from within the cloud.

Other future directions could include:

  • Advanced precision landing capabilities
  • On-board HD video streaming support.
  • Optical flow and GPS denied navigation.
  • Standardized vision processing.
  • Obstacle detection and avoidance (LIDAR, IR/thermal).
  • Out-of-the-box Search and Rescue capabilities.

The drone has become possibly the most complex consumer product outside of the car industry, and continues to evolve.

High Dynamic Range Photography/Photogrammetry – Part 1

High Dynamic Range (HDR) Photography

High Dynamic Range is a popular photographic technique that is used to produce more realistic photographic results or artistic images. It is a technique that can be used to try and replicate what the human eye can see as the dynamic range of a camera is limited and it is unable to record the lightest and darkest elements in a single photograph. This can be remedied by taking a number of photographs with varying shutter speed/aperture combinations and combining them using specialist software to produce a photograph with a greater dynamic range than can be recorded in a single photograph.

Many new digital cameras have the ability to produce HDR photographs using Auto Exposure Bracketing (AEB), special HDR settings (this may process the images for you resulting in an HDR photo on the camera but losing the originals) or manually setting the camera up.

Limitations of archaeological and cultural heritage photography

An intrinsic problem with taking photographs in archaeological and cultural heritage contexts is lighting; both too much and too little lighting are factors that hamper recording images that include as much detail as possible.

In the case of archaeological excavations attempts have been made to limit the problems in section photography by either reflecting more light in using white card or using a tarpaulin to cast a shadow. Both of these techniques work but require time and manpower.

The same problem is encountered in building recording where in an outside environment strong lighting can cause both bleached out areas and heavy shadows.

Netley Abbey - East Window

Netley Abbey, Hampshire – East Window. Photograph demonstrating the problem of strong oblique lighting causing both too much and too little light in the same image.

While lighting through windows can cause similar problems on the inside of buildings.

Netley Abbey, Hampshire - Sacristy/Library.

Netley Abbey, Hampshire – Sacristy/Library. Photograph demonstrating the effect of excessive light coming through a window causing the dual problems of both too much light near to the window and too little light in other areas.

In order to reveal elements in dark shadow a high exposure camera setting is required, while bright bleached out areas are only revealed with low exposures. These elements together with well lit areas cannot by revealed in one single photograph, this is where High Dynamic Range photography comes in.

HDR Photography in Archaeology

HDR Photography was introduced to Archaeology by David Wheatley in 2010, he provided examples of its use in improving the standard recording methods of excavations, cave sites and even using archived analogue archaeological photographs. Sadly its use was not embraced by the community probably due to technological limitations at the time and the inherent conservatism of the industry and museum archives which were yet to embrace digital photographic technology. Technology and the industry have now caught up with his ideas, with digital cameras being present on most if not all excavations, while other scholars have now begun to bring the technology to the technique of 3D recording using photogrammetry.

HDR Field Archaeology Photography

Photography is one of the primary recording techniques within field archaeology and has been since the introduction of discipline, but conservatism within field archaeology has meant that it was only fairly recently that digital photography became the primary recording technology.

Digital cameras have a number of benefits within archaeology:

  • The ability to take numerous photographs on one memory card.
  • No need to pay to process films.
  • No need to digitize the photographs.
  • Where once excavators may have been told to limit the number of photographs taken on an excavation to keep the processing costs down, digital media allows almost limitless photographs to be taken.
  • Photographs can be as easy as point and click with the camera controlling all of the settings.

But they also have drawbacks:

  • Where once archaeologists knew how to use an analogue camera to take bracketed shots, the automatic setting on digital cameras is commonly the only setting used as it produces results at a required level of quality, this means that the archaeologist may not know how to properly operate the camera.
  • Although almost limitless photographs can be taken, limits should be included as the archive may still need to be sorted through.
  • The requirements for digital storage can be complicated and costly.

Although not ideal, a number of modern cameras now come with an HDR setting on them which in many cases can be changed to the required level of bracketing, although only the merged photograph is saved losing the possibility of later re-processing the photographs with different settings.

Field Archaeology Archive Photographs

One benefit of traditional bracketing of analogue photographs for archaeological excavations is that they provide an ideal resource for conducting HDR processing. These archives have multiple photographs at different exposure levels which can be digitized and processed to provide better results than the originals and be re-entered into the archive with the digitized originals.

