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Old Oct 09, 2012, 11:54 PM
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Tricopter Blade Rotation?

Please NOTE I am a n00b and have not even yet ordered parts for a multi rotor much less built one but I have a theoretical question:

So I have seen a few different places suggest 2 setups on blade rotation of tri's:

Option #1. You should use 2 Normal and 1 Counter Rotation blade..The 1 one counter rotation being "Front Right".

Or

Option #2. All blades normal rotation but is less efficient, but is functional.

I would like to keep efficiency but also buy as few parts as possible and I want my front 2 blades the same color but the rear to be a different color.

How bad would it be for the front to motors to have the same rotation but have the rear being the counter rotation?

Again I a n00b but to me the math is still the same. 2 to 1... I would not think this matters to the FC on a tricopter as the yaw control is done by the servo and NOT the "torque" of the motors.

While on the subject of Efficiency and Yaw of a Tri... Because of the 2 to 1 (Blade rotation) of the a Tricopter, Has any played with a larger motor/prop in the rear or a longer "Tail-arm" to help offset or equal out the rotational difference? For example a large prop would require more torque to spin... Or great distance from the Center of Rotation would give great "leverage" over the rotation...

Just wondering how many have "played" with different set-ups...
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Old Oct 10, 2012, 12:03 AM
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If you put the same rotation props on the front arms might as well put one on the rear as well.

the only reason to have one counter rotating prop is to help with Yaw authority and easy the load on the yaw gyro/servo, this only works if you have the single counter rotating prop on one of the front arms.


John
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Old Oct 10, 2012, 12:25 AM
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Originally Posted by shultz View Post
this only works if you have the single counter rotating prop on one of the front arms.
Why does it only work on the front arms?

2 out of 3 is 2 out of 3
2:1 is 2:1
unless we get into Math done by Government
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Old Oct 10, 2012, 12:34 AM
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sigh.... 2 out of 3 or "goverment math" has not one thing to do with rotational torque.

good luck.....

EDIT:
sorry for not giving you a real answer. when you have both props on the front arm spinning the same direction the torque they create is in the same direction. by using one counter rotating prop you more or less cancle this torque of the front props making it easier for the tail servo and gyro to not only compensate for this torque but also over come it increasing yaw authority.

Putting a counter rotating prop on the rear motor does nothing to cancle the torque of the front motors.
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Old Oct 10, 2012, 12:45 AM
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Originally Posted by shultz View Post
Putting a counter rotating prop on the rear motor does nothing to cancle the torque of the front motors.
So because the rear motor/blade is on a servo it has NO rotational torque? That is pretty cool...

EDIT:

Sorry for being defensive but I like knowing how & why things are the way they are, being its just because does not work for me.

When I started this thread I was expecting something like the "FC is not programed for that" or "that it is bad idea because___." but hoping for "that works too!"

Being told A + B = C but C - B != A does not make sense to me...

I know that all 3 motors (equal in torque and equal in length from the center point) can NOT be configured to be perpendicular to level ground during a level hover without yaw movement... But as close as possible is the goal... Because that is the most efficient, right?

So 2 normal and 1 counter no mater which one is "tilted" has the same affect, unless you can show me the math other wise.... Actually lets think about this a little more...

If the Counter rotating is the one tilted... Well it has to spin faster to keep the craft level because some if its thrust is being "wasted" to keep the craft's heading. So faster spinning means more rotational torque... So it may even have to be "tilted" less??? I would love to see a physics teacher give us some real numbers on this???
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Old Oct 10, 2012, 12:55 AM
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Quote:
So because the rear motor/blade is on a servo it has NO rotational torque? That is pretty cool...
Of course the rear motor creats rotational torque... servo or not. Fact is, you can run what ever direction prop you want on any of the motors and it will fly as long as all the props are generating thrust correctly.

By running one counter rotating prop on the front you get better yaw authority and the gyro has less torque to compensate for.

John
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Old Oct 10, 2012, 11:24 AM
we dont NEED roads!
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Im not too sure about the math thing.

If you think about it, the motor on the YAW does not produce rotational torque the same, as it is not in a fixed position. There-fore the torque changes direction.

Your best bet would be to have the two opposing motors on the front. Then it would not matter which direction the rear rotates.

