collinbrake/electrakHDCAN

CAN bus interfacing with the Thomson Linear Electrak HD smart actuator.

Electrak HD CAN

CAN bus interfacing with the Thomson Linear Electrak HD smart actuator.

Usage Example

Note, this code is a first prototype for experimentation and has not been extensively tested.

Command actuator to move to 250 mm at 100% speed:

$ python3 python/gotoposition.py -p /dev/ttyACM10 -s 100 -l 250

The following plot shows data from a run like this:

Sinusoidal

Move the actuator from limit to limit repetitiously at 50% speed.

$ python3 python/sinusiodal.py -p /dev/ttyACM10 -s 50                      

There is no closed-loop control implemented. As can be seen, the position signal is very noisy, and no filtering is used at this point.

Logging

The core functionality of this library is to move the software interface with the Electrak HD actuator up one abstraction by handling both the J1939 protocol and the data format specified by the manufacturer, Thomson Linear. The logging will consist of two levels:

1. Logging of the address and data fields sent (before encoding) and received (after decoding)
2. Logging of the address and data raw bits sent (after encoding) and received (before decoding)

These two categories are logged in two different CSV files, both in the log/ directory which is created at the root of the repository if it does not exist. Timestamps are logged with each entry in both files, and will exactly correspond for correlating entries between the files.

Notes:

• Data values from the sent commands (ACM's) have column headings starting with a "C" character
• Data values from the sent commands (AFM's) have column headings starting with a "F" character

Electrak HD CAN Bus Interfacing

This section describes the interface with the Electrak HD and provides sources.

Here is a list of the sources used:

• Actuator Manual
• A Comprehensible Guide to J1939
  • "the book"
• Linux Kernel J1939 Documentation, Socketcan

Decoding Actuator Feedback Message

• Page 22 of the actuator manual specifies the use of the Proprietary A2 PGN, and on page 24 defines its use for feedback messages.

  • The book provides a specification of this PGN on page 67.
  • It is a peer-to-peer message, or PDU1 format

• Decoding the 29-bit ID

  • Field	Priority	PGN	R	DP	PDU Format	PDU Specific	Source Addr.
    Right Shift Amount	26	8	25	24	16	8
    Mask		0x3FF00	1	1	0xFF	0xFF	0xFF
    Value	6	126720	0	1	239	255	19

• Decoding the Data Bytes

  • The bits we are extracting each of the below values from may be 1 or two bytes, depending on data item length, specified at page 24 of the manual.

  • Each byte must be reversed before usage.

  • Each value's bit-order is reversed before it is scaled and used.

  • Field	Pos	Current	Speed	Volt. Err.	Temp. Err.	Motion	Ovrld	Backdrv	Param	Sat.	Fatal
    Right Shift Amnt	2	1	4	2	0	7	6	5	4	3	2
    Mask	0x3FFF	0x1FF	0x1F	0x3	0x3	1	1	1	1	1	1

Encoding Actuator Control Message

• Page 22 of the manual specifies the use of the Proprietary A PGN, and on page 23 defines its use for control messages.

  • See page 66 of the book

• Encoding 29-bit ID

  • We will need to reverse all the values to be least significant first

  • Field	Priority	PGN	R	DP	PDU Format	PDU Specific	Source Addr.
    Value	6	61184	0	0	239	19	Anything?

  • Reverse the packed bytes before they are sent out

  • The PDU specific is the destination address in peer-to-peer communication.

    • Same as the source address from the AFM