HDR using archive slides from excavations at the Cove, Avebury using archive slides (Wheatley 2010)

HDR using archive slides from excavations at the Cove, Avebury (Wheatley 2010)

HDR Building Photography

Building recording is an area that can be significantly enhanced by the use of HDR. It is difficult to provide adequate lighting in many cases, meaning that some areas are brightly illuminated while others are dimly lit loosing information in both cases.

Processing bracketed images into an HDR image provides a greatly enhanced image.

HDR Photogrammetry

Recent developments in camera technology, HDR software and photogrammetry software have allowed the introduction of HDR Photogrammetry. Thanks to the additional information present in the photographs models of higher detail and accuracy can be created in non-optimal lighting conditions.

As well as the ability to use tone mapped images produced from HDR images the Agisoft PhotoScan Photogrammetry software can also process .exr file format High Dynamic Range images into 3D models.

HDR Object Photogrammetry

One area under study is its use in photographing objects. The benefits are determined by the type of material used, some are greatly enhanced by HDR while others are little altered.

Image matching result from the images originated with different HDR processing: a) No HDR; b) tone mapped images from HDR processing (Guidi et al 2014)

Image matching result from the images originated
with different HDR processing: a) No HDR; b) tone mapped
images from HDR processing (Guidi et al 2014)

HDR Building Photogrammetry

We have already seen the benefits of HDR Photography in building recording and this can continue with photogrammetry.

Netley-Window-PG

Photogrammetry point cloud of the east window of Netley Abbey, Hampshire showing how the raking sunlight on the left-hand side of the window has bleached out the photographs and lost detail

Both the increased level of quality of the photograph and the higher amount of detail present in the 3D model can easily be seen in the HDR photogrammetry model.

Software Solutions

A number of software solutions are available for the processing of HDR photographs, these range from high end photographic software such as Adobe Photoshop and Lightroom, through to HDR specific pieces of software and even open source solutions. HDRSoft’s Photomatrix comes in a number of versions which include plugins for different software packages such as Adobe Lightroom, Photoshop Elements, Photoshop and Apple Aperture. With low cost solutions such as Fusion HDR or free open-source solutions such as LuminanceHDR also being available.

In order to be view-able on low contrast monitors and paper the images need to go through a process called tone mapping, this replicates the appearance of the high dynamic range photograph on these media.

Downloaded imaged can be batch processed in software such as Photomatrix setting up how many images need to be merged together with a number of preset or custom settings allowing the images to be processed exactly as required. These pieces of software can also compensate for slight movement between the recording of the multiple images. The resulting images can then be saved as either .hdr (Radiance) or .exr (OpenEXR) file formats which record the HDR information.

Batch processing of images within Photomatrix

Batch processing of images within Photomatrix

Benefits
HDR photography can record more information in both photographs and photogrammetry models. By using open Source HDR software it can be free. Many cameras allow multiple bracketed photographs to be be taken automatically only adding a few seconds to the recording process.

It is also possible in some of the software to open a folder full of images and have the software batch process it without any user intervention once the preset settings have been loaded.

Drawbacks
Among the drawbacks are the fact that as the camera is taking multiple photographs it is difficult to stabilize the camera by hand, otherwise there will be movement between the photographs. Although movement between photographs can be corrected if you are bracketing shots and using software the automatic HDR setting on the camera will probably result in a blurry image.

UAV HDR Photogrammetry

UAV HDR Photogrammetry is an area I will be studying in the future. It has great potential for recording but will require a careful balance of UAV hovering, a steady gimbal, fast shutter speed and an adequate depth of field. It will be discussed in a future blog.

Sources
Guidi, G., S. Gonizzi, and L. L. Micoli. “Image pre-processing for optimizing automated photogrammetry performances.” ISPRS Annals of The Photogrammetry, Remote Sensing and Spatial Information Sciences 2.5 (2014): 145-152.

Kontogianni, G., and A. Georgopoulos. “Investigating the effect of HDR images for the 3D documentation of cultural heritage.” World Cultural Heritage Conference 2014 – Euromed 2014 – International Conference on Cultural Heritage Documentation, Preservation and Protection. (2014)

Ntregkaa, A., A. Georgopoulosa, and M. Santana Quinterob. “Photogrammetric Exploitation of HDR Images for Cultural Heritage Documentation.” ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences 5 (2013): W1.

