minimum spacing for twin outrunners

[Jesse J]

I am gonna be putting a pair of counter-rotating outrunners in my new mono and I wonder if there is any consequence of mounting them almost touching?

The reason I ask, is that I notice that on the bench they are pulling on each other, could the magnetic fields interfere and cause any problems?

I will be designing my own mount, so I can place them whatever distance they need to be - although I want them as close together as possible.

thanks

[H2OCamel]

That is a very good question Jesse, I hope some one can give you the answer.

[Jesse J]

anyone?

[sundog]

I know what you mean by attracting each other. It's my guess that they would interfere with each other if put too close. You could stagger them (one more forward with longer shaft). That way the shafts/props could also be closer to each other than if motors were side by side, and there would be little magnetic interference.

[keithbradley]

My guess (completely unsupported by anything) is that it wont matter once they start spinning, and it probably wont really matter at all. I assume the magenets in the motors are attracted to the metal on the can of the motor next to it...I dont see where that would hurt anything. I wouldnt be afraid to try it.

[sundog]

My guess (completely unsupported by anything) is that it wont matter once they start spinning, and it probably wont really matter at all. I assume the magenets in the motors are attracted to the metal on the can of the motor next to it...I dont see where that would hurt anything. I wouldnt be afraid to try it.

But the magnets in outrunners are in the cans, and can have a powerful attraction when near another motor. This would be a good experiment. I was just offering a solution to what might turn out to be a problem. But, like you say, it may not even matter.

[Jesse J]

I doubt it also, but like the staggered idea... not staggering, but .. well anyway

Might just try this, heck the real ones have em!?!? I'm all for unconventional..........

[mm123521]

Interesting problem:
As the motors rotate past each other the magnatic attraction and repulsion would change at a very rapid rate. Wouldnt this cause noise and viabration?? Would these attraction and repulsion forces fatigue the motor mounts?

Mark

[sailr]

In my opinion, the attraction WOULD cause problems. It might create back EMF in the opposite motor(s). The idea to stagger them seems reasonable.

[Jesse J]

yes, interesting problem. I think I will be staggering just to be sure - wouldn't want to blow an ESC to learn. now to design a mount system for this staggering problem.

any more ideas are always welcome, even opinions - I don't know how much data exists or what kind of data would help explain this phenomenon.

[Jesse J]

Well now we have some data for this question. I was just hooking up a motor to center the servo and for some reason I hit the throttle - and I saw the coolest thing. As someone on RCGroups indicated, the magnetic field actually helps smooth out the motor action. In a sense, distributing the field between the two motors.

Answer to the question: still unknown, but more than 3"!

[sundog]

Wow, I've never seen that demonstrated. I'm guessing that staggering them is your best bet. Toocool.

[Jesse J]

To eliminate the effect, yes.
But, I don't know that this effect is necessarily a bad one - as long as they are counter rotating and perfectly timed, then they should be fine. It appears as if they might even share the load - kinda like positrac differential, i.e., when turning, and the outer one slipping will want to rev (opposite of a car) - I wonder if the inner one planted might act to slow the outer one and transfer a bit to the inner one... vedy interestink.

[sundog]

Since both motors turn the same direction when the 'sympathetic' effect takes place, couldn't you use left lay flex on both drives, with left & right handed props, motors wired to go the same direction? Then the effect could benefit each motor and your props would counter-rotate (if you want that).

[Boaterguy]

http://www.youtube.com/watch?v=Qyq4xSFAnsM one motor is plugged in, the other is not, this may be a problem, it may not.
(this is not my video)