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Aug 17, 2014, 06:11 PM
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Martin SJ's Avatar
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RC Bipe Under 2 inches

This is Thumbkin, so named because it is about the size of my thumb, and because when it flies to the other side of the gym you can hear me quietly singing the children's nursery song "Where is Thumbkin, where is ...". Wingspan is 50 mm, just under 2 inches. I designed it from scratch specifically to have this wingspan, just to see if it could be done. The design was driven by that constraint, and it came out the way it did as a result of following the consequences. Nevertheless, I think it turned out pretty cute!

Here's a flight video:

Yet Another World's Smallest Radio Controlled Model Plane (3 min 44 sec)

which was made before it got landing gear and eyes as in the photos. It still flies the same, though.

Everything in the plane, except the battery, was built from scratch. All the electronics is socketed, so the receiver, battery and motor can all be removed with no soldering. The motor is mounted on a plate that snaps in on a sliding bracket. The only things built-in are the rudder actuator and the on-off switch underneath. Charging the internal battery is done in a charging cradle through conductors under the fuselage. The wheels rotate and it has a rotating tail wheel, but I have not yet succeeded in an ROG in spite of several attempts at changing the position of the landing gear.


Wingspan: 50 mm, 1.97"
Weight: 1.3 grams
Prop: 0.8" x 0.8" carbon fiber
Motor: Single phase brushless, 42 awg, 20 ohms, 3 x 2mm magnet
Receiver: Rabbit, 900 MHz
Controls: Throttle and Rudder
Rudder actuator: 2mm ID, 50 awg, 150 ohms, 1/16" x 1/32" magnet
Battery: 10mAh Fall River
Construction: 0.020" Durobatics

Last edited by Martin SJ; Sep 21, 2014 at 05:26 PM. Reason: Added revised plans
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Aug 17, 2014, 07:01 PM
Registered User
Absolutely marvelous!!! Martin has long been an inspiration for me, but this is the tang in the cherry on top of the cake!!!
Aug 17, 2014, 09:25 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
Very nice. It has a look from the Disney Planes cartoon. I love it.

Aug 17, 2014, 10:28 PM
Registered User
Simply amazing work.... Would love to get a look at the electronics....
Aug 18, 2014, 06:59 AM
Registered User
Wow! It's a work of minature art.

I have a 50mm span carbon hoop and film IFO inspired contraption that needs finishing off but I think I'll give up now ;-( (only joking I am even more inspired to make it work)

Do you have any problems with torque reaction as it has such a narrow wingspan ?

Well done,

Aug 18, 2014, 07:34 AM
Toaster, not Toast
That's amazing... And cute. Nicely done
Latest blog entry: Evolution Woodie
Aug 18, 2014, 12:02 PM
Registered User
Marvelous, well done! I see that you and Joe M. are doing your very best to stretch your remaining supply of Durobatics.
Aug 18, 2014, 08:34 PM
Registered User
Wow that's totally awesome! Nice Job.
Aug 19, 2014, 01:47 AM
Veteran's Avatar
Truly remarkable!

Makes me want to dust off all the micro supplies and start making micros again!
Aug 19, 2014, 05:47 AM
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chulian1819's Avatar
awesome job!! 3ch? :P
Aug 19, 2014, 05:16 PM
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Petefoss's Avatar
Very cool Martin, I look forward to seeing it at NEAT.
Aug 21, 2014, 12:11 AM
Registered User
Hi Martin,

Beautiful model,I really like the cartoon scale look of the plane. Now we have to see how much smaller can we go! Can you design a lighter version of your Rabbit, maybe a 2 channel that weighs around 50-60mg?

I also think that you design would be a great room flier at around 5-6 inch wingspan.
Aug 21, 2014, 07:08 PM
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rogenstein1983's Avatar
That's amazing would love to see a build log or such, less really is more, more impressive at the least!
Aug 21, 2014, 08:21 PM
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Martin SJ's Avatar
Thread OP
Thanks for all the nice comments. I see a few things needing responses:

- Joel LeNoir on a picture of the electronics. It's a bit tricky to get a shot inside - rather crowded in there. But you can see what the receiver looks like on Nick Liechty's website - he sells them.

- RobT on torque reaction. Yes, this is a significant problem on small planes but can be fixed with lots of right thrust and offsetting the whole fin to the right. Just don't try gliding.

- epilot on use of Durobatics. This plane uses a 4" x 4.7" piece, so I think I'm OK to build about another 140 of these.

- Veteran on making micros again. Yes, do start again. There are so few of us still making planes like this.

- chulian1819 on a 3 ch version. Good idea. The Rx already provides outputs for 4 channels so all that would be needed is another actuator at about 40 mg. It would be nice to be able to trim it in flight. Tiny variations in CG can really mess it up.

- Petefoss on NEAT. I'm afraid I will not be going to NEAT this year - sorry.

- Joe Malinchak on a lighter Rx for going smaller, and on going bigger. I already made a lighter version of the Rx, called a Starving Rabbit, back in 2008 for my 1/2 gram plane. It weighs 65 mg and has 2.5 channels - throttle, rudder and up elevator. It was not easy so I'm not sure I want to do it again. As for bigger - good idea! Although I can't call it Bipe-50 any more - maybe Bipe-125? Such elegant names.

Aug 21, 2014, 08:34 PM
dll932's Avatar
WOW! I'm gobsmacked!

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