Wheatley, D. “High dynamic range imaging for archaeological recording.” Journal of Archaeological Method and Theory 18, no. 3 (2011): 256-271.

3D Printing and the UAV

3D printing provides a cheap method of creating objects from 3D computer model files. This, together with recent development in the field, have great potential for the future of the Unmanned Aerial Vehicle (UAV) industry.

3D Printing Parts
Many ready built UAVs can be purchased off the shelf configured to work with a number of different cameras building, but DIY systems can require parts that are not available from traditional sources. This is where the Maker community can come in, whether providing 3D models on such sites as Thingiverse to be 3D printed yourself or at a number of 3D printing shops; or providing ready 3D printed objects over the internet.

Among the objects that are useful to be 3D printed for UAVs are camera specific mounts and mounts for radio antennas. Complete 3D printed UAV frames are also possible.

Recent Developments
Until recently the materials that could be printed were limited, namely only thermoplastics or UV resins for the UAV body, recent developments have allowed the printing of everything from metal to human tissue and organs and even food; opening up whole new potential areas of use.

One example is the research by Dr. Jennifer A. Lewis, a founder of the Voxel8 company and Harvard University professor, which has led to 3D printers being able to print circuits such as the Voxel8 3D Printer developed by her company.

Conductive Ink Printing

Conductive Ink Printing

The Voxel8 3D Printer ships towards the end of the year.

Future developments planned by Voxel8 include the development of inks that are capable of printing resistors, sensors and even lithium ion battery cells.

In collaboration with Autodesk they have developed the Project Wire software which allows everything from design through to machine control of electrical circuits.

Autodesk Project Wire

Autodesk Project Wire

Potential
3D Printers have already been used for printing UAV components, but these recent developments open up the possibility of 3D printing almost complete UAVs in the near future. This would allow for UAVs specific to a task to be designed and printed on demand without the requirement of expensive manufacturing practices.

It would also link in with the idea of drones owning themselves, discussed in a previous blog, with the drones being able to print replacement or upgrade components straight from a 3D printer.

Drones Owning Themselves

On BBC Radio 4’s program FutureProofing of the 16th September the software developer Mike Hearn discussed the potential of cars and drones owning themselves. His ideas build upon collaborative open ventures such as Apache and Linux.

Cars
The cars could act as autonomous one machine businesses which would charge people for rides, then from the profits they could buy fuel, repair themselves and even buy upgrades. They would begin as a new car from a factory but would then become self sustaining/financing with even the ability to purchase a new upgrade car from the factory. Hearn suggests if the autonomous vehicles owned themselves they would provide cheaper fairs than those owned by major corporations.

This links in with the ambitious plans in the Finnish capital Helsinki to provide a ‘comprehensive, point-to-point “mobility on demand” system’ allowing people to purchase transportation options directly from a phone app linking in with availability of everything from driver-less cars, taxis, buses, bikes and ferries on the required route. This could potentially do away with the requirement of car ownership within the city by 2025 by beating it on cost and convenience.

More details of the car aspect of the idea can be found in an article at the BBC News Website.

Drones
He also discussed the potential for the development of delivery services for packages and parcels by drones; where the drones would sell their services to people or companies and use the money earned to maintain themselves. If demand in area was reduced they could move to an area with more demand.

Amazon are currently developing their Amazon Prime Air drone package delivery service.


Wile the first drone delivery took place in the USA in July.

Potential
With the growing importance of drones within archaeological recording this has great potential to make it easier and cheaper for companies to employ this kind of technology without the significant outlay that is required. Drones with a number of different recording packages could be setup in useful locations around the country. They could then be employed by a company or individual for a purpose and transported to the site by the individual who pays for their services. The drone would be paid and would use the finances to pay for charging, repairs and upgrades.

This could obviously go one step further with the introduction of driver-less vehicles; with the drone being based in a vehicle which deploys it to the required location, contains the software required for the processing of the data recorded and its control interface.

Limitations
The ideas of Mike Hearn are only a “thought experiment” and he is not involved in their development, although he is closely involved with the Bitcoin virtual currency which could be used as a method for the drone to pay for itself.

