200g/7oz. dc head pusher - the Micromum - Page 3 - RC Groups
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Mar 05, 2006, 06:33 PM
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JochenK's Avatar
Kevin,

that epoxy glue that keeps breaking loose in the wheel collar: I think I should have been a bit more elaborate on that from the start. Which is not easy, when you're living in different markets. I knew that was a critical connection and automatically used something called "UHU Plus endfest 300", something you most probably never heard of before and never will hear of again. This is noting special, just a normal high end epoxy glue. If you follow this link
http://www.uhu.de/_uk/indexx.html
and then click on "our adhesives", "2-component adhesives", then on the green tubes and finally on "instructions for use" you can at least have a look at the specifications of this glue. I had a quick look at the Loctite website and I think that Loctite Hysol 9463 A&B or something equivalent should do the trick for you.

If you are looking for something more simple if a bit heavier, try the arrangement in the attachment. Cut out this inverted U from PVC or similar. The PVC should at least be 4 mm or 3/16" thick. Drill a hole to take the wheel collar and then drill a 3 mm hole for the grub screw through the top of the inverted U. Epoxy the wheel collar in place and add the grub screw. Attach your push rods to the flat surfaces at the lower end of the inverted U with ball links. I use both arrangements on my two Micromums with equal success.

Now for the unwanted flex in your system. Three possibilities: the servo arm you are using is not stiff enough, the joint between the servo arm and the heat shrink tubes is too flexible, and the thickness of the heat shrink tubes you used is too much to give you a stiff connection between the servo arm and the cf axle.

I don't know what kind of material your servo arm is made of. It looks metallic and shiny and if it is aluminium, that's o.k. If it's made of plastic, replace it with something more serious.

As for the joint between the servo arm and the heat shrink tubes, I don't think it's such a good idea to glue the servo arm directly onto the heat shrink tubes. If you use a wheel collar at that point, you can make that connection mechanically rigid just by tightening the grub screw. The height of the wheel collar, which is about four times bigger than that of the servo arm, gives you additional leverage and keeps the flex down.

At last the heat shrink tubes. The inner one I used had an ID of just over 2 mm and an OD of 2.4 mm. The outer tube had an ID of 2.5 mm and an OD of 2.9 mm. When shrunk, the OD of both tubes was about 2.8 mm, which gave a good fit for a 3 mm wheel collar. If you have access to these kind of heat shrink tubes, you're o.k. If you don't, then use one heat shrink tube with a wall twice as thick and an OD of about 3.2 mm. This shrinks down to just under 3 mm OD. In both cases you have a material thickness of 0.5 mm, which is thick enough to hold the weight of the gyro and thin enough to give a stiff connection between the cf axle and the wheel collar.

If you can get that unwanted flex out of your system by these means, your control response should be much better. A gyrocopter is no 3D foamy, but I'd describe the response I've got as agile.

I hope that I've answered your questions satisfactorily, if not, don't hesitate to ask again.


Mario,

I've never tried to move the control to the rear of the rotor, but the push rods I use on both my Micromums are just 1.5 mm cf rods and I think they'd definitely fail if there was any push on them.


Jochen
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Mar 06, 2006, 07:04 PM
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JochenK's Avatar
Kevin,

Seems I've missed one of your posts.

I'm using servos called "Atom Mini Blue" (6 g, metal gears) and I think any servo with metal gears and a weight of about 10 g will do the job.

My blades are unleaded and as straight as I can get them.

Steerable tail wheel: I just don't know. The only ROGs I did up to now were with skis off the snow. And my tail ski was not steerable.

Jochen
Mar 07, 2006, 08:24 PM
Registered User
Thanks for the advice guys. I'm going to wait for my new blades to arrive and try again with a stiffer head using the PVC method. Just to make sure I understand, I drill a hole in the PVC and press in a wheel collar, then glue it in place. Then drill out a hole in the back side of the PVC to the wheel collar to put the grub screw in. Maybe not in exactly that order, but is that the gist of it?

