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GEMiNi tiny FPV racing hexrotor

Posted by W. Thielicke on July 16, 2013 at 4:30am

A video of the Shrediquette GEMiNi:

Hi everyone! I just posted this already in the internet somewhere else, but I think it might be worth a blog-post on DIYdrones as well, as it contains some information on motors / propellers / aerodynamics that might be interesting to you guys...:

I spent some time during holidays to design a new FPV hexacopter based on my latest flight controller (see details here: click) and a canopy which was designed using CAD.

_MG_9617.jpg?width=200Cheap hobbyking motors were shown to have the same performance as the more expensive Roxxy ones (see details here: click). I found propellers that I did not know before (see details here: click) and that are more efficient than the AirAce propellers. The props are tilted 10° forward in order to decrease the angle of attack of the copters body in forward flight, which, together with the canopy, decreases the net aerodynamic drag in fast translational flight by about 30% (see details here: click). This copter flies even faster than the BOLT (see here: click) and it seems more maneuvrable. The GEMïNï is however slightly larger, the max. dimension is 315 mm from propeller tip to propeller tip (diagonally). I use the CCD-Killer camera, and a 25 mW Airwave module for video transmission. The CCD-Killer is still my favorite camera in terms of image quality and exposure control vs. weight and size.

Ever since I built my first tricopter, I wanted to build a canopy that somehow resembles the Limulus, an impressive animal that seems to have survived from the primeval times (see details here: click)... I like the design of the Limulus ("Horseshoe crab") a lot. Now I had the opportunity to print the model in 3D and to cast it using thermoformed flat film (Polystyrol).
The GEMïNï is extremely fun to fly, it seems to be very fast and agile - better than any copter I built before. For one full FPV flight of the GEMïNï, see this video:

I am very much interested in FPV multirotorracing, anyone that likes to have a fun competition, please tell me!

All the best,

William (Bremen / Germany)

Tags: fpv, gemini, hexacopter, hexrotor, limulus, racing, shrediquette
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Comments

  • LTMNO July 20, 2013 at 7:40pm

    Very Cool!  Great work!

  • Jeroen van de Mortel July 19, 2013 at 6:37am

    Why don't sell this one and a bigger one ? The advantage of a small one is that is agile.

    Frame looks indeed strong.

     

    The move you make looked it was done in acro mode, I haven't seen fast movements with stable mode.

    Here is a video of my quad in stable mode:

    http://youtu.be/a68GB2XVJIQ

    I tuned the control loops for maximum performance and analyzed them by making bode plots of the complete system. I still have to work a lot on my flying skills

     

  • W. Thielicke July 19, 2013 at 5:22am

    Hi there,

    don't make it too much bigger! I like how small it is. Have you ever considered doing a BNF or RTF package?

    I think it really needs to be bigger, so that people are able to build it. At the moment this is pretty complicated for "the standard user": My flight controller is only about 16 x 18 mm (0.63 x 0.71 inch), I don't think that there are many similar sized controllers available for sale. Furthermore, the ESCs need to be rewired with thinner wires, and at half of the ESCs, the large electrolitic capacitor needs to be removed. Otherwise it doesn't fit. Also, only a 1000 mAh lipo will fit... All these restrictions will become much less strict if the size of the copter is increased... I think 5" propellers together with 2000mAh 3S lipos are a good choice. The size would be similar to my MM6 - which is still pretty small for a hexrotor.

    How strong is the frame ? Did you have crashes where things broke ?

    These sandwich frames are exceptionally robust I think. I never broke something up to now. Usually, I built sandwiches from carbon fiber and end grain balsa, but this time money was short and I used glas fibre. I do not see any difference in rigidity, but maybe it is some grams more heavy.

    Nice, I thought so on the acro mode.

    How did you notice? I never flew in stable mode, but when I look at other videos, it seems that flying via stable mode gives a less smooth flight when flying more dynamically. I wonder why...