Brushless Gimbals – Part 1 – Introduction

Camera Gimbals
Camera Gimbals are used for many different things in many different industries including stabilizing cameras for TV/Cinema. Their development can be traced from the introduction of the Steadicam in the 1970’s. This allowed the stabilized movement of a camera, revolutionizing filming by removing the need for a wheeled Camera Dolly running on expensive/time consuming tracks or leveled boards. Although the system is not motorized it introduced the principal of a stabilized camera.

Recent technological developments have allowed the construction of lightweight/low cost motorized gimbal systems which can be carried by UAVs.

Gimbals and Archaeological/Heritage recording
With the development of the UAV the development of a lightweight camera gimbal to enable it to carry stabilized cameras was also begun.

The gimbal has become an important element in UAV photographic/video recording, from taking vertical photographs for mapping purposes to cinematic style flypasts/throughs of buildings.

Mapping can be undertaken with cameras attached to the UAV with a static mount, but this removes the ability to use the camera for other recording methods without landing the UAV and changing the mount.

3D Printed UAV Mapping Mount

3D Printed UAV Downward Facing Mapping Mount

Although this series of blogs will concentrate on UAV camera gimbals,  much of what is discussed is transferable to other recording platforms/techniques.

There are also other recording systems that use gimbals which could aid in recording; including handheld GoPro systems such as the EasyGimbal Kickstarter Project.

EasyGimbal handheld GoPro Gimabl

EasyGimbal handheld GoPro Gimbal

Some of these types of systems, such as the FY G4 handheld gimbal, can be attached to extensions poles allowing low altitude aerial photography/video to be undertaken using a handheld remote control to rotate the gimbal.

FY Reach extension pole with FY G4 3-xis handheld gimbal

FY Reach extension pole with FY G4 3-xis handheld gimbal

Gimbals can also provide a stabilized camera platform on rovers such as the Flyoxis Buggy Cam allowing the recording of ceilings and tunnels.

Flyonix Buggy Cam

UAV camera gimbals

UAV camera gimbals are designed to:

1. Remove camera vibration using the anti-vibration rubber balls within the gimbal frame.
2. Stabilize the camera as the UAV moves, keeping it level and pointing in the required direction.
3. Allow the movement of the camera to point at the subject matter while flying the UAV, sometimes in completely different directions.

Types of gimbal

Gimbals come in two different types:

1. The two-axis gimbal.
2. The three-axis gimbal.

Two-axis gimbals are designed for UAVs where there is no requirement to pan the camera from left to right, such as those with fixed landing gear which precludes the panning of cameras whether physically or visually.

Zenmuse H3-2D 2-Axiz Gimbal on a DJI Phantom 2

There are many different gimbals for numbers of different camera, from GoPros through mirrorless cameras to Digital SLR cameras.

Some of these can be purchased already constructed and calibrated out of the box, such as the Zenmuse Gimbals supplied by DJI Innovations. Others come ready installed on a UAV. While the one I will be discussing is a DIY kit which needs to be built and setup.

The price difference between buying a ready made solution and building your own one from a kit in order to carry the same camera can can be quite significant:

Model Camera Price
DYS BLG3SN 3-Axis Brushless Gimbal with BaseCam SimpleBGC 32-bit controller Sony NEX size camera £299.94
Zenmuse Z15 Sony NEX 5 and 7 £1,915.00

Components
The brushless gimbal is made up of a number of different components:

  • Gimbal frame
  • Gimbal controller
  • IMU (Inertial Measurement Units)
  • Brushless Motors
  • Battery
  • Camera
Gimbal Frame

Gimbal frames are deigned for different types of cameras. The gimbal frame I am using for this project is the DYS BLG3SN 3-Axis Brushless Gimbal Frame kit with 3pcs BGM4108-130 Brushless Motors for the SONY NEX type of camera. I will be using a Sony α5000 Mirrorless Camera which is almost identical to the NEX series cameras.

DSC00792

DYS 3 Axis Brushless Gimbal

Gimbal Controller

In order to control the gimbal a gimbal controller board is required, there are a number available on the market. The Zenmuse gimbals supplied by DJI Innovations are designed to connect directly into the DJI UAV, while other  solutions require a separate board.

The gimbal controller board one I am using is the BaseCam SimpleBGC 32-bit board which is designed for 3-axis gimbals. The cheaper and simpler BaseCam (AlexMos) SimpleBGC (formerly called AlexMos) although designed for 2-axis gimbals can be upgraded to support 3-axis gimbals with the addition of an extension board. The 32-bit board is a lot easier to use as well as being more up-to-date and so was chosen as a first gimbal construction experiment.

