Design Control and Energy Minimization Strategies for the ARL Monopod

We have built a planar one-legged robot (the ARL Monopod) to study the design, control and energetics of autonomous dynamically stable legged machines. Our 15kg robot is actuated by two low power 80W DC electric motors, yet it operates in a stable and robust fashion up to a running speed of 4:3km=hr (1:2m=s). Both design and control of our machine borrow heavily from Raibert's work whose robots use much more powerful hydraulic actuators. Despite our comparatively low power available for actuation, only the hopping height controller had to be modi ed to achieve stable running. In order to improve energetic e ciency we introduced a scalar \locomotion time" variable, which maps one locomotion cycle onto a xed interval, independent of operating conditions. This locomotion time has allowed the implementation of a reference trajectory for ight phase leg angle tracking. We have performed a detailed energetic analysis of robot running for the ARL Monopod in order to determine how its e ciency may be improved. A comparative energetic analysis reveals our machine as the most energy e cient powered legged robot having a speci c resistance of " = 0:7 at 4:3km=hr (1:2m=s) running speed. i R esum e On a construit on robot marcheur a une patte (le Monopod ARL) pour etudier le design, le contrôle et la performance energ etique des robots marcheurs autonomes et dynamiquement stables. Notre robot de 15kg est activ e par deux moteurs electriques a courant continu de faible puissance (80W ). Malgr e cela, il se d eplace d'une mani ere stable et robuste et atteint une vitesse de pointe de 4:3km=hr (1:2m=s). Le design et le contrôle de base sont emprunt es des travaux de Raibert o u les robots sont activ es par des actionneurs hydrauliques puissants. Même avec une puissance disponible tr es r eduite pour l'activation, seul le contrôleur de hauteur a du être modi e pour atteindre un d eplacement stable. A n d'am eliorer encore les performances energ etiques du robot, on a introduit une variable de \temps de d eplacement" qui permet de faire correspondre un cycle de d eplacement a un intervalle xe, ind ependamment des conditions d'op eration. Cette notion nous a permis de calculer une trajectoire de r ef erence pour la position de la patte pendant la phase de vol. Une analyse comparative de consommation energ etique du Monopod ARL con rme que notre robot est le plus e cace compar e a d'autres robots marcheurs avec son coe cient de r esistance sp eci que de " = 0:7 a une vitesse de 4:3km=hr (1:2m=s). ii Acknowledgements First, I acknowledge the support of the Natural Sciences and Engineering Research Council of Canada who made this work possible by granting me an NSERC PGSA scholarship. The work discussed in this thesis would not have been possible without the support of a number of people. I would like to thank Mojtaba Ahmadi for his enthusiastic attitude and his encouragement. More concretely, he coded the simulations of the ARL Monopod and developed the dynamical equations used in the design of the hip actuation system. Nadim El-fata was always there to tell me what size capacitor I needed or whether a certain electronic component was destroyed. Without his good-humored attitude and willingness to untangle the mysteries of electronic design the experiments would certainly not have proceeded. I also thank Gregory Petryk who developed and implemented the XP/DCS interface for treadmill control and also installed the treadmill and planarizer. Joey Mennitto was always available when I needed someone to complain to about things going wrong. He provided a constant, moderating in uence which helped me keep going. Martin Buehler is responsible for my interest in legged locomotion and without him I would certainly not have been able to work on this project. His theoretical knowledge in the eld of locomotion as well as his practical experience with machines that don't always work made him not only a supportive reference but also someone with the patience and skill necessary to resolve elusive technical glitches. iii