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Patrick

Mon May 19 2014, 08:17AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

mind blowing !!!!

RCvertt's work...

Ash Small

Tue May 20 2014, 11:08PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Ok, this is a hypothesis, and is not proven.

Following on from my comments in Dr Spark's 'big bird' thread, Here is a 'concept heptacopter'.

The image represents the ducts and framework. The props are mounted centrally in the ducts. I think it's easy to see that the central propeller doesn't suffer from the same peripheral losses that a single prop would experience, hence greatly improving efficiency. The efficiency of the surrounding props is also increased.

Assuning 13.5 inch props, length is around one metre.

Efficiency could be further increased by adding another six props, increasing length to around 1.5M, but I'm not sure how much this would weigh. There are regulations applying to these things.

I don't know if other factors are involved, most hexacopters have their props placed far apart. This improves manouverability, but is this at the cost of efficiency (read 'flight time') or are there other factors I've not considered?

EDIT: I calculate the rduction in peripheral losses with the above design to be ~43%, compared to a design with the rotors spaced further apart.

Carbon_Rod

Wed May 21 2014, 04:42PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

For those interested in a variable pitch aerial quad:

kit $800:

These are not a complicated build project.

Ash Small

Wed May 21 2014, 05:39PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Carbon_Rod wrote ...

For those interested in a variable pitch aerial quad:

kit $800:

These are not a complicated build project.

Now I'd argue that a single rotor craft with swash plate is simpler than this quad. You do need four servos for a swashplate, but he has four on this quad anyway.

The efficiency gained by using a single rotor and swashplate would be considerable in this instance.

EDIT: you could use a similar belt drive system as used here to drive the tail rotor, though, and you will need a fifth servo for the variable pitch tail rotor.

You could also use the system depected here in the 'concept heptacopter' design I posted above, with a single motor and belt drive, but you'd need a separate servo for each prop.

Patrick

Wed May 21 2014, 06:09PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ash Small wrote ...

The efficiency gained by using a single rotor and swashplate would be considerable in this instance.

your starting to convince me, and to avoid a traditional tail, I'd use vanes. Like the German V2.

Ash Small

Wed May 21 2014, 08:34PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

Ash Small wrote ...

The efficiency gained by using a single rotor and swashplate would be considerable in this instance.

your starting to convince me, and to avoid a traditional tail, I'd use vanes. Like the German V2.

I can post a sketch of what I consider to be a fairly simple swashplate design if you like, but it probably won't be for a few days at least. I imagine most of it would survive a catastophic crash, especially if the props were designed to shear off.

Patrick

Fri May 23 2014, 05:37PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

id like to see it, please post when able Ash.

Ash Small

Fri May 23 2014, 07:59PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

id like to see it, please post when able Ash.

Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:

Patrick

Fri May 23 2014, 08:50PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ash Small wrote ...

Patrick wrote ...

id like to see it, please post when able Ash.

Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:

im starting to come around Ash, ive seen these before, and i typically ask those who advocate for it, if the motor, shaft and prop hub are all rigid but with the shaft going through the hole? so the motor casing torque is held where? and the motor is otherwise free to move by the servo-swash action.

reply when you can, TY

Ash Small

Sat May 24 2014, 10:07AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

Ash Small wrote ...

Patrick wrote ...

id like to see it, please post when able Ash.

Ok, I'll try and get something together this weekend. In the meantime here are some images of some spherical bearings:

The motor is fixed. the swashplate mounts on the spherical bearing. You then need something like a pair of taper roller bearings on the swashplate, which allows the swashplate to spin with the shaft while being controlled by the servos. I'll try to get a sketch together later today. It's all in my head, I just need to get it into CAD.

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