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agpraneet
09-16-2009, 03:22 PM
Well the topic may sound silly
What i was doing was to try and make a light motor to lift on its own just like a rc helicopter.

Can it be done?? Can a motor have a favourable weight to power ratio??

I tried it on a motor with a rotor made of cardboard but it failed horribly

pkshima
09-16-2009, 05:45 PM
Surely there would be such motors else there would be no rc helicopters.

The other most important factor besides weight is of course the propelor design. A cardboard thing will never fly.

agpraneet
09-16-2009, 09:45 PM
What rotor design should be used for the purpose?? And what material??

I seem to have a motor which is not rated but seems to have considerable rpm

it's weight is also fine

Any suggestions??

docel
09-17-2009, 03:58 PM
A motor cannot 'take-off' on its own. Newtons III law will make the motor spin in the opposite direction. Also, the Gyroscopic precession will make the horizontal motor vertical
The body of aircraft and Helis are designed to stabilise ( overcome these effects)) and assist lift in 1 direction only.

The weight of the motor has nothing to do with lift.

agpraneet
09-17-2009, 11:55 PM
@docel
Thanks for the input
I was looking for something like this
I had a feeling that the body must also be aerodynamically apt

But I also thought that even the most simplistic structure generate lift

I am reminded of very simple toys in which a rotor rotates and it goes up for a while. How do we explain them???

ice
09-19-2009, 06:27 AM
Praneet,
If you are really want to do something like a heli, the easiest way is to make a quadcopter. There are a few good projects out there.[ x-ufo, aeroquad, quadpowered]
These forums are good:
http://www.rcgroups.com/multi-rotor-helis-200/?s=12471a72f8d03b09003b2dc3df7ae253

search for "quadcopter"

The way these work is by using brushless motors which is very well suited for such an application. Since the motors do not have a brush like a dc motor, they have very less wear and can attain much higher speeds.

However, there is some cost involved. The way brushless motors are handled is very different from dc motors. But if you are interested in one, the heli forum would be your first place to start.

Here is a video, just to illustrate it to you:[watch 1:50 onwards]
http://www.youtube.com/watch?v=qI5po3O3Mi8

agpraneet
09-19-2009, 01:54 PM
@ice
Thanks a lot for the links
But considering my level of knowledge in this field, i wanted to start from basics and hence try and understand how a simple motor and rotor duo can be used to generate some amount of lift and then proceed with the helicopter

Nonetheless I will browse the links provided

Also, Do you have any experience in making such a thing?? Or any one else has some exp.??

Also its just for learning purpose and has no associated time limit. So i dont want to spend much money unless i have something concrete on my hands

ice
09-19-2009, 06:48 PM
Also, Do you have any experience in making such a thing?? Or any one else has some exp.??
I'm making one. It's a long term project, so it's going to take some time. I'm still researching stuff.



Also its just for learning purpose and has no associated time limit. So i dont want to spend much money unless i have something concrete on my hands
..which is good. I chose it since it was possible for me. Took quiet a while for me to decide.

It's a bit tough if you do not have much experience. But keep reading. Take it up if you think you can pull it off and have the necessary budget.

agpraneet
09-20-2009, 07:33 PM
I just bought a chinese helicopter for the body
With everything on, it weighs 300 gm

I thing by removing the non essentials, the weight can e reduced to 15o0gm without the motor

As far as the battery is concerned, i plan to use an adaptor presently and if successful, then go for battery

Would the helicopter be able to lift by a normal dc motor??

ice
09-20-2009, 08:31 PM
Try CD ROM motors. They are brushless and I guess also easily available.

http://www.google.com/search?hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&hs=PKO&q=cd+motor+helicopter&btnG=Search

http://www.angelfire.com/blues/heli_project/

agpraneet
09-22-2009, 12:38 AM
How much rpm do the cd rom motors provide??
Also, how much rpm is necessary to generate necessary lift??

