Dynamixel Protocol Tutorial

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Many hardware devices communication with the computer using a serial protocol. Some are simple ASCII-based protocols, but others can be more complex binary ones that require checksums. No matter, both can easily be made in FlowBotics.

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We've already [[covered the Lynxmotion SSC-32 protocol>>doc:ses-software.flowbotics.developers.lynxmotion-ssc-32-protocol-tutorial.WebHome]] as an example ASCII protocol, now let's use the Dynamixel servos as an example of a binary protocol.

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We made a small project to show how this can be done. You can [[download a copy of it here>>attach:dynamixel-protocol-example.fsp]]. Here's the main screen:

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|(% style="text-align:center" %)[[image:dynamixel-protocol-front-panel.png||height="457" width="300"]]

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|Here's the main schematic of the project:

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[[image:dynamixel-protocol-main-schematic.png||height="294" width="650"]]

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|Inside the "__//Dynamixel Protocol//__" module, you can see how the bytes are prepared. Since the Position and Speed are 16-bit integers, they need to be separated into their most significant byte (MSB) and least significant byte (LSB) to ensure they are sent in the right order (see [[endianness>>url:https://en.wikipedia.org/wiki/Endianness]]). We store them in an array to make them easy to process in the checksum calculation.

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[[image:dynamixel-protocol-message.png||width="650"]]

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|Inside the "__//Encapsulate//__" module, you can see how the message is assembled into a single hexadecimal string. The "__//COM Port//__" component (inside the "__//COM Engine//__" in the main schematic) has a Hex data parameter, so we don't need to worry about converting to binary.

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[[image:dynamixel-protocol-encapsulation.png||width="650"]]

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|Finally, inside the "__//Calc Checksum//__" module, you can see how we used a small clip of Ruby code to help generate the checksum.