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The THz Drone Project

I am working on a project to fly a THz Spectrometer on a drone. This will enable spot measurements of important atmospheric molecules.

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A Bakman Technologies portable THz spectrometer weighs around 7.8 lbs (3.5 kg) this is well within the lifting ability of a DJI-S1000 (I think you know where I am going with this). I am going to fly a modified spectrometer on a drone and make some point measurements of molecules of atmospheric importance starting with water vapor and then, someday pollutants like: CO, SO2 and NOX. We are doing the whole project on a shoe-string budget and documenting what we can on video. I am hoping the project raises the awareness of the ability of this technology for pollution monitoring. It should be a fun and interesting project.

In 2015 I bought the terahertz spectrometer business from my former employer. Having been the person who designed and developed these portable THz spectrometers over the last ten years, I simply couldn't let the technology vanish. While the spectrometers work very well and their cost has dropped dramatically over the last 5 years, there haven't been any real winning applications for the technology. The instruments that I have been manufacturing have been used almost exclusively for laboratory work even though they are portable. Then, in 2016, when purchasing a toy drone for my girlfriend's son it hit me: the THz spectrometers are small enough to fit on one of the larger consumer drones. Once on a drone, the spectrometer can be used to make point detection measurements of various gases of atmospheric importance such as: SO2, NOX, CO, CO2, H2O and Methyl Mercaptan (added to natural gas). A drone based solution is important. This is because the THz systems aren't sensitive enough to do remote detection and the only chance for them to be applicable is if they can be right at the point of interest.

What I am going to document in this project, is my attempt to modify a portable THz spectrometer and attach it to a DJI-S1000. Along the way I hope to find collaborators and partners that will make this happen. I have only recently found someone with a DJI-S1000 that is interested in flying this experiment. Most importantly, his DJI-S1000 has a parachute :-). I expect there will be more partnerships as I move forward and more challenges are encountered.

The current plans are this: after initial test flights, I plan to fly the THz drone over fields or recreational areas that have been recently watered and measure how much water vapor is in the air. I will compare the measurements to more arid areas. These are the types of measurements that could be of interest to drought stricken Southern California but more importantly there should be little concern about flying the drones over these two areas. I don't think that the same could be said about flying a drone based spectrometer through the rising smoke from a power plant or a docked ship.

You may be asking "Why hasn't anyone done this before?" Two reasons that I can see. The first is that portable THz spectrometers are not common. The second is that the scientists that I have spoken to had a "Eureka" moment (like I did) when they realized that this isn't remote detection (which isn't possible) but point detection, which is.

Endplate_B.pdf

This endplate was modified to allow us to mount the VGA output from the SBC and to have some USB ports.

Adobe Portable Document Format - 31.17 kB - 10/10/2016 at 06:03

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Endplate_A.pdf

This is a drawing of one of the endplates for the chassis. It doesn't need modification

Adobe Portable Document Format - 73.02 kB - 10/10/2016 at 05:56

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Chassis.pdf

This is the original drawing of the chassis before we modified it to lighten it. Feel free to print it in light weight plastic!

Adobe Portable Document Format - 120.39 kB - 10/10/2016 at 05:56

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Lid.pdf

This is the original drawing for the lid before we modify it for the SBC.

Adobe Portable Document Format - 84.02 kB - 10/10/2016 at 05:56

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Bakman_THz_Review.pdf

This pdf is an overview of how a THz photomixing system works. It explains coherent detection and how two semiconductor lasers and two semiconductor mixers can be used to generate and detect THz radiation.

