Sensors

[Vindication]

I decided to start this thread so that we can share knowledge of sensors that are currently out there with other UAV builders. I would like to know myself what sensors people are using and where to get them. I figured everyone else would too.

Please post about sensors that do the following [or anything else]:
Give us a link to the manufacturer/retailer...

Airspeed sensors
Altitude sensors
Attitude/INU - gyros, accelorometers, magnetometers, thermopile, etc.
GPS units

etc, etc.

Thanks!
-Vind

[djklein21]

I have the Eagle Tree unit. We have used the RPM, Exhaust Gas Temp, Thermo couple for cylinder head temp, GPS, A-D converter, Air speed, Altitude, G-force dual axis accelerameter, and wireless data link. It all works very well and is remakable accurate for the price. I recomend the system. The customer service and tech support are second to none. Bill the President of Eagle Tree systems is really great.

[LukeZ]

I have been working on an altitude circuit for the last several months, using Freescale's MPX4115A absolute pressure sensor. It reads from 115 to 15 kPa, which equates to a range from sea level to approximately 45,000 feet. You can read more about the sensor and the theory behind the calculations on my site, www.kansasflyer.org (http://www.kansasflyer.org). There is also an ongoing discussion thread (http://www.rcgroups.com/forums/showthread.php?t=372869) on the circuit design over in the DIY Electronics forum. I'm on version 2 of the circuit and making good (but sometimes slow) progress.

Luke

[Vindication]

I thought I'd throw in some that I've come across.

Heres a fairly comprehensive unit that does airspeed/alt, attitude, and gps.
Price looks like it ranges from $899-$1150. I don't think it has a autopilot built in.. but not sure. The link is: http://www.o-navi.com/phoenix_ax.htm

Does anyone know anything about this unit? IE is it good?

[Vindication]

Sparkfun has several sensor units include 6DOF IMU w/ accel and gyro. They also have magnetometers and stuff. Pretty cheap, but I'm not sure if they are all kits or some are fully asssembled.

http://www.sparkfun.com/shop/index.php?shop=1&cart=440159&cat=71&

[Vindication]

Theres an on going thread about these two:

Micronav from xbow. This seems like a nice unit that has pressure sensors/accel/gyro/magnetometers. It also has PWM outputs. price $1495

http://www.xbow.com/Products/productsdetails.aspx?sid=133

Altair has an INU that also has sensors/accel/gyro/magnetometers as well as a GPS reciever. I called them and they said the price was like $2375. This unit also does some Kalman filtering.

http://www.atairaerospace.com/inu/

[clolson]

Theres an on going thread about these two:

Micronav from xbow. This seems like a nice unit that has pressure sensors/accel/gyro/magnetometers. It also has PWM outputs. price $1495

http://www.xbow.com/Products/productsdetails.aspx?sid=133


For what it's worth, I just returned from a training class last week on the Xbow Micronav. After two days of training, I am now an "expert" on the device :-) I'm happy to attempt to answer any questions to the best of my ability.

It seemed really solid with the core sensers. The micronav can then plug into a stargate board (400mhz xscale processor running linux.) The stargate runs all the kalman filtering and autopilot code, ground station communication, etc. etc.

For hardware hacks that are terrified by code, this may not be the best unit for you. It requires some do-it-yourself programming in C.

But for people that run terrified from hardware (like me) but who like to code (like me) it's a dream come true. :-)

Best regards,

Curt.

[shedao]

One that I've been eyeballing is the Microstrain series of IMUs:
http://www.microstrain.com/inclinometers.aspx

They run anywhere from $500-$1500 USD and seem to offer some good features and good documentation. GA Tech seems to be very fond of this particular IMU as they use it in some of their UAVs. if anyone can chime in on this I'd love to hear about it.

[Unterhausen]

For what it's worth, I just returned from a training class last week on the Xbow Micronav. After two days of training, I am now an "expert" on the device :-) I'm happy to attempt to answer any questions to the best of my ability.
Curt.
Curt,
What software were they using to fly those? Did they use stargates? Can you start a thread that gives a synopsis of the class?

I just looked at their faq again, and they now have their own sourceforge project. That's a good first step. http://sourceforge.net/projects/micronav

Eric

[clolson]

What software were they using to fly those? Did they use stargates? Can you start a thread that gives a synopsis of the class?

I just looked at their faq again, and they now have their own sourceforge project. That's a good first step. http://sourceforge.net/projects/micronav


I'm not sure the legalities of posting their training materials ???

Their micronav unit is their sensor suite. This can be independently powered and will dump out the sensor data (including receiver output) via a serial port. It also does all their servo management so you can send up servo commands via the same serial port.

The micronav is designed to plug right into a stargate, so the stargate is not required but is pretty convenient. The stargate is running linux and they make all their kalman filtering code available via their open-source web site.

Interestingly they've only had their demo uav up and flying for a couple weeks so their autopilot code is really raw. We found a couple bugs for them in class while they were explaining the code structure to us!

So my impression is that they are pretty good on the sensor side, and I have no reason to believe their kalman filtering code isn't 100% solid. But their autopilot code and their ground station and ground station communication is pretty much in demo/proof of concept stage.

That's ok for me because I can rip all that crap out and write my own. It's the sensor stuff and the kalman filtering that I really need.

