So... after the first two rotorhead designs misfired (the first was to weak, yes very light, but to weak; the second had to much friction, my servos could not move the swashplate accurate enough) I approach now the perfect design...hopefully :-)
As you may remember, my first goal was a helicopter with four blades, pitch controlled. I have switched now to three blades, as I switched also from CH-53 to the famous Lama SA 315B , which has three blades. The body has the length of 30cm. I estimate the weight still around 120g. The rotorhead is now finalized. I hope to start first tests in the next weeks. Gear Ratio is currently set to 1:13. My aim is an rpm of about 1300 rounds per minute. My first design disintegrated on the first test run. I did not fix it strong enough...and surprisingly it lifted off...and immediately hit the table. As to wings and bearings broke off, I realized that the first design was to weak. I used 1mm carbon sticks, 3mm bearings and all glued to a carbon cross. The sticks were just to weak and broke of the cross.
So I went back to the thinking mood and the result is below. The rotorhead was made of aluminum. Inside are 4 M1 screws which hold the four bearings (3mm).
Since the friction was to much for the small servos, I went back to the paper and draw the following:
The centerpiece and one arm is finalized. Now it looks very promising, since there is no friction and it looks quite strong and is a little bit smaller than design two.
For the parts I use Delrin for the centerpiece and a 7mm aluminumstick, which I cut in pieces and turn down with a driller and a turning tool
Cutted pieces and first turning step
All pieces used: the screw is an M1.6 and the splints are 1mm (all bought at Knupfer Modell-Technik). The ball bearing is 6mm x 3mm x 2.5. The 7mm alu piece is drilled first 5mm and than opened 6mm just to the end, so that a small part remains 5mm to hold the ball bearing.
The golden clamping piece is a 10mm clamping piece which I found also at Knupfer Modell-Technik.
The Rotorhead is now nearly finished as the following pictures show:
In the next step I have finalized the swashplate and assembled it with the Rotorhead:
At this stage I have reached 24 grams. Moving the swashplate up and down
it works fine. If I nick it to one side only, some pressure has to
be established. I hope the pressure is not too much for the WES servos I
am going to use...otherwise I might have to use stronger and heavier servos,
which I really do not want to!
I have realized that I have to switch from the needles to move the swashplate (the arms at the swashplate with the yellow and weight head) to carbon, since the needles are not stiff enough. They bent a little bit which would reduce precision. Instead I will use carbon sticks.
But what control electronics I am going to choose?
| Components |
Weight in gram |
| 3 Light Servos 2.4 (from WES Technik) |
2.4 |
| 6 channel receiver Micro-6 light (from ACT Europe) |
8.5 (out of the box, I am going to tune it) |
| Gyro PG-03 (from WES Technik) |
4.8 |
| Motor Micro DC 5-2.4 (from WES Technik) |
10 |
| Motor Micro 4.5-0.6 (from WES Technik) |
5 |
| MOS-FET Speed Controller JMP 5-7 Twin (from WES Technik) |
1 |
Plus the 24 g of the rotorhead and frame brings it so far to 60.5 g. So it looks promising that I will stay below the attempted 120g
Unfortunately I could not use the JMP RX5-2.3 from WES, as my Graupner MC-12 needs a six Channel for the pitch control. The WES JMP RX5-2.3 weights only 2.3g r!
It Takes Form!
I have connected the electronics and the servos. The swashplate I have connected to the servos.
The weight is now 59.5gr (with batteries 99gr). The above friction I could reduce by adjusting one of the clamping pieces on the swashplate (it was just a little off and not aligned as the other two) So I tried a first run (this time without wings, not that it lifts of again...:-) )
and...
YEEEEEEEEEEEEEES, all works on the first look smovely! Absolut delight and my family asked themself:
Why is he jumping around the house?
Well, no comment...
The prototype looks now like this:
For those who would like to know how I connected the servos, receiver etc.:
W = white, R = red, B = Brown, Haupt = main engine, Heck = rear.
So, now I can start developing the blades :-)
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Na, not the blades, first the body...is more fun;-)
So to build the body I will use carbon sticks. To understand the right size, I used photoshop and a digital picture of the already build parts. I adjusted the picture size to real size and adjusted a lama drawing until my model fitted in. See the result:
Lama with my model incorporated, size is 1:1
Here are two pictures of the tail-building:
After building the tail, I started the cockpit. First I made a model in wood. I wraped then carbon fiber around and put it in the oven at 50° C for 1.5 h. I then removed the wood (took some time, cutting out little by little). Et voila, it looks now much more like the real thing:
Actually I tried a second one, as the first was a little to thin and its surface was not so nice. This time I used styrodur instead of wood, as you can remove it with aceton (it melts away). After cutting out the windows and adding the undercarriage, it is nearly finished. I am now just waiting for my repaired speedcontroller and than only the blades have to be added (later also the turbine lookalike)
