Parametric Contact Model (PCM) Development Plan

1
Parametric Contact Model (PCM) Development Plan
Milestone Date Software Goal Experimental Goal
4.1.2.1 Purchase DE (Dynamics Engine by Arachi) 10/1/03 (11/1/03) Revised Estimate
4.1.2.3 Identification of initial PCM for development 10/1/03 (10/17/03) Revised Estimate Have PCM Development Plan Characterized stage 1 PCM
4.1.2.5 PCM design review 10/31/03 (11/7/03) Revised Estimate Stage 1 implemented in DE Characterized stages 2-4 Have experimental goals and plan in place for gecko, roach, and robot feet.
4.1.2.7 PCM prototype v0.1 to be exercised by users 12/2/03 (1/7/04) Revised Estimate Stage 2 implemented in DE Test facilities in place and operating.
4.1.2.10 PCM v1.0 2/2/04 Stage 3 implemented in DE First batch of experimental results on various feet. Begin matching to Stage 3 parameters.
B
A
2
Stage 1 - Simple Contact
Ry
Model Description Rigid foot when in contact,
free when not Contact is event driven Release
is open-loop control based Leg can have linear
and rotational spring/damper at the foot
Rx
Model Complexity Only 1 PCM parameter the
angle of release Geometry of foot is a simple
sphere with appropriate springs/dampers at the
ankle
Questions Model Can Answer Measure reaction
forces to evaluate leg trajectories and foot
compliance, How much does leg squeezing reduce
reaction forces? Is 2.5kg excessive? How much
do we gain/pay for changing mass? What leg
trajectories minimize adhesion forces? How much
adhesion will feet need to provide? And for how
long?
3
Stage 2 - Simple Contact with time/random effects
Ry lt Limit
Model Description Rigid foot when in contact,
free when not Contact is state driven with
random element Release is time based or load
based (including time-dependencies)
Rx lt Limit
Model is extended to handle multiple surfaces
Friction
Model Complexity Additional PCM parameters
Slip force thresholds, time dependence,
chance of finding/losing a foothold, sliding
friction Geometry of foot is a simple sphere
with spring/dampers in leg
Questions Model Can Answer Evaluate gait
strategies, foot-hold finding strategies, role of
redundancy, Determine if gait is too fast
(cant find a foot-hold) or too slow (begin to
slip), Evaluate how to avoid catastrophic
failure when a foothold is missed
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Stage 3 - Non-trivial Geometry
Model Description Foot with multiple toes
(claws sticky pads) Toes with different
contact properties Compliance between toes
Claw
Pad
Model Complexity Additional PCM parameters Pad
friction model, claw adhesion model Geometry is
a set of simple shapes with spring/dampers
between
Questions Model Can Answer Foot Design
strategies How many toes? What arraignment? How
much compliance between toes? How many
claws/pads? We can begin to match experimental
data for claws, setae, prototype feet
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Stage 4 - Non-trivial Geometry on Surfaces
Model Description Foot with multiple toes
(claws sticky pads) Toes with different
contact properties Compliance between
toes Details of surface interaction including
Viscoelastic/plastic impact Time dependent
friction Statistical surface properties
Claw
Pad
Model Complexity Additional PCM parameters
Time dependent adhesion or friction, Surface
deformation properties, More complex pad and claw
models, Velocity dependent impact and
friction Geometry is a set of simple shapes
with spring/dampers between
Questions Model Can Answer Foot Behavior
designs for finding holds on different
surfaces Feed-forward vs. feed-back foothold
finding algorithms. We can better match
experimental data for claws, setae, prototype feet
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Foot/Substrate Contact Pairs
Substrates
Different Feet
Ia
A
1
Ib
Ic
B
3
2
2
1
C
B
A
C
3
Huge number of theoretical Permutations In
reality, only a few will be realized
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Initial Contact models

• Spherical joint created at contact, and persists
  until deactivated.
• Deactivation occurs when one of the following
  conditions are met
• When the leg angle passes some limit
• When the normal or shear force exceeds some
  limit
• After a specific time interval has passed
• All of above, plus contact, can have random
  element

1
Super-foot
Stages 12
Contact models Ia, Ib, and Ic will be created
by varying the parameters of the super-foot
2
Claw
Will be based on experimental data
Stage 3
3
Sticky-pad
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Parametric Contact Model (PCM) Development Plan
Milestone Date Software Goal Experimental Goal
4.1.2.1 Purchase DE (Dynamics Engine by Arachi) 10/1/03 (11/1/03) Revised Estimate
4.1.2.3 Identification of initial PCM for development 10/1/03 (10/17/03) Revised Estimate Have PCM Development Plan Characterized stage 1 PCM
4.1.2.5 PCM design review 10/31/03 (11/7/03) Revised Estimate Stage 1 implemented in DE Characterized stages 2-4 Have experimental goals and plan in place for gecko, roach, and robot feet.
4.1.2.7 PCM prototype v0.1 to be exercised by users 12/2/03 (1/7/04) Revised Estimate Stage 2 implemented in DE Test facilities in place and operating.
4.1.2.10 PCM v1.0 2/2/04 Stage 3 implemented in DE First batch of experimental results on various feet. Begin matching to Stage 3 parameters.
B
A
9
A - Simulation Interface Schematic
Controller Commands
Dynamics Engine (DE)
Real-Time Interface (RTI) Code
Geometry
Creature Description Language (CDL) Text File
State Info
(2) Contact Initiation, State Information
(3) Constraints, Forces
(4) Contact information
(1) Contact Properties
Parametric Contact Model (PCM) Code
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class PCMInterface Public DeContactEvent /
inherets so that it can be regerestered to handle
contacts / public PCMInterface() PCMInterfa
ce() ReadConfig() / This read a text file
to load any parameter changes. It calls
PCMContactType-gtChangeProperties to implement
these changes. / handle() / This
function is called when a contact event takes
place. It determines the contact material
types and decides which contactType to
instantiate / footstatedata update() / This
function is called each time step (either from
the idle function or the RIT, whichever is
enforcing the timing. It then calls the
appropriate contact's update function
/ Member Data An array of instances of
contacts ---------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
- class PCMContactTypeI /this is the actual
PCM file for each contact. There is a type for
each foot material (Isuperfoot, IIclaw,
IIIstickypad, etc.)/ public PCMContactTypeI(i
nt substrateType ) / A different set of
parameters is used for each substrate
/ PCMContactTypeI() ChangeTypeIProperties(s
ubstrateType, name, newValue) if (name
"cranklimit") cranklimitsubstrateType
newValue handle() / This function
creates a spherical constraint at the contact
point, so that the foot can rotate, but not
translate when it is active --- based on
engagepercentagei/ update( substrateType)
/ This function determines whether the
spherical constraint is active or not, and
returns information to the RTI / StateData
this-gtgetStateData for(i1,in,i)
if (substrateType i)
if(crankangle gt cranklimiti randomi
normalforce gt normallimiti
randomi shearforce gt shearlimiti
randomi time gt t_contact
timelimiti randomi ) release
True (and call release function)
return(footStateData) getStateData()
/returns information about the current foot
state including crankangle, normalforce,
shearforce, etc. / Member Data cranklimitnum
Substrates 30 deg, 27 deg, ... , etc.
(1) Read Contact Properties from CDL
(2) Get Contact Initiation, Info from DE
(3) Create Constrains in DE
(2) Get State Initiation, Info from DE
(4) Send Contact info to RTI
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B - Test Facilities and Sample Materials
Claws
Various grades of urethane
Emily Ma