Check out my thread on RCGroups for a recent 8 ounce flying weight plank MAV: http://www.rcgroups.com/forums/showpost.php?p=11923347&postcount=2445Specs:Flying mass: 225 grams (8.0 ounces)Motor: GWS model GWBLM001A for 2s LipoProp: GWS 6050Battery: Common Sense RC 700mA 2sESC: Castle Creations 15 ampServos: 2 HS-55Rx: Berg Stamp 4 with header pins removedControls: Elevon and throttleSpan: 18"Chord: 8"Airfoil: Eppler 186 (very reflexed)Center where motor is: Eppler 186 but 180% thick on top, 140% bottomRx/Autopilot and Battery bays: E186 140% top thick top and bottom.This is a plank flying wing. To get the C.G. forward enough, all gear has to be almost against the wing LE. This means the motor cannot be in the back, however I still wanted this to be a pusher. The solution: motor in the nose with a 3mm carbon rod shaft and ball bearings, 6" long.AttoPilot: This is without case and no header pins. The servos and all sensors are directly soldered to the PCB. The SD card socket is attached to the Atto with right angle headers. The pitot is a 1/8" OD brass tube sticking out only 6mm from the LE. The R/C Rx (Berg Stamp4) is around 2 grams without headers, and this is situated directly on top of AttoPilot. Autopilot + Rx + GPS + thermopile sensors + power sensor is 48 grams (1.69 ounces).The voltage/current sensor is also custom in that it has only 1 shunt resistor. This doubles the resolution (11 mA) and reduces the current range to 45 amps.There is no payload, camera, or modem on this now... however in a 8 ounce MAV package I think it significant to have these standard AttoPilot features:1) practically unlimited onboard data logging of 70 parameters at 5Hz2) Airspeed control (not simply hold)3) Power sensing and mAh abort triggers4) barometric altitude5) FULL SIZE gps (greater sensitivity and lock solidity than the really small GPS)6) all the other stuff (50 Hz attitude, exponential gains, line hold navigation, no pre-flight calibration of anything).I'll be using this to hone the automated landing code that is underway, and perhaps rework the autonomous take off to better suit planes with pusher prop (detection of hand toss then small delay before motor comes on).
Nice construction! I'd recommend not worrying about the derivative gain (turn it to zero) and turning down your proportional until it stops oscillating (I'm assuming its a pitch oscillation your seeing). The loop speed of your autopilot / system (including pitch inertia, which is super tiny) will only tolerate so much gain.
The GPS is doing great with solid lock and 8-11 sats... no loss of lock. Glad I used the full size module.
Honestly, this thing flies like CRAP actually! I added 1 ounce of lead to the nose and it is managable in RC, but I couldn't get the PID gains to my satisfaction this morning in about 30 minues of test flight. The winglets help the lateral stability. Maybe Jack is right in that I should focus more on the D gains to tame the oscillation. RC flight wasn't so bad, so I think in stabilized flight the autopilot was adding problems with too high of P gains and over control.
Noth - my current draw is around 3-4 amps, and I was getting 10 minute flights today.
Jack - the requirement for the reflexed airfoil in a plank airplane is to get the C.G. seriously far forward, as in 10% from the LE. Putting that 1 ounce motor in the back (not using the carbon shaft) would really screw up the C.G. even further. Right now I am not at 10% C.G., more like 20%, which is why I think this is so unstable. Based on what I saw today and the minimal effects of twiddling with PID gains, I can't imagine putting the motor in the back.
Make it statically unstable & use software rate damping instead of all that ball bearing rod stuff. You can do it. Must get myself some full size GPS rock solidity instead of the really small GPS.
Very nice one!!
What kind of flight times do you get?
I'm working on a MAV(foamie proto now) too - and I have 900mAh 2S lipos but they run out in a few minutes (2-3) to the motor cut point.
Dean,
I see you're using a reflexed airfoil to help with stability about the Y axis. Is that enough for this wing planform in autonomous mode or do you get pitch oscillations? I really like the clear covering so we can see all the cool stuff and layout!
Comments
Here is an IMU version, there are new videos up:
http://www.continentalctrls.com/
Although I realise it would'nt be a plank then.
Honestly, this thing flies like CRAP actually! I added 1 ounce of lead to the nose and it is managable in RC, but I couldn't get the PID gains to my satisfaction this morning in about 30 minues of test flight. The winglets help the lateral stability. Maybe Jack is right in that I should focus more on the D gains to tame the oscillation. RC flight wasn't so bad, so I think in stabilized flight the autopilot was adding problems with too high of P gains and over control.
Noth - my current draw is around 3-4 amps, and I was getting 10 minute flights today.
Jack - the requirement for the reflexed airfoil in a plank airplane is to get the C.G. seriously far forward, as in 10% from the LE. Putting that 1 ounce motor in the back (not using the carbon shaft) would really screw up the C.G. even further. Right now I am not at 10% C.G., more like 20%, which is why I think this is so unstable. Based on what I saw today and the minimal effects of twiddling with PID gains, I can't imagine putting the motor in the back.
What kind of flight times do you get?
I'm working on a MAV(foamie proto now) too - and I have 900mAh 2S lipos but they run out in a few minutes (2-3) to the motor cut point.
I see you're using a reflexed airfoil to help with stability about the Y axis. Is that enough for this wing planform in autonomous mode or do you get pitch oscillations? I really like the clear covering so we can see all the cool stuff and layout!