OpenServo.com

[Nathan Monson]

I have been lurking on this forum for a few months now. I currently have a humanoid using Dynamixel AX-12s. But, I would like to switch to the LynxMotion/OpenServo hardware with external gear motors in the future.

In the mean time, I am wondering if I can run OpenServo on my AX-12-based humanoid. The AX-12 firmware can be updated over the external bus, or by fitting an SPI connector inside the servo. The schematics of the AX-12 are online here: forum. robosavvy. com / viewtopic.php?t=2673 (Sorry, forum won't let me post links.)

The AX-12 has shortcomings: It only uses an ATmega8 uC. It lacks a back-EMF or current sensor. It only has a single external I/O meant for half-duplex serial -- so I2C is ruled out.

On the plus side: The AX-12 can monitor voltage, temperature, and position. The position pot does not have a stop, so continuous rotation 'just works'. The servo is very powerful and robust for the price ($40), and can handle a wide range of voltages. In theory, it could be flashed with OpenServo without being opened.

Would it make sense to port OpenServo to this hardware? Has anyone done a more serious investigation?

- Nathan

[robotjay]

Sorry for not replying to this thread sooner. But in short: It would be entirely possible to flash the AX-12 with modified OpenServo code. The real question becomes: Why would you?

To start, you would have to hand compile the firmware, excluding the temp, BEMF, and current sense. Because of the reduced memory space, you would also have to leave out the Beizer Curve algorithm, which IMHO, is the the best feature of the OpenServo.

That being said, if you take out the BEMF, current sense, temp, and beizer curves, what do you gain by putting OpenServo software inside an AX-12?

Your best bet would be to buy the OpenServos and put them inside cheap hardware, like MG995s. Then you don't have to worry about bricking your expensive Dynamixel servos.
_________________
"Nothing is fool-proof; For we fools are ingenious and will find a way."