Hello everyone (my first post   )

I am building a micro VTOL with a single rotor. In order to use only a single propeller I am using the wake sucked in to produce the anti torque. I have attached a rough design diagram. Total weight I am aiming for is 300-500g. The material of the frame is aluminum. The motor is also mounted using 5 mm aluminum pipes(plan to weld them). The motor I am planning to use is

http://cgi.ebay.in/RCFORALL-BRUSHLESS-MOTOR-A-2212-13-10T-COMBO_W0QQitemZ110292283917QQcmdZViewItemQQptZLH_DefaultDomain_203?hash=item19adeeb20d&_trksid=p4634.c0.m14.l1262&_trkparms=|301%3A1|293%3A1|294%3A30

The vanes will be made of balsa wood(most probably)

Since I am really new to this and this is my first experience of such kind. I have loads of doubts.

1.  Am I using the right motor?
2. How do I decide on the propeller to be used?
3. How do I know the thrust being generated at particular speed for the propeller?
4. Where can I get 5 mm aluminum tubes in India?

Any other help besides this will also be appreciated.

Many of these issues are already discussed in the following threads.

http://www.rcindia.org/electric-power/selection-of-motor-esc-prop-and-lipo-for-foam-planes/

http://www.rcindia.org/self-designed-diy-and-college-projects/help-needed-with-building-an-rc-spy-plane/

http://www.rcindia.org/electric-power/amp-rating-and-motor-size/

It would be good for you to start with going through the threads in following boards :

http://www.rcindia.org/electric-power/

http://www.rcindia.org/self-designed-diy-and-college-projects/

Thanks a lot for those links...From what I gather I think I should go with the A2212-13/10T motor and a 9x5 or 8x4 direct drive propeller. I found this really good site flybrushless.com which gives test data for various motors.
Could someone please give me suggestions as to whether my selection is right?
Also, how does one connect a propeller to the motor?

The Motors come with the Prop adapter  for connecting prop to motor
sai

does your VTOL have forward flight mode? this project looks promising. how are you stabilizing the whole thing on all axises.

Initially we are looking for just a stable take off and then we would look to improve upon it. The propeller at the top should provide the necessary thrust and the while landing the bottom fans should provide the necessary stability. I hope I understood your question right.

BOTTOM FANS!! i thought you had only one single motor at the top. i you meant vanes are they gyro stabilized. and can i get a detailed list of parts you are using. the model is fine. i want to know your stability system in detail. whenever you have time please answer my questions.

This is all I have to do for the next 3 months....Thanks for your interest
The bottom fans are not connected to anything but some sort of support along the same axis as that of the top propeller
They are not gyro stablized

Could someone please explain as to why a torque act on the fuselage of a helicopter when the main rotor works in a helicopter and how we are balancing it coaxial helicopter?

bump

Hey Aforadi ,
a ordinary single rotor Heli has a tail rotor to stabalize it , it is conected to a GYRO so it it maintains a proper(efficient) motor speed . For Belt driven helis , there is a servo that is connected to the tail rotor , maintaining its pitch for a stable flight .
For variable pitch helis , the tail rotor is given + pitch for pushing the tail backwards and - pitch for moving the other way giving a pull .

For a co-axial , there are two motors that are connected to two different rotors , a gyro is used to mix bot the motors and maintain a proper speed between the two motors . Now , you must be thinking how it stablizes , both the rotor are counter rotating , thus ones pitch is - and others is +

I hope this will give you an idea as to how a Heli works !

What I don't get is why is there a need to stabilize?

The motor is spinning the rotor in one direction , when the Heli is in the air , as the rotor spins to one side , it creates a torque  and make a tendency for the heli to rotate (some times violently ) . in such a situation , it cannot give proper inputs , if it give foreward , it cannot move because it is given inputs but the heli is rotating ....

Its very hard to Explain , I myself am not sure of what i typed is making sense , if it isnt , all heli experts pls give inputs .

Hi there,

Sahevaan is right. May be he did not use the right words to explain it properly.

Before I start explaining I want to point you out to a basic law of physics - The Newton's 3rd law - "Every action has an equal and opposite reaction."

Now, if the blades of the heli is spinning in clockwise direction, the motor that spins it will experience an equal and opposite force in anticlockwise direction. Since we are talking of spin here, we can replace the word "force" with "torque". The motor is obviosly in the fuselage and so the fuse tends to spin in anticlockwise direction as well. 

To counteract this "induced" torque most single rotor helis use a tail rotor. On coaxial Helis, you got two set of rotor baldes spinning in opposite direction. Now, each rotor will have an "induced" torque but they both will be in opposite direction and cancel each other. Hence coax Heli may not have tail rotor.

Hope this helps.

-Ismail

I can understand what you say but there are motors which are not used in such applications like say a cooler.....Here we don't do any such sort of thing........What am I missing?   (I haven't actually bought the motor yet so I may sound stupid as I have not hands on experience yet)...Doesn't just the shaft rotate like the motors which we use in robots?

