Micro Brushless Gimbal

I’ve built a micro brushless gimbal, i.e. a brushless direct-drive gimbal for cameras of the 808 key chain size, which I will describe here.

The worlds first 3-axis micro brushless gimbal has arrived!

micro brushless gimbal olliw
(picture of my first well working 2-axis micro brushless gimbal)

Camera
The camera is a key cam 808 #16 V2 with lense D. For all details see ChuckLohr’s great web page here. It’s not too expensive, and for its price it provides, IMHO, great video quality. Unlike its precessor (#3 etc.) it’s also quite well developped, i.e. a precise manual is available and a setup program making things really simple.

Gimbal
The gimbal itself is made from standard stuff found in any hobby shop. Building the motor holders had been the most difficult mechanical step. It’s not really difficult, but you need appropriate tools, which I don’t have. I only could succeed because a comrade had access to a lathe which he allowed me to use. The camera holder is magnetic, which adds quite a bit of weight to the gimbal, but is really cool since mounting/dismounting the camera is quite simple.

The weight of the whole construction seen in the above photo, i.e. gimbal + camera + contoller + cables + vibration damping + frame, is 90.5 grams.

Motors
The motors are IMHO key to the whole project, and searching for appropriate ones had been a major thing. If money is no issue then you will find excellent motors from Maxon (the maxon EC flat series looks very promising). I instead did test, with support from some nice fellows, see here, a couple of micro brushless motors, but they all showed IMHO way too much cogging. I went when with disc motors, since they usually come with a sintered magnet ring instead of individual hard magnets, which minimizes cogging torques. Among the several disc motors I tested, I liked this one most:

PS2 Slim disc drive replacement motor

  • 9n12p, diameter 24 mm, height of bell 5.5 mm, spindle 2 mm
  • original wind: 80 turns, ca. 0.17 mm wire, ca. 4 Ohm
  • new wind: wye configuration, 150 turns, 0.10 mm wire, 24.1 Ohm (perfekt for 2S and 3S)
  • bushing needs to be replaced by bearings, hence an approiate holder needs to be build
  • weight is ca. 10-13 g

Controller
I have designed the mini Brushless Gimbal Controller (all details here). The mBGC consists of an Arduino Pro Mini with an extension board, which carries TC4427 or TC4424 motor drivers. It also provides a voltage divider to measure the battery voltage, which allows to implement a lipo saver function as well as to make the PID controller adaptive to voltage changes.

Firmware
The firmware oBGC I’ve written myself. It has been developped from scratch, and is written in C using AvrStudio. I like the Arduino hardware, but I don’t like the Arduino language since it is very bad on resources… good performance is IMHO usually linked to optimized code. The firmware is in some parts quite highly developped, but in other parts, such as RC control etc., behind alternatives.

Background Theory
In the course of the project I stumbled across some things which I didn’t understand at first, and some which surprised me. So, I did also some basic theory considerations to understand better what’s going on. Some of them I’ve presented here.

Flying Vehicle
The gimbal is currently designed to be mounted on a Lama V4 coaxial helicopter, which has been modded substantially. I did a BLBL conversion using a GA250 gyromixer and Turnigy 1811-2900 motors. It runs from 3S, which provides plenty of power to lift the gimbal. I installed all tuning hardware I had available, but the single most important thing to minimize vibrations from the heli was to carefully balance the motors. The most serious thing with the coax is however its flying characteristic, it handles wind breezes badly. I gave it enough pop to fight it in the sense that it is able to move against it, but it then wobbles strongly.

Results
Some results I have already presented in a couple of places:

Articles:
Brushless Gimbal Direct Drive: Theory and Experiment
Mini Brushless Gimbal Controller

Threads:
Micro Brushless Gimbal – HILFE (@ FPV-Community)

Youtube Videos:
Micro Brushless Gimbal: 2nd step towards it

Micro Brushless Gimbal: Understanding better the dynamics of brushless direct drive

Micro Brushless Gimbal: 2-Axis Gimbal with KeyCam #16 V2

Micro Brushless Gimbal with oBGC Firmware: It’s flying ­čÖé

Micro Brushless Gimbal on a Coax Heli

(there are some more videos on the topic on my youtube channel OlliW42)


7 Kommentare

Hinterlasse einen Kommentar