Simple mechanism for a DC head - RC Groups
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Jul 14, 2005, 03:26 AM
Registered User
JochenK's Avatar

Simple mechanism for a DC head


Hi all,
here's a simple control mechanism for a DC head:
1. Take the drive shaft/cardan joint/wheel axle assembly from a 1:10
offroad car (fig. 1).
2. Cut off the ball of the drive shaft and tap the thread of the axle
as far as it will go (fig. 2).
3. For the rotor mast take a carbon fiber tube big enough to take the
drive shaft. Glue a short piece of aluminium tube over the end of the
cf tube to keep it from fraying. Drill a hole through the rotor mast for the grub
screws of a positioning ring that will fit over the aluminium tube
(fig. 3).
4. From a piece of PVC or other suitable material cut a control plate
as shown in fig. 4. Adjust the size of the control plate to give you
the desired amplitude for nick and roll. Drill a hole in the control
plate, so that it fits snugly over the rim of the cardan joint. Cover
the holes for the axle in the cardan joint with little pieces of
scotch tape and epoxy the control plate to the cardan joint.
5. Put a needle bearing and a thrust bearing over the axle and secure
with a self-locking nut. Insert the drive shaft into the rotor mast
and secure it with the grub screws of the positioning ring (fig. 5).
You may have to tape the drive shaft with a bit of scotch tape to get
a snug fit.
6. Postion the servos for nick and roll near and in front of the rotor
mast and connect the push rods (fig. 6). Use a delta or any other
suitable mixer in your Tx to distribute the nick and roll functions
to both servos.
7. Take off the needle bearing from the wheel axle and epoxy it into
the center of your dc rotor head. Reassemble and you're done. Figs. 7
and 8 show you my autogyro in full flight.
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Jul 14, 2005, 07:07 AM
Phantom Mechanic
PhantomII's Avatar
Brilliant!!!!!
Jul 16, 2005, 07:18 AM
Registered User
Lovely creative work and nice presentation.

Would like to see some photos of the airframe, airframe details, weight & power, etc.......when you get chance.

David
Jul 17, 2005, 09:40 AM
Registered User
JochenK's Avatar
David,
here's a close-up of the gyro and a shot of the central part of the airframe.
The rotor mast is made of a cf tube with an outer diameter of 6 mm (approx. 1/4") and an inner diameter of 4 mm (approx. 1/6"). The support strut is a 4 mm cf rod. The more or less horizontal cf tubes have an outer diameter of 8 mm (approx. 1/3") and an inner diameter of 6 mm. The upper tube holds a 6 mm wooden rod for the motor support while the lower tube takes the 22.5" tail boom made of another 6 mm/4 mm cf tube. Where the mast and strut pass through the 8 mm tubes, these tubes are strengthened by short pieces of 6 mm/4 tubes placed inside the 8 mm tubes. All joints are taped with cf rovings. The lower ends of the mast and support strut are epoxied into a 2 mm (approx. 1/12") cf sheet that supports the battery and the landing gear.
The rotorhead is of the usual delta three type with 2" aerobalsa blades and a diameter of 37". Control is nick, roll and throttle, no rudder or elevator. The gyro has a total weight of 18.5 oz. and is powered by a Plettenberg Freestyle 24 with a 9x4.7 APC prop with a lipo 3s/910 mAh battery. Flight time is about 7 min.
I hope this answers most of your qiestions.
Jochen
Jul 17, 2005, 12:39 PM
Registered User
I admire your craftmanship Jochen.

Was also curious as to your mast angle. While a rudder servo would add weight, do you wish you had a rudder? And what is the Amp draw of the plettenberg?

Appreciate the detailed response. Thanks for converting the mm dimensions, but I'm ok with metric.

Haven't heard the work "nick" since reading Schluter helicopter instructions.

David
Jul 17, 2005, 12:43 PM
Registered User
Oh, and down thrust? Looks like very little, if any.