Also, I can't seem to find a 10g metal gear servo in America. I was using hitech HS-55. Evertime the blades would strike the ground it wouldn't strip the gears, it would strip the motor. After seven of them, I ready to try something else.

Thanks again for your time. I'm determined to get this to work, last case If all else fails I'll buy Mickey's Begi kit.

Kevin
Mar 10, 2006, 10:21 AM
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JochenK's Avatar
Kevin,

I may have something for you. I went to a modelers fair in our area and, amonst other things, bought some servos: Dymond DS 62 MG. Digital, metal gear, 7 g, four servos for just less than $80. And while I was at it, I asked the german distributor why it's possible to buy these servos over here, but not in the US. He told me that the product spectrum of Dymond USA was a bit different from that of Dymond Europe. But, he said, if you were to contact Dymond USA (www.rc-dymond.com), they should be able to order these servos from Dymond Europe and supply them to you. At what cost I don't know.

Maybe it's worth a try,

Jochen
Mar 23, 2006, 07:40 PM
Registered User
Well, I've been looking now for almost 2 weeks and I can't find an 8g metal gear servo in the states. The lightest I've found is about 18g, it's Blue Bird and very expensive. I emailed Dymond and the ones they sell over here aren't metal gear and they can't import them because of small differences in the electronics. So do you think if I don't crash my regular servos might hold up better? I might give it a try anyway. Thanks,

Kevin
Mar 23, 2006, 08:30 PM
I'm not as bad as they say.
Quote:
Originally Posted by kp00rs
Well, I've been looking now for almost 2 weeks and I can't find an 8g metal gear servo in the states. The lightest I've found is about 18g, it's Blue Bird and very expensive. I emailed Dymond and the ones they sell over here aren't metal gear and they can't import them because of small differences in the electronics. So do you think if I don't crash my regular servos might hold up better? I might give it a try anyway. Thanks,

Kevin
http://www.allerc.com/product_info.p...oducts_id=2118

w-092MB, 9.2 gram, metal gear, $23

Also metal gear:
http://www.allerc.com/product_info.p...oducts_id=1813
10 gram, $25



mickey
Latest blog entry: AIrcraft I've built.
Mar 24, 2006, 07:28 PM
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Thanks Mickey, I guess I didn't look hard enough. Do you know anything about either one of these servos? I'll see if I can't find some reviews if not. I might be ordering one of your Begi kits pretty soon. Although I would still like to be able to say that I built a gyro from scratch. Thanks again.

Kevin
Mar 28, 2006, 10:01 AM
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JochenK's Avatar
Here - at long last - is a video of the Micromum v2 (without rudder) in flight:

https://www.rcgroups.com/forums/showthread.php?t=497857

Have fun,

Jochen
Apr 01, 2006, 10:09 PM
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imsofaman's Avatar
Jochen......nice flight! I really like your simple but effective design! Sometimes simplicity is best.

Dave
Apr 03, 2006, 04:20 AM
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JochenK's Avatar
Thank you, Dave. I like simple, especially if it saves work.

For all those of you that aren't comfortable with the idea of having a heat shrink tube pivot hinge, here's something more sophisticated. As there' not much work involved, you might even call it simple..

For this joint you'll need:
1 TopCad universal joint for a Team Associated RC-18T, part # 15208, see here:
http://www.rcmart.com/catalog/produc...0a5624152f281a
(the part number seems to be the same worldwide, the letter at the end is denoting the color)
1 piece of 3 mm PVC or similar, about 45 x 25 mm or 1 3/4" x 1"
1 pair of ball links
2 ball bearings ID 3mm, OD 6 mm, see here:
http://www.icare-rc.com/rotorshape_pricelist.htm, part # GL004
1 self-locking nut, M3
1 spacer, see text below

If you want to build a new rotor hub as well, you'll need three more things:
2 six-armed servo levers, see here:
http://www.multiplexusa.com/MPX_Cat_USA_2005WEB.pdf
(goto the last page of the catalogue and look for part # M85203, european part # is just 85203)
1 piece of 0.5 mm gf sheet, about 110 x 100 mm or 4 1/2" x 4"
3 screws with nuts, M2 x 10 mm


