Following on from the very successful H quad with vibration isolated arms I decided to build something that would lift a DSLR or larger.
Is seems a hex has marginal chances of surviving a single drive failure so I opted for an octa. The H8 was quite an attractive layout but the loss of efficiency and lift was too much so I decided to build a flat 8. It also had to fold down to less than 35cm wide if possible. I wanted to keep a vibration isolation system but the method used on the quad was not suitable. I opted for a separate frame which carries all the heavy and vibration sensitive items like controller and camera, all suspended on silicone ‘O’ rings. Rings can be added or tightened to ‘tune’ the system. Provision is in place for z axis O rings if required but with 6 rings it each corner it is already very stiff in all axis.
I was part way through the build and struggling to get the folding arm system working nicely when my son ordered a 3d printer. I was very sceptical despite their popularity on this site.
After the first few printed items came off I wondered how I ever managed without one and my poor son didn’t get a look in – sorry Leo.
Once all the plastic parts are printed it doesn’t take very long to cut the carbon to length and assemble it.
eCalc suggests it will have a max TOW of 8kg (inc 3.3 kg payload) and hover time of 11 mins at that weight. More realistically, with a DSLR and 4 x 5AH 4s is should be about 5.3kg and 22 mins. (This is using MT4008-12 with 14x4.7 props)
I am considering a production run of these frames once this one is proven.
Comments
Y6 and x8 yes,yes and yes....y6 and x8 is far better aircraft than quad...its not only efficiency(flight time in my case only drop from 23 to 20 minutes).
If you build multi by your own less carbon tubes(realy good ones are still expensive) and motor clamps,redundancy as well(its hard but u can fly y6 withot motor and x8 without two,been there than that)
Also one important thing;if you want to use 6s batt(and i have 2 of them in paralel,2kg together) for less amps greater efficiency,and some decent camera and gimbal you will have to use some really strong motors and big props for quad.
That lead us to another problem (wich is why coaxial is better) and that is big surface of your aircraft,twice as big,especialy with flat octa.Vince,your octa is champion in that,bcs of middle part,and air resistance must be really big.in normal flight and not to mention on windy day when is impossible to have stable aircraft.
Also bcs of two motors on same arm, they have stronger push force on windy day....not to mention cost of big motors and propelers wich can make your quad more expensive than x8..(motors and ESC does not fail almost never if you solder everything well)
Guy, I tend to agree with you.
I think the octa theoretically has a reliability advantage because it still flies with one dead motor (mine does anyway) but there are twice as many to fail as a quad. What are the chances of having two motors fail on an octa at the same time? I suspect its higher than pure chance because bits could take out the motor next to it.
Also, how often is a crash caused by a single motor/ESC/prop failure? The 3.01 thread would indicate there are a whole lot of other things that are more likely to cause a crash which only increase with complexity.
All other things being equal it is more efficient to have one big motor than two small ones. What about purchase economy? I haven't checked out $/per kg lift for equivalent quality motors but I suspect that also works out in favor of fewer motors.
Y6 and X8. no,no,no. Look cool but bad efficiency.
Hex? Why? Most cant survive a motor failure so you are just increasing you chances of having one and therefore a complete loss.
So why did I build this Octa? Well it was for reliability but my thinking has shifted slightly so my next heavy lift machine it will probably be a large quad as you suggest.
That was a long answer.
My printer is a Mendelmax 1.5 but I have almost finished a new big one that I have designed myself.
Here is a link. (The printer forum is dull compared to this one).
http://forums.reprap.org/read.php?2,264549
I am curious why people are opting for the complexity of and octa over a heavy lift quad with 4 honker motors? Seems it would be lighter and much less complex. I am sure folks have ran the numbers, but I am just curious.
Also, what 3d Printer are you using?
Thanks,
Guy
all u need for above method is thick wire for central loop,peace of temperatue resistant plastic and soldering iron,and you can shape it any way it suits you(squere,triangle,circle)...
Thanks Greg.
With 3d printed parts you can define the density if the internal framework. I think the wing nuts are about 90% hollow.
Ive learned that adding lightening holes often increases the weight as its the skin thats heavy. Bizarre but true.
That is just plain COOL.
I am impressed.
If you drilled some lightening holes in the wing nuts that hold the battery bracket down i would of fell out of my chair.
O yes, you did see my gimbal.
I tested one motor on the bench, fixed to the 12mm tube and able to pivot so that it presses on digital scales. At full power it produced exactly 2000g so in theory the copter should just pull 16kg off the ground, however I believe there is a software limit somewhere in the APM parameters that limit it to 75%. When I tied some gym weights below and tested outside it only lifted 6.5kg 'payload' which is 11kg total. (I was tempted to change this parameter and demonstrate the octa lifting my bicycle in the air).
The weights were tied to the outside frame and not the suspended bit. You are right to suggest the printed O ring things may be the weakest part. The first ones I made were much 'beefier' but I decided they weren't necessary.
I would be happy with 3kg payload on the center plate in its current configuration though. I may demonstrate that later.
How much and what are you hoping to lift?
Have you seen my gimbal blog?
http://diydrones.com/profiles/blogs/dslr-gimbal-using-3d-printed-pa...
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