Bandits @ 12:00 Operation "Depron" (Will Gareth take to the Air)
July 31, 2010
After a long absence from flying gliders and control-line aeroplanes, i have decided to take to the air again, with the experience/inspiration and ideas from LMR - i think i have enough guts to start right from scratch.
Yes you guessed it ........ this is not an "Off the Shelf" model, this will be a complete self build from solid floor to fluffy cloud.....
Yes it will be arduino / atmega328 controlled.
Yes it will have XBee Pros installed in a hacked RF radio control transmitter.
Video Part 1 :- RF TX/RX unit - Servo Mech - motor mount (non stream here) youtube at end of Blog
Video Part 2 :- Aileron Servo installation (non stream here) youtube at end of Blog
First stage was to download a PDF file from www.rcpowers.com
This is a 10 A4 sheet plan of an Extra300 aeroplane.
Out with the guillotine - (count fingers before and after)
Paste the whole 10 sheets together to get the Master Plan ...................
....."*+ç%++ç*&ç&ç%& .......... "This is tall Order" ....... (did i have the right scaling on the pdf print !!!!)
Also here you can see the "Depron" sheet that the aeroplane will be made from.......
After "Pasting it" all together again - its time to cut all the individual bits out - now it actually starts looking like a plane.
My better-halfs long dress making scissors came in real handy.
Time to cut the "Depron" - depron is simular to polystyrene but with about 3 times its strength.
All that is required is a new blade and nerves of metal.......i mean ruler of metal..
Hardest part is optimising the depron to save as much as you can...........
.......the more you save the more you have for making new bits when it breaks..........
Its a long job requiring lots of coffee and hot bath to cure the back from leaning over the table.
All the Depron is cut and here you see the simple construction pieces.
And here is the first "Mock-Up" - just for an idea of size.
First glimpse of the motor, its a 150W 11A 17,500rpm motor - no idea if it mates with the set up,
it will probably rip itsself out of its mounts - to early to tell yet.........
Not for the faint hearted - to strengthen the depron i have in-layed 3 mm carbon fibre rods,
the process is to cut 2 3mm deep groves in the 6mm depron (thats 3mm plus or minus 0mm)
the depron is then hacked out with a 2mm screwdriver
Hot glue or Epoxy.......
Here you see the Elevator with its newly glued carbon rod insert.
Quick check of rudder elevator combo - servos have to be mounted..........somewhere.....
Carbon fibre rod for the wings were more of a challenge (one single carbon rod spans both wings).
I bought the depron from here Sonnenhof -model building .
I asked the proprietor of the shop what he does with all the faulty electronic equipment he gets, he shrugged his shoulders and showed me a box of "Dead" stuff ..........and look what i came away with (no cost - i did offer but nono he was glad to get rid of it, plus a few other things to boot) .........
What to do with a dead TX unit..........well connect it to an oscilloscope and see if there is any life.......
......... sure enough its was already on its way to the RfTx heaven.
..... it was a case of bad crappy solder - the whole rf circuit board ....crappycrappy solder.
Rip it out and place in an arduino for starters (awaiting order for atmel chips - then i will be able to shoehorn it in)
For testing i have installed an 434mhz 4800baud RF link module until my XBee Pros arrive.
Four Micro Servos :-
- Right Aileron
- Left Aileron
Normally only one servo is used for the Ailerons - but i want to be able to use them as Spoilerons as well (Airbrakes) so both can be controlled independantly.
Servo Version 1
Time to fix it all together - no clue how to mount servos to control the flight surfaces - here was my first test rig.
You can see how i had to bevel the depron so it can tightly bend back on its self (it was a one cut job - no room for error)
Servo Version 2
I seem to have collect many Servo Horns during the last year, so time to reuse them in a different role.
I wanted to have some way of mechanically altering the linkages for on site tweeking.
This is just a mock-up , the final will have carbonfibre rods and turnbuckley things.
The servo will be mounted at 45° to the air surface, meaning that i can mount them on the fuselage.
Motor Mounting Version 1
Basic idea mount motor to firm base and screw it to firm base on fuselage.
(diss-advantage - not so tolerant in crash)
Motor Mounting Version 2
Idea :- mount an impact spring - right direction but not so easy to secure.......
Motor Mounting Version 3
Idea :- cut grooves in the firm base of motor and bind it with elastic bands - this works fine, however it needs a few more bands
Prop Selection :- I have two props..............but which to choose ...........
The fixed prop is good - but it means i would have to put some kind of undercarriage to stop it hitting the ground.
The folding prop would get around this problem - but it folds back on its self and my feeling it would chop up the depron on false landing.
My ESC has a "propellor brake" would that help!! .....but not sure exactly what this means !!!!!!!!!!!
Aileron Servos :-
Rough positionsal test of aileron servos.
Still no carbon fibre.
Servo horn as adjustable fixture on wing. (Tune-ing)
Wing hinges are super tack material tape - they are holding strong (will see how it holds up to air stress)
I Ummmed and rrrrrrred with positions of the Aileron servos and ended up with angle_ing them again, this time they are glued into position.
and also the carbon fibre push rods are installed.
Installed and glued the wings to the fuselage .........
...... bit of a long and story ....well a seven minute too long story............
...... i tried to glue the two bit together using 5 minute epoxy glue..................
...... you guessed it , it took me 5 minutes to put glue on all the bits, then being pressed for time it was now or never and i tried to fix them together...
....well i got half way and the two bits glued together in the totally wrong place duh ( i was on the wrong side of 5 minutes)
It took me the whole sunday morning to separate the two bit again and tidy the depron (i was impressed by its strength).
So i went for hot glue on the second run - in fact its better than the epoxy.
(the funny thing was, the Crash Test Dummies where playing on the radio during the 5 minutes :-( good omen i thought )
Moral :- Double up on everything by buying 10 minute epoxy glue next time.
Here you see the motor mount hole has been excavated, and LOOK at those "Air-Breaks"
Now that the wing and fuselage where united - i could press forward with the Elevator
Here are the two extremes.........
And next the Rudder
Working out how to mount the motor , still none the wiser.
Grrrrrrrr.........Menacing dont you think........
XBee Pros have landed.....
There is a big choice of Transceiver chips on the market - it took a while sift the "Chaff from the Wheat",.....
.... i went for XBee Pros (Note to Vendor :- how about Sponsoring some LMR Guys/Girls , you would make us all happy) as they have the biggest support and they have a good track history.
One stupid,stupid,stupid thing is that the standard FTDI module does not plug directly into the XBee interface board Grrrrrrrrr (just a minor annoyance) as you have to swap the RX/TX lines over.
Anyway i will have to make a changeover plug..............
and here it is ....... simple Male-Female headers with the RX/TX swapped - works like a dream.
(thats worth some free-bees Mr.Vendor Man)
Here you see the two XBees talking to each other..... green wire on bottom XBee is the "Loop-Back Wire" for testing.
All Straight "Out of the Box" , so easy glide into XBees for me. (havnt found the factory default option yet-just in case)
Next job is to attach the XBees to the Atmega328s with some form of data packet protocol.
TX XBee sucessfully attached to an Ardweeny @ an incredible rate of 57600 baud using NewSerialSoft library , very easy to implement.
Thats the story so far .........
Tip of the Day - Hot glue a peg to your solder reel - i makes one cool "Third Hand"
It helps if the two halves dont match too (more surfaces and curves than a sexy bottle opener)