Chainsaws have seen a constant improvement over the time of their production and are still an object of improvement by the bigger chainsaw companies. The chainsaw engine is highly developed and optimised for the assigned uses. This thesis project aims to further optimise the engine by implementing a system that allows for variable inertia on the rotational system. A high inertia is needed at higher velocity to reduce speed fluctuations but a high inertia also makes it harder for an object to accelerate, a low start inertia could help accelerate the system and then reach a higher inertia for stability at higher velocities.  The variable inertia system were developed for a Husqvarna 550 XP mk.II. Concepts were developed using the product development process and the evaluation is based on the interpreted needs of the product. The most promising concepts underwent dynamic system simulations to ensure the best performing concept is selected. The chosen concept were then further designed with an iterative process where each iteration was analysed with the finite element method to ensure structural rigidity. The developed product indicates a performance increase. The magnitude of this performance increase is mainly governed by the size constraints in the chainsaw.

The effect of variable inertia flywheel (VIF) on the driving speed fluctuation, and residual vibration of high speed machine systems is investigated in this thesis. Different variable inertia flywheels are proposed to an experimental purpose roller gear cam system and a commercial super high speed paper box folding machine. The effects of time varying inertia and intermittent cam motion on the dynamic responses of different high speed cam droved mechanism systems are simulated numerically. The nonlinear time varied system models are derived by applying the Lagrange¡¦s equation and torque-equilibrium equations. The dynamic responses of these two nonlinear systems under different operating speed are simulated by employing the 4th order Runge-Kutta method. The effects of VIF parameters on the dynamic responses, i.e. the output precision, variation of motor speed, and torque, during the active and dwell periods for these two systems are studied and discussed. The difference between the dynamic responses of constant inertia and variable inertia flywheel systems are also compared. The feasibility and effectiveness of depression of driving speed and torque fluctuations by analying variable inertia flywheel has also been demonstrated.

¡@¡@The dynamic power flow in a dual-input parallel planetary gear train system is simulated in this study. Different wind powers for the small wind turbines are merged to the synchronous generator in this system to simplify and reduce the cost of the system. Nonlinear equations of motion of these gears in the planetary system are derived. The fourth order Runge-Kutta method has employed to calculate the time varied torque, root stress and Hertz stress between engaged gears. The genetic optimization method has also applied to derive the optimized tooth form factors, e.g. module and the tooth face width. ¡@¡@The dynamic power flow patterns in this dual input system under various input conditions, e.g. two equal and unequal input powers, only single available input power, have been simulated and illustrated. The corresponding dynamic stress and safety factor variations have also been explored. Numerical results reveal that the proposed dual-input planetary gear system is feasible. To improve the efficiency of this wind power generation system. An inertia variable flywheel system has also been added at the output end to store or release the kinetic energies at higher or lower wind speed cases. A magnetic density variable synchronous generator has also been studied in this work to investigate the possible efficiency improvement in the system. Numerical results indicate that these inertia variable flywheel and magnetic density variable generator may have advantages in power generation.