Adobe Portable Document Format - 1.09 MB - 06/15/2016 at 19:16

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View all 8 files

  • 1 × PB7220-2000-T - Portable THz Spectrometer We take a base Bakman Technologies PB7220-2000-T and modify it by machinging away chassis material to lighten it, attaching the THz optics to the lid along with a PC-104 and a solid state hard drive.
  • 1 × Advantec PCM-3362 PC-104 (Intel Atom) We are attaching a PC-104 running Windows into the lid of the PB7220. This single board computer will operate the spectrometer during flight.
  • 1 × Intel SATA SSD with 40 gigs of space SSDSA2M040G2GC is being attached to the lid as well for the PC-104 hard drive.
  • 1 × Windows 7 Home The PB7220 software operates in a Windows enviroment, so need Windows runnin on the PC-104.
  • 1 × AMP Connector for PC-104 Power PN 1-480424-0 4 POS Mate-N-Lok - Adapter cable to connecto PC-104 to switched power on PB7220 board

View all 11 components

  • Future Hacking

    Joseph Demers09/18/2016 at 19:14 0 comments

    This has been a very successful project for illustrating the potential utility of a drone mounted THz spectrometer. The response to this project has been very positive. Thanks to everyone who showed interest or contributed. I have already received inquiries if the THz Drone is ready to start making atmospheric measurements of pollutants. The answer is, unfortunately, "No, not yet." There are several things that are required before the THz Drone can get out there and start spot checking local pollutant levels and enforcing pollution laws. As it turns out, the upgrades necessary are going to be an even greater Hack than what has been done so far.

    Thanks for reading!

  • Current Status

    Joseph Demers09/18/2016 at 17:46 0 comments

    For the last couple of months I have been working on organizing all of the video documentation that I compiled during the course of the THz Drone project. After doing that I set out to find a videographer with some drone experience. I took me some time to find someone, but I did. The videos are being pulled together and I should be able to post them before the end of September. The videos aren't just documentation, but also include discussions on how the THz technology works and why it is so important to take this Hack to the next step.

  • Yes, it was humid.

    Joseph Demers07/04/2016 at 21:52 0 comments

    We were flying the THz Drone at Paramont Ranch Park in the Santa Monica Mountains. They have an area set aside for flying drones. Earlier in the day there had been fog in the area, but by the time we had arrived the fog had burned off leaving it extremely hot and humid. The reported weather showed the humidity for the day varying between 96% and 45% with an average of about 75% and a high of 90 degrees.That water vapor lines are certainly extremely strong.

    Unfortunately, I hadn't gotten the humidity meter working yet. It was supposed to be attached to the drone to record the humidity while the spectra was being recorded. Since this was the maiden voyage and I thought this area was going to be very, very dry I hadn't concentrated on getting the humidity probe working.

  • THz Takes Flight

    Joseph Demers07/02/2016 at 00:53 0 comments

    Today, Edan (from Cheetah Logistics) and I flew a test flight of the PB7220-2000-T THz Spectrometer on a DJI-S1000. We simply wanted to see how it would go and how long we could fly. As it turns out we could stay airborn 8.5 minutes. The spectrometer weighed-in at 3.5 kg, so I obviously still need to shed some more weight to get longer flight times. The spectrometer was running during the flight and it was very hot and humid so we recorded some nice water vapor transitions at twenty feet in the air.

    Next time I need to bring a table and some shade.

    Kinda surprised it worked the first time without a hitch specially on our budget....

    I will post the data when I download it from the drone. Right now I just want to celebrate the fact that it actually worked!

    Happy 4th of July!

  • IT FITS!!

    Joseph Demers06/25/2016 at 22:27 0 comments

    Yesterday I went to Cheetah Logistics in Westlake Village to try and fit the THz spectrometer on one of their DJI-S1000 and much to everyone's surprise it fit perfectly!!!

    Even with the landing gear down it cleared! Even with the THz spectrometer attached it can be put into the standard traveling case. Given that the adapting plates were developed off of a picture of the mounting points with a ruler laid next to them made it somewhat astounding. And the center of mass seems to be aligned very, very well. The parachute on the DJI-S1000 seems to cause more of an off balance situation (but we are not getting rid of it). And the unit is low enough such that the landing gear just clears the enclosure (talking a millimeter here). It is fairly impressive with the arms out.

