SOme time back (within the last two or three months) I recall seeing a ground station setup where a guy was using a graphical LCD module similar to the one proposed for the NEW ArduStation Mega, and he had a very cool interface, even had an artificial horizon on the screen - DOES ANYONE ELSE REMEMBER SEEING THIS?? Wa it here or on some other forum??
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Sparkfun has just announced that registration is open for its second annual Autonomous Vehicle Competition (which we won last year). It will be held on April 17th. New this year: separate air and land categories, so the UAVs don't blow the rovers away again ;-) We're already registered. See you there!
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I am looking to make an electronic steering system for my magnet steered free flight model aircraft. GPS is not allowed by the rules. A gyro compass seems to be the answer, but I have not found any at a reasonable price. A gyro updated by an electronic compass to correct drift would also work I think. The aircraft dynamics are too much for a tilt compensated magnetometer.
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Can anyone give any advice on an autonomous landing setup. What should I use to sense change in altitude and do you think it could possibly work to land on water. Do you think laser or ultrasonic will work over water?
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Posted by Ryan Beall on October 14, 2009 at 3:30pm
In Bill's recent pod cast he talked about how the imudevboard experienced a random nose dive or extreme over estimation in the pitch (theta) axis. His theory was that the noise due to engine/aircraft vibration was causing the gyros to give inaccurate readings. He said that he put the imu in foam and the problem went away. I don't know how repeatable his experience was or how many test vehicles this "technique" was run on, but I find it no coincidence that I experienced the exact same effect on my imu.Here is my theory:I did some quick number crunching on some equations and found that it totally makes sense that pitch would "depart reality" more-so than roll and very rapidly as both him and I have both observed.(edit)For a 30deg AOB turn at about 1.5g's total the attitude solution if improperly estimated would be off in roll a couple of deg and about 30deg in pitch causing this nose dive affect.(correction)For a 60deg AOB turn at 2G's the estimation in pitch was off by 10 deg if centripetal was incorrectly calculated. The error would be in the positive direction causing the stabilty loop to push the nose over causing the "imu nose dive problem"I was extremely surprised at how quickly pitch departed at very shallow angles of bank. So this lead me to suspect one thing beings my math modeled exactly what I was seeing in the air....centripetal. Here are the pitfalls I evaluated:Gps latencyGps bandwidthPropper velocity mapping into componentsSo I will discuss in orderLatency. GPS has it...big surprise well how much is it and how much can it affect the solution. Depending on the module I have read 10seconds to about 0.5. Well for my Ublox it was about 0.75 to 1.5 depending upon the rep rate selected and positional accuracy (number of sats). I plotted it out and you can see how poorly the centripetal was accounted for in my "car test run". It's ok but in its worst case scenario could be off as much as 13 deg....which is better than 45deg with no centripetal at all for the runs I did. However 13 off and 1.5 seconds late quickly would cause things to go southGPS bandwidth. Its at best 4Hz....need I say more. You are going to miss changes in speed quite a bit and loose a lot of accuracy. Also note the graph where GPS clearly is reporting the wrong speed at the wrong timeVelocity mapping: This is how you map the velocity into the actual body velocities. Most people assume that the speed reported from the GPS is always out of nose of the airplane. This is mostly true except for in climbs. It is safe to assume that the v velocity (out the wing) is zero but not the w (out the belly of the aircraft). The total of u and w are the SOG from GPS and you must break them up. I'm pretty sure the imudevboard code does this but if it doesn't this is another large source for mis calculation----------------------------------------------------All of these things together are issues that can clearly throw off one thing....Centripetal estimation which was why we determined there was a 30deg offset in our crappy estimation. So with that solved (use airspeed instead) the problem goes away. I have hours of flight time on my IMU both with and without GPS and the nonGPS filter has yet to diverge from reality under self stabilized flight. GPS filter on the other hand....it depended on the airplane the autopilot....amongst a lot of other random variables that never made sense like calendar day. Some days it was fine and others it wasn't on the same aircraft which leads me to my next topic.
<Noise/Vibration:Gyro drift is due to temperature. When I tried to follow the drift using an integrator in software we had issues. Same idea and same effects and just as random. Some days fine and some days not. The filter DCM or what have you is a very dynamic thing and if you try to model a temperature drift with an integrator (in my humble opinion) it will only work assuming that your other estimations are perfect. Else the other errors will map into your temp compensation.....which does happen no denying it. Its ok if your gyros don't move that much with temperature and you keep an eye on the integrator however its way too unpredictable of a problem to assume your error state is a fixed target....It simply isn't.I run a temperature comp on my gyros and get repeatable results every time. With my comp equations the end result is a gyro that will hold itself +- 5 deg for 5 min or so. There are a lot of other tricks here like circuit noise reduction and oversampling that can be done but this is huge if you want to keep your solution converged.As far as vibration.....If a gyro gave crap results because of vibration then it wouldn't be any use in a 6dof filter. Your accelerometers produce noise with vibration and hence the reason we use gyros. I just don't see any room for allowance of gyros to be noisy in vibration. Pick good gyros and temp comp them and so many problems dwindle away very quickly-----------------------------------------------------------------------------------------------------------------update: addressing the airspeed questionMy acceleration model
<Best Regards and good luck in the IMU world-Ryan
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Posted by Josh Hathaway on October 14, 2009 at 7:17am
I just wanted to say hello to everyone on this great website and I can't wait to get started on my project!I'm out in Orlando, FL and me and a few guys are looking at pricing components for our system. I want to work with the UAVDevBoard b/c I'm familiar w/ programming PICs. Any suggestions for data recorder boards that work well with it?Is it really possible to control an aircraft just from a single microcontroller? Don't autopilots need inertial navigation, guidance, and control algorithms? That seems like a lot of number crunching for these little guys...
