Tricopter updates

Having established that I could build and fly a tri it was time to update to decent quality components.

I bought carbon fibre arms, power distribution body (with onboard BEC) and tilt mechanism with Blue Bird digital servo from rcexplorer.se 

Prices are very reasonable for these excellent components and postage is only US$7 from Sweden, better than most Australian outlets.

David's tricopter parts are almost works of art, especially the 10mm square woven carbon fibre arms.

From HobbyKing I bought Hextronic DT750 motors and some Turnigy Slow Fly 10x4.5 props.


Hextronic DT750 motors

I need to share my experiences with these DT750 motors. They are well suited to tricopters but do have some design faults which need to be dealt with first.

ESC wire support
The 3 wires are not flexible, just continuations of the single core windings, and will break with bending and vibrations. To prevent this they must be supported around the base with big blob of epoxy glue. I used 5min Araldite and it worked well.

Motor shaft "pull-up"
The shaft is about 40mm x 4mm and threaded. In theory you don't need a vibration inducing prop adapter, just a nyloc nut. BUT unfortunately the shaft is not rigidly fixed to the motor bell. Tightening the nut enough to stop the prop slipping pulls the shaft up through the motor bell. This increases the bearing friction making the motor heat up and draw more current. The shaft is only held in the bell by one tiny grub screw, which is not enough to resist the "pull-up" from the prop nut.

I had some nasty crashes caused by a slipping tail prop because I couldn't tighten it down enough. Broke an arm and ruined an expensive digital servo.

The solution is to put a nut onto the shaft right down to the unthreaded part, then a washer, prop, washer and nyloc nut. That way the prop doesn't push down on the motor bell. Unfortunately I had already cut the shaft too short before I discovered this problem so have had to resort to bulky 4mm prop adapters.

Quest for the best propeller
Turnigy Slow Fly 10x4.5 props are OK but very thin and flexible.

10x5 Gemfan Carbon nylon Graupner copies from Banggood are much stiffer but less efficient giving shorter flight times.

Emax 10x4.5 props from Banggood are a bit stiffer than the Turnigys and may be the perfect choice. Testing continues.

Tricopter build

Here's a quick and dirty tricopter build mostly using materials from my local hardware store.

It covers the basics of design and assembly. The tri flies OK but performance would be improved with more balanced motors and prop adapters and some P and I adjustments.

I haven't covered KK2 setup and tilt mechanism construction but David Windestal's has...

KK2 setup
Tricopter V2.5 build (including tilt mechanism) 

Tricopter

Thanks to great build videos by David Windestal I have recently become interested in tricopters. 

Until now I have not bothered with multi rotors at all and still prefer wings and airfoils to motors. But it looked easy enough and searching through my spares box found most of the required electronics. I had three 2822 1450kV motors and three 25A Plush ESCs so only needed to buy a flight control board and some counter rotating props.

Why a tri and not a quad? 

Well every man and his dog has a quad which makes tricopters cooler.

Tricopters have a tilting tail rotor for steering, which gives more "plane-like" flight characteristics. Also there are only 3 motors / ESCs rather than 4 so they are cheaper.

KK2 flight control board

The brains of a multi rotor is the flight control board. I chose the simplest board, the KK2 (A$26 from Hobby King).

The KK2 takes your Aileron, Elevator, Throttle and Rudder commands (or stick movements) and translates them into motor speed changes and tilt servo movements.  

The KK2 has 2 flight modes: Manual, where the tri will stay at the flight angle you command until you make a correction. Self-level, where the tri will return to level when the sticks are centred. The KK2 also supports the Super Simple Gimbal which is really simple and really works, kind of like steady-cam for an onboard camera.

KK2, Rx and servo power supplies
KK2 board on a tricopter requires two power connections, one to power the board and the receiver, and the other to power the tail servo. They need to be separate for it all to work smoothly. Something about gyros and servos and power loops can cause jittering and instability apparently.

The ESC from motor 1 (front left) plugs into the M1 pins on the KK2 (top right) and provides 5V to power the board and receiver. Do not be tempted to plug 12V in anywhere or you will have to order a new KK2 board (yes I did). There are battery monitoring pins but make sure you know what you are doing before connecting, or just dont use them.

On tricopters a second BEC must be connected to M2 pins (or M3...M8) to provide 5V to the servo. You can use the built-in BEC from the ESC on motor 2 if it is rated high enough. Otherwise add an external BEC.

