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small coaxial heli and source of motor specifications?


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dav1d
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PostPosted: Thu Dec 03, 2015 4:56 am
PostPost subject: small coaxial heli and source of motor specifications?
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Hello,

This is a two part question:

1) Does anyone know of a coaxial rc heli with a main rotor diameter in the neighborhood of 9 inches? How would I find out online, say, the make, model and specs on such a model's motor?

2) Is there an online source for rc helicopter motor specs?
Thanks
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tombo242
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PostPosted: Thu Dec 03, 2015 5:55 pm
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Hi David and welcome to the forum,

We have a select few dedicated helpers here - you will probably soon get to know them.

This heli might suit, it is about the size you quoted. Flybarless will be easier to fly. The inbuilt computer takes care of a lot of your stress.
http://www.banggood.com/WLtoys-V977-Power-Star-X1-6CH-2_4G-Flybarless-RC-Helicopter-p-914247.html

The spec looks good for a first heli. I have used this company for years, however this is only a starting point and a search will find many more. If you narrow it down to say 3 choices and post links we will give you our opinions of the selection.

Keep smiling,

Tom.
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dav1d
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PostPosted: Thu Dec 03, 2015 10:18 pm
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Hi Tom,

Awesome! Thanks. I'll check it out. Any chance of you knowing of a co-axial model with a main rotor diameter in the neighborhood of 9 inch?

David
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tombo242
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PostPosted: Fri Dec 04, 2015 12:42 am
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You're are very welcome David,

The link I gave is for a 9.5" (245mm) main rotor diameter, would that be near enough? You will find that just about all dimensions outside of the USA are in the metric system, it will help you in your searches to get used to it. The changeover is a lot easier than it seems. Just keep looking in the mini/micro sections.

If you want to really lift things then the better machine is a quad. Single rotor helis do not always handle well with extra weight.

Tom.
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dav1d
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PostPosted: Fri Dec 04, 2015 2:45 am
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Thanks, Tom.

Unit conversion is not a problem. I'll try to stick to SI units in the future.
I'm only interested in counter-rotating co-axial twin rotor ships at present.

Thanks again,

David
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admiral
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PostPosted: Fri Dec 04, 2015 2:46 am
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Hi David, I know of Servo Specification Comparison charts and Battery Comparison charts but I don't think I've ever seen on for Electric motors and if there where it probably would not include Co-Axial size motors as they are normally brushed and not taken very seriously.

I know that doesn't help very much, but if you tell us what your trying to achieve we still may be able to help.
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dav1d
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PostPosted: Fri Dec 04, 2015 4:24 am
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Hi Admiral,
I'm looking for suitable motors to try in a ship of my own design. It uses an alternate (different from the conventional) rotor configuration which is why I am analyzing the performance of co-axial counter-rotating twin-rotor model electric RC helicopters. The ~ 229 mm main rotor diameter is arbitrary.

I'd like to know what motors are used in co-axial RC helis so that I can (hopefully) find the specs on motors for, say, the Blade CX2.

In the case of the CX2, I'm in luck because the spec sheet tells me it's got two "180" motors, but that doesn't tell me much. Is "180" the motor constant, e.g. the RPM at which the motor will turn when supplied with one volt to the motor? At what RPM does the motor produce the optimum torque?

I need to know the torque I can expect at what RPM, how much the 7.4V 800mAh Li-Po battery weighs, etc. It should be plain by now that I don't know which end is up when it comes to electric flight. Embarassed

Mabuchi Motors is one manufacturer of motors that I've found that provides specs on their website but not that many ships are using Mabuchi motors.

Does this make sense?

David


Last edited by dav1d on Fri Dec 04, 2015 8:38 am; edited 2 times in total
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dav1d
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PostPosted: Fri Dec 04, 2015 4:53 am
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This is what I came up with for the left motor in the CX2 after downloading the manual(s):

http://tinyurl.com/jsvarzx

I suppose I could just build my rotors, drop in the motors and see if it flies, but I'd rather try it on paper first!

EDIT---> Heck, I think I'll just resize my rotors to 13.60 in (345mm) and try the 180 with them.
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Burgess
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PostPosted: Fri Dec 04, 2015 7:20 am
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Hi Dave
Scratch building a small heli sounds interesting.

Where you say you're intending to use an ‘alternate to conventional rotor configuration', have you settled a spec for rotor blade foil section? Disk loading and the disk operating rpm?

Here's a useful site for RC heli setting up tech info
http://dhrc.rchomepage.com/calc.htm

With small helis where the all up weight is critical, small high revving dc motors with optimum gear ratio may be the way to go.

Here's some links you may well find useful
Here's a link to a site all kinds of spares including motors
http://www.helipal.com/spare-part.html

Here's another link again loads of stuff for RC builders
http://www.technobotsonline.com/

Here's link to an example of their level of info on small electric motors:
http://www.technobotsonline.com/solarbotics-gm15-25-1-6mm-planetary-gear-motor.html

Here's some more links if their site don't have the depth of info needed they may be able to point you in the right direction.
http://www.micronradiocontrol.co.uk/parkscale_whim.html

http://www.indoorflyer.co.uk/7mm-motor---17ohm-blue-448-p.asp

http://micromodeldrome.com/8mm-brushed-edf-motorhot-300-p.asp


Burgess
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dav1d
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PostPosted: Fri Dec 04, 2015 8:36 am
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Hi Burgess

Thanks for all the links.

