Your arguments seem to be some of the standard arguments I've read before.
I agree with FGA. Yaw and 'swooshy' flight is why I have a tricopter. Now that I know how to tune a quad, that difference is gone.
Tricopters are more maintenance, more money, less efficient and less flight time (due to the maintenance) than a similar quad. The tail pivot mechanism and servo weigh as much if not more than the 4th motor on a quad without providing any thrust. The tail pivot mechanism requires more maintenance than a 4th motor. They are a constant maintenance issue if you fly over sand and I mean EVERY flight maintenance.
The
servos I use are 16 grams. The
SunnySky motors weight 23 grams. A sheetrock screw adds another 5 grams maybe?
Tricopters have one less motor and ESC which can save your initial budget around $25. Servos are
$6.99 and a
SunnySky motor is $18.50. Your ESC will be around the $8 price. Tri's also use 25% less propellers.
I have broken 4 servos but I've also gone through 3 motors over the last year.
The tail pivot mechanism can be as complex as you make it. Use a sheetrock screw and you adjust it with a screw driver. Not much complexity there.
Most of the sand in Kansas is in sandboxes. Who wants to fly over kids?
The pivot mechanisms are notorious for breaking in a crash where the copter 'landed' on the tail boom (common since the servo and pivot tend to make the tail boom heavy) and seem to be the weakest part on the whole copter. They also cost the most in time or cash to repair/replace.
When you make your initial rear platform, just make a second while you're at it. It will require another piece of wood and an extra screw. If you replace your servo with an identical one, it is faster to replace than a motor and does not require any soldering. If you're buying the HS-81 or HS-82MG, you are spending money needlessly (I use to buy these). The only thing special about those servos is how proud Hi-Tech is of them with their $30 price tags. Dumb... I have 2 broken ones sitting around - You can see me break one in
this video at 1:30 and see it move freely with broken gears at 1:49. Get this
servo for $6.99. It has metal gears and is digital.
If someone comes up with a solution to the tail pivot that doesn't outweigh a motor and won't break in a minor crash or seize with a little grit kicked up by a rotor. I will consider one.
Until then, we have mini-quads and hexes.
I've never had one stop working because of something getting inside of it, that is an argument I haven't heard before.
Perhaps the biggest difference between our experiences resides in the frame itself. The tricopters I've built are all made of wood and based off HallStudio's (
simplecopter.com) design. When an arm breaks, it costs $3 for a piece of wood which can be purchased at any hardware store and from it you can make 3 more arms. The rear swivel is a wooden platform for the motor with a sheetrock screw through it into the end of the arm. The landing skid is plastic and held on with 2 screws or pieces of wood attached to each arm. If you crash hard enough to break the main plate, you will have a little more time in replacing it - that did happen to me once where it fell from a failed flip in
this video, you can hear a crunch right at 8:39 when I straighten the front arm. It took me a while to figure it out what was broken. I'd guess.... only guessing here.... that you were using a fancier frame than my $8-built-at-home-frame. The rear servo is what I think scares a lot of people off. If it does, it should scare them off for the "complexity" it adds rather than frailty or cost. It sure isn't a stationary motor screwed in place.