More than one "switching" style BECs should not be connected on these pins at the same time. Linear BECs are OK. If the ESCs on both motor 2 and 3 have switching BECs remove the red servo wire from one of them to disconnect it's BEC.

On a Quad you can use one normal ESC connected to M1 and three OPTO ESCs because there are no servos needing power. OPTO ESCs do not have an onboard BEC.

Firmware upgrades

There is a lot of chat on RCgroups about which firmware is best for the KK2 and the ESCs on a multi rotor. Apparently Stevis for the KK2 gives more options and better performance than the stock firmware, and SimonK firmware for the ESCs gives smoother and more responsive performance. To start off I used the stock firmware on everything just to get a feel for flying multi rotors, and it all worked perfectly well.

I have since flashed the KK2 with Steveis V1.9 using a $5 USBasp programmer from ebay, and bought Afro ESCs pre flashed with SimonK. Performance is smoother and more responsive.

Here are some early videos. I'll add a build video and onboard footage soon. 

At the moment I'm spending time learning to fly better and optimising the tricopter to reduce vibrations. Stay tuned.

Testing and maiden flights

Arm repair time-lapse

SPECS

Motors - Turnigy 2822/14 1450kV

ESCs  - Turnigy Plush 25A (stock firmware) x 3

Updated to Afro 30A (simonK firmware) One with BEC to power the board and 2 OPTO (no BEC) plus a Plush 18A ESC (which has a linear BEC) just to power the servos

FC board - KK2.1.5 stock firmware
Updated to steveis V1.9 firmware

Props - weak flexy green 8 x 4.5" Hobby King / Gemfan
Updated to much stiffer Gemfan 8045C carbon nylon CW/CCW pairs from Banggood

1.2m Acrobat

I was keen to try some aerobatics with powered planes but The Red was not quite up to the task. Too much of a glider and not enough rudder. So this is what I came up with.

It has a 1.2m x 180mm 12% chord Armin wing and a 700mm fuselage both made from 6mm depron covered with 75 micron document laminating film. That is the thicker laminate and it added lots of strength.

I also wanted to try a design with the tail as part of the fuselage, and test a full flying elevator setup. Both are working very well so far.

Fuselage construction started with the side and bottom panels in uncovered depron

The sides were glued on top of the bottom panel, which defines the width of the front area.

The tail halves were glued together giving the taper curve, then top and bottom panels added.

The fuselage was then covered with 75 micron laminate. 

This added a great amount of strength, especially to the narrow tail area. 

The 2826/10 1400kV motor is mounted to 5mm plywood with ventilation holes drilled out. Initially I built in some down thrust but I am still testing to find the right amount. Plastic washers can be added or removed to vary the angle.

The most radical feature of this design is the flying elevator. The whole horizontal stabiliser pivots on a 3mm carbon fibre rod which also acts as the spar. The rod passes through a brass tube glued into the tail. The inner diameter of the brass tube must be just bigger than the CF rod to give free movement but minimal wiggle. To hold the brass tube firmly there are 25mm discs of foam sandwiched between ID card plastic on either side.

Plans

Overview and build video

Field and slope flights

SPECS

Armin wing span - 1.2m (47") 

Airfoil chord - 190mm (7") including 45mm (1.5") ailerons

Airfoil thickness - 23mm (12%) using 9mm formers 

Spar - Skyshark P4X 7.5mm x 850mm, 57mm back from LE

Fuselage Length - 700mm (27.5")

Flying weight (2200mAh LiPo) - 770g

Full span Ailerons / Flaperons

Full flying Elevator

Large Rudder

TGY 9018MG servos x 4 

Motor - Turnigy 2826/10 1400kV with 8x4 prop
ESC - Plush 40A

MATERIALS and LINKS

http://newtonairlines.blogspot.com.au/2015/03/materials-and-links.html

RC plane building materials

Latest Update Feb 2021

Carbon fibre

Skyshark P4X woven tubes - Wing spars and tail booms
7.54mm OD x 825mm (32.5") - Kites and fun things                

US$3.50 each. Freight is about US$45 to Aus. These are woven carbon fibre tubes, which are lighter than pulltruded tubes and less prone to splitting. Great for big kite spars also.