Take the universal joint and cut the drive shaft to a length of 33 mm, measured from the rim of the bell of the joint. Slip one of the ball bearings over the wheel axle. If it doesn't slide over the non-threaded part of the axle, take some fine sanding paper and revome the black paint from the axle (picture 1).
Cut a control arm out of the PVC piece as shown in the first drawing. Drill a 4 mm hole to take the inner end of the wheel axle and mount the ball links at the ends of the arm (picture 2). Slip the arm over the wheel axle and epoxy in place. Use some strong epoxy glue, not the 2 minute type (picture 3). That's your new pivot hinge.

Remove the original 2 mm cf rod from the push rod end piece and enlarge the hole to 3 mm. Enlarge the hole in the top of the rotor mast to 3 mm, too. Epoxy the drive shaft of the universal joint into the push rod end piece and put everything on top of the rotormast.

If you already have a rotor according to the Micromum plan, just take out the 2 mm ball bearings and replace them with the 3 mm ones. Slip the rotor over the wheel axle of the universal joint and secure with a self-locking nut. You may have to put a spacer between the top of the upper ball bearing and the nut, to keep the nut from touching the servo arm. Use some 3mm washers, if you can find washers the are small enough, or use a piece of brass tube (ID 3 mm, OD 4 mm), or simply use a piece of fuel tube.

If you want to build a new rotor hub as well, have a look at the second drawing. I've switched from the original disk type servo arms to the six-pointed star type, because these levers have all the holes you need predrilled, you only need to enlarge them. Take those six-armed servo levers and trim off the little rim on the top side. Remove the teeth from the hole on the bottom side with a 6 mm drill or preferably a 6 mm moulding cutter with a flat cutting surface. Insert the ball bearings. Enlarge the three holes in the servo arms that are marked in the drawing to 2 mm (picture 4). Print out the .pdf-File without adjusting the size of the printout and use the printout as a template for the cutting of the 0.5 mm gf delta3 hinge. Drill all holes with a 2 mm drill, the enlarge the central hole to 3.5 mm. Put the sheet between the sero arms and use the 2 mm screws to hold everything together. Slip the hub on the pivot joint and fasten as mentioned above.

Picture 5 shows you my Micromum v2 equipped with the new hinge. Right now I've got three different types of pivot hinges (picture 6): the original one, as shown in the plan, the modified version from post 31 of this thread, and this new version with the universal joint. They weigh - as shown in picture 6 - 5.7 g, 6.5 g, and 6.7 g. I cheated a bit though, because for the control arms I did
not use PVC, but some cf-balsa composite I had lying around, which is very light and very strong - though not readily available. I estimate that you'll have to add about 3 g to these weights when you're using PVC.

Jochen
Apr 08, 2006, 07:11 PM
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Mango's Avatar

Pushrod end piece


Hi Jochen.

I got my blades from Aerobalsa yesterday so now I have got (almost)everything to start building my micromum except for the pushrod end piece.
I have searched for it in several Swedish shops without results.
Where did you get yours?
Another thing I have been thinking of is what kind of material you
put on the rotorblades is it some kind of film like solarfilm?

Thanks /Magnus
Apr 09, 2006, 03:44 AM
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JochenK's Avatar
Magnus,

the push rod end piece is a Graupner part # 226. I've glued the lower part of the rotor axle into this end piece and then fixed the end piece on top of the rotor mast with a 2 mm screw for easy disassmbly. If you can't find this end piece or something similar, tape the top of the rotor mast with cf rovings for about 30 mm, drill the 2 mm or 3 mm hole - depending on the type of pivot hinge - into the mast and glue the lower end of the motor axle into the hole. This is only the third best solution, though. If you're using the universal joint, the second best solution would be to try to drill a 2 mm hole through the cf, the balsa, and the rotor axle, and the use a screw again. A bit tricky.

