200g/7oz. dc head pusher - the Micromum - Page 2 - RC Groups
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Dec 16, 2005, 05:30 PM
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Jochen, what software did you use to draw the above pictures?

Wahid
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Dec 17, 2005, 12:43 PM
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JochenK's Avatar
Sorry, uploading the drawings of the Micromum as *.jpg files did certainly not work out as planned. Next try, this time with *.pdf files. If you print those files without adjusting them to the size of the paper you use, you may - hopefully - get what I intended you to.

David,

thanks for your appriciation, wasn't too difficult, though. See below.


Wahid,

I used Corel Draw9 Essentials to create those drawings. Sufficient, affordable, somtimes a bit unstable - at least my version is - and some things you really need to know are hidden rather deep in the dungeons of the documentation. But I've gotten used to it over the years, which is most important.

I document practically everything I plan or do with Corel Draw. Drawing things before you build them reduces the number of silly mistakes you make and builds up a good archive.

Jochen
Jan 08, 2006, 01:00 PM
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JochenK's Avatar
Had my first crash with the Micromum yesterday while flying around on a dark and misty winter's day. Let it get away from me and lost orientation. Maybe I should start listening to my own advice.

The joint between the mast and the tailboom broke and I decided to do something about that. I have changed the plan accordingly. Nothing big, but the balsa triangle holding the servos is now an integral part of the rotor mast as well as the tail boom instead of an add-on. Everything else is unchanged.

Today was bright and sunny and I had some fun flying the Micromum again until all my extremities were frozen. I'm waiting for spring.

Jochen
Jan 10, 2006, 05:30 PM
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Hello JochenK,

I understand that you use glass fibre sheet for your rotor blade hinges. How thick is it & where do you obtain it?

Thanks,
Bob G
Jan 11, 2006, 04:04 AM
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JochenK's Avatar
Bob,

the gf sheet is 0.5 mm thick. I buy these kind of materials at local internet shops over here in Germany. I'm sorry that I can't help you any further, but I've no idea what the supply situation is like in Canada.

Jochen
Jan 11, 2006, 09:22 AM
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I'm using 0.7mm glass fiber board. You can find them in DIY electronics shops, they are used as PCB (Printed Circuit Board).
My supplier is radiospares.

Fabien
Jan 29, 2006, 11:19 AM
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JochenK's Avatar
Hi, all,

we have snow over here in Germany and for once our airfield is perfectly flat and without the usual bumps, so the Micromum and I went skiing. Big fun. This version has got a rudder, and after some mishaps I was able to do my first ever ROG with an autogyro. I feel great.

Jochen
Jan 29, 2006, 12:57 PM
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StephanB's Avatar
Very nice, Jochen. I can see the point, where your Micromum left earth.
Cool copter, cool adventure
Stephan
Jan 29, 2006, 02:48 PM
dougmontgomery's Avatar
Jochen, Nice work....Did the ski in the back aid in your your take off angle due to not having a the distance of the tailwheel? Or did you adjust the front skis also?
Doug
Last edited by dougmontgomery; Jan 29, 2006 at 02:49 PM. Reason: add
Jan 29, 2006, 04:15 PM
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JochenK's Avatar
Doug,

the angle of the tail boom to ground is the same with skis as it is with wheels (~5), the tail ski is just to keep the tail end from sinking into the snow.
As the rotor mast is tilted 8 backwards, the total angle of attack of the rotor is ~13 during take-off, which is quite o.k.. The trouble I had came from my mixing throttle onto roll to compensate for motor torque, which is useful while flying. But when you try to ROG with this configuration, you have to open up throttle very carefully for the rotor r.p.m.s to be able to follow. Once I got all this synchronized I had no trouble taking off.

Jochen
Mar 03, 2006, 06:28 PM
Registered User
Not sure if anyone is still reading this thread, but I have a question. I'm using the method you discussed to build my rotor head and I'm getting a lot of unwanted flex once the blades spin up. It trys to tilt backward knocking off my tail. Let me know if I'm doing something wrong. I can post pictures if you need. Thanks.

Kevin
Mar 04, 2006, 05:27 AM
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JochenK's Avatar
Kevin,

I'm still around.

Having to replace a broken tail unit on a Micromum is not unknown to me, but up to now that happened only after some horrible kind of touchdown or after a tilt-over when trying to ROG. But let's see if we can find a solution to your problem and learn something from this. Please post some close-ups of your head and a detailed description of the spin-up procedure that ends in those rotor strikes.

Jochen
Mar 04, 2006, 09:11 AM
Registered User
Jochen,

I first tried building it exactly like you showed with the lock collar and all, but that didn't hold up, the epoxy glue kept breaking loose in the collar. I then drilled out a servo arm to fit snuggle over the heatshrink and then glued it in place. I flew it like this, but the control seemed very sluggish and I could see that the rotor was tilted back further than it should on low flybys.

Ignore the website address on there, the resizing program that I use puts my website on there

Kevin
Mar 05, 2006, 11:36 AM
Registered User
Jochen,

I just ordered some blades from aerobalsa.com and I'm going to get some new servos. Any servo you recomend? I'm thinking of going with something like the MX-30. Also, do you put weight in the tips of your blades and do you twist them?

I'm going to start building this thing over from the ground up today. Im determined to get this thing to fly consistently. Would you find it easier to do ROG with a steerable tailweel, or is it not an issue? Thanks again.

Kevin
Mar 05, 2006, 02:26 PM
Suspended Account
Mario I. Arguell's Avatar
KP,

I have found that on flex heads that use fibeglass for control plate, moving the control to the rear instead of the front of the control plate helps a bit, as the forces are not as promounced on the control link and arms, with the control links towrd the rear of the control plate, they will be more on angle like a 90 degree bracket holding a shelf so to speak, and puts more support on the plate at the rear where the head always want to tilt back naturally from the wind force on the rotor. Also putting the control plate or arms closer to the rotor helps in minimizing forces on the servos and making the head less sensitive which can be good if you have an oversensitive gyro.

Also a servo control horn the way you have it mounted has flex in itself because it is made of thin plate nylon. I noticed you have the servo arm positioned at 90 degres, use the double arms like on JoechenK's original setup, you will need elevon mixing, this is preferable since it distributes the rotor load over both servos instead of one like the way you have it now.

Edit: Pardon me I looked over your picture and you are using mixing I think.

Picture of one rotor I built using the heat shrink method but I modiied some of the control parts a bit. I have not tried this heat shrink tehnique yet, but it should work just fine on a small rotor gyro. I wouldn't rely on it for a larger rotor gyro or one with a high rpm, for the possibility of the heat shrink joint breaking loose.
Last edited by Mario I. Arguell; Mar 05, 2006 at 03:00 PM.


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