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prerotator

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Old 03-07-2007, 03:16 PM
  #1  
ciervapilot
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Default prerotator

I’ve got the idea to add a prerotator to my DC autogyro (see pics) to achieve a very short take off running even in no wind conditions.
In my opinion, there are two solutions:
1) A mechanical prerotator (see pics)
A servo controlled clutch is driven from the engine shaft by reduction gears. Bevel gears lead the motion upwards. Two universal joint couple the bevel gears with the reduction gears in the rotor head by a length compensating shaft. The rotor axis is driven by a one way bearing.
2) An electric prerotator (see pics)
An electric motor is coupled by two universal joints and a length compensating shaft to the reduction gears in the rotor head.

What do you think of these ideas? Which one is more realistic?
Problems: What kind of clutch to use? Reduction ratio? What electric motor to use? Change the receiver battery to lipoly battery (7,2 V) to drive the motor and reduce the voltage to 5 V for the receiver?
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Old 03-07-2007, 03:25 PM
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mnowell129
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Default RE: prerotator

I went the simple route and just put the electric motor right on the head.
After going through all the options with clutch, gears, extra servo for the clutch,
etc., the lightest solution turned out to be a small brushed motor up top.
Lots of current gyrocopters have the pre-rotator on the head, generally a hydraulic
motor where the pump is on the main motor.
mickey
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Old 03-07-2007, 03:35 PM
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Default RE: prerotator

Check this pic out!

Wahid
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Old 03-07-2007, 06:51 PM
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Default RE: prerotator

Hi Wahid,

are you using a freewheel head or is the motor driven when not under power?

Regards.

Karl.
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Old 03-07-2007, 07:30 PM
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Default RE: prerotator

This pre-rotator is my mine. It was submitted by Emilio Cabezas. See the link below:

http://www.rcuniverse.com/forum/m_47...tm.htm#4744190
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Old 03-08-2007, 07:57 PM
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Default RE: prerotator

Ah! eye fort eyed ceen the foto befour. [sm=wink_smile.gif]
I contacted Emilio concerning the unit but he couldn't help as as it's not his contraption. But out of curiosity, if there is no freewheel wouldn't the friction be too much for the rotor? Or does one have to provide a larger rotor to overcome the problem?
Regards. Karl.
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Old 03-12-2007, 02:39 PM
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Default RE: prerotator

I am also interested about the free wheel issue? The electric motor slows the rotor down without free wheel.

I have sometimes thought a brake for the rotor would be more useful than prerotator. After you land in windy conditions, rotating rotor is vulnerable if the gyro tips over by the wind.
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Old 03-14-2007, 12:46 PM
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Default RE: prerotator

Hi,
of course there must be fitted a freewheel between the upper gear and the rotor axis! But this was not my question.
What do you think of the mechanic drive from the ic engine?
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Old 03-14-2007, 04:32 PM
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Default RE: prerotator


What do you think of the mechanic drive from the ic engine?
Complicated, heavy, small benetifs for model airplanes but very cool

We must keep in mind that most of us do these (autogyros) because we love to do strange and interesting mechanical things. Not because there would be much use of it in our life
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Old 03-14-2007, 05:52 PM
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Default RE: prerotator

Hi,

What is the weather like in Finland now?

Phil
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Old 03-15-2007, 04:53 AM
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Default RE: prerotator

The weather is here getting wet already. I still hope to have ice on the river for next 4 weeks so I can fly my models there. Here is a picture from my backyard today how does it look.
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Old 03-15-2007, 05:49 AM
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Default RE: prerotator

I would totally forget the idea of using universal joints. Not only they will add considerable weight, but a lot of complexity to get them to operate right and they are quite sensitive. Big gyros behave differently (that's why 2 blades work fine, but on models they are tricky to trim), not because different laws apply to them, but because those laws depend on the size of the object.
And, after all, autogiros are about simplicity. I also believe that the simplest solution is often the best one.

The engine starter is the best aproach IMHO. If you can find a good combination of motor and reduction, which is the "difficult" part, and mount it right on the rotor (the pic shows it very clearly). On top of that, a brushed motor and gears won't cost you much.

I also have a very promising idea in mind for my ECDC (great flyer, by the way!!! ), but I want to try if first. It's very simple and reliable, or so it seems in theory. In fact, probably someone has already tried it.

BTW, have you tried Aerobalsa blades for the model? I'm quite tired of making my own blades...
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Old 03-15-2007, 02:45 PM
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Default RE: prerotator

Hi JCaste!

"I also have a very promising idea in mind for my ECDC (great flyer, by the way!!! ), but I want to try if first. It's very simple and reliable, or so it seems in theory. In fact, probably someone has already tried it."


What is this simple and reliable idea that you have in mind? Don't tantalize us!
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Old 03-15-2007, 05:06 PM
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Default RE: prerotator

Ciervapilot, as I said I would like to try it first, and then I won't have any problem to post my discoverings. It's not a revolutionary discovery, just a stupid and simple gadget to give that initial spin, but I want to know if I can do it. So simple that can be cheap, light and easy to use. Really, it's nothing special, but could be of some use.
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Old 03-15-2007, 05:28 PM
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Default RE: prerotator

A rubberband that twists around the mast and falls off after it doesn't have any tension ? That would be one cheap and simple way to do it. If that is not your solution for the pre rotation, then I will try that one. I think I must start thinking about it if it would work and how to do the details
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Old 03-15-2007, 05:51 PM
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Default RE: prerotator

Hi,

I had a large dual rotor that had a small cylinder attached to the bottom of the rotor blades and I would wind a few feet of string around the cylinder. I would stake the ends of the string to the ground and when I would take off the string would spin the rotors. About 5 feet and I was flying.

Phil
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Old 03-15-2007, 05:53 PM
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Default RE: prerotator

Oh!! I like the pictue from Finland. I'm originally from Vermont and it looks just like winter there.

Phil
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