Basecam SimpleBGC 32 Bit Gimbal Controller with IMU attached

IMU (Inertial Measurement Unit)

Another important element is the IMU , in the case of this 3-axis gimbal two of these are required. One is connected to the main frame of the camera gimbal while the other is connected to the camera mount. These tell the gimbal controller which direction the gimbal/camera is pointing and the gimbal controller can then control the motors to point the camera in the required direction.

IMU attached to gimbal frame

Brushless Motors

The importance of brushless motors in the development of lightweight/high-powered UAV systems has already been discussed in another blog.

Those in gimbals are slightly different, rather than being designed to spin quickly they are designed to hold the camera in position with enough torque to stop it moving and also to rotate to level the camera when required.

In the case of a 3-axis gimbal one motor is required for each of the 3 axis.

DSC00798

Brushless Gimbal motor

Although originally it was required to rewind the wires inside motors designed for the rotor blade with thinner wires to increase the motor resistance and torque, it is now possible to buy ready made motors for the purpose. These motors come in different sizes depending on the size of the camera they are required to stabilize.

Calibration
In order to use the gimbal it needs to be calibrated. This is done using the OpenSource SimpleBCG program. The is installed either as a Windows program or Android app and the gimbal is calibrated using the USB port on the gimbal controller board.

Detailed instructions on how to do this can be found in many places including YouTube videos.

In the case of a 3-axis gimbal two IMUs need to be calibrated, one for the camera and the other for the gimbal frame.

SimpleBCG Gimbal Calibration Software

A triple axis camera spirit level can be used to accurately calibrate the two IMUs.

DSC00918

Camera Triple Axis Spirit Level

A number of other settings can be altered in order that the gimbal works as required.

3 Axis Brushless Gimbal for Sony NEX size cameras

3 Axis Brushless Gimbal for Sony NEX size cameras

Once the gimbal controller has been calibrated the camera will remain in place as the gimbal is moved around it. This is done by calibrating the IMUs to a nominal position, the IMUs determine the actual position of the gimbal and the motors are turned on to correct the position, less voltage is sent to the motors the closer to the nominal position that the gimbal is.

Sources
http://www.simplebgc.com/eng/

http://www.simplebgc.org/

http://www.unmannedtechshop.co.uk/3-axis-brushless-gimbal-sony-nex-size-camera/

http://www.unmannedtech.co.uk/manualsguides/blg3sn-brushless-gimbal-assembly-guide

http://www.dronetrest.com/t/how-to-connect-and-setup-alexmos-3-axis-brushless-gimbal-controller/53

http://www.dronetrest.com/t/balancing-your-brushless-gimbal/55

https://en.wikipedia.org/wiki/Gimbal

Mirror-less Cameras and UAVs

UAV (Unmanned Aerial Vehicle) photography and photogrammetry has long been a balance between weight and the quality of the camera equipment carried.

Cameras

Low cost camera solutions such as the GoPro can be carried on almost all UAVs because they are small and lightweight, but these benefits are also drawbacks because limited size/fish eye lenses and small image sensors reduce the quality of the photographs they take, together with this the lack of control of many of the camera settings is a drawback.

High quality DSLR (Digital Single Lens Reflex) cameras have superior quality lenses and image sensors together with the fact that they have extensive control of the camera settings meaning that they take much better photographs. But they can only be carried by much higher power/cost octo and hexo-copter systems.

One solution is the lightweight point-and-shoot camera/compact camera used in some mapping solutions, such as those provided by 3DRobotics (Canon PowerShot S100). Although these cameras provide a better quality solution than the GoPro, and may be all that is required for mapping exercises; they are still limited in their optics and higher megapixel sensors which are much more important in the recording of complicated structures and photogrammetry work.

Changes in the camera industry due to competition from the phone industry has enhanced development of a different solution. This is the MILC (Mirrorless Interchangeable-lens camera) or DSLM (Digital Single Lens Mirrorless) Camera. These cameras don’t have the mirror reflex optical viewfinder of a DSLR camera, and the associated weight, replacing it with a LCD screen or with an app on a mobile device which controls the camera. As a result they have the capability to carry high quality interchangeable lenses without the weight associated with DSLR cameras. The system comes in two different forms; the first resembles a standard digital SLR camera, while the second resembles just a lens with all control being provided by an app on a mobile device.

