What is the minimum number of RC channels required to control a Quad Copter?

Question

Most of the blogs/website say we need a minimum of four channels for a quadcopter (pitch, roll, throttle, yaw):

1. One channel for throttle
2. A second channel for turning right and left.
3. A third channel for pitching forward and backward.
4. A fourth one for rolling left and right.

But looking at the RC transmitter, I see that at a time you can change a maximum of two sets data (left and right joy stick). Even if you want to send Rudder and Throttle information at the same, can it not be sent in the same packet?

My understanding is two channels should be sufficient to control a quad copter. Please provide more clarity on this.

Answer 1

Ironic answer: you do not need any channel, but your quadcopter will just hover stationary :)

Practical answer:

• The throttle controls translation on the vertical axis. This allows you to gain or loose altitude. Depending on how the quadcopter is programmed you may control the vertical acceleration or the vertical speed (aka autolevel mode).
• The rudder controls the rotation around the vertical axis. This allows you to face North, East, South, and West.
• The ailerons and elevator (2 channels) control the roll and pitch. This allows you to get the quadcopter at an angle compared to the horizontal plane, and move forward, backward, left, or right. Depending on how the quadcopter is programmed you may control the angular rate (aka manual mode) or the angle (aka attitude mode).
• In addition you may have any number of spare channels to control the flight mode, trigger a camera, control a gimbal, retract the landing gear, etc.

As commented in the ironic answer none of this is required, but more channels will make your quadcopter experience more fun. You don't say what your goal is, but if you want to build a quadcopter for fun I would recommend at least 6 channels, and advise against using a 4-channels transmitter. For instance the mainstream DJI Naza controller requires 6 channels to use all the features.

Extra information: Each joystick counts for 2 channels, because they can move on 2 different axes. The number of channels does not mean anything on a hardware/packet level on modern controllers (2.4GHz), as all the channels are multiplexed into digital packets and demultiplexed at the receiver. Multiplexing 4 channels into 2 on the transmitter and demultiplexing them on the receiver is possible but it would require a significant amount of DIY and is not practical or sensible for any actual application.

Answer 2

You have two channels on each stick. Commonly throttle and yaw on the left stick and pitch and roll on the right.

Answer 3

In this case, you can think of a "channel" as a "linear control" -- a single-dimensional value. For example, throttle can go from 0%-100% (or -100% to 100% if you're doing some really crazy things); roll, pitch, and yaw are expressed as a range of degrees.

The RC transmitter you refer to has 2 joysticks, each with 2 dimensions, for a total of 4 channels that can be controlled -- this covers all the channels you mentioned.

However, since a quadcopter can move freely in any cardinal direction, you need only transmit 3 channels: throttle, roll, and pitch. This prevents you from controlling what direction the quadcopter is facing at any one time, but does not limit its mobility.

Answer 4

I would have thought the control would only need to transmit a single packet on a single channel which gets sent only when the operator changes something.