Ultimately all the interfacing is done through the stargate board. It has a compact flash slot (i.e. you could plug in a wireless card), it has usb support, ethernet support, and a serial port. So there are a number of interesting interfacing options depending on what you want to do.

A couple downsides for those that are keeping score:

1. You need to crack open your reciever and tap a raw ppm line off it to send to the micronav.

2. Everything runs through the micronav, so if your micronav fails or loses power, you are completely sunk. There are no good pass through options for regaining manual control in the event of a uNav failure.

3. There aren't any additional IO lines available for things like temperature sensors or rpm sensors or anything else you might want to wire in. However, you could add another small pic board and interface it to the stargate.

I got the impression that this was clearly a rev1 board. The sensor stuff is pretty complete, and the kalman filtering looked solid, but the autopilot and ground station stuff was clearly hacked together quickly for demo purposes.

So while not perfect, it seems to be a pretty good price for what you get and I think people could get a *lot* of mileage out of it, especially as more code springs up to do a better job with autopilot, navigation, and ground station tasks.

Regards,

Curt.

[Unterhausen]

I'm not sure the legalities of posting their training materials ???
Don't do it. I just wanted your take on the class.

The micronav is designed to plug right into a stargate, so the stargate is not required but is pretty convenient. The stargate is running linux and they make all their kalman filtering code available via their open-source web site.

Until just recently, they had a link to AutoPilot instead of their own site. Nice way to keep people guessing.

Did they have the daughterboard on the Stargate in addition to the micronav? I was wondering if the daughterboard and the micronav will work together since they share the same serial lines.

I just build a platform to mount our stargate/micronav in our airframe.

I noticed the control problem in the case of a dead micronav. Not only will this cause a problem, but losing your ppm signal will also cause a lockup. Probably not a good plan.

[clolson]

Did they have the daughterboard on the Stargate in addition to the micronav? I was wondering if the daughterboard and the micronav will work together since they share the same serial lines.

I noticed the control problem in the case of a dead micronav. Not only will this cause a problem, but losing your ppm signal will also cause a lockup. Probably not a good plan.

I'm not very familiar with the stargate and had never seen one before this past week, but my understanding is that the micronav is setup to be the daughterboard. There is no option of plugging in an additional daughter board. However, the stargate does have a compaq flash slot + usb + ethernet + one more serial port so there are options to interface with other onboard hardware if need be.

I'm not sure why losing your ppm signal will cause a lockup. I think you could just code things so you go into an autopilot mode in that case. (And for better or worse, it's the end user that would need to write all that code.)

Personally, I'm really excited about getting our unit up and flying. I realize there are some limitations, and it's still really new, but it's a heck of a lot of [potential] functionality for the price.

Curt.

[Vindication]

So I wonder if that source code for the stargate will compile and run on a gumstix...

[LukeZ]

The stargate is running linux and they make all their kalman filtering code available via their open-source web site.Hmm, I'm really going to have to look into this. So far as I know this would be the only open-source Kalman filtering software available to the UAV hobbyist, and intended for fixed wing. The Autopilot project is open source but their filters were developed for rotary-wing craft.

Nice tip Curt, thanks.


Luke

[Unterhausen]

Curt,
The reason I wrote that about the ppm signal is because that's the way the Windows demo progam works -- the servos don't move until you have a ppm signal coming in. We stumbled around looking foolish for a few days before we figured that out. It was a pain rigging up a ppm signal, we used a buddy box cable to our tx since we don't have a ppm receiver yet. I guess we'll have to verify that with the current firmware. If it is in the firmware, we can always change it. It seems that it would be a good idea to have a function that tells the autopilot that ground contact has been lost so it can return to a predetermined location.

I'm pretty excited that there is software ready, I'll see if I can get it running tonight.

[Unterhausen]

So I wonder if that source code for the stargate will compile and run on a gumstix...
Vindy,
It should. The problem would be interfacing it with different sensors. The micronav has a communications protocol between the ARM and the AVR. Seems readymade for your purposes. I would assume that the AVR code would run on the gumstix with some adaptation.

Did you see the link to the sourceforge site? Download the unav package and try to compile it for us.

[Vindication]

Does anyone know of a differental airspeed/altimeter sensor that is temperature compensated and has some usable interface?(ie serial or i2c).

Thanks
Vind

[LukeZ]

Vindication, I am developing one, but it is not likely to be completed before Christmas, and quite likely not until later in the winter. You can see this thread (http://www.rcgroups.com/forums/showthread.php?t=372869) for some discussion of the altimeter aspect, as well as my website for a few bits and pieces. I had to take a break from it for a while but have started back in earnest more recently.

The sensor package will include airspeed, altitude, temperature, humidity (if you want it), voltage and maybe current. All the information will be accessible through a standard RS-232 port. It pretty much all works now but there's still quite a way to go before it's perfected.

As you can read on the thread the altimeter will be temperature compensated and resolution will range from about 8 inches at sea level to about 4 feet at max altitude of 45,000. Airspeed indicator is also temp compensated and the humidity sensor is used to give an even more precise reading (it allows one to subtract out the effect of water vapor from the air density assumptions). This will be quite a bit more than even full sized aircraft do.

I know this doesn't do you much good now... but just so you know there are some things like this in the works. I think I am not the only person doing this...


Luke