    So what is next? We are going to do more work with the spectrometer and get it running and start taking some data to see how long it will operate with the new, smaller battery. We could run the system from the battery on the drone, but for now, we will continue to employ the internal battery.

  • Back to Windows 7

    Joseph Demers06/15/2016 at 19:21 0 comments

    So I made a couple of changes to what I was planning.

    First - I ended up having to relocate the battery to be more in the middle of the spectrometer and I switched to a smaller battery with half the cells and capacity. I will have to see how long the system will operate on this battery.

    Second - Windows 10, for whatever reason, doesn't work well on this SBC. When I had Windows 7 installed it ran much faster. I am switching back to Windows 7. I will not share my comments and what I think about Windows 10 in this public forum. Yes, it would be nice to make the spectrometer OS independent. That was always the goal. Just haven't had the programming resources :-(

    Third - I bought a USB humidity sensor that I will attach to the system. I will try and make both THz readings and humidity sensor readings at the same time. This way I will be able to correlate the two measurements. Some of you may ask "If you can just buy a USB humidity sensor, why strap a THz spectrometer to a drone to measure water vapor content?" We are doing this as a demonstration and test. The real end goal of the THz spectrometer is to measure and classify many different gases, not just water vapor.

  • Moving the battery

    Joseph Demers06/01/2016 at 23:00 0 comments

    Today my 2mm taps came in so I will be able to tap the holes that were somehow missed when the chassis was made. While I was looking at the modified PB7220 I realized that with the heads and the battery all on the same side that the weight was going to be really off centered. I would have liked to put the THz optics on the other side to balance things out but then the cables will not clear the SBC..... So, I moved the THz optics more towards the center of the unit and I am going to try and move the battery more towards the center as well.

  • Almost back together

    Joseph Demers05/29/2016 at 22:27 0 comments

    From the pictures you can see how close I got to actually getting the PB7220 back together.

    It is possible to connect the SBC computer to a monitor a keyboard and the PB7220 and it fires up, the software works, it runs off of battery - everything is great! Except I can't connect the heads to the unit with the fibers and electrical tethers. The small threaded holes that hold the end plates to the chassis were never tapped. They should be tapped with a M2 x .4 thread but the aren't. If it weren't for this then this thing would be taking data at this point. Instead, I had to order some taps and a tap holder and hope that I don't break a tap!

    On the next log I will have this thing together and taking some water vapor data here in the laboratory. In the meantime, Thomas designed an aluminum bracket to allow us to attach the system to the drone and I am designing a stand that will allow the unit to be turned upside down and set on a table.

  • Putting it back together

    Joseph Demers05/28/2016 at 20:37 0 comments

    I have received the machined lid and chassis back from Descher Automation They did a fantastic job machining away the parts of the chassis I didn't want and putting the features in the lid for mounting the PC-104 and the SSD. They even made a drawing of the changes to the stock PB7220 chassis that I have posted in the supporting info. The machining had removed around .2 kg from the chassis. Next, the PP7220 parts were transferred to the modified chassis. Everything fit as it should and having the large holes in the bottom of the chassis made getting to the underside of the board easy!

    While the parts were out for machining I figured out how I was going to mount the THz optics to the lid. Originally I was going to have a special mounting bracket made, but I realized that the off-axis parabolic mirror mounts could be mounted directly to the lid with little effort. This would save a little bit more weight. I would try and keep all the parts towards the center of the chassis so that the weight distribution would be good. I drilled the holes and mounted the THz optics with little trouble.

    During the rebuild, I also realized that the stock 14.4 volt battery was likely a much greater capacity than it needed to be at 69 Wh. What is the point in operating the spectrometer for hours when the drone can only operate for 15 or 20 minutes. The Ultralife battery weighed in at .35 kg. They had a 14.4 volt battery that was half the size so I assume it would save us another .15 kg if we swapped it in. However, the battery would be an extra $100 bucks plus shipping. So, for now, we will stick with the stock battery.

