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Saturday, February 2, 2019

Make your own BlueTooth RC Throwmeter !


by Yannick Selles and Pierre Rondel

Introduction

The purpose of this article is to propose you to "build" your own Bluetooth throw-meter for a very reasonable cost. It doesn't require any soldering or cabling. You just need to have access to a 3D printer and that is all !

The original idea came to Pierre's mind after finding by chance on aliExpress an all-in-one 6 Axis Bluetooth Digital Angle Accelerometer Module.

Initially, he bought 2 exemplars of the board, then bought a 1s lipo, a micro switch, and designed the case and the clips. Later he discovered that the same component existed with a case the battery, the switch, the charging plug, and a charging cable for 4 euros more. It saves a lots of soldering and cabling, so the final version we propose hereafter is based on this model.

The component

The component is the BWT61CL  from Wit Motion, a Six axis Bluetooth attitude angle sensor with battery incorporated. It can by bought on aliexpress or amazon US and cost around 20 Euros, free shipping.

It is based on the JY61 sensor, has Bluetooth or serial connectivity, integrates a dynamic Kalman filter algorithm, an internal voltage stabilizing circuit module, voltage 3.3v~5v. The only drawback it has is that the Bluetooth BLE is only compatible with android. The battery has  a 150mA capacity so last for a long operation time.

Where to buy

Characteristics

  •     Voltage: 3.3V-5V
  •     Current: <40ma li="">
  •     Size : 51.3mm x 36mm X 15mm
  •     Weight : 16gr
  •     Dimension: Accelerated speed -3d Angular speed -3d Magnetic field-3d Angle-3d
  •     Air pressure 1d
  •     Range : Accelerated speed -±16g Angular speed -±2000°/s Angle---±180°
  •     Stability: Accelerated speed -0.01g Angular speed -0.05°/s
  •     Attitude measurement stability: 0.05°
  •     Output content: Time, Accelerated speed, Angular speed, Angel.
  •     Output frequency:100Hz
  •     Date interface: Serial TTL level Bate rate--115200(default and cant be changed)
  •     Bluetooth transmission distance : >10m
  •     Support for Android
  •     Working time: 2 to 3 hours (full charge)

Documentation  

Building your RC Throw-meter

As I said in introduction, the work is limited to the 3D printing of the clips that allow to fix the device on the trailing edge of the glider. It has been designed on DesignSpark (original file .rsdoc), and I'm providing the .rsdoc original file in addition to the STL file.

The clips is removable so the device, its clips and the charging cable can be carried/stored in the plastic box it was received in.

Just print the part, in PLA or PETG or ABS, 100% in fill for me. The dimension is optimised for F3x plane wings and tailplanes. To protect the surface of the control surface and avoid the clips to slide/shift, I added a piece of rubber (a small piece of bicycle inner tube) on the clips surfaces, with double side tape.



Print the sticker using the .pdf provided. Prior to apply it, don't forget to remove the other sticker. Protect the printed paper with transparent tape at the top, and double side tape on the other side, and position it on the top of the case, respecting the correct orientation (Charge, On/Off). This will give you the orientation when using it, pointing where is the hinge.


The App

The Android App has been developped by Yannick. The .apk file can be downloaded from here:   Android App .apk file (new version available from the 6th of February 2019)

The App is divided in several screens, the start screen giving access to the top left menu, the "Sensor BT" screen to bind the App with the throwmeter, and finally the "Throw Meter" screen where everything happens once binded.

Using your RC Throw-meter

Charging the battery 

Connect the cable provided to the balancer Plug. The red led is ON during the charge and switch off once charged

Switching on your Throwmeter

Move the sliding switch from right to left. The blue led is blinking which indicates that the device is waiting for the binding.

Pairing your Android smartphone for the first time

On in the parameter/bluetooth menu and scan for new device. The RC throwmeter will show as HC-06. When asked, enter the code 1234. The throwmeter is now paired, you can open the App.

Binding with the App

Select the menu on the top left, then open "Sensor BT" and select HC-06 or click on SCAN if the device doesn't appear. Once selected you can return on the start page, Open the menu on the top left and select "Throw meter"

Very first calibration

If the device is providing inconsistent or weird measures, it probably needs a full calibration using the manufacturer App you can download here.  To do so, once selected the correct chipset model, click on SET (top left) and then "Acceleration calibration".



