custom ROS service bus assignment

2 min readSep 23, 2021

I am trying to call a ROS service using a custom service message in simulink. I have successfuly followed the instruction here to load the custom message into Matlab.

I need to do some string assignment in the message, I have been following the JointState publisher example to assaign the string array.

The problem I am running into is I cannot figure out what the Bus type should be sent too.

My message type is rbdl_server/RBDLInverseDynamicsRequest

So I assigned the bus type: SL_Bus_sliding_controller_rbdl_server_RBDLInverseDynamicsRequest

Which is causing the follow error:

=== Update Diagram (Elapsed: 1 sec) ===
    Error:Expression 'SL_Bus_sliding_controller_rbdl_server_RBDLInverseDynamicsRequest' for type of data 'msg' did not evaluate to a valid type.
    Caused by:
        Invalid setting in 'sliding mode controller/MATLAB Function - String Array Assign1' for parameter 'Datatype'
            Error evaluating MATLAB Function parameter data 'Datatype' in its parent workspace.
                Unrecognized function or variable 'SL_Bus_sliding_controller_rbdl_server_RBDLInverseDynamicsReques'.
                    Variable 'SL_Bus_sliding_controller_rbdl_server_RBDLInverseDynamicsReques' does not exist.

what am I doing wrong? It seems like the message name is being truncated (missing the “t” at the end of the name) but I am not sure why that is happening or to fix that.

ANSWER

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Thanks for the information, that was helpful. From the snap-shot of your model, it seems you are using R2019b (please verify using “ver” command in MATLAB).

Verify the names of the buses in your base-workspace.

whos SL_Bus_sliding_controller*
% Output should look as follows:
% Name                                                            Size            Bytes  Class           Attributes
% 
%   SL_Bus_sliding_controller_RBDLInverseDynamicsReques_3qoi39      1x1              1890  Simulink.Bus              
%   SL_Bus_sliding_controller_geometry_msgs_Point                   1x1               220  Simulink.Bus              
%   SL_Bus_sliding_controller_std_srvs_EmptyRequest                 1x1               148  Simulink.Bus              
%   SL_Bus_sliding_controller_std_srvs_EmptyResponse                1x1               150  Simulink.Bus

The service request bus name (if it followed the convention of model name appended by request message name) would have been longer than 63 character limit.

length('SL_Bus_sliding_controller_rbdl_server_RBDLInverseDynamicsRequest')

So, generated bus name is truncated to meet the 63 character limit and unique hash string is appended to it.

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