6 x 1mm and 3 x 0.5mm CF strip - light weight spars and reinforcing

2 to 5mm CF rod and tube - wing tie downs rods and elevator axle
12k CF tow (ribbon of unwoven fibres) - reinforcing and repairs

Carbon fiber Aus and Tates Hobbies Geelong, HobbyKing

Rubber bands Size 64 (87 x 6mm) wing tie downs - Officeworks

Buy a 500g bag, they need frequent replacing. Dont buy the coloured version, they are weaker and fail sooner.

Laminating film and Packing tape
Iron-on document laminating film (covering)
3 mil (75 mic) is the most useful thickness, you can also use 1.7 mil (42.5 mic) for lighter builds. I bought 305mm wide rolls of GBC EZLOAD Lamination film but it may no longer be available

This laminate from Bound to Impress may be suitable but not tried by me 75 micron laminate

Scotch heavy duty exterior double sided tape (motor mount, servos) - Bunnings

Norton Bear cloth tape (reinforcing) - Bunnings

PPS clear 43 and 60 micron packing tape (covering, hinges) - Officeworks

PPS coloured packing tape (covering - 5 pack) - Officeworks

UPDATE: October 2015 - Looks like this coloured packing tape is no longer available at Officeworks. Need to buy Hobby King covering tape or Ebay from now on.
UPDATE: Jan 2016 - KMart now sells coloured packing tape (Thanks Joe)

Scotch Transparent Tough Tape (joining, reinforcing) - Bunnings

This is my favourite reinforcing tape but it's more expensive. Strong holding, flexible and lighter than cloth tape. Used to join wings, hold landing gear on and to reinforce control horns and hinges. Use cheaper Bear cloth tape where weight and strength are not as crucial.

3M Blenderm Tape for hinges - HobbyKing, Medical Supplier

Glue

Hot glue gun - Crescent 60W Bunnings and this 12V battery one from Hobby King
Brown Gorilla Glue
Accent Polyeurethane Glue - Mitre 10
Z-Poxy Epoxy finishing resin - ebay and Tates Hobbies Geelong
Foam Safe CA - Hobby King
Thread locker (Blue = releasable) for motor bolts - Supercheap Auto

UHU Por Foam safe contact glue - HobbyKing

Foamboard
If you cant get Flite Test or Adams foam board (only available in US), then depron is the best alternative.

Depron - Depron Australia

Genuine depron is stiffer and stronger than other uncovered foamboards.

Beware - Paper-covered foam boards in Australia, like Quill from Officeworks, are much heavier and way more expensive than Dollar Tree foam board used by Experimental Airlines and Flite Test. Dollar Tree foam board is not sold in Aus so I use depron with tape or laminate covering. Depron is waterproof and lighter and much more durable than paper covered foam board.

Hot wire cutting bits
Knauf XPS insulation foam 30mm and 50mm thick - Bunnings
Hotwire wire - 40kg (90lb) single strand SS fishing wire
Template aluminium - 0.3mm Weatherflash window flashing

Bits and pieces

Blank ID cards - Search Ebay for CR80 blank ID cards

Piano wire for Push rods (0.047" or 1.1mm) or Landing gear (2.5mm to 3mm) - Tates Hobbies 

Linkage stoppers - Hobby King

Z-bend pliers (worth having) - Hobby King

DuPont connectors useful when you need more or less pins than three (servo style connector kit) - Search Ebay

FrSKY Lipo voltage sensor

This sensor (cost about A$22) enables telemetry for the total battery voltage and individual cell voltages. Also called the FLVSS sensor.

It is small and lightweight and has a very clear OLED screen which means it can be used as a stand alone battery checker.

It plugs into the balance lead of the battery and connects to the X series receiver via the Smart Port.

This video covers connection and setup directly on the Taranis Plus transmitter. Spoken values and on-screen display of total voltage and the lowest individual cell voltage, with a little flight at the end.

FrSKY 40A current sensor

This sensor (cost about A$27) enables current, voltage and consumed mAh telemetry. This is one of the most useful modules for flying powered planes because it means you don't need to keep landing to check the battery level.

It plugs in-line between the battery and ESC and connects to the receiver via the Smart Port.

This video covers connection and setup using OpenTX companion, Taranis Plus transmitter and OpenTX 2.0. On-screen display and spoken voltage and mAh consumption values. Viewing of recorded logs in OpenTX companion.