There are generally two micro-helicopters ( indoor ) in the RC market. I have already planned to buy one of them as they can fly inside the living room and even take off on ours hand. Unlike those operated by gas, these electric helicopters are very clean and give out no terrible noise at all. In one nightfall, I visited a web site, which is about how to make a hand made RC helicopter. I was totally impressed and started designing my own helicopter. Here is my helicopter:
Step 1: MAIN BODY
The circuit board is cut to the rectangular shape as above( 98mm*12mm). As you can see, there is a hole on it which is used to house the main shaft holding tube as below: (2)
Brushless DC, Brush DC, And Stepper Motors From Allegro.
Step 2: MAIN SHAFT
Up to now, the basic structure of the helicopter is completed. The next step is to install the gear as well as the motor. You can take a look at the specification first. The gear I used is from Tamiya gear set that I bought long long time ago. I drill some hole on the gear in order to make it lighter and have a better look.
Step 3: LANDING GEAR
All the rods are glued together by instant glue first and then by epoxy adhesive.
The skid set is made from balsa. They are very light and can be shaped easily.
Step 4: MAKING THE SWASH PLATE
Swash plate is the most sophisticated part of a RC helicopter. It seems to be a simple unit of a factory one. However, it is a whole new thing of making one by yourself. Here is my design based on my own little knowledge about the swash plate. What you need includes:(7)
1 ball bearing ( 8*12)
1 plastic spacer (8*12)
rod end set ( for holding of the aluminum ball in the swash plate )
aluminum ball ( from ball linkage set 3*5.8 )
The rod end set has first been cut into a round shape. It is then inserted into the plastic spacer as shown below:
Make sure that the aluminum ball placed in the rod end can be moved freely. 2 holes were drilled on the plastic spacer in order to house two screws that used to hold the ball linkage.
The back of the swash plate In my design, the swashplate is fixed on the main shaft. This is simply done by applying some glue between the aluminum ball and the shaftbe careful when applying epoxy to this tiny unit or you would get every part being glued together.(11)
My instructions are too confusing? Here is my draft of the swashplate which might help you. I still find that my design is a little bit too complex. If you have a better design, please let me know!
Step 5: MAKING ROTOR HEAD
For the rotor head, I choose the same material as the main body - the circuit board. First of all, I have to claim that the rotor head must be sturdy enough to withstand any vibration or it could be very dangerous.
The control system I used here is the Hiller system. In this simple control system, the cyclic controls are transmitted from the servos to the flybar only and the main blade cyclic pitch is controlled by the flybar tilt only.
The first step is to make the middle part:
It is actually a 3mm collar which can be fit into the main shaft. A 1.6mm bar is inserted horizontally into the collar. The above unit makes the rotor head movable in one direction.
There are two holes just above the collar which is used to, as you can see, house the flybar. All the parts that I used was first fixed together by instant glue. They are then fixed firmly by tiny screws (1mm*4mm) as shown below.
In addition, I add epoxy adhesive. The rotor head will spinning at very high speed. Never overlook the potential for causing injury this little machine has if anything got loose. Safety is paramount!
Step 6: MAKING CYCLIC CONTROL SYSTEM
As I mentioned before, the Hiller control system is used in my design. All the cyclic controls are transmitted to the flybar directly.
There is a metal bar ironed perpendicularly to the flybar. It holds the metal ball of the ball link in position. Here is how the ball link is made:
The rob ends are shortened and a metal bar is used to connected them together. the metal bar should be inserted deep into the rob ends and fixed with epoxy adhesive.
In addition to the ball link, an "H" shaped anti-rotating unit is a must for the control system. It helps to keep the ball link in position. The materials needed are showed in the above photo
Step 7: MAKING TAIL ROTOR
Would you think it is just too simple? Well, it is really a very simple design as the tail rotor is powered by a separate motor. This eliminates the needs not to construct a complicated power transfer unit from the main motor to the tail. The tail boom is simply fixed on the main body by 2 screws together with some epoxy adhesive:
The tail rotor consists of a motor, tail blades, tail shaft holding tube and a blade holder. The tail control is managed by changing the RPM of the tail motor. The drawback of this kind of control system is its sluggish response as the rotor pitch is fixed. However, it makes the whole design much more simpler and reduces a lot of weight.
