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 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.

Stage 1 - Simple Contact

Model Description:Rigid foot when in contact, free when notContact is event drivenRelease is time basedLeg has linear and rotational spring/damper at the foot

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?

Model Complexity:Only 1 PCM parameter – Tr the time of releaseGeometry of foot is a simple sphere with appropriate springs/dampers at the ankle

Rx

Ry

Stage 2 - Simple Contact with time/random effects

Model Description:Rigid foot when in contact, free when notContact is state driven with random elementRelease is time based or load based (including time-dependencies)

Model Complexity:Additional PCM parameters: Slip force thresholds, time dependence, % chance of finding/losing a foothold, sliding frictionGeometry of foot is a simple sphere with spring/dampers in leg

Rx < Limit

Ry < Limit

Questions Model Can Answer:Evaluate gait strategies, foot-hold finding strategies, role of redundancy, Determine if gait is too fast (can’t find a foot-hold) or too slow (begin to slip), Evaluate how inhomogeneous surfaces affect getting a foot-hold

Model could be extended to handle foot slip, with no motion until force limit is exceeded, then planer sliding with simple friction rule

Friction

Stage 3 - Non-trivial Geometry

Model Description:Foot with multiple toes (claws & sticky pads)Toes with different contact propertiesCompliance between toes

Model Complexity:Additional PCM parameters: Pad friction model, claw adhesion modelGeometry is a set of simple shapes with spring/dampers between

Claw

Pad

Questions Model Can Answer:Foot Design strategies: How many toes? What arraignment? How muchcompliance between toes? How many claws/pads? We can begin to match experimental data for claws, setae, prototype feet

Stage 4 - Non-trivial Geometry on Surfaces

Model Description:Foot with multiple toes (claws & sticky pads)Toes with different contact propertiesCompliance between toesDetails of surface interaction including: Viscoelastic/plastic impact Time dependent friction Statistical surface properties

Model Complexity:Additional PCM parameters: Time dependent adhesion or friction, Surface deformation properties, More complex pad and claw models, Velocity dependent impact and frictionGeometry is a set of simple shapes with spring/dampers between

Claw

Pad

Questions Model Can Answer:Foot & Behavior designs for finding holds on different surfacesFeed-forward vs. feed-back foothold finding algorithms. We can better match experimental data for claws, setae, prototype feet