Tri-Copter and Quad-copter Rotations - RC Groups
Thread Tools
Jul 01, 2010, 06:21 AM
Registered User

Tri-Copter and Quad-copter Rotations

Hi all,

I'm new to this forum and to RC'ing in general.

I've been looking into building a tri-copter and have seen many of the wonderful builds some people have put together.

I understand that in tri-copter builds, there seems to be a convention of adding a servo motor arm to the tail propeller to control the rotation of the tri-copter.

My question is; Is there any way to rotate the tri-copter without the need for an angled prop?

Also, some of the quad-copter builds i've seen use perfectly level props, how do these control rotations?

By rotation, i'm talking about absolute rotation around the Z axis (vertical axis). To simply rotate the copter with a tri-copter build using a servo arm I can understand. How do quad-copters rotate? Is this a combination of the counter rotating props?

I'd very much like to build my own and have started sourcing out parts for a tri-copter but I'd like to know if rotations can be handled without making the 3rd prop redundant with it's sole purpose being to spin the copter around.

Forgive me if this sounds a daft question, i'm just starting out with this so am trying to gather as much info as possible before splashing out any cash on parts.

Thanks for reading, any info you can provide would be much appreciated
Sign up now
to remove ads between posts
Jul 01, 2010, 06:56 AM
destructive testing expert
dcaspi's Avatar
Quads use counter-rotating props: 2 rotate in one direction, 2 in the other direction. Yaw (rotation around Z) is done by reducing the speed of one pair and increasing the speed of the other.

You can't use this trick in Tris, thus the need for rotating at least one prop around the X or Y axis.
Jul 01, 2010, 07:58 AM
Registered User
So there is no way to rotate a tri-copter around the Z axis without an angled prop?

I guess I kind of understand how it works for quads and why you can't do the same with a tri-copter.

Wouldn't varying the speeds of each prop on a tri-copter induce some form of rotation at all?

I'd like to build a tri-copter but would prefer one without a dedicated prop solely for rotation. Perhaps I should just build a quad instead and be done with the confusion =P
Jul 01, 2010, 08:24 AM
destructive testing expert
dcaspi's Avatar
The props on a quad are arranged such that for yaw rotation, prop speed variations cancel out all other effects (at least theoretically). To do this you must have symmetry. The same, BTW, is true for rotations around the other axes. That's the beauty of the quad design.
Jul 01, 2010, 08:46 AM
Registered User
Does this mean that tri-copters are incapable of aerobatics due to the lack of props that provide thrust?

Ie: is a tri-copter still capable of performing a front-/back-flip?
Jul 01, 2010, 11:31 AM
Speed Nut
The tail motor has 3 functions, it provides Elevator for front and back flips by slowing down while the front accelerate and vice versa for down eleveator.

It also provides pitch control together with the other 2 motors, accelerating and decelerating together with the front ones, and then it provides yaw (rotation) to the tricopter.

That motor does not have the sole purpose of yawing the tricopter as it happens for the tail rotor of conventional helis.

The tri builds that you see without a servo, actually don't have a servo at the tail end, but they do have a servo in the middle of the frame, driving a torque rod that goes throught the tail boom.
Jul 01, 2010, 11:52 AM
If you are after the orientation and look of a tricopter but do not want to use a tradtional tail servo, then consider building a coax hexa which does not require a tilt servo. You would need either a special board and corrrect firware, such as the KapteinKuk, Mikrokopter, Quadpowered, or UAVX, or a computer Tx and V-tail mixers, or the mini-mixer by ClarkST. More info here: Quadrocopter and Tricopter Mega Link Index

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Wanted Wanted to buy - TRI / Quad / HEX Copter AJD i2 Aircraft - Electric - Helis (FS/W) 0 May 19, 2010 12:24 AM
Discussion Tri-Copter vs. 500class Helicopter vs Quad. fr4nk1yn Electric Heli Talk 0 Feb 08, 2010 07:23 PM
Question Tri vs Quad copter Zirt57 Coaxial Helicopters 24 Dec 03, 2009 11:03 AM
For Sale tri-copter or quad-copter blades HyperHelis Aircraft - Electric - Helis (FS/W) 0 Sep 17, 2009 05:22 PM
Question Tri/hexa-copter or Quad/Octa-copter and Spartan AP2000i or Helicommand Arthur P. VTOLs 2 May 20, 2007 04:02 PM