In an ordinary R/C helicopter, the gyro work together with the tail servo. However, in this design, the gyro has to work together with the ESC (electronic speed controller). Will this work??? At the beginning, I try this with an ordinary gyro ( the large one for the gas helicopter). The result is really bad that the RPM of the tail rotor changes from time to time despite the helicopter is standing on the table. I buy a micro-gyro later which is specially designed for small electric helicopters and to my surprise this works great.
Here is the measurement of the tail blade. It can be shaped easily from a 2mm thick balsa. the tail blades make an angle of ~9°on the blade holder
The photo shows all the things that the tail part consists. The two balsa blades are hold by a hardwood holder which helps to give a fixed tail pitch. It is then secured on the gearwheel by 2 screws. The motor is simply glued on the tail boom by epoxy adhesive and the tail shaft holding tube with the same way on the motor.
The tail blade is made of balsa. They are covered with heat shrink tube in order to reduce the friction between the blade and the air.
The pitch and the weight of the two blades must be exactly the same. Tests must be performed to ensure that no vibration occur.
Step 8: INSTALLING SERVO
Only two servos are used in my design. One is for the elevator and the other one is for aileron. In my design, the aileron servo is installed between the motor and the main shift holding tube. In this way, the tube has made use of the sturdy plastic case of the servo as one of its supporting medium.
This arrangement gives extra strength to the main shift holding tube as one side of the servo is glued to the motor while the other side is glued to the tube. However, the mobility of the servo as well as the motor is lost.
In order to make the whole structure sturdier, an additional support is added to the main shift holding tube. It is also made from circuit board with some holes drill on it.
Step 9: ELECTRONIC COMPONENTS
The receiver I use is GWS R-4p 4 channel receiver. Originally, it is used with micro crystal. However, I can't find one which fit with my TX's band. So, I give my try to use the large one from my RX. It eventually works great and no problems have occurred up to now. , it's really big when compared with the micro receiver. The receiver is only 3.8g ( extremely light weight ) which is very suitable for indoor helicopter.
#Although the receiver has only four channels, it can be modified to a five channel RX.
The tail Esc
Here you can see the speed controller that is used in my helicopter. It is placed at the bottom of the gyro. Woo!! Really small size with only 0.7g. It is a JMP-7 Esc that I bought from eheli. I really can't buy one from local hobby shops here in Hong Kong. Also, this tiny Esc works great with the gyro. I just simply connect the signal output of the gyro to the signal input of the Esc. (26)
This perfect micro-gyro is made by GWS. It is temporarily the lightest gyro that I can find in the world. Unlike the previous GWS gyro that I used in my gas helicopter, it is very stable and the center point is very accurate. If you plan to buy a micro gyro, it would certainly be a good choice for you!
Step 10: THE TAIL MOTOR
The motors in the above photo are 5v DC motor, micro DC 4.5-0.6, and micro DC 1.3-0.02 ( from left to right ) In my first attempt, the micro4.6-0.6 is used. The motor burns out quickly ( or I should say that the plastic component in the motor melts) as the power demand of the tail rotor is much larger than that I expected. At the moment, the 5v motor is being used in my helicopter which is still in very good condition.
The current tail motor is a 16g GWS motor which provide much more power. For more information, please go to the page "flybarless CP modification II"
Step 11: SPEED CONTROLER
The following diagram shows how the components are connected to each other. The connections at the receiver is not in order. The GWS R-4p is originally a 4-channel Rx. It is modified in order to provide an extra channel for the pitch servo.
In a fixed pitch design, only 2 servos are needed.
A computerized Tx is needed as the the tail control must be mixed with the throttle control. For a Piccolo micro helicopter, this task is performed by the Piccoboard. For my design, this is done by the function "Revo-Mixing" in the Tx.