Autonomous landing of a tethered multi-rotor unmanned aerial vehicle on a stationary platform

Mfiri, Tatenda Joshua (2019-04)

Thesis (MScEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: This thesis contributes to the research of persistent tethered aerial vehicles by presenting a strategy to autonomously land a tethered multi-rotor UAV. A flight control system is developed for a quad-rotor UAV which was inherited from a previous project. A winch system is also added and a control system is designed to winch the tethered quad-rotor. A novel point-mass model of the tethered UAV is formulated and utilised to design a tethered landing strategy which is robust against inaccuracies in aircraft position measurement. The work culminates in the demonstration of autonomous landings of a tethered quad-rotor UAV on a 2.4 m × 2.4 m stationary platform. The flight control system is designed by using successive loops of Proportional- Integral-Derivative (PID) controllers. Flight control loops are designed based on an untethered quad-rotor model and integral control laws are implemented to aid the rejection of tether disturbances. A spring-damper model proved to be sufficient in modelling tether dynamics. A novel point-mass model of the tethered UAV is utilised in deriving closed-form analytical expressions for the tethered system poles both in the radial and angular directions as functions of quad-rotor and tether parameters. Flight control systems are designed and simulated in a software-in-the-loop environment. Control loops that are critical to the landing strategy are also simulated in a hardware-in-the-loop environment. Practical results show satisfactory performance in horizontal control in wind speeds of up to 2 m.s−1 while the vertical control system exhibits relative immunity to an increase in wind speed.

AFRIKAANSE OPSOMMING: Hierdie tesis dra by tot die navorsing van aanhoudendevlug lugvoertuie deur ’n strategie aan te bied om outonoom ’n vasgehegde multi-rotor onbemande lugvoertuig (OLV) te laat land. ’n Vlugbeheerstelsel is ontwikkel vir ’n vier-rotor OLV wat beskikbaar was vanuit ’n vorige projek. ’n Katroltoestel is ook ontwerp met ’n beheerstelsel om die lugvoertuig in te katrol. ’n Nuwe puntmassamodel van die vasgehegde OLV is ontwikkel en gebruik om ’n strategie vir ’n vasgehegde landing te ontwerp. Die werk word afgerond met ’n demonstrasie van outome landings van die vasgehegde OLV op ’n 2.4 m × 2.4 m stilstaande platform. Die vlugbeheerstelsel is ontwerp deur van opeenvolgende lusse met PID beheerders gebruik te maak. Die vlugbeheer ontwerp is ’n multi-lus tipe gebaseerd op die vrye vier-rotor model met integraalbeheer om steuringinsette te verwerp. ’n Veer-demper model blyk genoegsaam te wees vir die modellering van die vashegdinamika. ’n Nuwe puntmassamodel van die vasgehegde OLV word gebruik om die geslotelus analitiese uitdrukkings van die vasgehegde stelselpole vir beide radiale en hoekrigtings as funksies van vier-rotor en vashegparameters te onttrek. Vlugbeheerstelsels is ontwerp en gesimuleer in ’n sagteware-in-die-lus omgewing. Beheerlusse wat krities is vir die landing word ook in ’n hardeware in-die-lus omgewing gesimuleer. Praktiese resultate wys aanvaarbare prestasie in horisontalebeheer vir windsnelhede tot 2 m.s−1 terwyl die vertikale beheerstelsel redelik immuun is vir windspoed.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105897
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