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Gimbal

This page describes micro direct drive brushless gimbal.

Any materials here are free for personal use, any commercial usage is permitted with the reference to the author (Mikhail Sharonov) and link to this page.

© Mikhail Sharonov, 2013. (aka obelix662000)

 

References

The idea of simple direct drive BLDC gimbals belongs to Aleksey Moskalenko (aka AlexMos) http://simplebgc.com
Open source brushless gimbal software: http://code.google.com/p/brushless-gimbal/
In my first experiments Martinez board was used http://fpv-community.de/showthread.php?22617-Gimbal-Brushless-Controller-V3-0-50x50mm-by-Martinez

Video

Single Pitch axis test (May 21, 2013) (http://youtu.be/otTO-glUc8g/)

Pitch/Roll axis and new board test (May 28, 2013) (http://youtu.be/FDD1ExUTHEI/)

 

Electronics

Lightweight version of BLDC board was developed, weight of this board (both drivers and Arduino) is 7.8 g (compared to 14.8 g of Martinez board). L293DD drivers can handle continuous current upto 600 mA. Another advantage of the board is possibility to use it with 2S batteries (V>5V) (drivers used in Martinez board work only at voltages >7V). The board is add-on to Arduino nano board and soldered to it with pin headers. Eagle files and gerber files archive (ready for upload to oshpark.com (inexpensive USA fab), $5 for 3 boards, 3 weeks time) can be found at the downloads section. Note, image below shows board with roll/pitch titles mixed up (this is corrected in provided files)

Fig. 1a Martinez board shown at left for comparison, Fig. 1b assembled gimbal controller and unpopulated PCB board.

Solder Arduino nano and driver board together through the holes in the driver board (check holes to connect Arduino Vin to the board's Vcc, and Gnd to Gnd; other hole is used for battery power source). Connect motors to pitch and roll pads of the board, connect Vcc (5-36V) and ground to Vcc and GND pads. Other signals are shown below (Arduino side):

 

 

 

Motors

Motors are hobbyking.com AP-02 (pitch) and AP-03 (roll), the weight is 2.4g and 3.1g. The motors are 9 stator / 12 magnet poles. They must be rewound to hold constant current while gimbal operation. I used AWG44 (0.051 mm) wire. The scheme is ABCABCABC, star, see fig. below. 120 turns per tooth, both motors. Resistance of each phase (between output and "star" common point is 27 Om for AP-02 and 33 Om for AP-03; therefore between phases (between any of 3 output wires) the resistance is 54 Om and 67 Om, correspondingly. AP-02 (pitch) works well starting from 8V (255 (full scale) setting; with 3S power I set this value to 180. At this settings the current is about 160-180 mA). AP-03 has higher resistance and requires 10-12V for operation (255 setting at 3S power). The current is also about 170 mA. At this current motors are warm and obviously far from dangerous overheat.

9/12 rewound scheme (taken from http://www.bavaria-direct.co.za/models/motor_info.htm):

Here are some photos of AP-03 rewound:

Disassemble the motor, remove wire.

Use water based glue to fix wire sometimes ( after each phase, or after the tooth is rewound). Put wire through thin syringe needle

Second tooth of phase 1 in process; put some glue to the finished tooth to fix the coil (small amount to the top only, to prevent penetration to the space between teeth).

Phase 1 is done. starting phase #2:

After all 3 phases are finished, put some glue everywhere.

Now we need some sort of lightweight flexible cable. Firstly, envelop small piece of scotch over the frame:

align wires (but do not tight) and attach to the tape shown above with another piece of scotch tape.

Fix the motor and wire ends to the table with tape.

Put scotch from the top, press firmly

Do the same from the other side , cut to desired width.

Solder together the beginning ends. Cover the ends with some tape and gently move into housing to hide.

All done!!!

 


Frame

This design is not final. I've decided to use this design to have a chance to change parameters of the frame. The frame is made of carbon fiber tubes (0.196"/0.126" outer/inner diameter tube) attached with home-made aluminum parts. The design is self explanatory. Here are some weights: 1) Motors: 2.4 g and 3.1 g, 2) camera 17.5 g 3) electronics 7.9 g 4)MPU6050 board 1.3g. Total weight of everything is 50g, so the frame itself is 50-2.4-3.1-15.5-7.9-1.3=19.8g.

Pitch motor has PCB board to attach wires, later I switched this design to the described above.

Camera bed foam exactly follows camera shape, so balance does not change when camera is reinserted. Cover the camera with thin plastic film and push into freshly sprayed insulating foam. After the foam dried out, cut the foam to the shape.

sensor board attached to the bottom with tape.