  • Dave C July 19, 2013 at 5:22am

    William this is great!

    I too can highly recommend skew planar and clover leaf pair antennae. Using these i get better range straight out of the box but also multipathing is almost reduced to zero. So you can bank hard, flip, roll, go through trees and greatly reduce the 'interference'.

    Then if I also want range i use my diversity setup that has the Skew planar on one channel and a 13db patch antennae on the other, that's pointed in the general direction of travel. Far out, the patch will do all the work and give you great, interference free range, then the cloverleaf with pick you up if you accidently go out of the reception area for the patch - i.e you fly behind you out way out to the side!

    Link to cheap aerials 

    http://www.hobbyking.com/hobbyking/store/__35654__5_8_GHz_Circular_...

    http://www.hobbyking.com/hobbyking/store/__27750__ImmersionRC_5_8GH...

    Link to diversity setup 

    http://www.hobbyking.com/hobbyking/store/__38604__ImmersionRC_DUO58...

    Link to patch antenna.(remember it needs to be a circularly polarized one to work best.

    http://www.firstpersonview.co.uk/antennas/5.8ghz/immersionrc-spiron...

    Then there's the antenna tracker option!

  • Jim Brett July 17, 2013 at 3:48pm

    3692775447?profile=original

  • HeliStorm July 17, 2013 at 12:42pm

    I want one...take my money...don't make me throw it at you...haha.

  • Michael Johnston July 17, 2013 at 5:26am

    Regards racing..... presumably you are aware of this site / group.

    http://fpvmultirotorracing.ning.com/

    (and yes it seems you are given that you've posted there too)

    MJ

  • Jeroen van de Mortel July 16, 2013 at 10:59pm

    Nice, I thought so on the acro mode.

    Indeed don't make it bigger, this is a nice size also for inside flying. I would be interested in the frame and dan make one or 2 PCB's for flightcontrol and one PCB with 6 esc's. And do everything closed loop.

     

    How strong is the frame ? Did you have crashes where things broke ?

  • W. Thielicke July 16, 2013 at 1:23pm

    Thanks for your positive feedback :-D.


    If you ever sell the frame let us know I would be interested


    I am in the discussion with someone to make this frame available as a kit. But in a slightly larger version, because that will be much easier to assemble.

    do you fly in acro or stable mode ?

    I always fly acro mode (angular velocity control). But I just ordered an APM flight controller, and I am really looking forward to play around with it and test a stable mode for FPV. But I am pretty sure already that I will always prefer acro mode...

    Does the controller do anything special to deal with motor angle ? Does it hover in an angle ?

    No, the flight controller is also mounted at an angle (parallel to the propellers). The GEMiNi hovers at an angle (the tail is hanging - which looks awesome btw...). But I never hover ;-D. There is no problem with the motors operating at different levels.

    Couldn't find any further info on your controller, some links are broken unfortunately

    I fixed the links in the blog post, but unfortunately this made my post disappear on diydrones... My flightcontroller is really small (click on the first link in the post, or here), but it only works well in Acro mode. Although everything is open source, I stopped to document it properly as this took 90% of the time I worked on this project.

    what's the total copter weight?

    It is 265 g. The thrust to lift ratio is 3.7:1 in theory (in practice the battery voltage will drop under the load and reduce this ratio).

    some circular polarized tx/rx antennas will greatly help with that multipathing on your video feed

    Never tried them, because I still think that a Patch antenna might give the best range... But one day I'll try...

    What is the flight time?

    About 9.5 minutes of hovering (never tried that in practice however), and about 6 minutes if I fly like I do in the video.

    Please tell you'll productionise this

    I won't do it personally due to the fact that I became father of gemini (well, now guess where the copters name came from..., but hopefully someone else does it. Promise that you'll buy one! ;-D

  • Euan Ramsay July 16, 2013 at 12:44pm

    WANT! Please tell you'll productionise this...

This reply was deleted.