2 axis camera stablizer using dynamixel servos, Which way?!

[sadtab]

Hi every body,

I have 2 RX-24F servos and I want to build a 2 axis (tilt & roll) camera stabilizer. The gimbal should be capable to receive serial communication (eventually RS232) in order to move in tilt direction by its user. I have a CM-700 but I'm not sure if cm-700 is a good choice or not. (I have also an ODROID XU4).

I'm newbie in dynamyxel systems. Its been several days I'am searching every where to find the best and easiest way to develop this system. So far I found three possibilities :

(1) Using CM-700 and RobotPlus software and task manager
PROS : Easy and robust, well documented with tutorials
CONS : It seems very limited, Specially for interpreting the gyro data and receiving tilt movement command from a third party component

(2) Using Dynamixel SDK & USB2Dynamixel and a SBC (ODROID with linux)
PROS : Fast ,easier than embedded c, easier to handle the gyro data and receiving tilt movement command from a third party component, possibility to use ROS packages (I never used ROS before, so get it easy on me)
CONS : Heavy , big, expensive, and eventually less robust compared to CM-700

(3) Using Dynamixel SDK & CM-700, embedded c environment
PROS : Seems very robust
CONS : I never did something like that before, I'm newbie in Dynamixel, and I dont know if its possible to handle the gyro data and receiving tilt movement command from a third party component



I really appreciate if somebody can help me find my way through this, It would be great if somebody have done this before and can share his experience or project here.

Peace

PS: I have a IMU 10DOF, it uses I2C protocol and seems to be impossible to pair IMU to CM-700, should i have a Gyro Sensor GS-12 ?

[tician]

The CM-700 uses the same AVR as the Arduino Mega, so you could potentially use the Software I2C Library to interface with an I2C sensor on the 'Ollo' port pins. If my old code is still accurate and I am reading it correctly, then the CM-700 has six pins on PORTA (PA2 through PA7) available on pin 1 (MOTxP) of the Ollo headers.

[jwatte]

Your best bet if you want an IMU-based stabilizer is probably to use the OpenCM 9.04.
It's actually more powerful, as CPU speed and programmability goes, than the CM-700, at a fraction of the price ($10 + a $5 bag of connectors + some soldering.)
To talk to the RS-485 servos, it needs an additional base plate, but it's still a lot cheaper and easier to program IMO.

Then hook up a IMU of your choice, like an MPU9050 or a BNO055. There are tons of tutorials / libraries for the Arduino which generally can easily be ported to the OpenCM.

The main concern I have about your idea is that the Dynamixel servos aren't very fast. If you're used to brushless Gimbals, which are direct coupled, you will not get the same speed out of the Dynamixels. However, you'll get a lot more torque out of the Dynamixels, so there is that :-)

[tician]

When was the OpenCM IDE last updated?

If one must use something more powerful than the 8-bit AVR (CM-700) already in one's possession, why not just get a Teensy-3.x and wire up an RS-485 transceiver to one of the UARTs? Compared to the OpenCM plus RS-485 shield, the various Teensy-3.x cost less, have a smaller size, have more powerful processors, and have much better software support.

[jwatte]

Yes, if you are good with electronics and are comfortable making a board on OSH Park to wire up some 422/485 transciever/s to a Teensy, the Teensy is a great option!
The software for the OpenCM 9.04 is older, but has more Dynamixel-specific support, so again, it depends on how much roll-your-own you're comfortable with.
I'm a big fan of Teensy and have run them in a number of robots!

[tician]

Plenty of dynamixel libraries for Arduino and Teensy, some written by members of this forum... And do not necessarily have to make a board, just get a transceiver IC in DIP-8 package (or mount a SOIC-8 it on a generic SOIC breakout board; or get a fully assembled RS-485 breakout board from adafruit or sparkfun) then use jumper wires between the headers of the two devices. Not the cleanest option, but certainly works well with everything mounted on a single small breadboard.

Suppose I should try testing the Teensy-shindy board (9-DOF IMU, TTL DXL port, RS-485 DXL port) I assembled so long ago but never actually powered on (not sure it was electrically sound after assembly). Should also test out the ESP-8266 boards I built for MechWarfare. And test my code for the little OLED displays. And my code for RFM69HCW modules hopping about in the 915MHz band. And get Ripley reassembled and walking.

[sadtab]

Thank you tician, Evidently you expertise these things very well but As Im a beginner, I prefer to don't go through embedded c as far as its not necessary. I think maybe the jwatte solution is more adequate with my level of expertise.

[sadtab]

Thank you guys, you're amazing, some of your advises seems an alien language to me ))
My inventory is : an OpenCM, an CM700, an ODROID, a usb2dynamixel), 2 RX-24f and a IMU 10DOF (Supporting I²C and SPI)
The most understandable solution (I'm not very experienced) for me seems de stick to Open CM, i will buy a http://www.robotis.us/opencm-485-expansion-boar/ and try to develop the codes on Open CM IDE.

For jwatte concern :

The main concern I have about your idea is that the Dynamixel servos aren't very fast. If you're used to brushless Gimbals, which are direct coupled, you will not get the same speed out of the Dynamixels. However, you'll get a lot more torque out of the Dynamixels, so there is that :-)

I did a fast search on google :



Dynamixels are not as fast as brushless motors but their speed seems to be enough, even best DJI gimbals can't control over 180°/Sec. Anyway nobody used dynamixels for a gimbal before ))

[tician]

The CM-510/700 can be used with Arduino as it is the same microcontroller as the Arduino Mega but in a package with fewer pins and a different bootloader. Might not even require creating a copy and slightly modifying the hardware/arduino/avr/variants/mega/pins_arduino.h file to remove the non-existent pins as long as you are careful not to use the non-existent pins in your code. The bootloader could be re-written with an arduino compatible bootloader, but not difficult to grab the hexfile output from the Arduino IDE and use the RoboPlus Terminal to push the firmware to the CM-700.


Dynamixels have been used to control small cameras on robots since they were first released and hobby servos were used before that. The MechWarfare sub-forum is almost entirely dedicated to robots using dynamixels for pan-tilt control of a camera and airsoft cannon.

[tician]

I was a little bit wrong. The CM-510/700 use three pins on PORTE that are not connected on the Mega, so do have to slightly modify the pins_arduino.h file to add those pins. Did not bother to remove the Mega pins not used on the CM-510/700, and do not have access to a CM-510 or CM-700 to check everything actually works.

The cm510/cm510.h file is all the pins as used on the CM-510/700. The variants-cm510/pins_arduino.h is the slightly modified Arduino Mega pins file stored at 'hardware/arduino/avr/variants/cm510/pins_arduino.h' and will be accessible as Robotis CM-510/700 if using the updated board file. Still have to use the RoboPlus Terminal to upload the hex file grabbed from the temporary files produced by the Arduino IDE during the firmware build process.