My first design build: Indoor gyro - RC Groups
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Dec 20, 2005, 01:04 AM
dougmontgomery's Avatar
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My first design build: Indoor gyro

I will wait for a name somewhere down the road when I actually get it to work.

anybody offering any advice is welcomed- This is what I have so far. I will post pictures and progress and I will probably need some help down the line with flapping. I really liked Jochens rotor head pivot shaft.

I plan on using 3) 169mmx1.5" handsanded, weighted balsa blades.
10 g fuse shown with cf landing gear 5" blanks only
23 g feigao direct drive 4100 kv
18 g polyquest battery
38 g 3 servos, 2 main wheels,1 tailwheel,rotor shaft and bearings

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Dec 20, 2005, 05:57 AM
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JochenK's Avatar

cool! From my experience with Depron I'd add two more strips of cf, though, both parallel to the tail boom. One at the top of the mast connecting the two vertical cf strips -the Depron is likely to rip at that point - and one to reinforce the motor suspension. this one should go from the first vertical cf strip to the end of the little boom sticking out of the mast.

Do go on, Jochen
Dec 21, 2005, 12:34 AM
dougmontgomery's Avatar

Landing gear, Head assembly

Jochen, Thanks for the support, I hope you will be able to assist me with this style head and direct control later on down the line. I decided not to use simple head assy. due to the fact I didn't have those parts. I will in the future to save weight.

I will work on the blades and head support disc the rest of the week.

as shown weight:
.8 oz
24 grams
Dec 21, 2005, 07:13 AM
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JochenK's Avatar

I've got another, more conventional head assemly for you. It looks smaller than yours, but may not be lighter.

What you need is a rotor axle, three wheel collars, a cf control rod fitting into the wheel collars, a cf control arm, two normal screws with the same thread as the grub screws of the wheel collars, and two ball bearings to take these screws.

Drill a hole opposite the existing hole into one wheel collar and tap a thread of the same size as the original one in this hole. Repeat this procedure with a second wheel collar, but this time size the hole and thread to take the rotor axle. Tap a corresponding thread on the lower end of the rotor axle. Screw the rotor axle into the wheel collar. Glue the control arm onto one end of the control rod.

Now slip the thre wheel collars on the control rod as shown in the drawing and tighten the grub screws of the outer wheel collars. The rotor axle should be perpendicular to the control arm. Insert the ball bearings into their holes in the support structure. Put the control arm between the ball bearings and fix the middle wheel collar with two screws. The control rod end with the control arm should be able to move up and down and turn freely.

If you use steel wheel collars and screws, I estimate the total weight of the assembly without support to be about 9 g. If you take aluminium wheel collars - the heli people seem to use them - and two plastic screws, the weight should go down to 4 g.

Dec 21, 2005, 07:42 AM
dougmontgomery's Avatar
Jochenk, Your head assy on your 7 ounce gyro seems a lot simpler. Is it lighter? If mine does not work I would like to try that one. I also have concerns about on this design, is the angle at which I want to connect my control linkages. Does it need to be at 90 degrees to the pivot point?
Second, how did you make your bearing hub on the gf. What material?

After looking at it closer, I do like it but how would I attach my rotor shaft? And where?
Last edited by dougmontgomery; Dec 21, 2005 at 07:49 AM. Reason: add
Dec 21, 2005, 01:31 PM
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JochenK's Avatar

yes the Micromum head assembly is lighter. Without the rotor and the push rod end piece I use as a support it's about 3 g. But it's a bit difficult to attach to your mast. For the lower end of the shaft you'd have to use a cf rod about 50 mm long and push it into the Depron from above, which seems a bit tricky. You even may have to reinforce the Depron with little bits of plywood at the bottom end of this rod.

The angle of the push rods is a bit awkward. But as this is a very light gyro I think it will work. Just keep the servo arms parallel with the plate holding the rotor shaft. And, when dimensioning the push rods, keep in mind that due to the rotor drag you've got a push - push situation for the rods.

The hubs holding the gf hinge sheet are some old disk type servo arms I had lying around. I've attached a cross-sectional view of the Micromum head for clarity.

Dec 21, 2005, 09:31 PM
dougmontgomery's Avatar

blade build

Here are the blades process.

Cut templates of the Clark Y out of 1/16th ply and take a marker to the top and the out sides of templates. Saturate in thin CA.

Cut out 3/8" balsa stock proper length and width of airfoil templates.

3m Glue templates onto sides of stock cut.

I Bench top sanded two at a time to making a total length of 338mm.

Sand both together initially,
then I split them into the two halves of 169mm.

Re-attached templates to the shorter airfoils for more precise sanding.

slotted blades for 41mm of weight(1oz)

covered and balanced

Blanks cut- 3g
blade reinforcements and weighted- 4g
leading edge /bottom covered for protection/less drag- 6g
Last edited by dougmontgomery; Dec 22, 2005 at 03:11 AM. Reason: add more
Dec 21, 2005, 09:38 PM
dougmontgomery's Avatar

Landing gear and gyro hub installed

I will defrinitely be using Jochens Micromum head next. There is way to much tension on this style in roll.
Ran it up in front of the fan but I believe it needs some tip weights, or possibly less flapping. It tends to lean on its right wheel upon spin-up.