The flight controller wont care what direction your motors are spinning... so long as they produce downward thrust.
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Old Oct 10, 2012, 02:15 PM
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Subaru/Shultz,

So as far as it concerns me... It will not matter if I do this odd layout of the 2 front in one direction and the 1 rear as counter rotation. It may not be as effecient but other than that it should no ill effect.

That is what I needed to know. Thanks and sorry for being confrontational.
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Old Oct 10, 2012, 02:19 PM
we dont NEED roads!
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Then i guess you answered your own question.

When I first built my tri, I did just as you are planning. I had my two front motors rotating against eachother and I cant remember which direction my tail was rotating.

After I blew through all my props I decided to just buy R props and use all the same rotating props since I had alot of those props left. I have been flying my tricopter ever since that way and i have no complaints.

But now I do have a bunch of CW & CCW props again. So maybe for grins I'll reverse one of the front motors and see if I get any more battery life.
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Old Oct 11, 2012, 04:01 PM
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I found this on tricopter prop directions the other day.

http://www.rcgroups.com/forums/showt...=rotat+tricopt

I have a CW and CCW prop on the front and whatever I have spare for the back. I buy props in CW & CCW pairs. I found I quickly ran out of the type on the yaw so I reversed the yaw motor and used up some spares
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Old Oct 11, 2012, 05:05 PM
but thats not soon enough
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look here

Tricopter Counter Rotating vs. Non-Counter Rotating Propeller Demo (2 min 39 sec)
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Old Oct 13, 2012, 09:41 AM
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Too bad he didn't do the CR prop on the back too? It looks (to me) like you can see the rear prop tilted more to counter the prop torque in the no CR props case. This angled thrust then needs to be counteracted by the tilt in the front arms, no?

I also don't see why opposite direction on the back wouldn't help. Sure it's tilted a bit (at times) but at pretty low angles. The overall torques need to balance out regardless.

Maybe I'll give it a try when/if I get my tri all sorted. The suggested (default) rotations on the KK2 board have CR props on front left and tail. Seeing as how I have more regular props, plus orange ones, I reversed the tail. I only got half a battery through before I stripped my tail servo, so I'm rebuilding things with a stronger one.

I seem to recall seeing something that the suggested rotation for the front was having the forward blade turning in (like the KK suggestions). Can't remember why though.

cheers,
Andrew
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Old Oct 13, 2012, 09:41 AM
Posted as eflightdude 06-07
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Quote:
Originally Posted by shultz View Post
Putting a counter rotating prop on the rear motor does nothing to cancle the torque of the front motors.
Sure it doesn't, cause the laws of physics just stopped working for tricopters...

Assuming that all three arms are the same length, and the tail servo is level, putting a CCW prop on the tail and 2 CW props on the front gives the same net torque as putting one a CW prop on the tail and then having a CW and a CCW prop in the front.

Now, the tail rotor won't be level, so you will lose some of the torque that helps cancel the torque from the front rotors as it tilts. How much depends on how much the tail rotor is tilted.

During the last quarter of my Engineering Statics course we cover equilibrium in 3D, and at that point I could tell you guys just how much torque you lose for a given tail rotor angle, if you are curious.

End result, adding the torques is as simple as FatN00b said at the start, IF the arms are the same length AND the tail rotor is level. But, since you loose torque when the tail rotor tips..well, actually you don't, it starts translating into vertical torque, which means the motors have to adjust speed for that, which means the torques change....so the calculations get more complicated.

From an intuitive standpoint, I would agree with shultz, it's probably more efficient to run the front ones in opposite directions. But it's also probably small potatoes, so do whatever you'd like.
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Old Oct 14, 2012, 07:51 AM
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Originally Posted by jseyfert3 View Post
From an intuitive standpoint, I would agree with shultz, it's probably more efficient to run the front ones in opposite directions. But it's also probably small potatoes, so do whatever you'd like.
I've run my tricopter both ways - now I run the all of the props the same way, simply because I only need to keep 1 kind of spare prop in my cupboard!
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Old Oct 14, 2012, 11:28 AM
we dont NEED roads!
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I noticed when using all the same props on my tricopter, that it has to "lean" to keep from drifting. Just like in that video.

I ran out of 'R' props and had to reverse all 3 motors to start using my backup props. Now the tricopter leans the other way.
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