I've spend the whole weekend working on the 4#3 and now it flys like a dream! Indeed it is now totally adequate for a beginner! It is able to hover hands free for 5 seconds in ground effect at 5cm height. I even managed to land and start it on a 20cm cookie box sitting on the table! It flys as good and controlable as any bigger fp can do. I'm totally thrilled.
This is what I have done:
1) all walkera connectors are gone and substituted by 1/20" pitch gold contacts
=> servos finally stoped moving erratically
2) replaced rx crystal socket with gold contacts and changed antenna to a plugable 0,1mm magnet wire
=> glitches are gone. The pulsing tail seems to appear when reception is less than ideal! I've noticed it when testing how short I can go with the antenna.
3) wire to the tail is gone and substituted by 0,3mm magnet wire
=> easier to put into the tail tube, less resistance, no more "semi cable breaks" making the tail work erratically
4) The inside of the rx is now completely filled with sponge rubber and covered by heat shrink. The heat from the motor doesn't affect the gyro anymore.
=> Gyro drift is gone! I now have to trim the tail only once and it holds during the whole flight!
EDIT3: Unfortunately the gyro drift is not totally gone. In the first minute it still drifts and I have to retrim. After that it does not need any changes in trim. It must be the piezo gyro heating up itself in the beginning.
RE-EDIT3: No, it does not drift! I forgot that the rx recenters the yaw signal on initialisation. I programmed the tx to supply the found yaw trim automatically when engaging the throttle. Kind of an automatic subtrim. Now I don't have to touch the trim anymore.
5) fixed the swashplate axially with tubes below and above and a second collar
=> now I can tune in the axial position of the swash where all the endplay in the linkages is gone and the head still moves freely. No more endplay in the rotorhead assembly means crisp control! It makes a BIG difference!
EDIT: Changed design to be spring loaded due. See picture.
6) moved the servo linkages to the inner hole and the nick servo to the inner position on the frame (had to drill new holes on the upper servo holder).
Reasons:
- the movement is still more than mechanically allowed by the head so it is enough
- the angular endplay in the servo gear translates to end play in the head. The longer the arm the bigger the end play, so a shorter arm means more precision
- the servos are digital and have very few steps of movement. We should use the maximum amplitude available to get it "as analog" as possible!
6a) The metal balls on the servo arms are too small and that is another source of loosing presicion. I squeezed the plastic part of the ball ends so that they fit thightly on the metal balls.
6b) Lube every linkage you find with a little bit of silicon oil! It makes everything move really smooth!
7) reinforced the original rotor head. I used a kind of epoxy clay that you can press into the gap simply using your fingers. Very easy to apply and using your bare fingers you can assure that the gap is really totally filled. I roughed the inside of the gap before applying the epoxy. I think that it works good. I have removed the blade holder several times and the head is still one piece and the epoxy keeps adhering to the plastic
7a) The pin holding the gear to the rotorshaft is a pain in the ass to insert and remove. The pin in the original shaft was impossible to remove I had to cut the shaft to get it out. I rescued the gear by making two small cuts on the gear down to the pin. The material of the gear is elastic so givin a small punch with the hammer to the shaft the shaft comes out without removing the pin. After the shaft was out I applied a little CA with a needle to the cuts in the gear and rescued the gear.
I now use a long (10mm) piece of 0,8mm carbon rod instead of the original pin. It is easier to put in and out using pliers and stays inside due to the higher friction.
8) balanced the tail and the rotorhead without blades till all vibration is gone. Do it indepently! First balance the head without plugging in the tail and then balance the tail without main motor moving. You can see if everything is balanced by gently touching a cookie metal can with the carbon pin on the tail. The vibrations are amplified by the can and you can hear from the sound if everything is ok. I used transparent tape with the trial and error method till everything was balanced well. First of all check with a caliper that the paddles are exactly on the same radius!
9) Changed the battery holder. The battery now sits between the front wire of the skids. I've cut the original battery holder in pieces and reglued it to make a new one. I've used ABS plastic and pieces of a 3,5" floppy disk to make parts of it. Diffcult to describe. Pictures will follow. I've glued it with CA and the bond is amazing. Actually it is like one piece of plastic when finished. Indestructible!
=> The bird is stock incredibly tail heavy! Not just a bit. Now COG is perfect.
10) The paddle bar is now a 1mm steel wire. The carbon cracks even when thightening the screws. It is simply inadequate for the application! I was not able to get the head into perfect balance with the carbon bar.
11) Feeling that the headspeed is too low I've cut the original blades to have nearly the same root and tip width. I decreased the width in 2mm steps till the bird behaved like I'm used from the bigger ones.
Every step was lots of work getting them into exactly the same shape and thickness. You've got to thin them out at the trailing edge and that is lots of precision grinding. I used a 1/100 gram scale to get them to same weight and then balanced them till vibrations were gone. It takes lots of patience but with the high headspeed you really need to have everything in balance!
The final size of the blades is now 10,7mm at the tip and 12,7 on the inner radius. The cut has to be made at trailing edge!!!
=> The headspeed is now much higher. Hovering in ground effect at 3200 and peaking at 4500 RPM (I forgot to mesure the original head speed. Can somebody help?) ! The flighttime is up to 11minutes with a new lipo and 9-10 with the old ones from my 5#6. The original motor stays cooler. A stable hoover in ground effect is NO PROBLEM. The dynamic in "pitch" is better now. The headspeed goes immediately up when you move the stick and so does the bird. The control authority is great. Another thing is that the headspeed is more constant when doing bigger cyclic inputs. With the stock blades the bird goes down when you are hovering and you go hard on the sticks. The effect is nearly gone. Last but not least it looks really sharp with the narrow blades and the sound is amazing.
EDIT: TurboCinqy supplied the head speeds with stock blades. Stock is hoover (most likely not in ground effect) at 2900 and peak at 3400.
Wow.... thats a lot of words. I hope nobody gets bored when reading
All together it flys now like a dream. It behaves like a much bigger heli. Floating in ground effect and precision landings on the coffe table are a real blast now!
I still have to address the motor/brush issue but for now I will simply enjoy the flying. I've spend round about 30h to get it where it is now and thats enough for now.
I will post pictures later.
Cheers,
Ruben
EDIT: Corrected the stated head speeds. The rev meter was accidentally set to single blade. Measured more than 8000 RPM first.
EDIT2: Forgot some things. Added 6a/6b/7a
EDIT3: Added pictures
EDIT4: Added video
EDIT5: Added specs of new blades