David
Jul 17, 2005, 02:38 PM
Registered User
JochenK's Avatar
I've used "nick" on purpose, to differentiate it from "elevator", which the gyro hasn't got. And, well, like Schlueter I'm a German. But if you know a better expression, please share it with me, I'm still learning (same with the "positioning rings" which I just picked out of a dictionary):
Angles. All angles I'll give you are referenced to the axle of the motor, so naturally there is no down thrust. The rotor mast is tilted 8° backward, the strut is tilted 8° forward, and the tail boom is pointing 6° upwards. The planes of the elevator and rudder fins are set to 0°. Hanging angle is -7° right now, but I think I'll change that to - 10° to get more stabilty when pulling full nick. To obtain a negative angle of incidence I've put a 40 mm wide and 3 mm high wedge below the rotor blades. The control plate has a maximum angle of 15° to each side for roll and a maximum angle of 10° backwards and forwards for nick. And I've mixed throttle onto roll, so at full throttle the control plate is tilted a further 7° to the right to compensate for motor torque.
According to my measurements, the Freestyle 24 draws 12.5 A at 11 V with the 9x4.7 APC spinning at about 8650/min.
Right now I'm not missing the rudder. When I feel up to it, I can bank the gyro up to 45°, pull nick to get it round the turn and give full throttle to keep the flight path level. Horizontal cruising needs a little less than half throttle.
At the moment I can't think of anything else to tell you.
Jochen
Jul 17, 2005, 05:17 PM
Registered User
imsofaman's Avatar
I have a question.....what type of axle/universal joint are you using? I am not into the truck and cars, it looks as if they don't come apart. If you stear me in the right direction...that would be great. I really like your concept!
Jul 18, 2005, 01:38 AM
Restricted User
StephanB's Avatar
Jochen,
it seems, that you are using an electronic gyro (the little box with the "fuzzy" on it)
Any details?

Grüsse
Stephan (D-65527) :-)
Jul 18, 2005, 02:02 AM
Registered User
JochenK's Avatar
Let me describe this as best as I can.
On the right of the very first picture is the axle part, on the left is the drive shaft. The inner end of the axle part is a sort of hemispherical bell, the inner end of the drive shaft is a ball, which resides in the hemispherical bell. This ball has a sort of slit going through its middle. On the outer rim of the bell are two holes, opposite each other. A steel pin goes through these holes and through the slit in the ball and keeps the two parts together. To prevent this pin from falling out, it is fixed in the slit of the ball with two grub screws. When you epoxy the control plate to the rim of the bell - don't forget the little pieces of schotch tape I mentioned -, it will automatically hold the pin in place and you won't be able to dismantle the joint any more. In fact, if you happen to glue the pin to the bell while epoxying the control plate, you can loosen the grub screws and the joint will work again. Please don't ask me how I come to know about this.
Hope this helps.
Jochen
Jul 18, 2005, 02:22 AM
Registered User
JochenK's Avatar
Stephan,
yes, it's a "wing gyro" from ACT. I use this gyroscope to stabilize the roll axle. It has two channels and is normally used to control the ailerons of a wing plane. It will not stabilize "common mode" signals going to both servos, like flaps or butterfly or in this case nick, but only "differential mode" signals - in this case roll. I found this gyroscope very useful when doing my first hand launches, although now that I've found the correct trim settings I can easily turn it off. It still helps in gusty winds.
Jochen (D-69126)
Jul 18, 2005, 02:44 AM
Restricted User
StephanB's Avatar
Jochen,
thanks for posting this pic. I damaged my new autogyro at maiden on saturday.
Was too slow against ground and my autogyro rolled over when turned into backwind.
When i saw yr. pic i was sure, that i will add an wing-gyro on roll for the next attempts.
Will make it easier to find correct trim-settings.
Stephan
Jul 18, 2005, 06:48 AM
Registered User
Quote:
Originally Posted by imsofaman
I have a question.....what type of axle/universal joint are you using? I am not into the truck and cars, it looks as if they don't come apart. If you stear me in the right direction...that would be great. I really like your concept!
Dave, if you have a Tower 2005 catalog, look at page 153, center column, MIP CVD Kits. Should get you started.

David
Jul 18, 2005, 07:10 AM
Registered User
Again Jochen, (your post 7) great details.

Was curious about the Amp draw of the Freestyle 24 and it's ability to provide power for the 18.5 ounces of autogyro. I find the differences in model autogyro's mast angle, hang angle, down thrust, etc, fascinating. Thanks for sharing your design and talent.

David
Jul 18, 2005, 07:16 AM
Registered User
JochenK's Avatar
David,
there's one detail I forgot to mention. The vertical cg is practically in line with the motor axle. I think that's why I haven't need downthrust up to now.
Jochen


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