Pressure Sensor Findings and Thoughts on Future Work

Miguel PiedrahitaBDML5/13/04

Pressure Sensor Motivation

• Normal force information will be useful for climbing

• May be able to get dynamic signals related to slipping

• Pressure approach could integrate nicely with dry adhesive pads

Chamber FabricationMold #1: Mold for Cavity Insert

Completed Cavity Insert (wax or hard urethane)

Mold #2: Mold for Membrane Exterior

Cavity Insert placed in Mold #2, leaving gap for membrane

Membrane cast from soft urethane

Mold #3: Mold for sealing off membrane

Membrane sealed with layer of hard urethane

Finished Chamber

Testing

• Applied normal force from 0g to 1000g back down to 0g, in 50g increments.

• Several trials conducted on two different days.

Mass

Results

Day 1

Day 2

Sensor Performance (Day 2)

Sensitivity: 1.06 kPa/N, (1.06 V/N)

Accuracy: +- 0.33 N, or +- 0.35 kPa

Observations• Drawbacks to practical implementation

– Difficult to fully bleed air from system – affects repeatability

– Size of system limited by rather large sensor– Likely not effective for adhesion forces (front

feet)• Other technologies may be better for

normal force measurement– Strain gage– Piezoelectric

Thoughts on Future Work:What do we want from RiSE sensors?• Climbing-related information:

– Foot impact events– Slip events– Tangential & normal forces on each foot– Measure of penetration of claws/engagement of dry

adhesives (i.e. a way to predict likelihood of slip)• Surface-related information:

Information about climbing surface would be useful! We could then tailor aggressiveness and climbing strategy (claws vs. dry adhesives) accordingly

– Inclination– Surface hardness– Roughness

Array of Instrumented “Lamellar Fingers”

• Force distribution throughout foot – in tension & compression. Useful for evaluating foot design & performance.

• Surface roughness by comparing deflections

Embedded PVDF or

strain gage

Why Lamellar Fingers? Good Question!

• Examine advantage of lamellar structures• Work on optimizing geometry for front feet

and rear feet– Front feet: Maximize surface contact, minimize

stress at edges & Poisson shrinkage– Rear feet: Maximize shear force

• Solid mechanics, FEA, experiments (RoboToe)