My first Tricopter started life as the simple wooden framed Mongrel Gear Trilogy
using 4 cheap rate gyros, 3 cheap ESCs, 3 cheap motors and the RC Tx's CCPM mix.
The rear motor was mounted on a platform supported by a heli blade shaft and pivot
which is a popular option for Tricopters.
However, during the learning process (having never flown any rotor-craft before), I
found that any crash on the rear arm bent the heli blade pivot. In fact any
hard landing would do it as the weight of the motor simply bent the shaft down.
That meant the yaw trim changed constantly and eventually the shaft just
I rebuilt the rear tilting motor mount using steering parts from a crawler
so that it was a tilting platform with the pivot point directly over the center
of the rear arm. That mount is totally cobbled together with zip ties
but it has been absolutely bulletproof. I tweaked the servo position but otherwise
transfered that mount over from old frame to my new one, unmodified.
It wasn't long before I was buzzing around low between and below trees, over water,
etc. Accumulation of crashes including an inverted water landing went through
the first batch of motors pretty quickly. When I got into the 2nd batch
of motors (and some ESCs) ordered from HK I found some un-subtle differences
in power. I was having to use a-lot of trim to get it flying level. Problem is,
that wasted precious flight time, and if I tried to leave it trimmed when changing
batteries, one or more of the gyro's wouldn't arm because the center position
was too far away from true center, the ESCs wouldn't arm because their throttle low
position was no longer low. I'd have to center all the trims, plug in the battery, try to
remember the exact number of clicks of pitch and roll trim.. take off, trim some more.. get
it steady, fly for a while, land and repeat. I finally got fed up with that, and ordered
a v5.5 Black KK multicontroller board. That eliminates all four rate gyros and
it initializes the throttle signal independently of pitch/roll trim so I can maintain
trim changes between battery packs (trim still changes with differences
in motors, ESCs, battery size, cameras on-board etc).
KK controller is pretty much plug and play. Only quirk in latest Tricopter firmware
is that it won't let me reverse the gain on the yaw gyro, and it happened to
be backwards for my current servo and mounting position. Eventually switched
to a digital servo that I could reverse programatically. Digital servo jittered a lot
so eventually moved to HS85MG which happened to turn the correct direction.
Moving on, the Trilogy has a single plywood layer in the central platform, and 3
square arms with bolts through the arms connecting them to the platform.
I found that most hard crashes would result in either the platform breaking down
the middle, or one or more of the arms splitting out around the bolt holes.
Went through a lot of PU, gluing those arms back together.
About now you're going "Why don't you just stop crashing?"
Well, besides the fact that I like to fly fast, close to and under things so was crashing
into and falling out of trees regularly I was also having random motor mount failures.
The Trilogy was originally designed (may still be) to mount the motors to the
arms using zip ties to hold two of the 4 arms of a standard motor mount cross
down to the top face of the square arms. Zip ties could take the flight load, and a little
CA kept em from sliding off. Idea was, that in a hard enough crash
the zip ties would break, saving the motor itself. Ultimately though, I had several
failures of those 4 armed crosses themselves. They were vibrating and twisting causing
metal fatique of the cheap aluminum until the cross failed, the motor departed the
arm, and the tricopter falls from the sky like a brick. Once or twice might have
written off as a fluke but it happened about a half dozen times. I needed to be able
to mount the motors using all four arms of the motor mount cross, but still retain
some way to absorb crashes and hard landings.
My old Trilogy frame finally just gave up so I retired it. Looking around for
an alternative, stumbled on a very popular link.
Dual layer central platform simply clamped to dowels for the arms
with motor mount platforms also clamped to the arms.
A minor crash results in the arms or mounts shifting or rotating.
A major crash also breaks nylon bolts. Every component is field replaceable,
and it's fairly easy to break down for travel.
Here's my version.
Close-up of how each motor is mounted
It's a pretty easy build. The platform and all the plates were cut from aircraft ply with
a handsaw, and the holes made with a drill press, but could have been done
with a regular hand drill.
Close-up of the gear on the central platform.
It ain't pretty but it gets the job done. The GoPro is strapped down to
an anti-vibration platform (gel mounts inside). Flight camera is
in a block of foam.
5V BEC to power Rx and KK board.
KK board has real simple wiring.
2.4Ghz FrSky telemetry Rx works fine for my usual relatively close buzzing around.
Video Tx mounted on another pair of clamped together plates,
a bit lighter than the motor mounts, so it rotates more easily, which helps
prevent damage to the low pass filter and CP antenna stuck on top.
It's already proven that it can take a beating. I broke some nylon bolts and plates
but had spares in the field. I've reinforced the bottom plates
with a layer of Kevlar cloth since then, and they're holding up better. A hard, fast
forward landing from a dead battery resulted in every arm moving and every motor
mount twisting, with no damage at all.
If you look at the tail mount photo above, can see that the servo is simply clamped
between the two plates with a little stick on sandpaper to add friction. Hopefully
any hard impact will basically just disassemble the whole mount rather than
break the servo arm or something else.
Here it is in action
Since that flight, I've done some more work on motor/prop balancing and
freeing up the anti-vibe mount to do its job better.
It's a bit heavy but there is some room for weight savings by trimming down
some of the plates. I might try thinner, but dual reinforced kevlar plates
for all the motor mounts. The video Tx plates can be much smaller.
May also poke some large round holes in the bottom plate in unstressed
Here's another showing how it handles crashing.
Platform was unharmed. Broke one nylon bolt a few props.
Recently switched KK board firmware to KapteinKUK v1.6 and that got rid of some of
the glitching I was seeing on the motors and tail servo. That plus the FY30A stabilizer
in series, has made it quite a lot more stable in high speed flight.
Here's an example of what it can do now.
I take no credit for the design, as I borrowed directly from others.
I went with this approach because I like flying a lot more than building/repairing.