Lecture 2: Locomotion

Question 1

What are the 5 types of motion?

Answer 1

Flow in a channel, crawl, sliding, running, walking

Question 2

What are the three resistances to motion? Name the respective type of motion.

Answer 2

Hydrodynamic forces–>flow in a channel
Friction forces–>crawl, sliding
Loss of kinetic energy–>running, walking

Question 3

What are the 5 basic kinematics of motion?Name their respective type of motion.

Answer 3

Eddies–>flow in a channel
Longitudinal vibration–>crawl
Transverse vibration–>sliding
Periodic bouncing on a spring–>running
Rolling of a polygon–>walking

Question 4

What are the 3 locomotion concepts?
(Nature, Concepts, Most tech)

Answer 4

Nature evolved a multitude of locomotion concepts,
Concepts found in nature,
Most technical systems today still use wheels or caterpillars

Question 5

What about ‘nature evolved a multitude of locomotion concepts’?

Answer 5

Adaptation to environmental characteristics;
adaptation to the perceived environment(e.g. size)

Question 6

What about ‘concepts found in nature’?

Answer 6

Difficult to imitate technically;
do not employ wheels;
sometimes imitate wheels(bipedal walking);
the smaller living creatures are the more likely they fly

Question 7

What about ‘most technical systems today still use wheels or caterpillars’?
(Legged Locomotion)

Answer 7

Legged locomotion is still mostly a research topic

Question 8

What 5 things cause the question of walking or rolling?
(#,s,c,ee,m)

Answer 8

Number of actuators,
structural complexity,
control expense,
energy efficiency,
movement of the involved masses

Question 9

What about energy efficiency?

Answer 9

terrain(flat ground, soft ground, climbing…);
Cost of transportation
CoT = …
E = energy, P = power, m = mass; d = distance, v = speed

Question 10

What about “movement of the involved masses”?

Answer 10

walking/running includes up and down movement of COG
Some extra losses

Question 11

What is locomotion?

Answer 11

Physical interaction between the vehicle and its environment

Question 12

What 2.5 things is locomotion concerned with?

Answer 12

interaction forces, and the mechanisms and actuators that generate them

Question 13

What are the 3 most important issues in locomotion?
(S, Ch_o_Con, Ty)

Answer 13

Stability
Characteristics of contact
Type of environment

Question 14

What are 4 things about stability?
(#, Center, s/d, incl)

Answer 14

Number of contact points
Center of gravity
static/dynamic stabilization
Inclination of terrain

Question 15

What are the 3 characteristics of contact?

Answer 15

Contact point or contact area
Angle of contact
friction

Question 16

What are the 2 things of the type of environment?
(S,M(h/s))

Answer 16

Structure
medium(water, air, soft or hard ground)

Question 17

Positions are represented by?

Answer 17

Displacement vectors

Question 18

Rotations are represented by?

Answer 18

rotation matrices

Question 19

Why legged robots?

Answer 19

Adaptability and maneuverability in rough terrain.
Legged systems can overcome many obstacles, cross a hole or chasm, that are not reachable by wheeled systems!

Question 20

Why is it quite hard to achieve legged robots ?
(p&mc, coordinated, detailed)

Answer 20

power and mechanical complexity;
many DOFs must be controlled in a coordinated way,
the robot must see detailed elements of the terrain

Question 21

A minimum of how many DOF is required to move a leg forward? What motions?

Answer 21

two; a lift and swing motion.

Question 22

How many DOF does the human leg have?

Answer 22

More than 7 major DOF, combined with further actuation at the toes

Question 23

What does additional joint(DOF)do?

Answer 23

It increases the complexity of the design and especially of the locomotion control and maneuverability

Question 24

What are the 3 disadvantages of additional joints and actuators?
(E,C,M)

Answer 24

energy,
control,
and mass

Question 25

How many DOF are in each leg in most cases?

Answer 25

3

Question 26

What does the 4th DOF for the ankle joint?

Answer 26

It might improve walking and stability

Question 27

What is the gait characterized by?

Answer 27

the distinct sequence of lift and release events of the individual legs

Question 28

What is the number of possible events N for a walking robot with K legs ?

Answer 28

𝑁 =( 2𝑘 − 1) ! factorial

Question 29

What is the number 2 associated with?
(irony)

Answer 29

the number of events of a single leg

Question 30

For a biped walker, what does k equal and what is the number of possible events N?

Answer 30

K = 2;
(2k-1)! = 3! = 321= 6

Question 31

What are the 6 possible events?

Answer 31

1. Both legs down – right down / left up – both legs down;
2. Both legs down – right leg up / left leg down – both legs down;
3. Right legs down – both legs up – both legs down;
4. Right leg down / left leg up – right leg up / left leg down – right leg down / left leg up;
5. Right leg down / left leg up – both legs up – right leg down / left leg up;
6. Right leg up / left leg down – both legs up – right leg up / left leg down

Question 32

What are the requirements of Statically stable walking?

Answer 32

bodyweight is supported by at least 3 legs;
even if all joints freeze instantaneously , the robot will not fall;
safe, slow and inefficient

Question 33

What are the requirements of Dynamic walking?

Answer 33

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

Question 34

What are the 3 pros of Biped Walking?
(rolling, polygon,step)

Answer 34

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)

Question 35

What are the cons of Biped Walking?

Answer 35

Rotating joint was not invented by nature
Work against gravity is required

Question 36

What about the modeling Legged locomotion? What can it be represented by?

Answer 36

It follows an inverted Pendulum.
It can be represented by walking.

Question 37

How can gaits be optimized?
(Nature, “elastic”, different)

Answer 37

Nature optimizes its gaits
Storage of “elastic” energy
To allow locomotion at varying frequencies and speeds, different gaits must utilize these elements differently

Question 38

What are the 6 gaits?

Answer 38

Crawl, bound, trot, pronk, pace, gallop

Question 39

What are the 4 types of Unmanned Aerial Vehicles?

Answer 39

Helicopters
Fixed Wing Airplanes
Blimp
Flapping Wings

Question 40

What are the 3 movements of a Quadcopter?
(R,Y,P)

Answer 40

Roll, Pitch, Yaw

Question 41

What are the rules for determining vertical movement?

Answer 41

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.

Question 42

What are the rules for determining lateral movement?

Answer 42

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.

Question 43

What are the rules for determining rotational movement?

Answer 43

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