    In order to power the SBC and hard drive, it was necessary to create an adapter cable that would connect to the PB7220 motherboard and deliver switched 5 Volts. The parts were ordered and the cable was easily constructed. The parts are listed.

  • Modifying the Chassis

    Joseph Demers05/28/2016 at 20:23 0 comments

    After making sure that the SBC would operate the system, the next question to answer was could the drone lift the system: I had a 7 kg weight limit. I put all of the components onto a scale and did an initial weigh in. Surprisingly everything together weighed 3.8 kg - well under the 7 kg weight allowance. I was told this would give me approximately 15 minutes of flight on the DJI-S1000. While this is adequate, it would be nice to have more time. So I set about trying to find ways to cut the weight. I took a careful look at the chassis and found section of the chassis that could be physically removed to save weight. I then marked these sections and sent them to Descher Automation in Raleigh NC out for machining. I also sent along an extra chassis cover that needed to be modified to allow the SBC and hard drive to be mounted to it.

View all 11 project logs

  • 1
    Step 1

    I did my best to document the build in the videos and the project logs.

  • 2
    Step 2

    Acquire a PB7220 along with an extra chassis an oversized lid and some end plates you don't mind modifying. Also acquire a SBC, a hard drive and a copy of Windows. Yes, it has to be windows because that is all the software works under.

  • 3
    Step 3

    Modify the extra chassis and lid as detailed in the drawings. You can used a Dremel to modify the endplate and allow a VGA connector and extra USBs

View all 16 instructions

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Discussions

EngineerAllen wrote 02/14/2017 at 16:29 point

Hi, I don't get the purpose of the instrument, you forgot to mention that?

Also DJI drones are awful amd over priced

Build a tarot / rctimer / hobbyking combo you'll get better results for less money. I don't know what kind of fool would buy DJI

Are you going to make a product out of the instrument?

  Are you sure? yes | no

EngineerAllen wrote 02/14/2017 at 16:29 point

Hi, I don't get the purpose of the instrument, you forgot to mention that?

Also DJI drones are awful amd over priced

Build a tarot / rctimer / hobbyking combo you'll get better results for less money. I don't know what kind of fool would buy DJI

Are you going to make a product out of the instrument?

  Are you sure? yes | no

Joseph Demers wrote 06/22/2016 at 19:18 point

@Raul Ocampo

Raul, I agree that a balloon may work for some applications, but the goal here is to be able to fly the spectrometer through the area of interest like the smoke from a power station or the smoke from a ship cruising into the port. Possibly map out an area where there is a gas leak. The balloon can't be directed like a drone - you are at the mercy of the winds.

  Are you sure? yes | no

Raul Ocampo wrote 06/22/2016 at 18:54 point

I like drones as much as the next guy but a tethered balloon and gps with your spectrometer package might simplify things a lot.

  Are you sure? yes | no

Joseph Demers wrote 06/22/2016 at 19:21 point

Raul, I agree that a balloon may work for some applications, but the
goal here is to be able to fly the spectrometer through the area of
interest like the smoke from a power station or the smoke from a ship
cruising into the port. Possibly map out an area where there is a gas
leak. The balloon can't be directed like a drone - you are at the mercy
of the winds

  Are you sure? yes | no

Joseph Demers wrote 06/20/2016 at 01:36 point

 @riot

Yes, it should be possible to build these to be very resistant to a saltwater environment

- even waterproof - without much trouble. There are plenty of examples of fiber-optic systems that are used in extreme environments.

  Are you sure? yes | no

riot wrote 06/19/2016 at 12:06 point

Would these shiny spectrometers work on a seafaring vessel? I.e. can they perhaps be built in a fashion that they are saltwater resistant? I think, measuring with them directly on the oceans could yield interesting and valuable science data.

  Are you sure? yes | no

Joseph Demers wrote 06/22/2016 at 19:21 point
Yes, it should be possible to build these to be very resistant to a saltwater environment
- even waterproof - without much trouble. There are plenty of examples
of fiber-optic systems that are used in extreme environments.

  Are you sure? yes | no

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