Camera Comparison
Camera Type Megapixel Weight Cost
Canon EOS 5D Mark III Digital SLR 22.3 Approx 950g £2,544
Nikon D5300 Digital SLR 24.2 Approx 840g £549.99
Sony A5000 DSLM Digital SLM 20.1 Approx 388g £250
Sony ILCE-QX1 Lens Style Camera 20.1 Approx 332g £250
Canon PowerShot S100 Compact Camera 12.1 Approx 198g £195
GoPro Hero3+ Black Sports Camera 12 74/136g (with housing) £349.99
Canon EOS 5D Mark III

Canon EOS 5D Mark III

Nikon D5300

Nikon D5300

α5000 E-mount Camera

α5000 E-mount Camera

ILCE-QX1 Lens-Style Camera

ILCE-QX1 Lens-Style Camera

3DRobotics UAV Mapping Solutions, discussed in another blog entry, carry the Canon PowerShot S100 digital compact camera.

Canon PowerShot S100

Canon PowerShot S100

GoPro Hero3+ Black

GoPro Hero3+ Black

UAVs

UAVs come in a number of different configurations and increase in price with a higher level of complexity and ability to carry heavier loads.

UAV Comparison
UAV Type Payload Capacity Price (Without Gimbal)
3D Robotics Iris+ Quadcopter 400g £599
3D Robotics X8+ Octocopter 800g – 1Kg with reduced flight time £880
Spreading Wings S900 Hexacopter 4.7 – 8.2Kg £1,291-£1,540
DJI Spreading Wings S1000+ Octocopter 11Kg £1,750-£2,057
3D Robotics Iris+ Quadcopter

3D Robotics Iris+ Quadcopter

3D Robotics X8+ octocopter

3D Robotics X8+ Octocopter

Gimbals

Gimabls are an important element in stabilizing cameras during photography and video recording, as well as providing a motorized solution to move the camera to a desired angle during flight. They can add significantly to both the weight and price of any UAV solution depending on the camera equipment they are carrying.

Gimbal Price Comparison
Gimbal Camera Weight (Camera excluded) Cost
DJI Zenmuse H4-3D GoPro 168g £249
DYS 3 axis brushless gimbal Sony NEX size camera 388g £231.95 – £299.94
DJI Zenmuse Z15-A7 Sony α7s and α7r 1.3Kg £1,915
DJI Zenmuse Z15-5D III (HD) Canon EOS 5D DSLR 1.53Kg £2,831

Solutions

The 3DRobotics Iris+ Quadcopter has a payload capacity of 400g which would allow a rather small 15g for a mount to attach a Sony A5000 DSLM or 68g to attach a Sony QX1 Lens-Style Camera without weighing too much, although the system could be flown with excess weight reducing the flight time. A downward facing 3D Printed Sony A5000 Mapping Mount  is available for both the Iris+ Quadcopter and X8+ Octocopter, it weighs 36g.

Although the X8+ is a octocopter by definition, it gets over the intrinsic problems of size, weight and cost caused by eight separate arms by having two rotors on each arm, one pointing up and the other downwards. With a maximum payload of 1KG it can carry a Sony A5000 DSLM camera (388g) together with a gimbal such as the DYS 3 Axis Brushless Gimbal for Sony NEX size cameras (609g) to support and move it, the gimbal is designed for the NEX range of cameras, but they are almost identical to the A5000 in design. Although a lighter mount could be used.

3 Axis Brushless Gimbal for Sony NEX size cameras

3 Axis Brushless Gimbal for Sony Nex size cameras

Conclusions

The mirror-less camera would seem to provide a solution to the problem of how to carry a high specification camera capable of capturing high quality images on a fairly low-cost UAV solution.

Sources

http://en.wikipedia.org/wiki/Mirrorless_interchangeable-lens_camera

http://www.dummies.com/how-to/content/gopro-cameras-understand-the-cameras-limitations.html

http://www.japantimes.co.jp/news/2013/12/30/business/mirrorless-cameras-offer-glimmer-of-hope-to-makers/

Quadcopter vs Hexacopter vs Octocopter: The Pros and Cons