Hello,
I have been looking at various autopilots to add to my collection but I have one less common issue. I fly all winter and its not unusual for me to fly at -20C. I have been playing with the ardupilot code and looked into the devboard but now that I am getting into the stabilization aspect of the AP I am wondering if IMU's will even work without massive temperature drifts at cold temperatures. I have read thermopiles have difficulty getting a reading when snow is involved.

I assume an IMU would work so long as I let it temperature stabilize before flying (I let me heli's sit outside for 10min or so before I fly to keep the gyro drift down). My 2 IMU's I would be considering are either ardunio based IMU or the UAV devboard IMU but I am wondering if its worth purchasing either of these units if they will not function during colder temperatures. I am working to wrap my head around DMC and how they help eliminate drift but its all fairly new to me.

Opinions are greatly appreciated,

Curt

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Hi, I think that most problematic sensor to maintain in working order in rain and cold is airspeed sensor, i.e. pitot tube. It needs to be in airflow and is therefore open to rain and potentially freezing temperatures. Full scale aircraft has heated pitot tubes, I'm wondering what experience UAV people have with that.
My experience with Pitot tube is to get rid of it. It breaks, gets water, dirt, bugs, hits bushes.
Necessary for precise angles in pro platforms, but not the best for everyday use.
Hi, what might be alternatives? GPS only is not good because of wind. GPS with wind correction may work, but gusty wind can still cause problems. Pitch control via accelerometers and open loop motor control then?
Alternative is a very precise IMU plus good kalman rejecting vibration but thrusting smooth changes.
I think I should be able to have the auto pilot system I need without needing an airspeed sensor. I figure a well built imu with my ublox combine with good software filtering should provide me the stabilty I need. My main use for an autopilot system would be simple rtl functions and to help with stability. Although with all the posts about these waypoint challanges I figured I might as well work toward a full AP. You guys look like you are having way to much fun.
Autopilot design is 99% time indoors. Around 2-3 years. I don't see where the fun is. There is achievement, potential business, that's all. Unless you don't care about 20% flight success rate in which case you can do it during afternoons.
Hi, I find airspeed useful for determining desired bank angle when executing a turn. Also, airspeed + ground speed enable me to determine turn rate of the airplane from turn rate of gps:

plane_turn_rate=gps_turn_rate*ground_speed/airspeed

I guess its possible to do without airspeed, but then you need to be quite conservative. RTL will probably work quite well, but T3 times will be disappointment.

I'm wondering, arent there any "clever" ways to dermine airspeed: for example, by measuring battery voltage, throttle setting and current drawn by engine - or smth similar. Somthing, that would not be affected by plane configuration too much.
Haha, it's the tinkering and tweeking I love. I spend just over 3 months in school tweeking a 2 wheeled robot to balance on it's own...in the end all it did was balance but the progress to get it to do that was the fun part. I try and keep hobbies and work seperate and right now messing with UAVs is great fun and I have no plans to make cash from it.

Andrus,
I realize I will lose out on some accuracy without airspeed but I am really aiming at keeping all controlling systems and sensors inside the body for protection and simplicty.
Even the pros haven't figured this out. I believe it was condensation in the pitot tube that cause the B-2 to crash on Guam.
Autopilot on its way,
I just placed my order the other day for the UAV devboard so I should have it in my hands within a few weeks. I'll need to build/buy a FTDI cable since my ublox is set to the ardupilot configuration (which I understand has a higher baud rate making software programming thru the UAVdevboard impossible without dropping it down). Other then that I am good to go. Cold weather is starting to set in here and my wing is nearly all flight tested so I should be able to do some walk around tests in the cold soon.


Thanks Guys!
Curt,
If you have ardupilot FTDI (3.3v) that will also work with UBLOX..All you need to take care is that your UBLOX is supplied 3.3v only. I have used same arupilot FTDI cable to change baudrates to 9600 seccesfully w/o any problem. YOu can also power from Uav board with Jordi's adapter just remove Tx/Rx pin from GPS connector and conenct it to your FTDI..with a common ground.

Sid
Thanks Sid,
This is what I plan on doing I just dont have said FTDI cable. :) I read about using the Jordi adaptor for power and removal of the Tx/Rx pins and thats what I'll use. I have an old USB - RS232 adaptor I used to program a Motorola board back in school and was looking to see if I could use a simple level converter to connect to the ublox.

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