Tuesday, August 21st, 2012 09:47 am GMT -7 Tuesday, August 21st, 2012 09:47 am GMT -7Tuesday, August 21st, 2012 09:47 am GMT -7
 
UAV Quadcopter with camera

Wondering which type of multirotor has the edge?


 

 

 

Simplicity

Quadcopters cannot be beat for their simplicity. They are just a simple cross with four identical motors. The motors are simply bolted on the frame. There is nothing mechanically complicated about any of it. To top it off, there are many prebuilt frames on the market. Just pick the type of construction and frame size. It could not get easier.

In comparison, tricopters are a handful to build. Their three arms defy a simple construction method. Pivoting a rotating motor with large gyroscopic forces is harder than it looks. You are more likely than not to get bit by hidden challenges. On top of that, I do not know of any commercial tricopter frames for using in your own builds.

Cost

On the other hand, a tri is bound to be less expensive than a quad. You only have three motors and speed controls to buy. One less propeller to buy, too. A quad has four of each. Chances are, you already have a servo you can use to pivot the motor. Lower cost is probably the main reason why tricopters continue to be popular, despite their more challenging construction.

Efficiency

An advantage of tricopters that you may not have thought of is efficiency. With only three propellers, each one has to be larger to carry the load. Having three larger motors instead of four smaller ones might also work better. Designed properly, the power system of a tri will be more efficient than a quad. Being a bit less efficient, a quad might need to carry a larger battery to meet the flight duration goals.

Ease of Building

To build a tricopter, all you really need is three motors of about the same size. Chances are, we all have the parts already to build a tricopter. A quadcopter cannot work unless you have reverse rotation propellers. These are surprisingly rare. You will seriously limit your propeller choices. Also, don’t go looking in your local hobby shop for replacements. You will likely be disappointed.

Control System

A couple of years ago the preferred way to control a tri or a quad was to use chained single axis helicopter tail gyros. Because quadcopters are very symmetrical, it led to simpler control setups than for tricopters. Nowadays, fully integrated control boards are very inexpensive and commonplace. A series of dip switches can be flipped to control any number of different rotor configurations. Bottom line: all configurations are about equal in ease of setup today.

Reliability

In theory, quadcopters have some redundancy built-in due to the extra rotor head. A control board could do a controlled descent in case of a system failure. In practice, I do not know of any that have this feature. Sadly, pretty much any power system failure in a tricopter or quadcopter will lead to a crash. Due to their mechanical simplicity, quads have an edge when it comes to surviving a crash.

Recommendation

If the goal is extremely long flight durations, look into a tricopter. They can be more efficient and the lower parts count can also be more reliable. A tricopter is also a great choice for an inexpensive homebuilt experimental platform.

The Achilles heel of quadcopters is the need for reverse rotation propellers. If you want a more rugged platform than a tricopter and are not so sensitive about cost, just go out and buy a quad frame. Then buy the motors and propellers and you will be in the air in no time.

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