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Old Dec 07, 2012, 08:43 PM
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.........................

Terry
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Old Dec 07, 2012, 10:02 PM
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Fort Collins, Colorado, USA
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So....had ordered 3 HS 775MG mega scale servos through local hobbyshop 3 weeks ago.....only one came in and I was told they werent sure why the other two hadnt shown up. So...I waited a week and was told the other two should arrive any day.
Well...now Im told they didnt even order 3 and only the initial first one. GRRRRRRR. ARGGGGHHHHH!!!!!

So...now Ive got to wait yet another week for the next 2 to show up. These servos are crucial to the build as they are what I have to build the wings and tail section around. I can tdo that without them in hand.

I know I could have ordered them myself online, but, I only have to pay 15% above dealer cost with this shop, so it ends up a decent savings.
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Old Dec 10, 2012, 12:57 PM
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Quick video showing a home depot bucket with rimfire .60 650kv installed and running. 11x7x3 MAS prop on 25c 6s 5000 turnigy. Its just an initial test but is encouraging. Bucket lifted off the ground at a tad over 1/3 throttle and held steady a few inches off the ground at 1/2. My hands are only making sure it doesnt topple over...I am not holding it up and you can see the bucket slowly spinning while I have it steady.

I never went over 1/2.....kinda made me nervous...didnt want it to shoot up to the ceiling or lose my fingers LOL.

With better batteries...it'll surely prodice even more thrust at same throttle settings. At least I know that Ive got some room for weight of the vehicle with 3 of these running. Probab ly will still have to add additional motors or extra ducted fan units within the frame...but this is a good start.

FILE0004 (0 min 56 sec)
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Old Dec 10, 2012, 01:02 PM
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Very inspiring!!!
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Old Dec 10, 2012, 03:57 PM
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Another in-process test video while we wait delivery of the new 1700kv motors. 750kv is not enough for this build. I ordered the wrong size wire for rewiring the existing motors, so I took the easy way out and ordered new ones. On all of my builds after the initial Tricopter, I have used 900kv, 1100kv, 1300kv and now 1700kv motors. I know at one time, the 750kv motors were and still is the standard by which all other motors for multi-rotor copters are compared against, but I just do not understand why.

In this test, I am working out the mixing requirement for the servos and motors to be able to taxing on the ground and in close quarters.

Mollie VTOL-Test02 (1 min 48 sec)
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Old Dec 10, 2012, 04:13 PM
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Why are the 1700's required? Just curious.
Didnt seem you were any where close to full throttle in your tests in the video?
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Old Dec 10, 2012, 04:21 PM
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Quote:
Originally Posted by kahloq View Post
Why are the 1700's required? Just curious.
Didnt seem you were any where close to full throttle in your tests in the video?
No, just my thrust calculations to lift this copter, requires 1500kv with the props used due to the limited duct size. 1700kv is a luxury.

Here is a link the ones or similar I will end up with.



http://www.rctimer.com/index.php?gOo...4&productname=


Here is a basic static thrust calculator: http://personal.osi.hu/fuzesisz/strc_eng/
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Old Dec 10, 2012, 04:52 PM
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Just for reference: http://www.ecalc.ch/xcoptercalc_e.htm?ecalc will give the entire picture but I like KIS.
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Old Dec 10, 2012, 04:54 PM
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Hi Richard,
The 750Kv motors using 10-12" 38-45 pitch props recommended for about the 1-2kg quadcopter is still a working formula. However today there is now much more build size, weight and variety now since that was a very common build as you note along with your experimentation. You are trying to use some ducting with higher RPM motors and comparatively smaller props on a bi-copter setup, so it does in fact make sense that you need higher Kv motors. Other examples are the sport multicopters that use 7-8" props and 1800-2300kv motors. The mini and micro sized quads that Gents are building and flying typically use about 2" props and 16,000-20,000Kv+ motors. There are very efficient multicopters now flying that use 360Kv motors and 1645 props and are getting up to an hour of flight time with 8k 4s lipos. It is all in the design and requirements and we have learned much about those in the last 10 years of experimentation.

Congrats and keep up the great work!
Cheers,
Jim
Quadrocopter and Tricopter Info Mega Link Index
Quote:
Originally Posted by rimshotcopter View Post
... I know at one time, the 750kv motors were and still is the standard by which all other motors for multi-rotor copters are compared against, but I just do not understand why.
...
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Old Dec 10, 2012, 04:57 PM
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Thank you Jim! Glad to see ya about. Merry Xmax.
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Old Dec 11, 2012, 12:39 AM
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Quote:
Originally Posted by rimshotcopter View Post

Here is a basic static thrust calculator: http://personal.osi.hu/fuzesisz/strc_eng/

According to that calculator, my three fan/motor setups will produce 16 pounds of total thrust.
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Old Dec 11, 2012, 07:50 AM
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Quote:
Originally Posted by kahloq View Post

I do not know total weight nor am I close to having an idea....but probably around 9 to 10 pounds. The total size of the vehicle will be roughly 8 feet wide and similar length long. Because of the size of the vehicle, if the 3 duct/fan rotors is not enough to lift it, there is plenty of space in the wing/pylon areas to add in additional thrust producers and hide them.
Quote:
Originally Posted by kahloq View Post
According to that calculator, my three fan/motor setups will produce 16 pounds of total thrust.
It would appear, you are right on the money with the 1.5 to 1 thrust to weight ratio. From personal experience (and I have built some heavy copters ), I would not go any lower than the 1.5.
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Old Dec 11, 2012, 11:36 AM
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The 9 - 10 pound estimate was just that...a guess. I really hope it comes out around there given the total thrust I SHOULD see from the three fans.
With my luck though....it will come out more like 14 pounds and obviously that would require additional motors/fans to make it fly.
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Old Dec 11, 2012, 11:39 AM
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Quote:
Originally Posted by kahloq View Post
The 9 - 10 pound estimate was just that...a guess. I really hope it comes out around there given the total thrust I SHOULD see from the three fans.
With my luck though....it will come out more like 14 pounds and obviously that would require additional motors/fans to make it fly.
The major part of the AUW is the batteries, second are the motors. Adding more just complicate the problem in my opinion, I want to strongly emphasize, my opinion.
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Old Dec 11, 2012, 11:05 PM
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In my case, the 5 gal buckets weight more then the motors do. I will have to use a decent amount of wood to brace the wings with the weight of the buckets/motors hanging way out at the edges.

I might be on a losing path, but somehow, someway...it will fly.
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