(More construction photos in link below)

I was flying with an APM2 equipped X525 quad frame but there were a couple of thing I didn't like, namely:

if using a GoPro or other wide angle camera the props would show in the far corners of the video.

Also, orientation at a distance was difficult even with two bright neon-orange legs.

Thirdly, it didn't fold as compactly as I would like for transportation.

Lastly, it looked like all the other X525 framed quads.

So after seeing an H-frame quad on the 'net somewhere I set out to build my own. The first frame was from 3mm ply and balsa using the aluminium arms and feet from the X525 but stiffness was a major issue with motors 1 & 2 sitting higher and at a slight angle while in flight. This caused some strange yaw problems... well, there wasn't any at times, the motor angles cancelling out their yaw effect. I tried covering the ply with very light carbon tissue and epoxy and even some carbon tow braces but could never get rid of the twist between the front and rear arms. A fumbled toggle switch at the wrong moment caused a crash and showed another reason why ply is a bad idea, it breaks very easily!

So...

Next was to find something really stiff and strong, either fiberglass sheeting or carbon, prices were a bit unreal both locally and online, while some suppliers showed no interest at all in selling me any (I'm still waiting for some replies).

I eventually found some 1.5mm woven carbon sheet at Hobbyking but it was only 300mm x 100mm.
The 100mm was fine but I needed 600mm (23") long. This is when an engineering friend came to the rescue (HUGE thanks again, Wladek!), he said I could join 2 sheets mechanically with fiberglass sheet and rivets! So 4 carbon sheets were ordered and some plans drawn up in CAD.

Wladek has some nice machines at his work so we were able to do some very accurate drilling, milling and cutting. 12mm aluminium square tube was sourced locally and milled into a C-channel, saving 1/4 of the weight. Two 0.5mm plastic strips were used to make up the extra 1mm thickness (the X525 arms are 13mm). The carbon is riveted with 3208 rivets to the c-channel.

At first we used the carbon in it's original rectangular shape but we have since cut down the sheet to its present form saving 1/3rd of the weight. If I had to do it again I'd use 1.0mm sheet rather than the 1.5mm saving another 1/3rd. Also initially the ESC's were inside the frame but after many unexplained "ins" and other problems in which I started to suspect an overheating ESC, I have now moved them out into the airflow under the props and all seems well.

Anyway, it flies really well, looks great in the air and fulfils all my requirements, especially no props in the video! (See here). Final weight is 1279g (45oz) dry, with a 3 cell 5000mAh LiPo adding 353g (12oz) totalling 1632g (57oz), about 250g (8oz) heavier than the X525 with the same hardware. Flight time is about 13 minutes. Motors are 20-22L's, ESC's are Super Simple 20A, batts are Zippy Compacts (3S 5000mAh), props are 11x4.7 APC SF.

More construction photos here: Picasa Album

Cheers

link to CAD file>H-Frame2.dwg

Views: 22396

Comment by Carl La France on September 29, 2012 at 5:01pm

Hi Graham Looks Awesome! I like the way you went ahead with form follows function  Thanks for sharing Have a

great day!


Developer
Comment by leonardthall on September 29, 2012 at 6:56pm

Love it!!!!!


I have been working on a design like this to reduce the size of my quad when it is folded. Currently the arms both fold back leaving the propellers sticking out the back.

The idea was then to put the gopro on the front just in front of the arm pivot point!

Like!

Comment by bbberrey on September 29, 2012 at 8:58pm

I personally fly this frame, I do like I/ H frame designs since they provide a clearview, and it is my main fpv/filming rig, solid, and wood is actually one of the best materials to use since multirotors create alot of vibration, if anyone is looking into fpv and doesn't want to wait for a china ship for a frame that isnt repairable without more china parts, i just back from homedepot with the dowels for this months arms (12) for 4.00, btw BLUESKYRC is a quick ship

Comment by Crashpilot1000 on September 30, 2012 at 12:14am

I wonder if 11 inch props aren't too much for theses 56gr motors?


Moderator
Comment by Graham Dyer on September 30, 2012 at 12:39am

No they're not, I did some testing when I first started using them (http://diydrones.com/profiles/blogs/volts-current-watts-with-9x5-3-...) .

11x4.7's actually use less current than 9x5 3 blade props at only 3.1 amps per motor and although it's a bit heavier now the current is still easily below 5 amps per motor which is right in the efficiency curve for those motors and anyway they're rated for 17 amps . I don't have 12x3.8 or 10x4.7's but maybe I'll do a test one day to see what they draw.


Developer
Comment by leonardthall on September 30, 2012 at 7:30am

Hey Graham, do you have a photo of the quad with the camera on it?


Moderator
Comment by Graham Dyer on September 30, 2012 at 7:38am

Not off hand but I'll take one and put it up here. The FPV camera fits on my own design vibration absorbing mount which is a 10x10mm balsa beam parallel to the front arms (orange). The video cam sits just in front and below the FPV cam.

Comment by John Githens on September 30, 2012 at 8:19am

Looks great! And looking at the plastic container, it would be nice to know if you have experienced any issues related to pressure changes during your flights, as discussed on this thread and this thread. (have you found that you needed to add holes to the cover/box?)


Moderator
Comment by Graham Dyer on September 30, 2012 at 8:44am

Thanks guys!

John, the base to the cover has holes in it for the servo and telemetry cables, so on the bottom. It's just a domestic container for food which I "borrowed" from the kitchen, similar but smaller than Stephen's cold cuts box, the holes open up on the other side to the carbon and not straight into any possible airflow.

I haven't experienced any problems with alt hold at all, had a few flights this morning with alt hold on and also a long loiter where there was about a 25cm up and down variation which I understand is about the best one can expect from the APM2.

Comment by Oliver Wetmore on September 30, 2012 at 8:50am

Graham, that is very nicely done.. that is exactly what I want to build for my next project.  Nice to have all that space to mount things on such as extras like FPV equipment, cameras etc..  Will get started asap!!

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