Posted by Steff Davies on January 4, 2009 at 7:34am
When I was a small boy, I used to watch the Jindivik target drones take off from Llanbedr (see http://www.airsceneuk.org.uk/hangar/1999/dera/targets.htm) on family holidays to North Wales, where my father was born. I've been interested in unmanned flight ever since.Currently, I have built nothing whatever in this line, but I have done a lot of reading (not least here - thanks Chris!). Ultimately, I'm thinking of a small electric fixed-wing based on a simple kit like the Multiplex Easy Star or Twinstar. My current thoughts on the rest of the kit:Mainboard: Gumstix OveroThe familiar Linux environment is too tempting to pass up, I think (I'm a Linux/BSD sysadmin by trade). Also, the surplus of CPU horsepower means that I can concentrate on getting something working in a scripting language and then making it faster rather than having speed as a constriction from the outset.Servo control: http://www.seetron.com/ssc.htmcheapish and lets me outsource the servo-control nastiness (of which I know very nearly nothing) in favour of talking to a serial port, which is more familiar territory.GPS: A 5Hz GPS module of some sort - there's a San Jose 32-channel on sparkfun which looks impressive. It appears to do serial output over two pins at 2.8V.IMU: I think this is going to have to be the Sparkfun 5DOF. I simply don't have the electronics chops to build my own, and anything nicer is going to cost too much for a first go-round.Telemetry: at least initially, wifi looks like the way to go. Unfortunately, the Overo currently lacks a wifi implementation, but there's a known-working USB dongle.This gives me a functional diagram like this:
Some Unresolved Questions (in no particular order):1) Serial connections. The Gumstix Summit board claims two "2-wire serial" connections - are these right for direct connection to the GPS module? To the servo controller board (I suspect not in this case)?2) Are the AD convertors on the Overo accurate enough (10bit) to be useful?3) Are they electrically compatible with the output from the IMU in any case?Have got the wrong end of any very important sticks? Have I made some glaring omission? I throw myself on your mercy.
Hi Steff,
It's a year now since this last post, so how has it been going? I'm playing with the idea of getting myself a Gumstix, too, so I would be extremely interested in anything you can report about your project.
Gumstix is up and running with bitbakery a-go-go. USB connectors have been obtained to make the magic OTG cable so I can connect up a hub and thus a wifi dongle (for the time being - I'm hoping the host UDB stops being experimental sooner rather than later). Sparkfun order is in (2 x gyro breakouts, 1 x 3-axis accelerometer breakout, a load of the level convertors). I'm leaving GPS for the time being, as it's more familiar technology and doesn't constitute The Hard Bit.
Cheers Curt! All excellent information. The Linux environment is certainly a big plus for me, since that's what I work with every day and what all my other computers run (apart from the one running Solaris).
One word of caution on the gumstix overo. The summit expansion board provides the usb connector, but the "host" portion of this is still listed as "experimental" on their web site. I saw in one of their forums that experimental means that no one has gotten the driver to quite work yet. I haven't actually worked with an Overo/Summit yet so I can't say anything for sure, just reporting what I've read. Usually when I'm optimistic with this stuff, I'm disappointed ... better to take what they say at face value.
I can tell you that the Verdex usb host functionality is great. I've gotten a GlobalSat hocky puck usb GPS running on it with gpsd (talking sirf-binary protocol.) I also got it to recognize my web cam. (On my todo list is to compile up open-cv and do some onboard image processing.) Basically any usb device that linux supports can be compiled into your custom kernel and used. That's pretty cool. I plugged in a 4-port usb hub and that was recognized automatically. Packaging issues aside, this sort of setup gives you all kinds of options. The breakout-vx board gives you 3 serial ports, and then with USB, you can stack on additional usb->serial converters if you need more ports. I've never got the bluetooth to work reliably so I've mostly ignored that ... it's always been hit or miss, sometimes I can connect and sometimes not.
I think the gumstix boards are a great option for folks that aren't so good at soldering up their own boards from parts, and for folks that are comfortable working with linux. You get pretty small size, pretty thrifty power consumption, and a full blown linux environment (or as much or as little of that as you want to install on the board.)
Point taken about not rushing to expensive conclusions - that's definitely part of the reason why I'm doing a lot of preliminary thinking out loud here. I think my initial plan now look something like this:
1) More reading, particularly on the digital electronics side of things (SPI look as if it's going to be essential for a start)
2) Gumstix order and familiarise myself with it.
3) Sparkfun order ditto.
4) Solder, swearing.
5) Write something that does pure sensor logging via the gumstix.
6) Mount the whole mess to my bicycle to get some raw data from a non-crashing platform that travels fairly quickly, vibrates and has roll and yaw at least.
7) Easy Star or similar.
8) Once semi-competent with it (if ever), mount sensor/gumstix mess in Easy Star, repeat data gathering.
9) Kalman filter head-hurting maths fiesta and flight control model.
10) Repeat 8 and 9 until the flight model's impressions resemble reality.
11) Give servo control over to flight computer and inevitably crash.
12) Debug and repeat 11 until I have something useful or the world runs out of Elapor.
Steff,
I did the Tamiya thing too a long long time ago too but apart from left and right being reversed when coming back at you, that's about the limit of similarity. The wrong prop on the wrong motor will fry it and/or the ESC and possibly puff your LiPo (one reason why I have chosen A123 batteries). And cars don't fall out of the sky ;oP
The cheapest way to buy the 10 CAP is to get it with just the dedicated 10ch 2.4GHz TX module, no RX no servos (you can buy a 2.4GHz RX later should you need to for as many or few channels as you require)
I did this, got the Futaba 72MHz Synth TX module, a Corona 72MHz Synth RX and some HXT900 servos. That set me back by about 470USD total.
