|Mar 15, 2004, 10:54 PM|
12.5" FF electric
Hey, I saw Graham Stabler's orni, and just thought I'd post mine too. I went with a little different wing arrangement. I haven't decided which is better. The root hinge (Graham's) can be tuned to flap pretty much symmetrically, but needs a two-stage crank. Mine has some inherent flap-offset, but has a simple single crank. I think the root-flap style may end up lighter. Ill have to make another.
Im also working on a biplane model of similar dimensions.
I was wondering if the m-20 motor is overkill for such a small plane. I dont have any experience with that motor, and am new to electric rc.
I plan on putting in a bit-rc reciever and DIY coil actuator. I am currently using a stock bit-rc motor coupled to a diy 28:1 gearbox made from zip-zap steering gears I found behind a radioshack in the trash.
Speaking of the zip-zap, they seem to be the ideal donor for micro-orni parts: ~100:1 steering gearing in what appears to be of the sort of workings as a standard micro servo, propo controls,
small coreless motor, transmitter with 6 selectable channels, all for $25.
The reciever board seems to be rather heavy though. I dont have a gram scale so I dont know what it weighs. I think they are powered off of single cell nimh 110mh.
I just dont have the money right now to drop on one of those, or I would.
|Mar 15, 2004, 10:58 PM|
Here is a zipzap reciever (trashed) that I have for comparison with the standard bit-rc one. Also pictured is the 100:1 steering gear box. These are the gears I used for the flapping mechanism in mine.
|Mar 15, 2004, 11:03 PM|
Oh yeah, I relly enjoy this site. Ive been reading its contents for about a year, and decided I would like to contribute back to the information base.
Im really getting into the whole indoor-rc scene, and am also working on some Micro Air Vehicle stuff with the Cal Poly team for the 2004 competition.
Expect some more small scale stuff from me for sure.
|Mar 16, 2004, 12:08 PM|
Joined Mar 2004
Great Job Beebe...!
I am trying to understand the wing arrangement and
I think some images in better quality will be very helpful.
|Mar 16, 2004, 04:36 PM|
Yeah, sorry LeBy, I appologize for the poor image quality those were the worst my camera was capable of. Ive taken a few more on the highest quality, but I seem to have problems with close range photos being out of focus. But Alas, those were too large to post. Therefore I have drawn a picture using paint to illustrate the mechanism. I hope this clarifies any confusion.
The wing is hinged at its "elbow" by a piano-wire pin CA'd to the wing which rides in an aluminum tube bearing on the frame.
The wing is then held in the bearing by a piece of orange tape at the the trailing edge root which serves as a second hinge also.
|Mar 19, 2004, 04:24 AM|
My double crank is working fine now I added the moulded carbon piece that locks it to the spur gear. That said, if I were to start again I would go for a single crank design. The maximum you can get out of the 40mAh cell is about 200mA, this just might not be enough for flight on this ornithopter. Perhaps a 90mAh Etec would be more suitable but I don't know your current draw.
The other thing is you may want a higher gear ratio, the pager type motors genrally need a high ratio even with propellers.
All of this you will find out in due course. The real advantage of your model is that in will not destroy itself because of the low weight. On mine the motor is more heavy than the battery and when the bird stops flapping unless I am lucky it take a pounding. I hope it does work, a low wing loading super light ornithopter would be great.
|Mar 28, 2004, 03:50 PM|
Sorry I forgot to post the most important details, its flight performance.
Original flight tests in the living room appeared very satisfactory, with it gaining altitude before crashing into the wall. It also flew straight.
However, after several flights the 0.00025" mylar wing membranes began to tear loose from the spars. I patched it up with the orange tape seen in the pics.
Subsequent flight testing was very dissapointing, it would bank sharply to the left and crash. I agree about the motor, gearing, and battery suggestions Graham made. The battery would noticably weaken after a couple flights, and the motor does turn at high rpm under no load.
Perhaps a new gearbox with ~40:1 gearing would be more appropriate.
I have moved on to a different design and Ive put this on the back burner. Ill start another thread about that one (10.5" rc)
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