Well, you cannot cheat laws of physics. Even in air cooler you have the "induced" torque. However, in cooler the motor is secured to a framwork and the framework is sitting still on ground. The force to topple and spin the framework is much more than the "induced" torque. So, you do not see the framework spinning in opposite direction.

In helicopter the framework is on air and there is nothing to restrain it. When you have the heli on ground you will not notice the "induced" torque as the frictional force between the ground and the landing gear is greater than the "induced" torque. But when the heli lifts up, you will see the torque effect as the fuse does not have any restraint.

As an analogy. Imagine yourself on a raft and you try to spin a pole hanging from a tree. The pole is connected to rusted bearing on the tree. You can spin the pole only by applying considerable amount of force (read torque here). Now, when you try to spin the pole with all your effort your raft will move/spin in the opposite direction to that of the force/torque you apply. This is called the "induced" torque.  If you do not want your raft to spin around the pole, then you would need to secure your raft to the ground (like heli on ground)... but you are already in the middle of the river (like heli on air) and cannot do that.. So, you would need a motor that would propell the raft in the opposite direction of the "induced" torque. Now, you need to have a gyro so that more torque you apply on that pole the more force is applied by the motor to counteract and stablize the raft. Thatz exactly the same concept for helis as well.

In fact the same effect happens in linear motion. For example, when step out of the raft on to the peir. As soon as you put your foot on the peir and push yourself foward, the raft will move backwards... Thatz action and reaction...  Once the raft is secured to the peir (like heli on ground) you can safely step out.. But if its not secured (like heli on air) then again you need a motor that pushes the raft forward while you step out on the front. The propelsive force of the motor should be synchronised with the force you apply on the foot... and thatz where the gryo does its job.

The air coolers you mentioned is like a secured raft. But helis on air is like raft on water without a mooring rope!  

Isn't physics an interesting subject??.. Ever wondered about theroy of relativity..

-Ismail

Thanks a lot for that answer....Now consider a normal DC electric motor which has a positive and negative terminal...What is the framework for that? I have seen those small motors where you just connect it to a battery and the axle starts rotating. Is the frame work inside...If so then  how is the brushless motor different and how can I feel that torque as in what part of the motor feels that anti torque? Is it the outer body of the motor?

I apologize if my questions seem ambiguous and repetitive.

If I hang the DC motor in air and give it power you suggest that whole motor will rotate?(assuming the torque is sufficient)

thats what happened to one of my 2ch power systems , i hung them in air and because of no stablization , the motor spun , but then Chopped of the wire connecting to it 

Quote from: aforadi on June 12, 2009, 01:47:20 AM
If I hang the DC motor in air and give it power you suggest that whole motor will rotate?(assuming the torque is sufficient)

Yes, that is right. Lets say you hang the motor on its +ve and -ve wire like a pendulum. Now, if you attach the battery terminals.. the motor goes zzzzooommm..  at that moment you would see a jolt on the motor and it tries to spin the opposite direction of the propeller. In this case the wires will not allow the motor to spin continiously so all you see is the sudden jolt... but imagine if the battery is struck on the motor casing itself... then the whole thing just spins.

-Ismail

Quote from: aforadi on June 12, 2009, 01:32:31 AM
Thanks a lot for that answer....Now consider a normal DC electric motor which has a positive and negative terminal...What is the framework for that? I have seen those small motors where you just connect it to a battery and the axle starts rotating. Is the frame work inside...If so then  how is the brushless motor different and how can I feel that torque as in what part of the motor feels that anti torque? Is it the outer body of the motor?

I apologize if my questions seem ambiguous and repetitive.

The word "framework" is a generalised term. For motors, the spinning part that is connected to the propeller is called rotor... and the stationary part that is connected to the plane/heli is called the stator. When rotor spins, stator will see an opposite torque effect.

For brushed motor, the stator is the outer shell of the motor. For brushless outrunners, the stator is the inner core which attaches to the aircraft.

Think of anti-torque as a recoil of a gun. When you fire the gun, the bullet moves forward but you get a nasty recoil from the gun's butt!

Thank you all for the answers..They definitely cleared my doubts.

Can I get an inexpensive (low on budget) 2 or 3 channel radio system with the receiver (AM or FM)?
I am not too particular about the range. I am fine with small range also. No particular choice for single or dual conversion also.  I checked out the Indian sites. They don't have a cheap one. I was looking for under Rs 3000(Tx and Rx).

I might have missed something. Can you guys help me out in finding such a system? 

Hey ,
I dont think a 2-3 ch Tx would be suitable for a VTOL , I think Mr.Sai has a great 6ch Radio for a mouth watering price of about 3500-4000/- , but if you are intreasted in a Tx , I have 4ch Tx on 27mhz , if you are intreasted PM me .
happy flying ,
sahevaan

Subbu -

I was looking at the RC Powers videos, and saw that they are also into VTOL stuff.  These videos may be useful to you.

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