I Have not yet found a light stick-on film for my blades. That's why I just paint them with filler 3 times and sand them down after each painting. Then I spray the blades with a thin coat of paint (0.5 g per blade) for better visibility. But as weight is not too critical, you may as well cover them with fiilm.

One more thing. If you build the pivot hinge using the universal joint, replace the three outer M2 screws holding the blades with plastic screws. Now you'll rightly say: there are no M2 plastic screws. To which I'll reply: make them yourself. Cut off 12 mm pieces of an inner bowden cable tube, which happens to be 2 mm thick. Cut M2 threads onto both ends and use M2 nuts to hold the thing in place. With the universal joint the head is now very rigid and I think one should offer at least some protection to the blades in case of a crash.

Jochen
Apr 15, 2006, 05:53 PM
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Mango's Avatar
Hi Jochen.
I did'nt find a graupner end piece but found a part of a fuseholder that works
But looking at the photos I just discovered I put the blades the wrong way around does it matter?
I tried to fly it yesterday but it was going to the right both times slowly descending.
I'm not sure but I don't think the rotor autorotates how do you know when i does?
I have worked a bit on the rotor this evening so now it spins better so perhaps it will work better tomorrow.
By the way should the screws holding the rotorblades be fastened firmly or should the rotorblades be able to move slightly back/forth?

Thanks /Magnus
Apr 16, 2006, 12:36 AM
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JochenK's Avatar
Magnus,

I have some theories about your problems, but in order to do a proper diagnosis instead of just speculating, I need some more information.

Can you please post some close-ups of your rotor hub, one from above and one from below, a picture of your motor and prop and one of your fuseholder - that sounds very interesting.

And please answer these two questions:
Did you follow my advice about the 5 tilt to the right at full throttle to compensate for motor torque?
What motor and prop are you using, what's the rpm of the prop at full throttle?

Waiting to hear from you.

Jochen
Apr 16, 2006, 04:44 AM
Registered User
Mango's Avatar

Micromum


Hi Jochen.

Here's some pictures of the Rotor, Motor & Fuseholder.
The motor I'm using is a homemade cd motor sorry can't tell the RPM
because I have no meter to measure it.

The prop I used is'nt marked so I can't tell for sure but as you can see I have to replace it anyway cause it got damaged while "landing".

I used 2cells 630mA since I don't have any smaller, that is why I had to
place the battery that close to the mast, I will try using 3cells but I'm afraid I might burn the motor.

I did'nt mix in the throttle so that's the answer to why it was turning right,
but I got an advice from a guy that has been flying these things before
to hold the gyro in the rotor, apply throttle & if it turns adjust the motor
horiz. angle until it stops moving.
I have done that, now when applying throttle It does'nt turn.

Here's some questions:

1. Should the screws holding the rotorblades be fastened firmly or should there be a certain amount of glapp allowing the blades to move a bit backwards/forwards?

2. Does it matter that I put the blades the other way around making the rotor spin the other direction?

3. When finding out the hang angle should I hold the gyro in the rotor adjusting the battery so the mast is pointing straight down since it is normally tilted 8 deg backwards?

Thanks for your help
/Magnus


Update!

It flies!
I was out testing it today & managed to fly it 4 times well, to be honest
2 times lasting about 1 minute each & two crashes.
It was too windy I guess & blowing randomly varying from no wind at all to quite strong winds, anyway I got it flying & got some kind control over it.
The response was quite slow, I'm not used to this kind of aircraft I even
found myself worrying about it to stall
The third time just after takeoff a strong sidewind smacked it straight into the ground destroying one of the rotorblades.
But I quickly glued the blade together with ca & gave it another try this time It flew for about 40 seconds but then same thing happend a sudden wind got it making it land upsidedown killing one of my cheapy servos.
I'm happy anyway cause now that I know it flies I'm going to order proper
servos with metal gearboxes & I might even paint it
By the way I loosened the screws holding the rotorblades a bit making it possible for the blades to move about 1mm back/forth & secured them with glue.
Sorry to say the Pilot got injured & lost both feet

/Magnus
Last edited by Mango; Apr 16, 2006 at 07:19 AM.


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