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.

FrSKY GPS sensor

This is the FrSKY GPS sensor which enables position, altitude, speed and distance data on the Taranis. Cost about A$49.

The UP side must face upwards with a clear view of the sky, under foam may be OK.

Once connected it takes a few minutes for the sensor to acquire satellites. 

When it is ready the red led will change from fast to slow flashing and Lat and Long will appear on the telemetry screen 3.

This video covers connection and setup, how to enable spoken altitude, speed and distance values, telemetry logging and displaying flight tracks in Google Earth.

FrSKY Telemetry sensors

One of the most exciting functions of the Taranis X9D is telemetry. 

As well transmitting signals to the onboard receiver, the Taranis can receive data sent back from sensors on the plane. That data can be recorded on the SD card for later viewing, or presented live on the screen or even as spoken values and audio prompts.

In the next series of posts I will explain the functions of each sensor and how to get them working.

Here are four of the FrSKY telemetry sensors with the X8R receiver. 40A current sensor. LiPo voltage sensor. Variometer sensor. GPS sensor.

Each sensor is supplied with a female to female servo lead to connect it to the S-Port on the receiver. A second set of S-Port pins allows more than one sensor to be connected to the receiver at a time. You simply connect one sensor to the next in line.

Once correctly connected to a powered receiver the red LED on the sensor will change from fast flashing to slow flashing. That may take a few more minutes with the GPS.

At this stage the sensor is transmitting telemetry data but you can't see it anywhere. You need to go to the Special Functions screen for the current model to activate telemetry recording and sounds, or the Telemetry setup page for on-screen displays.

Activating SD logs

In the Special Functions screen select a switch (e.g. SG-), select "SD Logs" from the list of available functions, select how often telemetry data points are recorded (e.g. every 1.0s) Now whenever the SG switch is in the middle position telemetry data is recording onto the SD card.

SD logs include all the available telemetry data. RSSI (signal strength) and the position of every stick, knob and switch on the Taranis are recorded without any sensors required. With the appropriate sensors connected data like speed, position, altitude, distance, current, power usage and voltage are recorded. It's a mass of fascinating information to look at after your flight using OpenTX companion. If you're in to graphs you will love SD logs. 

Here are a few examples of what is available via OpenTX companion on your PC. 

I will go into more detail with each sensor in following posts.

Signal strength

Flight battery voltage

Current draw 

Telemetry display screens

To view the data in real time you need to go to the Telemetry setup page for your current model, scroll down to Screen 1 and select the values to be displayed. You can choose Bars for bar graphs or Nums for numbers on the screen.

In this example I have selected RSSI, Current and Timer 1 to be displayed on Screen1 of the telemetry screens. The 40A current sensor would be required in this case.

Here's how it looks on the live telemetry screen. Of course numbers greater than zero would appear if the plane was powered up and flying.

Spoken telemetry

The most useful way to present live telemetry is via sound or voice. Dependng on which sensors are connected the lovely lady in my Taranis can tell me such things as the altitude of my glider or how many mAH have been consumed, no need to look at the screen at all. 

To activate audio telemetry go to Special Functions, select a switch, select PlayValue, select which value to play and select how often to repeat.

In this example the Taranis will tell me the Consumed Power (Cnsp) in mAH every 10 seconds when the SC switch is down. (As long as the 40A current sensor is connected)

This is only scratching the surface of what is possible with the Taranis and OpenTX. 

There are logical switches to play with and LUA scripting as well. LUA scripts are like little programs that you can run on your transmitter. They can add functions like the Model Setup Wizard or extra graphical telemetry screens. There are hundreds of scripts available for download on the OpenTX forums. The possibilities are endless.