I have not settled on an airfoil for the blades.

The rotors will definitely be geared. I read somewhere that inrunners are better for geared setups. Is that correct?

EDIT------> WOW! those are great links!
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tombo242
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PostPosted: Fri Dec 04, 2015 5:34 pm
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Hi David,

On 180 motors, I use this type in my "Wee Jock" (totally rebuilt, only the front frame is original) small coax. Canopy is printed on card - cut and stuck. I can send you the pattern if it will help.


http://www.xtreme-production.com/xtreme/index.php?main_page=product_info&products_id=297

The ball bearings make a big difference in power and long bearing life, the replaceable brushes are useful too. A search on Ebay may well produce better prices.

Tom.
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Burgess
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PostPosted: Fri Dec 04, 2015 8:07 pm
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Tom that canopy looks good, I've used computer graphics and 80g paper and that clear self adhesive book protection plastic film to fix them on with.



Burgess
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Burgess
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PostPosted: Fri Dec 04, 2015 8:16 pm
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Hi Dave,
All rc heli rotors are driven via a pinion gear on the motor shaft driving the main gear on the shaft. The main gear on small coaxal's fixed, on larger via a one-way clutch bearing.

All small ‘toy grade' helis are fitted with tiny brushed motors.

Going up in scale to hobby grade and you'll find some small Walkeras fitted with brushless in-runners and some with brushed motors.

Early 400 class Walkeras were powered by brushed motors, earlier this year I built an Align XL 450 and installed a Walkera 400 motor, however, out-runners are the norm for 450 class.

Now with in-runners and out-runners you can wind the motors to perform to a specific specifications, torque, RPM, max wattage and max current, generally, the higher the volts the lower the watts lost to heat throughout the whole power train -battery, ESC, and motor.

If you look at specifications for Scorpion motors, this will give you some idea regarding performance which is relative to the windings that is, the gauge of wire, number of strands and turns, also winding patterns. Thereby the same basic mechanical motor form will perform differently depending on the winding type and pattern. From specs you may be able to source a motor or pair of motors just right for your project. With brushless motors the current is pulsed onto the coils so a level of vibration is produced, however, up market speed controllers have variable timing settings and soft start settings.

http://www.bavaria-direct.co.za/scheme/common/

http://www.flyelectric.ukgateway.net/winding.htm

http://www.rcgroups.com/forums/showthread.php?t=666877

https://www.google.co.uk/search?q=winding+brushless+motors&tbm=isch&imgil=XsNB4Id6gukbsM%253A%253Bo3JIyBCqFE7uXM%253Bhttp%25253A%25252F%25252Fwww.bavaria-direct.co.za%25252Finfo%25252F&source=iu&pf=m&fir=XsNB4Id6gukbsM%253A%252Co3JIyBCqFE7uXM%252C_&biw=800&bih=495&usg=__M-FmoHT18wTu_yFdN090rBCKB4I%3D&ved=0ahUKEwj-x_KklsLJAhUB8RQKHfCLD9UQyjcIPA&ei=s4JhVr6iM4HiU_CXvqgN#imgrc=XsNB4Id6gukbsM%3A&usg=__M-FmoHT18wTu_yFdN090rBCKB4I%3D

A lot will depend on the size of heli you have in mind to build, if you look at the specs of those on the market relative to your intended design, AUW, disk diameter, and power train. Note how as the disk diameter gets smaller the foil section used has more under camber.





Burgess
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dav1d
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PostPosted: Fri Dec 04, 2015 11:53 pm
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That good to know Burgess, very helpful. Thanks. I've got MotoCalc. Even though it has not been extended to include much, if any, information for helis, I exported the motors to a comma separated values (CSV) file and using MS Excel looked up some 180s. It listed four Hacker motors and two Scorpions, weighing anywhere from 35.5 oz (1006.408 g) to 67.02 oz (1900 g). I suppose the heavier motors are direct drive for propeller driven fixed-wing model airplanes.
So the "180" designation is the motor constant, the RPM/V value, correct? Regardless of the weight of the motor, 10 volts would theoretically turn the armature 10 RPM, right?
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dav1d
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PostPosted: Sat Dec 05, 2015 1:38 am
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tombo242 wrote:
Hi David,

On 180 motors, I use this type in my "Wee Jock" (totally rebuilt, only the front frame is original) small coax. Canopy is printed on card - cut and stuck. I can send you the pattern if it will help.


http://www.xtreme-production.com/xtreme/index.php?main_page=product_info&products_id=297

The ball bearings make a big difference in power and long bearing life, the replaceable brushes are useful too. A search on Ebay may well produce better prices.

Tom.


The motor info and the tip on the ball bearings helps, Tom. Thanks
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