Lecture 2: Locomotion Flashcards
What are the 5 types of motion?
Flow in a channel, crawl, sliding, running, walking
What are the three resistances to motion? Name the respective type of motion.
Hydrodynamic forces–>flow in a channel
Friction forces–>crawl, sliding
Loss of kinetic energy–>running, walking
What are the 5 basic kinematics of motion?Name their respective type of motion.
Eddies–>flow in a channel
Longitudinal vibration–>crawl
Transverse vibration–>sliding
Periodic bouncing on a spring–>running
Rolling of a polygon–>walking
What are the 3 locomotion concepts?
(Nature, Concepts, Most tech)
Nature evolved a multitude of locomotion concepts,
Concepts found in nature,
Most technical systems today still use wheels or caterpillars
What about ‘nature evolved a multitude of locomotion concepts’?
Adaptation to environmental characteristics;
adaptation to the perceived environment(e.g. size)
What about ‘concepts found in nature’?
Difficult to imitate technically;
do not employ wheels;
sometimes imitate wheels(bipedal walking);
the smaller living creatures are the more likely they fly
What about ‘most technical systems today still use wheels or caterpillars’?
(Legged Locomotion)
Legged locomotion is still mostly a research topic
What 5 things cause the question of walking or rolling?
(#,s,c,ee,m)
Number of actuators,
structural complexity,
control expense,
energy efficiency,
movement of the involved masses
What about energy efficiency?
terrain(flat ground, soft ground, climbing…);
Cost of transportation
CoT = …
E = energy, P = power, m = mass; d = distance, v = speed
What about “movement of the involved masses”?
walking/running includes up and down movement of COG
Some extra losses
What is locomotion?
Physical interaction between the vehicle and its environment
What 2.5 things is locomotion concerned with?
interaction forces, and the mechanisms and actuators that generate them
What are the 3 most important issues in locomotion?
(S, Ch_o_Con, Ty)
Stability
Characteristics of contact
Type of environment
What are 4 things about stability?
(#, Center, s/d, incl)
Number of contact points
Center of gravity
static/dynamic stabilization
Inclination of terrain
What are the 3 characteristics of contact?
Contact point or contact area
Angle of contact
friction
What are the 2 things of the type of environment?
(S,M(h/s))
Structure
medium(water, air, soft or hard ground)
Positions are represented by?
Displacement vectors
Rotations are represented by?
rotation matrices
Why legged robots?
Adaptability and maneuverability in rough terrain.
Legged systems can overcome many obstacles, cross a hole or chasm, that are not reachable by wheeled systems!
Why is it quite hard to achieve legged robots ?
(p&mc, coordinated, detailed)
power and mechanical complexity;
many DOFs must be controlled in a coordinated way,
the robot must see detailed elements of the terrain
A minimum of how many DOF is required to move a leg forward? What motions?
two; a lift and swing motion.
How many DOF does the human leg have?
More than 7 major DOF, combined with further actuation at the toes
What does additional joint(DOF)do?
It increases the complexity of the design and especially of the locomotion control and maneuverability
What are the 3 disadvantages of additional joints and actuators?
(E,C,M)
energy,
control,
and mass
How many DOF are in each leg in most cases?
3
What does the 4th DOF for the ankle joint?
It might improve walking and stability
What is the gait characterized by?
the distinct sequence of lift and release events of the individual legs
What is the number of possible events N for a walking robot with K legs ?
𝑁 =( 2𝑘 − 1) ! factorial
What is the number 2 associated with?
(irony)
the number of events of a single leg
For a biped walker, what does k equal and what is the number of possible events N?
K = 2;
(2k-1)! = 3! = 321= 6
What are the 6 possible events?
- Both legs down – right down / left up – both legs down;
- Both legs down – right leg up / left leg down – both legs down;
- Right legs down – both legs up – both legs down;
- Right leg down / left leg up – right leg up / left leg down – right leg down / left leg up;
- Right leg down / left leg up – both legs up – right leg down / left leg up;
- Right leg up / left leg down – both legs up – right leg up / left leg down
What are the requirements of Statically stable walking?
bodyweight is supported by at least 3 legs;
even if all joints freeze instantaneously , the robot will not fall;
safe, slow and inefficient
What are the requirements of Dynamic walking?
the robot will fall if not continuously moving;
less than three legs can be in ground contact;
fast, efficient, and demanding for actuation and control
What are the 3 pros of Biped Walking?
(rolling, polygon,step)
Not too far from real rolling when moving on flat ground
Rolling of a polygon with side length equal to the length of the step
The smaller the step gets, the more the polygon tends to a circle (wheel)
What are the cons of Biped Walking?
Rotating joint was not invented by nature
Work against gravity is required
What about the modeling Legged locomotion? What can it be represented by?
It follows an inverted Pendulum.
It can be represented by walking.
How can gaits be optimized?
(Nature, “elastic”, different)
Nature optimizes its gaits
Storage of “elastic” energy
To allow locomotion at varying frequencies and speeds, different gaits must utilize these elements differently
What are the 6 gaits?
Crawl, bound, trot, pronk, pace, gallop
What are the 4 types of Unmanned Aerial Vehicles?
Helicopters
Fixed Wing Airplanes
Blimp
Flapping Wings
What are the 3 movements of a Quadcopter?
(R,Y,P)
Roll, Pitch, Yaw
What are the rules for determining vertical movement?
If total lift is greater than the force of gravity, the quadcopter moves up.
If total life is equal to the force of gravity, the quadcopter doesn’t move vertically.
If total lift is less than the force of gravity, the quadcopter moves down.
What are the rules for determining lateral movement?
If propellers ¼ add up to more than lifts of propellers ⅔, it moves right
If propellers ⅔ add up to more than propellers ¼, it moves left
If propellers ½ add up to more than propellers ¾, it moves backward
If propellers ¾ add up to more than propellers ½, it moves forward.
What are the rules for determining rotational movement?
If propeller ⅓ add up to more than propellers 2/4, it rotates counterclockwise
If propellers 2/4 add up to more than propellers ⅓, it rotates clockwise
Otherwise there is no rotational movement