You'll start with the Easy Star but you'll want ailerons, you'll want a gyro, you'll want.. oh there goes 6 channels! I almost got the 9 CAP but at the last minute went with the 10 CAP and am very very happy with that decision as it will save me a lot of money in the future.
make expensive decisions slowly :o)
You're quite right to surmise that I have no RC aircraft experience (though I was very into RC cars as a kid and some of the principles appear to be transferable). Fortunately the world seems to be full of people who like to modify their Multiplexes and document the process. Once I get to the airframe stage, I'll be asking a lot of questions though I'm sure. The 10 CAP looks like a very nice bit of kit, but possibly overkill for my purposes (the Easy Star RTF is only three-channel and a six-channel set look as if it should be enough to get started with).
Hi Steff,
you make no mention of RC kit/experience - if you have none then you have a hell of long way to go before you go UAV - also puts you in the same boat as me ;o)
I'm just putting a Twinstar II together right now so I can fill you in on the details should you need some input.
Don't hesitate to ask. It IS complex - prop size/RPMs/current drawn/ESC/BEC etc... but its not complicated.
If you have no RC kit right now, my advice would be to go with Futaba 10CAP TX. Its a 10 channel modular and can take 72MHz or 2.4GHz modules. Its also easy to hook up to a flight sim with no hardware/software purchase required (soldering iron and freeware is all you need). It is also what most FPVers with head trackers opt for too.
Comments
It's a year now since this last post, so how has it been going? I'm playing with the idea of getting myself a Gumstix, too, so I would be extremely interested in anything you can report about your project.
I can tell you that the Verdex usb host functionality is great. I've gotten a GlobalSat hocky puck usb GPS running on it with gpsd (talking sirf-binary protocol.) I also got it to recognize my web cam. (On my todo list is to compile up open-cv and do some onboard image processing.) Basically any usb device that linux supports can be compiled into your custom kernel and used. That's pretty cool. I plugged in a 4-port usb hub and that was recognized automatically. Packaging issues aside, this sort of setup gives you all kinds of options. The breakout-vx board gives you 3 serial ports, and then with USB, you can stack on additional usb->serial converters if you need more ports. I've never got the bluetooth to work reliably so I've mostly ignored that ... it's always been hit or miss, sometimes I can connect and sometimes not.
I think the gumstix boards are a great option for folks that aren't so good at soldering up their own boards from parts, and for folks that are comfortable working with linux. You get pretty small size, pretty thrifty power consumption, and a full blown linux environment (or as much or as little of that as you want to install on the board.)
1) More reading, particularly on the digital electronics side of things (SPI look as if it's going to be essential for a start)
2) Gumstix order and familiarise myself with it.
3) Sparkfun order ditto.
4) Solder, swearing.
5) Write something that does pure sensor logging via the gumstix.
6) Mount the whole mess to my bicycle to get some raw data from a non-crashing platform that travels fairly quickly, vibrates and has roll and yaw at least.
7) Easy Star or similar.
8) Once semi-competent with it (if ever), mount sensor/gumstix mess in Easy Star, repeat data gathering.
9) Kalman filter head-hurting maths fiesta and flight control model.
10) Repeat 8 and 9 until the flight model's impressions resemble reality.
11) Give servo control over to flight computer and inevitably crash.
12) Debug and repeat 11 until I have something useful or the world runs out of Elapor.
I did the Tamiya thing too a long long time ago too but apart from left and right being reversed when coming back at you, that's about the limit of similarity. The wrong prop on the wrong motor will fry it and/or the ESC and possibly puff your LiPo (one reason why I have chosen A123 batteries). And cars don't fall out of the sky ;oP
The cheapest way to buy the 10 CAP is to get it with just the dedicated 10ch 2.4GHz TX module, no RX no servos (you can buy a 2.4GHz RX later should you need to for as many or few channels as you require)
I did this, got the Futaba 72MHz Synth TX module, a Corona 72MHz Synth RX and some HXT900 servos. That set me back by about 470USD total.
You'll start with the Easy Star but you'll want ailerons, you'll want a gyro, you'll want.. oh there goes 6 channels! I almost got the 9 CAP but at the last minute went with the 10 CAP and am very very happy with that decision as it will save me a lot of money in the future.
make expensive decisions slowly :o)
You're quite right to surmise that I have no RC aircraft experience (though I was very into RC cars as a kid and some of the principles appear to be transferable). Fortunately the world seems to be full of people who like to modify their Multiplexes and document the process. Once I get to the airframe stage, I'll be asking a lot of questions though I'm sure. The 10 CAP looks like a very nice bit of kit, but possibly overkill for my purposes (the Easy Star RTF is only three-channel and a six-channel set look as if it should be enough to get started with).
you make no mention of RC kit/experience - if you have none then you have a hell of long way to go before you go UAV - also puts you in the same boat as me ;o)
I'm just putting a Twinstar II together right now so I can fill you in on the details should you need some input.
Don't hesitate to ask. It IS complex - prop size/RPMs/current drawn/ESC/BEC etc... but its not complicated.
If you have no RC kit right now, my advice would be to go with Futaba 10CAP TX. Its a 10 channel modular and can take 72MHz or 2.4GHz modules. Its also easy to hook up to a flight sim with no hardware/software purchase required (soldering iron and freeware is all you need). It is also what most FPVers with head trackers opt for too.
Cheers Marc - I'd probably have found it after an hour or so of increasingly irritated Googling ;-)
http://www.sparkfun.com/commerce/product_info.php?products_id=8745
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