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Old Mar 20, 2011, 05:54 AM
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HobbyKing CR23L Contra Rotating Brushless Motor


I just got my hands on this little beauty yesterday. I have been waiting for an affordable contra system for a while. So when this came up I was keen to check it out.

http://www.hobbyking.com/hobbyking/s...dProduct=16618

The specs on the HK website must be wrong somewhere I reckon. A 300 gram motor only putting out 560 watts? Hopefully they are underspeccing this a fair bit. If I can get 800-1000 watts out of it without stressing it too much I will be pretty happy. So I need to do some testing.

First, is there an easy way to work out the Kv? I don't have a rpm meter or hyperion emeter?

I need to buy some bolts to mount the motor to something to start testing, so until then a breakdown of the parts....

It doesn't look like a bad motor. The way the front prop attaches may need some slicing and dicing. The way it works at the moment it's a long way from the rear prop. At least a couple of centimeters.

The way the rear prop will also need some tweaking if a prop with a large pitch is used, as the plate holding it down is rather large (4.4cm). Might need some washers to space it out from prop hub.

Pics to follow......
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Old Mar 20, 2011, 07:20 AM
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My dream machines.....
Old Mar 20, 2011, 10:48 AM
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HK lists the motor(s) as 1100 KV, you could of course check this out with kv meter available from, wait for it.......HK! As far as getting 800+ watts out of it, it may be possible however, this is a $30 package deal and.......good luck!

BTW, I built the Turnkey Bugatti, flys well and looks great in the air! Most comments after landing are "that swept forward wing thing just looks wrong!" Gotta love it!

Michael (if your not fryin, your not tryin!)
Old Mar 21, 2011, 04:53 AM
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Lol, 30 bucks. It will be interesting to see what it can handle.

No progress today. Work way too busy. Forgot to stop by the bolt shop to get the mounting hardware. Hopefully tomorrow.....
Old Mar 21, 2011, 12:06 PM
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Never surrender, never give up, never stop building! Ok, so maybe I spend a litle too much time in this hobby

Have you decided which plane to build yet? Or, are you first thinking of building a test mule to evaluate your contra rotating motor system?

Other neat possibilities:

Martin Baker M.B.5
Boeing model 400 (F8B)
Douglas A2D Skyshark
Fisher P-75 Eagle
If really ambitious, there are also multi contra rotators, Convair R3Y Tradewind.

Michael
Old Mar 21, 2011, 02:50 PM
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Old Mar 21, 2011, 05:21 PM
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A 300 gram motor only putting out 560 watts?.

The windings are sloppy and tiny gauge... so maybe 280W into each motor is as much as you can expect. What comes out won't be anywhere near the equivalent of 280W x 2 = 560W!
Old Mar 21, 2011, 06:44 PM
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Quote:
Originally Posted by elecfryer View Post
Never surrender, never give up, never stop building! Ok, so maybe I spend a litle too much time in this hobby

Have you decided which plane to build yet? Or, are you first thinking of building a test mule to evaluate your contra rotating motor system?

Other neat possibilities:

Martin Baker M.B.5
Boeing model 400 (F8B)
Douglas A2D Skyshark
Fisher P-75 Eagle
If really ambitious, there are also multi contra rotators, Convair R3Y Tradewind.

Michael
Quote:
Originally Posted by Dr Kiwi View Post
A 300 gram motor only putting out 560 watts?.

The windings are sloppy and tiny gauge... so maybe 280W into each motor is as much as you can expect. What comes out won't be anywhere near the equivalent of 280W x 2 = 560W!
I'm thinking the Reno Racer first.

You mean more or less watts Dr. Kiwi lol. I'm guessing less.......
I may have to finally learn how to wind a motor. It was going to happen sooner or later. I'll still give this a thrashing first and see what it can do.
Old Mar 21, 2011, 07:27 PM
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rule of thumb = 3-4 watts per gram... 300 gram motor ~900 watts.. granted the contra rotating mechanism must weigh a good part of the total..
Old Mar 21, 2011, 08:45 PM
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Thanks Jim, thats a good base to go from. I guess the motor mount and extra prop adapters etc add a bit of weight to the whole setup. Maybe I'll just be happy with 700-800 watts
Old Mar 22, 2011, 12:00 AM
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Keep in mind what goes in does not all come out when it comes to "watts in". Dr. Kiwi is very knowledgeable about motors and he may be trying to tell you that while you may get close to 600 watts in the effective output will be much less.

If you are all ready aware of this, I apologize! Put a watt/amp meter on your system (one motor at a time of course!) and (with a props on it) run it up to full power and record the numbers and get a rpm reading. Take your voltage underload and multiply that by the kv and that result is the rpm's that the motor wants to do. Divide the rpm's that you recorded by the rpm's that the motor wants to do and that is a "gross efficiency percentage". It is not an exact number however, it is close enough to be usefull! For many planes (say flying speeds from 40-80 mph) if the % is in the range of 80% - 90% you are probably close. When you start getting under 70%, too much prop load. When you start seeing over 90%, there is room to load up the motor with more pitch or diameter or both. People like me always recommend checking out things like this prior to the first flight! You can also use the amp draw numbers to see if your esc and battery are well matched for the job.

Electrics are all about matching up the components to the job!

I am sure that you can probably load up each motor enough to draw in say 500 watts however, the efficiency will be horrible and results will tell the tale! Forewarned is forearmed!

Looking forward to hearing/reading your results as for an inexpensive system, it may have possibilities!

Have you checked out the Himaxx doubles?

Michael
Old Mar 22, 2011, 02:55 AM
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Thanks Michael, yeah, I did have some sort of idea that there are losses in the system. I like the % efficiency calculation though, I have never used that before.

I have looked at the himax motors before, and I like them. I found it hard to find specs on those as well. They have some details on their website for a couple of the smaller setups, but the larger setups are lacking details. Anyways, for $30 I thought this one was worth a try.

Time to get me a rpm meter.....
Old Mar 22, 2011, 05:35 AM
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Keep in mind that the rear prop will be in the wash coming off the first prop, and will need a much higher pitch to be loaded the to same draw. It is not necessary to make the motors draw equally, but it helps keep everything tidy. Fwiw, I would put the reversed prop on the front, there are many times more choices for the normal rotation props to get the right size to make your motors balanced. Was that clear? It is a bit early here
Old Mar 22, 2011, 06:42 AM
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Lol, yep that made sense. I guess I'll work out what prop to put on the front first. Then figure out if I can get that size in a pusher prop, then work out the rear prop.
Old Mar 22, 2011, 02:31 PM
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years ago Keith Shaw built a Bugatti racer .
It was magnificent.
Curiously after it was built he managed to measure amp draws in use. He found that the rear props' motor was drawing far less than the front (prop) motor. Despite the rear prop having twice the pitch.
Summary was that the rear prop/ motor were Less than effective, being mostly 'along for the ride'
Do some information hunting ?.. Some myths seemingly persist, in defiance of fact:-)


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