CAN bus reverse-engineering
This looks like CANopen traffic (RPDO is also mentioned in the question). 0x80 is SYNC, and it seems
it is send at regular intervals (about every 26 ms, 38-39 Hz). And
some device responds to the SYNC messages by sending out messages
with ID 0x181 and 0x281. But that is just a guess at this point.

It could also be that the content of ID 0x181 and 0x281 are set points
to a servo (thus the same device sends out 0x80, 0x181, and 0x281) and
that the feedback position is contained in the 0x301 messages.

It should be possible to correlate physical positions of the
robot with the messages. A set point is (probably) set immediately
and the actual positions are lacking behind.

Note: 181h is not a node, and you are not sending messages to it. 181h is
a CAN message ID. As it is likely CANopen, 0x181 is the message
"PDO1, transmit" for the device with ID 1. Note that it is
not always clear if the device ID indicates what device sends it or if
the device is the destination.

Type            Function code: Device ID range:
                Binary Decimal ID in  Hex             Decimal
                               CAN ID
--------------------------------------------------------------------
NMT             0000   0       No     0 - 0             0 -    0
SYNC            0001   1       No     0x80  -  0x80   128 -  128
Emergency       0001   1       Yes    0x81  -  0xFF   129 -  255
Time stamp      0010   2       No     0x100 - 0x100   256 -  256
PDO1, transmit  0011   3       Yes    0x181 - 0x1FF   385 -  511
PDO1, receive   0100   4       Yes    0x201 - 0x27F   513 -  639
PDO2, transmit  0101   5       Yes    0x281 - 0x2FF   641 -  767
PDO2, receive   0110   6       Yes    0x301 - 0x37F   769 -  895
PDO3, transmit  0111   7       Yes    0x381 - 0x3FF   897 - 1023
PDO3, receive   1000   8       Yes    0x401 - 0x47F  1025 - 1151
PDO4, transmit  1001   9       Yes    0x481 - 0x4FF  1153 - 1279
PDO4, receive   1010  10       Yes    0x501 - 0x57F  1281 - 1407
SDO, transmit   1011  11       Yes    0x581 - 0x5FF  1409 - 1535
SDO, receive    1100  12       Yes    0x601 - 0x67F  1537 - 1663
NMT error ctrl  1110  14       Yes    0x701 - 0x77F  1793 - 1919