As there are Rs 1500 helicopters available in the market, it shouldnt be that difficult to generate lift, should it??

ice
09-22-2009, 03:20 AM
If those are heli's like Airhogs, then they just use a very tiny DC motor coupled with a large reverse gear ratio- meaning 1 turn of the motor results in several turns of the propeller. They also have a foam body and a stabilizer propeller at the rear.

Again if you search rcgroups in the multi-rotor forum forum, you will get info for CD-ROM motors.

docel
09-25-2009, 02:20 PM
Moving bodies are are weird; rotating bodies are absolute Magic. Not for nothing that we have Statics and Dynamics as separate topics of Motion Physics.

The behavior of a body is governed by forces acting on them. The question is whether it is moved by something or it moves by itself.
The following is a jist of motion facts relevant to this discussion:

1. A Rotating body is not governed completely by Gravity.
If you rotate a sphere at some angular velocity, it will move away from the gravitational pull ie., it is now governed by centrifugal force which will try to negate gravity. This is how the planets and other stuff stay up in space.

2. If the body is rotated by , say a motor, Newtons III Law will show up by rotating the body and the Motor in opposite directions.
When a motor drives a body, for all practical and sane purposes, one of it should be fixed. Fix the motor, the body will turn. fix the body, the motor will turn. Suspend the motor by its wire, it will lift itself with the body that it is turning and the entire system will rotate in the horizontal plane around the wire. This is the Gyroscopic effect.

Now, consider the body to be a Propeller.

The propeller is shaped so that it pushes the air as it rotates in a particular direction, when static ( it acts as a fan). If it is free , then the air remains static and the propeller will move, but in the opposite direction. It moves through the air in a helical, screw-type movement.
How much it moves depends upon the amount of air it can push per unit time. Simple design is to twist it at an angle; more the twist more the air pushed in time. At some RPM & degree of twist, it will over come gravity due to Newtons III Law.
The propeller can be designed to produce huge amounts of power with some trick engineering. These tricks use Bernoulli's principle, Coanda effect etc.,
Now the power delivered by the propeller is Thrust. It depends on speed.

Flight is a balance between different forces- Weight , momentum and thrust. These are aided by Aerodynamics and inertia for stability.

Your toy propeller flies because it is the only component that rotates. It generates lift due to its rotation and the shape of its blades. The thrust generated is quite high and makes it rise up quite fast.

prashant29
10-03-2009, 12:25 AM
hey ice i am building a quadcopter as my final yr BE project need some help frm u.....

prashant29
10-03-2009, 12:55 AM
can u plz tell me is it possible to design my own ESC?...coz i have budget of around rs10k....n if not CDROM motors; then other high rpm brushless cost abt RS1300 and i am designing my own transmitter and receiver circuit...

allbits
10-03-2009, 10:52 PM
it is possible to make an ESC, buti would recommend you buy one, it will be cheaper and consume less footprint, and weigh much less than when you make it.

http://indianhobbies.com/shop/index.php?main_page=index&cPath=8

the link will give you an idea of how much things cost. Its just for an idea, and not a recommendation, as i have not purchased anything from them other than a couple of BLDCs. So I do not know how these ESCs perform.

prashant29
10-04-2009, 12:54 AM
thnx for replaying buddy....these indianhobby guys have shop in mumbai..i have visited them but at tht time they wr nt having enough components so am planning to visit thm again......where can i get brushless outrunners with speed sensors(hall sensors in built)?....is every outrunner is sensored?...and is thr any diff ESCs r available for sensored ones?....n can i interface a wired joystick wid ASK transmitter....as i said i am building my own wireless controller for quadcopter...plz help

allbits
10-04-2009, 10:17 AM
Its better to go sensorless. I have made speed control for both types, and thats why i said its better you buy them if you want to put them in something that goes up in the air.

Sensorless is better. less wires and less mess. There ARE speed controllers available for sensored ones, but the ones i have and know about are heavy, and will not suit your purpose. and there is this site i browsed http://rotor.co.in/ ., i have not purchased anything from them, but i thought it might be useful for you.

:idea:
ask/PM docel. He will be able to guide you well.