SpeedControl Demo Project

This guide introduces a simple speed control function written in C to help you get hands-on experience with the CppModel environment. The function performs the following calculations:

• Computes the percentage value of the left wheel command based on the percentage speed and direction angle.
• Computes the percentage value of the right wheel command based on the percentage speed and direction angle.

For simplicity, the direction angle is given in degrees. Input values are in the range:

• Speed: [0, 100]%
• Direction: [-90, 90] degrees

Input validity checks are skipped, and output values are directly assigned to minimize code length. Under these assumptions, the C function is implemented as follows:

speedControl.h

#include <stdint.h>

typedef struct SpeedControlContext_s
{
    int8_t directionAngleDeg;
    int8_t controlCommandPercent;

    int8_t leftWheelPercent;
    int8_t rightWheelPercent;
} SpeedControlContext_ts;

void speedControlCyclic(SpeedControlContext_ts *const ctx);

speedControl.c

#include <math.h>
#include "speedControl.h"

void speedControlCyclic(SpeedControlContext_ts *const ctx)
{
    ctx->leftWheelPercent = (ctx->directionAngleDeg <= 0)
                                ? ctx->controlCommandPercent
                                : cos(((float)ctx->directionAngleDeg * M_PI) / 180) * ctx->controlCommandPercent;
    ctx->rightWheelPercent = (ctx->directionAngleDeg >= 0)
                                ? ctx->controlCommandPercent
                                : cos(((float)ctx->directionAngleDeg * M_PI) / 180) * ctx->controlCommandPercent;
}

This code can later be used in an embedded system.

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Setting Up the Simulation

Before running the simulation, ensure you have installed the CppModel client-side libraries, which can be downloaded from the Downloads page.

To visualize the results of the speed control function, it can be integrated into a simulation with proper execution timing and cyclic call events. In CppModel, this is achieved using the Simulation class. Below is the implementation:

SimulateSpeedControl.h

#pragma once

#include <cppmodel/Simulation.h>

class SimulateSpeedControl : public CppModelBase::Simulation
{
public:
    SimulateSpeedControl();
    void RunCyclic(double simulationTime);
};

The Simulation class provides a RunCyclic() method, which is called at every simulation step and provides the current execution time in seconds.

SimulateSpeedControl.cpp

#include "SimulateSpeedControl.h"

extern "C"
{
#include "speedControl.h"
}

SimulateSpeedControl::SimulateSpeedControl()
{
    name = "SpeedControl";

    time = 20;       // Simulation duration in seconds
    stepSize = 0.02; // Step size of 20 ms
}

void SimulateSpeedControl::RunCyclic(double simulationTime)
{
    SpeedControlContext_ts speedControlCtx;

    speedControlCtx.directionAngleDeg = inputs["Direction"];
    speedControlCtx.controlCommandPercent = inputs["Speed"];

    speedControlCyclic(&speedControlCtx);

    outputs["LeftWheel %"] = speedControlCtx.leftWheelPercent;
    outputs["RightWheel %"] = speedControlCtx.rightWheelPercent;
}

Key Properties of the Simulation

1. Name: Used to distinguish between models in the visual workspace.
2. Time: Total simulation duration in seconds.
3. Step Size: Interval between cyclic calls to RunCyclic().

The RunCyclic() method is responsible for:

• Reading input values (e.g., "Direction" and "Speed") from the workspace.
• Calling the speedControlCyclic() function.
• Writing output values (e.g., "LeftWheel %" and "RightWheel %") back to the workspace.

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Running the Simulation

To execute the simulation, call its Simulate() method:

execute.cpp

#include "SimulateSpeedControl.h"

int main(void)
{
    SimulateSpeedControl sim;

    sim.Simulate();
    
    return 0;
}

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Compilation Instructions

To compile the project, link it with the CppModelBase library. Below is an example CMakeLists.txt configuration:

project(SpeedControl)

add_definitions(-DCPPHTTPLIB_OPENSSL_SUPPORT)

add_executable(SimulateSpeedControl speedControl.c SimulateSpeedControl.cpp execute.cpp)

if (WIN32)
  target_link_libraries(SimulateSpeedControl CppModelBase crypto ssl crypt32 ws2_32)
else()
  target_link_libraries(SimulateSpeedControl CppModelBase crypto ssl)
endif()

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Viewing Results

After execution, the simulation results can be found in the workspace at workspace.cppmodel.com.