Wednesday, September 28, 2011

Flight Rules

From the Champ Thread:

1. Try to stay in the middle of the air - do not go near the edges of it.
2. The edges of the air include the ground, buildings, water, trees and people.
3. It is very difficult to fly near the edges.

Wednesday, September 21, 2011

Using a LiPo in a Turnigy 9X radio

Here's how I replaced the battery pack on my Turnigy 9X radio.  Andreas did it first... I just copied what he did.

It's pretty simple: cut the connector off of the original battery pack (the one that holds 8 AA cells) and solder on your favorite connector to the just-cut wire.  I picked JST because it was small and didn't take up much room in the case.
I used an old 3S 1800 mAh battery that I wasn't using for anything else.  A 2S battery will also work.  RC Model reviews has a popular article on swapping out the battery.  It's a comprehensive solution, and involves resoldering the motherboard.

The method presented here is a lot simpler.  You don't have to touch the main board, but you lose the low voltage beeper.  That means it's possible to discharge the LiPo battery below 3V/cell.  You just have to be careful at the start of the day to have the battery charged to 10V or more.
The discharge rate is about 0.1V/hour, so if you're charged to 10V or above, you will probably be OK.

Be careful when soldering your connector not to reverse the polarity.  There's no polarity protection on the motherboard, so if you get it wrong you'll fry your unit!

That being said, it's working well for me.

Update: the old battery I was using started having problems with one of the cells.  I didn't have another conveniently sized LiPo, so I replaced it with a LiFe battery from HobbyKing.  Notes on that are here:

Update: Javio left me a great comment on diydrones that goes into detail on how the LM7805 voltage regulator works:

There is a little confusion about the best 2S vs 3S better battery for the 9X. If conceptually it is true that a bigger dropout voltage between input and output leads in a bigger heat dissipation, the 7805 regulator has been designed to give the best performances with a differential voltage between input and output of about 5 to 10V. With the 7,5V (from 6V depending on the model) minimum input required voltage (2,5V of differential dropout voltage between input and output for 7805) the output peak current can not be achieved (the regulator can´t work at full dynamic range). In fact the factory testings of the LM7805 are done with a typical input voltage of 10V. Following this lines, and assuming that the input regulator is a 78xx, a 3S Lipo battery should be a better candidate than 2S to power the turnigy 9X. You can check the Peak Output Current Vs differential input-output voltage characteristic in the figure of page 21 of the attached datasheet or the Droupout voltage characteristic googleing "7805".
This explanation does not means that a 2S is a bad option, but in this case the regulator won´t work at full dynamic range of its output current. By the way, looking the datasheets a dropout of 5 to 7V between input and output (corresponding to an input voltage between 10 and 12V) doesn´t lead in a significative amount of heat increase.
Cheers from Spain.

APM Success!

What a great day!  Launched the Hawk Sky with APM and took it into both stabilized and fly-by-wire-a modes.  Flew like a dream in both.  The FBW mode is surreal... no matter how you jerk the stick around, the APM controls the plane smoothly.  I used all the default PID values.

I'm rather ecstatic... there's been a lot of work and study to get to this point and to see it go so smoothly has been very gratifying.  Thanks to all who have helped me get this far!

Here's a quickie minimally edited video.  The hatcam ran out of battery before I got to FBWA mode, so I'll add that later.  I think the FBW mode might be ideal for FPV and AP, since it looks so smooth (at least from the ground).

This video is from a couple of days later.  Winds were high, gusting to 20mph, and the plane flew so smoothly in fly-by-wire mode.  I forgot the hat-cam, but grabbed the video with my iphone.  Just the fact that the wind could be blowing so hard and I could fly one-handed while working the phone impressed me!

APM Control Surface Tests

Hooray, got all the control surface issues figured out.  Here's a video of how things should look, and a few pointers.

  • In manual mode, do any reversing necessary on the radio.  APM just passes the signal through in this mode, so reversing via the software won't do anything.
  • Be sure you're not backwards on how ailerons move. See this page for full details.
  • Test in three modes: manual, stabilized, and fly-by-wire A.
  • In stabilized and FBWA, rudder will be mixed in with the ailerons.  Be sure pushing the aileron stick left produces left rudder.
Tomorrow, prayer breakfast and then flight!

A nice diagram for prop orientation

Which side of the prop faces forward?  It can be tricky, coz you can put the prop on backwards and still get the plane to go forward.

Here's the general guidelines:

  • Most props have the size molded in.  The numbers face the front of the plane, no matter if the motor faces front ("tractor" configuration) or the back ("pusher" configuration).
  • If you cut the prop in half, it will look like an airfoil.  The concave "undercambered" side faces the rear of the plane.  Think of it as an airfoil (which it is!) pulling the plane forward [diagram from rcgroups].
  • If you feel something "wrong" with the thrust and the electronics seem fine, land and check your prop.  There's a good chance you've got it backwards.
jj604 sums it up nicely:

'Why the hell they didn't just mold a big "FRONT FACE" and "<- ROTATION DIRECTION" on the prop is beyond me.'

Monday, September 19, 2011

LiPo Battery Voltage numbers

Some handy voltage numbers.

cells                   1S      2S      3S      4S      5S      6s
nominal voltage         3.7     7.4     11.1    14.8    18.5    22.2
absolute low voltage    3.0     6.0     9.0     12.0    15.0    18.0    
low voltage warning     3.3     6.6     9.9     13.2    16.5    19.8
maximum voltage         4.2     8.4     12.6    16.8    21.0    25.2
storage voltage         3.8     7.6     11.4    15.2    19.0    22.8

Sunday, September 18, 2011

Aileron Motion

Here's the aileron controls spelled out.  Apparently my brain constantly works backwards on this.  Ironically I do all right when flying, but when setting up I consistently get the ailerons reversed.

All directions are relative to facing the front of the plane.  I should therefore probably say "port" and "starboard", but there's even less chance I'll get that right.

Stick motion:

Move stick to left, left aileron moves up, right aileron moves down, right wing moves up.
Move stick to right, right aileron moves up, left aileron moves down, left wing moves up.
When left wing is too low, give right stick. left aileron down, right aileron up, left wing moves up.
When right wing is too low, give left stick. left aileron up, right aileron down, right wing moves up.

The same information in a table:

stick    left   right  roll
motion   aile   aile   motion
------   ----   ----   ------
left     up     down   right wing moves up
right    down   up     left wing moves up

wing     stick    left   right  roll
too low  motion   aile   aile   motion
-------  ------   ----   ----   ------
right    left     up     down   right wing moves up
left     right    down   up     left wing moves up

Andreas gave me this page which I'm guessing is from when he got his pilot's license.

Saturday, September 17, 2011

First Try with APM

First try with with the APM on the Hawk Sky.  Got everything up in the air in manual mode, but had problems when switching into stabilized mode.

Posted a note to, got some good suggestions which I'll try out this afternoon and follow up with.

Update: I had ailerons backwards, duh!

Sunday, September 11, 2011

John Bernard's Power Distribution

Via the CrashCast, an interesting way to solder up a multi-ESC power distribution system by John Bernard.  It uses a short length of brass tubing to splice the wires together.  It looks quite tidy, and Crash Hancock liked the results when he tried it out.

It's written up in a PDF here.