This is a "Prototype" octacopter for my actual plan of octa.

Frame: 1250mm
Motors: 5010 360kv
props: 16" CF
APM : 2.6 with Arducopter 3.1.3 Firmware.


Frame is 1250mm Carbon fiber and it can not fit props more than 15" as a plain octo. and for my "Actual Plan" I don't want to make an X8, because as I read many thread, X8 has 30% less efficiency than a plain octa. My idea is to make an octa with 20" props , but for this size of props, required frame size could be too big to carry around. So, this prototype is like a "proof of concept".


I had 360kv motors for a long time, so i tried a new Prop layout to make 17" props fit on 1250mm frame and they are about 1 inch overlapping each other.
I inverted all CCW motors down and accordingly mounted props.
and left all CW motors on top and mounted props as usual.

I Just did initial setup and Without any PID tuning of APM2.6, it flies very well on default PIDs.

Question is : Is this setup/layout is less efficient or more efficient ?
Is it reliable ?

My actual plan is to build a copter that equals SteadiDrone QU4D X in performance.
for that I have following items in hand.
1- KDE Direct XF4014-380kv Motors
2- 18" and 20" High efficiency CF props.
3- Hobbywing Platinum 40A ESCs

              OR

4- T-Motors 40A ESCs T40A
5-I have many frames that could be used , or DIYing a frame isnt a matter.

For my Dream copter, that could be and octa or X8 or a simple quadcopter, I think this list is good to go.
As Gary McCray wrote in "Advanced MultiCopter Design" that :
"It is feasible to produce a QuadCopter that will approach the performance of the $15,000.00 Steadidrone at a fraction of the cost."
Suggestions are appriciated.

Views: 1931

Comment by Rob_Lefebvre on May 26, 2014 at 7:05pm

Nothing new here. I did this 1.5 years ago, and I think somebody else did it before me.  It'll work out just fine, you'll get efficiency almost indistinguishable from a standard Octo, other than the fact it'll make more noise and vibration which you'll need to manage.

Comment by Tipu on May 26, 2014 at 11:32pm

Thans Rob.

Can you refer a link for further reading this design ?

and yes it seems more noisy.

Comment by Gary McCray on May 27, 2014 at 10:18am

Hi Tipu as Rob says above, this should actually work fine and is a perfectly valid concept.

Maximum prop overlap should be limited to less than 30 percent and less than 20 percent is probably better.

There are working examples in this range that show that loss' are very low if kept in this range.

Since these are asynchronous, prop coincidence will be variable and it will no doubt make some interesting sounds from time to time, but effect on performance and efficiency should be minimal.

In all likelihood the control scheme will not be negatively affected in any noticeable way either and you should just be able to fly as though it were a conventional Octa.

Although the vertical offset of thrust from adjacent motors may have some slight effect on roll and pitch, there is a good possibility it won't even be noticeable.

Here is Brad Hughey,s response to Robert aboves own octocopter build about this from Brad Hughey our genuine resident expert on propeller applications:

 Reply by Brad Hughey on September 9, 2012 at 7:15am

Just to be clear, the whole idea behind overlapping rotor disks was to increase the effective disk area in a more compact footprint.  Dr. Leishman's efficiency "bucket" prediction is only ~5% of unity, so I would expect to find no difference at 20% overlap unless the lab conditions were very tightly controlled (which is what he said in the paper).  It may very well be that a grid layout is best for this approach versus a classic multicopter "star" pattern.

However, the efficiency cost of a coaxial configuration is easily discernible in testing, at a range of 20-40%.  To be fair, the downstream rotor should have a higher pitch (which you can calculate via the induced velocity of the air stream of the top prop) for it to work the best.  That said, the whole disk-loading vs. thrust-spacing vs. control-response vs. center-of-mass conversation is a whole other kettle of fish.

The efficiency of motors peaks at about 1/3rd of rated power and falls off rapidly after that.  A unit rated at 85% peak efficiency might only be about 60% at full power (remembering too that our friends in Asia tend to play fast and loose with rating numbers).  In other words, a 300 watt motor is trying to scrub off 120 watts of waste heat...so, yeah, it will get hot.

Anyway, nice work Robert.  I'm sure the finished product will exceed expectations.

Basically coaxial props = big loss.

But up to 30 percent prop overlap = very small loss.

Rob built an H Octo with I believe 30% overlap and it performed very well.

I would expect the most negative effect you might see could be some very slight control instability related to the vertical offset of the adjacent propellers, but probably entirely within the scope of the APM/Pixhawk to compensate.

I notice you are already using KDE motors, good choice, I think they are the highest quality most durable motors you can currently buy.

http://www.kdedirect.com/XFMRBrushlessMotors.html

Best Regards,

Gary

Comment by Rob_Lefebvre on May 27, 2014 at 11:31am

Tipu, here is the thread on my Octocopter:

http://diydrones.com/forum/topics/new-octo-copter-design-build-thre...

Last summer, I built another one that was an H-8 layout.  I never found any control problems from this setup. The only thing is as I said, it's quite noisy.  Theoretically, vibrations might also increase, but I didn't have any problem with that in reality.

The only real problem I had was that both machines suffered a propeller system failures, that were not caused by the overlap in any way.  However, when the rotors failed, they took hit adjacent props, making the failure worse.  So the design somewhat negates the advantages of multirotors if you have a prop failure.  If the motor or ESC failed though, it would be fine.  Video of the two incidents.  One ended badly, one ended well as the second motor was able to restart. 

Comment by Tipu on May 27, 2014 at 12:52pm

Thanks a Lot Gary and Rob.

I flied it in my Badminton court last night and in a 15 minutes flight , i didnt noticed any control problem.

I takes off very well and landing is very smooth too. Pitch and roll are fine as well.

https://vimeo.com/96626025

All i am trying to build a copter with Maximum efficiency , with KDE motors.

Will start from a Quad , then will go to Octa for batter endurance with payload.

Thanks for your help guys..

Comment

You need to be a member of DIY Drones to add comments!

Join DIY Drones

Groups

Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service