Electric Pre-Rotator

@Jazzenjohn My starter motor, prerotator is mounted onto the rotor head, therefore, with my setup the torque is surely between the starter motor mounting and the rotor head, completely apart from the mast ... I think.
 

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Thorically supercapacitors have a 10W/hour capacity per kilo, if you need 6000W during one minute (pre-spinning time), so you would need a a 100Wh supercapacitor pack to pre-spinn one minute at 6000w,
The energy in a capacitor is W*h = 0.5 C * V ^ 2
Therefore, if your controller operates between Vmax and 3/4 Vmax, the usable energy is only .43 times 10W*h per kg.
 
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My starter motor, prerotator is mounted onto the rotor head, therefore, with my setup the torque is surely between the starter motor mounting and the rotor head, completely apart from the mast ... I think.
The reaction torque of the pre-rotation rests on the ground. Consequently, if the engine is at the top of the mast, the reaction torque can only descend through the mast.
 
@Jean Claude Thank you, got it now, whilst the starter turns the rotors the starter itself has to be "held in place" and that is done at ground level, I therefore assume, just for arguments sake, if the gyro was sat on a turntable with zero friction that the whole gyro would turn in an opposite direction with a force equal to the starter.

When I trained, it was in a MTO, the force on the joystick (manche) was at the start of the pre-rotation very marked and had a tendancy to pull the stick to one side until the rrpm had begun to build up, I am right that it is this initial prerotation period that represents the greatest force against the mast.
 
The torque on the mast is equal and opposite to that of the prelauncher.Even if this torque is constant from 0 rotor rpm to the maximum, the rpm increases according to this curve. Rapidly at the beginning and very slowly at the end.

Side force on the stick of MTO is certainly due to the angle of the shaft on the Cardan's joint. An electric pre-launcher attached to the plate does not produce transverse torque in the stick
Sans titre.png
 
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Thank you Jean Claude for your very clear explanation, important for an old fart like me to comprehend, helped enormously with your diagrams, what does the blue line define?

phil (de fer)
 
Phil, Blue line shows the times of natural decay of rrpm if the prelauncher is stopped
 
Please post a close-up of that rotorhead and drive motor.
Spooled up pretty quick WITHOUT the rotor; can't wait to see what it does WITH the rotor attached.
Battery-powered?
Very nice.
Brian
 
Ah yep I was about to watch that tonight.
On your rotor head why do you have 3 gears between the pre rotator shaft and the Bendix? You have the same direction rotation and what appears to be the same speed output as the input, maybe hard to tell from the pictures though.

wolfy
 
@DarDow101 post 161 do you have any further data on the pre-rotator, motor and gearing? On the video they suggest reaching 300rrpm(y)
 
You may want to reconsider your reduction ratio.
 
From your vantage point what do you estimate the ratio is and what would you estimate the ratio should be?
Your current reduction is 12-1 like Jeff says. 108/9=12. Pretty much the same as every Wunderlich ring gear/ Bendix system out there. As far as your system, It appears to me you are using an Ampflow motor A28-400 and you've said previously you are using it at 36 volts. There are a few variations of the motor, so I'm assuming you are using the most common. At 36 volts I'd experiment with ratios between 2.5-1 and 3.5-1 . The 3.5-1 might limit max RRPM in favor of a faster spin-up time and lower demand on the motor and batteries. 2.5-1 might get a bit higher max RRPM with the trade-off of higher current demand, especially when starting up and running it at full blast. Running it as is will put a huge demand on your batteries and wiring. Be careful when you start experimenting as you have a very powerful system. The RPM's you are seeing now will not be possible with blades on.
Are you using a servo tester for control?
 
The easiest way to add some reduction would be with a chain and sprocket between the motor and the shaft going to the head. Chain and sprockets are very inexpensive and allow for fast and easy sprocket changes to try out different ratios. You can get the sprockets at Surplus Center for a couple dollars already bored out with the appropriate key. #35 chain is what most people use. It is no problem using a chain in this situation because it doesn't run in flight. Make a plate that bolts to the end of the motor and has a bearing for the driven sprocket. You'll just have to work out how to attach the driven sprocket to the shaft. You can see how Mike is doing it in this pic. He used a piece of angle instead of a flat plate bolted to the motor to mount his speed control.
 

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It would seem that Wing Commander Wallis incorporated a Sturmey Archer 3 speed gearing in his pre rotation set up, but very little is published about this.

This was in post No 8 by Dinoa on this thread.

In the PDF diagram I suspect the gearing in question may be No 35 which is described as a 'commercial epicyclic gearbox'.

Wallis prerotator.png

wallis-gyro4-flight-mag-pdf.1036898

And how it works,

 
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@ Leigh, I've heard Wing Commander Wallis used a 3 speed hub for a reduction on some of his gyros. I don't see it as useful in this case as it would weigh and cost more, and be more difficult to set up, but I can see it being very useful in a different application.

@ Dar, Mike is Mike Vadney, he doesn't get on the forum much. I'll ask him for additional pics if you want. Adding a chain and sprocket shouldn't cost very much at all. Be very cautious testing, it will cost less to add that than to replace batteries or other electrical components...
 
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