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Preliminary Test Track Experiments

April 16, 2004Motohide Hatanaka, Emily Ma

Stanford University

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Preliminary Test Track Experiments

Goal: Validate simulations and to generate insights to improve on first generation foot design. Focus on three phases of leg trajectory.Attachment Generate strong contact between claws and surface.

• Timing of attachment• Impact velocity• Orientation angle (compensate for motion in thru-

stroke?)

Through-stroke Ankle compliance – how much and for which axes?Detachment Detachment with least resistance and without breaking

claws.

• Orientation angle• Timing of detachment

Preliminary tests focused on timing of attachment and detachment.

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Test Track Coordinates

force plate

foot

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Timing of attach/detachment

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Observations[all cases]The robot is always pushing itself away from the wall. (-Z)

[early attachment]high lateral pull in (+X)robot pushes itself down at initial contact (-Y)robot pushes itself away from surface at initial contact (-Z)[late attachment]small lateral pull in (+X)[late detachment]lateral push out at detachment (-X)significant pull down or drag (-Y)large kick off away from surface (-Z)[early attachment, late detachment]largest pull down (drag) at detachment (-Y)

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DetachmentEarly Nominal Late

Attach

men

tVe

ry E

arly

Early

Nom

inal

Late

Lateral Force: X-direction (+X = pull in)

High pull-in force (+X) after early attachment

Low pull-in force (+X) after late attachment

Lateral push out (-X) at late detachment

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optimal

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DetachmentEarly Nominal Late

Attach

men

tVe

ry E

arly

Early

Nom

inal

Late

Vertical Force: Y-direction (+Y = pull body up)

Robot pushes itself down (-Y) at early attachment

Significant pull down = drag (-Y) at late detachment

7

optimal

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DetachmentEarly Nominal Late

Attach

men

tVe

ry E

arly

Early

Nom

inal

Late

Normal Force: Z-direction (+Z = pull body into wall)

Large kick off away from wall (-Z) at late detachment

Robot pushes itself away from wall (-Z) especially at early attachment

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optimal

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Summary of findingsAssuming we want lateral pull in, vertical self push/pull up, and pull into wall, (i.e. +X,+Y,+Z):

• Early attachment is to be avoided for -Y and -Z but useful for +X.

• Late detachment is to be avoided for all parameters.

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Next Steps (1)Further analyses with current

setup• Measure or calculate forces and torques at contact point (current contact point is offset from center of the force plate)

• Study the torques• Find out the reasons for the results

obtained (e.g. by closer observation at slower operation rate)

• Look at work generated in a cycle and quantify performance of each setup

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Next Steps (2)Experiment modification

• Modify the trajectory to have +Z values to measure claw attachment strength on wall

• Include amplitude as an additional parameter for optimization

• Use pull-up motor to emulate the five legs that are not there

• Identify control parameters to match ideal force & torque profiles derived from biology.