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Just a FYI: we're doing an average of 15,000 page view a day here, with around 4,000 unique visitors/day. Total membership will hit 6,000 in the next week. The site's traffic has more than doubled over the past year!
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http://cbs5.com/local/skeletal.remains.found.2.1244063.htmlGetting freaked out? Maybe he was in 1 of these shots & we didn't know it. Maybe he lost an airplane in the toxic waste area & didn't make it back. How many skeletons R near your flying area?
Posted by Tj Bordelon on October 12, 2009 at 9:09pm
This Saturday I had 15 mph winds gusting to 25 mph.. Still landed without issue. Wind is coming from the top of the image towards the bottom. You can see the aircraft try to land down the runway (right to left) but fighting the wind made the path a bit weird. But impressive given that the wind was something I wouldn't have flown in myself. Here's the plot:I have to say that windy flights are far more impressive. I had a nice crowd watching the airplane land in the crazy winds. One guy complimented me on my flying skills, at which point I had to tell him I wasn't flying at all ;-)
Here's today's video. Only 5mph today, but this is the only video I have showing a full flight from takeoff to land. Unfortunately my flare angle was accidentally set to -5 degrees!So with a working autopilot... windy days are actually more fun. I'm 90% there. Still a bug where my integral terms wind up if it can't punch through the wind. 2 good flights, one not so good.
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Posted by Jordi Muñoz on October 12, 2009 at 2:30pm
Hi there! I'm happy to announce the new ArduIMU firmware and ground station, you can download it from here:http://code.google.com/p/ardu-imu/downloads/listWhat new in the firmware:-You can now select DCM, Euler Angles our both.-Enable GPS output data.-Some minor bug fixed.-The orientation of the gyros and accels are now corrected.Whats new in the Ground Station:-Now the Baud speed is set to 38400 bps to be compatible with ArduPilot uBlox GPS.-You can see now the Euler Angles generated on the uController.-Better debug tools.-GPS information.-Raw Data.What i'm doing now:-Designing new PCB's.-Improving ArduPilot code.-FPV testing with ArduPilot.-Taking care of the business and shipments.-Improving the Store.-Going to School.-Trying to answer some emails.-Always trying to get a beer and some Sushi..Please be patient, I'm always working for you! ;-) Thanks for you support!
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Posted by Dimitar Kolev on October 12, 2009 at 3:19am
Hi,beginning of next month I plan to visit Airtec (especially UAV and Heli world exhibitions)http://www.airtec.aero/english/the-airtec/http://www.airtec.aero/documents/Dokumente/2009/090715_a4flyer_uav_world.pdfMostly for fun and take some pictures.Anybody have been before on this exhibition or plan to go this year?Seems to be interesting and is close to Frankfurt-Hahn (Ryanair, so it is cheap :-). Entrance fee is 23Euros(for three days), but conferences and exhibition are quite expensive.Delete the message if it seems offtopic.BR,Dimitar
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This time a flight in the rain.Should be a part of 'National UAV Mission Readiness Enhancement Programme'.If there would be any development.Note a few details:-Landing along the 'runway', fully automatic-Nice agreement with preflight mission simulation-No dramatic events due to rain thanks to IMU sensor-Low-tech video reception, almost a trademark. Sorry, my focus is not FPV, but fully autonomous photoshooting-Roll stabilisation failed because the pitot tube got water in it, lowering perceived airspeed and diverging roll angle. Using standard servo didnt helped - 45deg/s is not enough.
Read more…3D Robotics
Tonight we'll be recording a podcast with guest Bill Premerlani of the UAVDevBoard fame. But I'll be in a car so we're not using Skype. That means we can't livecast it on UStream or take question in the chat board this time. We will be recording, however, so you'll be able to download the podcast on Mon. We should be back to our normal livecast next week.
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Yesterday I went to my local hobby store to pick up some spare parts. I had a T-Rex 250 on its way. At the store I found a T-Rex 600 being sold used. I asked for a demo, and found my self walking out with it. The cost would have been a little bit more than fully assembling the T-Rex 250.I am trying to think of the UAV Heli project I am trying to get started. My first phase is designing the system. So today's post will be about the hardware I will be using for the T-Rex 600.Orientation Sensors:- Digital compass- Altimeter- Need to find a sensor to determine the angle of the Heli.Distance Sensors:- Stereo Camera (need to find a low cost high res, low power camera)- IR Sensors below the HeliStabilizer:- Cyclic Gyro-Stabilizer Flybarless SystemComputer Hardware:- robostix
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I know that most countries have legislation in terms of radio / video transmitters. I also know that many people do not always comply with this legislation.What are your experiences and opinions with video transmitters?
1. Frequency2. Power3. Range4. Range with Antenna tracker.5. Effect on GPS signal.6. LAWI know that there is no reason to discuss range since the law says in line of sight when you fly with RC. But still there is also some who "accidentally" gets to fly just a little outside the LOS.I have recently been in contact with a company who produce video / data transmitters.Any one in here who has experience with these transmitters.1.
We've done a long-needed reorg of the store categories to make things easier to find. And one of the thing you'll now find is our new video/OSD category. Between the excellent Remzibi OSD (back in stock!) and this camera we've got one of the cheapest and best OSD combos available, and best of all it's ArduPilot compatible!
Other new products include the uBlox GPS module programmed for Paparazzi, ArduPilot or straight NEMA, either with or without the adapter, and the ArduIMU board without the sensors.
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