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Jun 25, 2001, 11:38 PM
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soholingo's Avatar

Difference between 6v and 7.2v speed 400 engines???


Can someone tell me the difference between these two engines? Which one is faster? Which one is more powerful, which one is cheaper, etc... I see a lot of people replacing 7.2v versions with 6v versions...

Thanks,

Jay
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Jun 26, 2001, 12:17 AM
Registered User
They cost about the same. They both put out about the same amount of power using the number of cells that they are intended for.
The 7.2 volt will put out about the same amount of power under 7.2 volts as the 6V version will put out using 6 volts.
HOWEVER, a 6V version will put out more power than the 7.2V version using the SAME voltage. But it also can not handle as much voltage as the 7.2V without burning up.
Basically, the 6V is limited to 8 cells or under, and the 7.2V version is limited to 9 cells direct or even 10 cells with a gear drive. You can exceed these numbers, but the motor will not last very long.

Shawn
Eflightpower.com
Jun 26, 2001, 11:37 AM
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Thanks for the reply. So if I have a 7.2v engine and replace it with 6v engine, then I will gain more power, all things being equal?

Thanks this is great information...

Jay
Jun 26, 2001, 03:22 PM
Registered User
You will get little more power assuming that you will use same amount of cells like you used with the 7.2V.
With 8cells you may shorten the life of the 6V but not drastically. And when they cost less then 10 bucks, who cares anyway.

Quote:
Originally posted by soholingo:
Thanks for the reply. So if I have a 7.2v engine and replace it with 6v engine, then I will gain more power, all things being equal?

Thanks this is great information...

Jay
Jun 26, 2001, 04:50 PM
Registered User
Exactly. All things being equal, you will get more power with the 6V.

Shawn
Eflightpower.com
Jun 27, 2001, 08:03 AM
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Andy W's Avatar
Quote:
Originally posted by soholingo:
So if I have a 7.2v engine and replace it with 6v engine, then I will gain more power, all things being equal?[/B]
FYI: Around here, we call them motors..
..a
Jun 27, 2001, 01:07 PM
Administrator
jbourke's Avatar
With the same propeller and voltage, the 6V will spin the propeller faster. The laws of physics demand that this requires more power. So the current draw is higher.

Both motors have the same torque limit since they are the same basic design. The 6V motor produces less torque per amp than the 7.2V. So that means that the 6V can handle more amps.

Because of the above factors, the 6V motor will typically be best for a performance setup and the 7.2V will be best for a more leisurely setup.

The situation becomes a little more confusing if you are going to play with the cell count or propeller when you compare motors. But, as a general rule ignoring some second-order losses, it is true that two motors of different winds but the same general design will have the same RPM and torque limits. The reason to choose one wind over another is not to get more power to the propeller, per se, but rather to choose how the power is taken from the battery pack. E.g. Do you want to run many cells at low current or few cells at high current? Either way, turning a certain prop at a certain RPM requires a certain amount of power. This is inescapable.

You wanted to know which motor is faster. The simple answer is that the 6V is faster, but this is categorically untrue if we remove most of the assumptions that people have. In reality, both motors can be equally fast assuming that we can change the battery pack and propeller to match the motor.

You asked which motor is more powerful. Again, the simple answer is the 6V, but this ignores the fact that the torque and RPM limits are the same which really means that they are equally powerful.

They are also roughly equivalent in price. Its the same basic motor. Its just that one has a different winding in the armature. Thats what makes one motor a "6v" and another a "7.2V".

The 6V will always be "faster" or "more powerful" than the 7.2V up until the point that the limits of the motor are reached. At that point the 6V will be really, really slow compared to the 7.2V.

Note that "6V" and "7.2V" are names and nothing more. Technically there is no such thing as a voltage rating for a motor. Aveox uses designations like 2Y, 3Y, and 4Y which are analogous to the 4.8V, 6V, and 7.2V specs for speed 400 motors. The difference is that Aveox names their motors by the number of winds, which is a far better way to describe the difference between them.

I know that you probably want a simple answer to the question, but the actual inner workings of electric motors is very intriguing and is useful information for a hobbyist.

Jim
Jun 27, 2001, 11:15 PM
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Jim

Thanks for the blow out. That was exactly what I was looking for, and I appreciate the effort.

Jay
Jul 16, 2001, 02:51 AM
Registered User
So, how does a 7.2 volt motor on 8 cells compare with a 6 volt motor on 7 cells?
Jul 16, 2001, 08:05 AM
Schumacher USA
exactly the same, but the airplane is "one cell lighter"

Shawn
Jul 16, 2001, 08:54 AM
Registered User
Andy W's Avatar
Not exactly the same.. you'll have less power overall, and different efficiencies. Run it thru motocalc and compare..
..a
Jul 16, 2001, 01:37 PM
Registered User
swami's Avatar

Here in Europe we have those wonderful little white props for speed 400.
They are called "Gummiprops", and are made by Gunter Flugspiel.
They have great performance, are difficult to break (unless you fly at below zero temperatures) and cost only about 1.25 US$.
they are also great for speed 280 (4 Amp on 6 cells).
Anyone seen them in the US yet?

Dirk.

Jul 20, 2001, 05:37 PM
Model Designer
keven64's Avatar
Hello,

The little white 'Gunther' props are available world-wide and distributed with Multiplex Twin Stars, Twinjets, Pico-Jets etc etc.

Soho - Put a 6v motor in the new Skyscooter . . .

Keven.
Jul 20, 2001, 10:50 PM
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Kev,

that's my plan, I have 2 6v speed 400's. But after watching Dave go through the same trials that I did, I know it was the batteries that were the cause of my low power... But fully charged batteries and a 6v should keep me up for a bit...


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