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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@creyes123 http://t.co/hp9FLzmo
That was helpful, now I want one of each!
Yeah, each type really has its uses. Which also explains why they are both still popular.
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About four years ago, I saw my first quad at an indoor meet in Virginia – the owner had built every part by hand bar the electronics and motors, and spent a lot of time getting it to perform. It was a major achievement, no doubt. Now you can barely move on EBay for ready-made quads! Progress?
Sure. You can still build one from scratch, you just don’t have to!
Hi Carlos,
Sorry this comment is a bit late. Your remarks about tricopters v quads puzzle me a bit. You seem to suggest that tricopters do not used handed props. I’m no expert, but have a couple of quads and a tri. All of them use handed props. In the case of the tricopter the two leading motors use a left and a right hand prop respectively, while the trailing motor (rudder) wears a conventionally handed prop, but is mounted at the end of a servo driven shaft aligned with the axis of the chassis arm.
I find the tri particularly easy to fly, and very smooth.
Hope this makes sense.
Hi. Yes, I understand what you are trying to say. With a tricopter, using reverse rotation propellers is optional. I suppose there might be an advantage to using them if the goal is to have a stable platform that does not have to be very maneuverable. Frankly, I think you are better off just using regular rotation propellers with a tricopter. The pivoting motor is what gives you yaw stability. Having two reverse rotation propellers in a quadcopter is essential.
Interesting. I had no idea you could use normal handed props all round on a tri. It would surely be working the gyro harder though. You are right about the stability though. As set up, it is almost numb, but at my age, that’s an advantage!
>but at my age, that’s an advantage!
Funny. No, you would not be driving the gyro any harder. I suppose it is a little bit less efficient, since you have to use more thrust to counterbalance the rotational force.
The bit about quadcopters having the redundancy of an extra motor is incorrect. It’s impossible to have a stable descent on 3 rotors of a quad.
If you run the motor opposite the failed one at all, you’ll flip towards it. If you don’t, it’s going to fall one way or the other along the axis of the two that are running.
If by some chance the weight happens to be offset so the centre of gravity is well between the 3 working motors, then it could possibly hover for a second before the yaw got completely out of control and crashed.
I agree. It should go without saying, all four rotors need to be operational for it to be stable and fully controllable.
I can imagine that it is possible for some clever piece of software to shut down the rotor opposite the one that failed. Then it could enter into some sort of semi-controlled descent. That would be better than what typically happens nowadays.
But regardless, such software does not exist to my knowledge. So in practice quads have no advantages over tris in a failure condition. We may not have gotten there via the same route, but we reached the same conclusion.