I will be removing the blades to weight and balance. I just wanted to see how it looked.

I will be off work tomorrow so I should be able to complete it.

Weight as shown is:

1.9 oz.
or 54 grams

JochenK, I really appreciate your layouts. You do really nice work. I wish I had that kind of knowledge.Thanks for your time.
Dec 22, 2005, 03:20 AM
dougmontgomery's Avatar


Did some fan run ups and seems to be smooth and throws seem to be alright too. With this set-Do I also need some right down aileron?

Still concerned with this method of flapping....I'm not sure what is recommended as minimum and maximum.
What are signs to look for an gym run-up?

weight without battery is 4.5 oz
127 g

with kokam 3 cell 340 is 5.8 oz

Dec 22, 2005, 04:17 AM
Registered User
JochenK's Avatar

look at the attachment. This may be a possible solution for your push rod angle problems. The upper drawing shows a rough sketch of your existing head, the lower drawing shows the modified head. Just glue two strips of cf or something to the movable part of the hinge and move the servo connections to those strips.

One more thing. When using this delta three head, the blades should not only flap up but also forward. This is usually obtained by cutting the inner ends of the blades at an angle of about 15, making the leading edge shorter than the trailing edge. You might have to do that for reasons of stability. Mickey explained this in post #21 of

Right down aileron: generally you do need some, depending on the torque of your motor. This Feigao uses a very small prop, so there's not much torque involved. My guess is about 2 to 3 to the right, but you'll have to test this out - the hard way.

Don't do any gym run-ups, go outside when there is enough wind to spin up the rotor while you're standing still. Hold the gyro loosely behind the upper end of the landing gear. Feel the lift of the rotor. Does it seem enough? Turn on the motor. Does it give enough thrust to move the gyro forward? Does the gyro seem stable, or does it want to tilt over to one side? If so, adjust the aileron. If all the answers are yes, prepare your mind for the first flight.

Dec 22, 2005, 06:36 AM
I'm not as bad as they say.
This is all interesting. Just letting you know that someone else is reading.

I'd suggest covering the blades completely. The rough upper surface contributes to reducing the L/D significantly at this blade size.

Latest blog entry: AIrcraft I've built.
Dec 22, 2005, 12:55 PM
dougmontgomery's Avatar
Jochenk, I don't think I am having a problem now with pitching the blades.

I am still having the rotor torque and vibration, I initially used two lids cut out for a rotor disc platform because I do not have any g10. It would not flap enough. I took one out and the blades sag to much and takes a lot of power get them to start working. These also do not provide good support for my shims.

Next try will be to cut a rotor disc out of some 1/32 plywood and then if that doesn't work I will try a second one.

I am going to match the micromums scale rotor disc for the 1.5 blades.
Don't give up on me.

Thanks Mickey for looking in. I should learn from you....Read lots build less. Doug(I still have lot of catching up to do.)
Dec 22, 2005, 02:58 PM
Registered User
JochenK's Avatar

this is a bit strange. Up to now I've never had any vibration problems with three-bladed rotors. Have you balanced the rotor? Have you cut off the inner blade ends at a 15 angle?

Concerning the rotor disk material: the 0.5 mm gf sheet I used is pretty stiff. When you look at the pictures of the Micrmum you'll see that there's practically no sag in the blades. So I don't really think your two-lid solution is causing this problem. But it's hard to tell from several thousand miles away.

Dec 22, 2005, 09:07 PM
dougmontgomery's Avatar
Jochen, No I have not balanced the rotor by itself. The blades all have been balanced. I don't think I should of added the tip weight. That cost me 2 grams and I think it is making it harder for the rotors to flap. I did cut the inner blades the 15 degrees to the leading edge but I had mitered the back edge before all of this possibly being detrimental to the affect. I still have my torque issue, but I think with the blades being 6.66 inches there is not enough leverage to flap with the tip weight I added.

Dec 23, 2005, 12:03 PM
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JochenK's Avatar

I think you should at lest check the balancing of the rotor by tilting the gyro over on its side and watching, if one of the blades drops down rather fast.

With a small rotor like yours you are likely to need those tip weights. A small rotor has no great centrifugal force pulling on the blades and is prone to excessive coning. I found that out, when during the preliminary test of the rotor I used some soft plastic hinge material. It worked well enough but did not look good and I went over to a 0.5 mm gf sheet without great discussion. That's why I consider the two-lid solution as probably the right decision.

Anyway, how did you come to the conclusion that you don't have enough flapping? I've never really seen my blades flap when the rotor is up to speed. I just concluded that they have to be flapping because the gyro is flying without problems. What you might do is hold the rotor horizontally at the hub between thumb and forefinger and move it up and down about an inch at a rate of about two per second, meaning fast. If the ends of the blades take some time to follow the hub movement or even stand still, you're o.k. in my opininion.


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