Module: scalarJointStatesToRWSpeed

Executive Summary

The scalarJointStatesToRWSpeed module is an adapter that converts a set of scalar joint state messages into a single reaction wheel speed message. The module reads \(N\) input messages of type ScalarJointStateMsgPayload, each containing a scalar joint rate \(\dot{\theta}_i\). At each update, the module packs the joint rates into the output RWSpeedMsgPayload such that

\[\Omega_i = \dot{\theta}_i, \quad i = 0, 1, \ldots, N-1\]

where \(\Omega_i\) is the \(i\)-th reaction wheel speed in the output message. This supports using MuJoCo hinge joint rates (or any scalar joint rates) as inputs to Basilisk flight software that expects a reaction wheel speed message.

Message Connection Description

The following table lists the module input and output messages.

Module I/O Messages

Msg Variable Name	Msg Type	Description
jointStateInMsgs	ScalarJointStateMsgPayload	Vector of input messages containing the scalar joint states and rates
rwSpeedOutMsg	RWSpeedMsgPayload	Output message containing the packed reaction wheel speeds

Module Functions

Below is a list of functions that this simulation module performs

• Reads all ScalarJointStateMsg inputs

• Copies each input joint rate into the corresponding element of the RWSpeedMsg output

• Writes the packed RWSpeedMsg output message each update cycle

Module Assumptions and Limitations

• The mapping is order-preserving: input message index \(i\) maps to output wheel speed index \(i\)

• The module uses the joint state from each input message

• The module assumes \(N\) does not exceed the maximum wheel speed vector length supported by RWSpeedMsgPayload

Test Description and Success Criteria

The unit test for this module is defined in test_scalarJointStatesToRWSpeed. The test initializes the module with a configurable number of joints \(N\) and drives each joint input message with a distinct constant rate. The test passes if the output wheelSpeeds vector matches the expected values for every index to within numerical tolerance.

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class ScalarJointStatesToRWSpeed : public SysModel

#include <scalarJointStatesToRWSpeed.h>

Adapter module that maps multiple ScalarJointStateMsg inputs directly into a single RWSpeedMsg output.

Public Functions

ScalarJointStatesToRWSpeed()

Default constructor.

explicit ScalarJointStatesToRWSpeed(uint32_t numJoints)

Constructor specifying number of joints.

Parameters:

numJoints – Number of joint inputs.

~ScalarJointStatesToRWSpeed() override

Destructor.

void Reset(uint64_t CurrentSimNanos) override

Reset the module.

Parameters:

CurrentSimNanos – Current simulation time [ns].

void UpdateState(uint64_t CurrentSimNanos) override

Read joint states and publish RW speed message.

Parameters:

CurrentSimNanos – Current simulation time [ns].

void setNumJoints(uint32_t numJoints)

Set the number of joints.

Parameters:

numJoints – Number of joints.

Public Members

std::vector<ReadFunctor<ScalarJointStateMsgPayload>> jointStateInMsgs

Joint state readers.

Message<RWSpeedMsgPayload> rwSpeedOutMsg

RW speed output.

BSKLogger bskLogger

BSK Logging.

Private Functions

void ensureSizes()

Ensure internal buffers are correctly sized.

Private Members

uint32_t numJoints

Number of joints.