Reset Angle 

The device is supposed to do a calibration at startup. It is recommended to do it with the device installed on a horizontal surface. Once done, you can clip the device on the leading edge of control surface you want to measure. When your control surface is at its neutral position, proceed to a  new "Reset Angle" in order for the device to know its spacial position and be ready to measure the angle.


Travel setup 

Measure the chord of you control surface and click on the chord field at the top of the screen to enter the value. There is no unit so it can be mm or inches. Travel will be shown in the same unit.

Max UP and Max DOWN

This is a very useful feature that allow you to quickly measure the Max UP and DOWN travels of a control surface.



SET Max UP and Max DOWN

If your objective is to do the settings, not to measure, you can enter the Max UP and Down value separately to indicate to the App to display an alarm (Red color) when the max value is exceeded.


When the travel value exceed the max Value set, the corresponding line is going RED, but will continue to record the max value, even if it is above the limite. So you need to reset time to time to erase the max travel recorded and check your setting.



Hope you will enjoy this Bluetooth RC Throwmeter ! We will probably release new versions in the futur, but be patient.

15 comments:

  1. Well done !! need an Android smartphone now :-)

    ReplyDelete
  2. Be carefull to order the one with cable from aliexpress, it is not included by default.

    ReplyDelete
    Replies
    1. Pierre, la version avec cable, c'est un cable TTL pour commiquer avec le PC, pas le simple cable de charge comme le mien. C'est bien la version standard que j'ai commandé. Je viens de vérifier.

      Delete
  3. Hi, there is also a WiFi Version available - WT91WIFI -
    Bluetooth BLE 4.0 should work with an iPhone - you can check it with a serial Terminal.
    regards
    gecko

    ReplyDelete
  4. Interesting info from Gecko .... so would need an iphone app ?

    ReplyDelete
  5. Having some issues with the app crashing when trying to set the MAX/MIN settings. The other features are working great!

    ReplyDelete
  6. Thank you very much for that. I did build my own, but it seems my BWT61CL does not calibrate at power on and has a big drift when measuring throws. I mean moving surfaces up and down a couple of times and zero is off about 2° each time. I can see in your video that it does zero well.
    Ric

    ReplyDelete
    Replies
    1. I think this mistake is due to the app measuring and summarizing outputs from all axis. So the drift on Z axis is what I see as a general drift.

      Delete
    2. Progress: I finally found the software version with calibration option (there are several versions around). The item does not calibrate at power on, it remember last calibration instead.
      When it is calibrated the error is way less, similar to that in the video, but don't yaw the plane, otherwise you have to start over again.
      So, what I could suggest for a next version is to read only Y axis values and have an always on screen, because otherwise the BT connection get lost. Of course only if you like it, it is already working well as is.
      Thanks,
      Ric

      Delete
  7. i try to install the app in an android tablet, but it says:
    "analysis error" :(

    ReplyDelete
  8. This article is awesome, I'm searching to buy a Bluetooth beanies and found this page.

    ReplyDelete
  9. Hello, I can not install the app on a tablet android 4.4.2 😢. an idea ?

    ReplyDelete
  10. This comment has been removed by the author.

    ReplyDelete
  11. Bonjour,

    Merci pour le partage.
    Pour information, le BWT61CL fonctionne sur androïd 6.0.1, mais les valeurs étaient très instables et le retour à la position initiale affichait des valeurs fantaisistes.
    J'ai chargé mini IMU mais cette fois j'ai un message disant que ma version androïd est insuffisante.
    J'ai donc chargé et fait la calibration avec un smartphone doté d'une version plus récente (7.0), de retour sur mon smartphone le résultat est nettement amélioré, retour beaucoup plus précis.

    Je regrette juste que l'appli ne tienne pas compte uniquement de l'axe Y, des erreurs de mesure peuvent être générées.
    J'avais également remarqué que la fonction "min travel" fonctionne correctement alors que "max travel" ne se déclenche qu'au double de la valeur demandée.
    Je me suis rendu compte que tout rentrait dans l'ordre si après entrée des valeurs je faisait un "reset angle"

    ReplyDelete
  12. Essais de nouveau ce soir, finalement max travel bloqué à 20mm, malgré redémarrage de l'application et avec 2 versions d'androïd différentes.
    Min travel lui fonctionne normalement, une idée d'où cela peut provenir ?

    ReplyDelete

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