The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-1 Skyworker - Mobile Manipulator Critical Design Review Field Robotics Center November 18, 1999 William “Red” Whittaker Peter Staritz Chris Urmson

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-2 Constellation of SSP satellites in GEO 1GW of energy to the ground Microwave transmission antenna 1 km in diameter Mass of 4800 MT (10X as massive as ISS) Assembled over 1 year, maintained for 30 years Space Solar Power (SSP) Facilities 4000 m

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-3 Assembly, Inspection, Maintenance Extremely large scale structures Poor accessibility Long life cycle Dangerous environment Necessitates a robotic workforce –Assembly, Inspection, Maintenance (AIM) Radiator Parabolic Reflector Radi ator Parabolic Reflector

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-4 ObjectivesObjectives Demonstrate the viability of using robots for orbital construction Prove the validity of using structure walkers for orbital AIM Demonstrate SSP AIM relevant tasks using robotics Simulate prospective SSP AIM robots and tasks

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-5 Representative Tasks Walk, turn, and transition across planes on a truss structure Pick up and place a payload at arbitrary locations and orientations in space Carry a payload while walking, turning, and transitioning Conduct calibration and inspection tasks Connect power and communications cables Cooperatively carry massive or large payloads Perform tasks that require multiple robot collaboration

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-6 DemonstrationDemonstration Prototype Robot –Pick up and carry a model transmitting element the length of the truss, turn while carrying, couple the element to the structure –Connect Power Management and Distribution (PMAD) to the element –Perform a mock calibration Simulation –Large scale construction utilizing multiple robots –Coordinated installation of full scale transmitting elements –Demonstrate extended lifetime operations

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-7 Configuration - Key Metrics Continuous Gait Forces exerted / Forces experienced Workspace Control Complexity DOF Mass Cost Energy Consumption

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-8 SkyworkerSkyworker Continuous Gait –Reduced forces on structure –Low energy consumption –Constant contact with structure –Requires 4 joint synchrony 11 Degrees of freedom Extensive Workspace

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-9 Skyworker - Specifications Tetherless Mobile Manipulator Processor: Pentium166 Walking Speed: 10cm/s Mass: <37kg Dimensions: 3m x 0.5m x 0.1m Degrees of Freedom: 11 Material: Aluminum Power: 200W peak

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-10 Force Analysis Mass Estimates Forces Due to imperfect GC system Maximum torque 16 N-m Maximum force 12 N Original Mass Estimates

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-11 Joint Development Determined maximum torque, speed, and travel needed for gait Modularity considerations Motor / Reduction Combination –16 Nm torque + –44 degrees/second + Skyworker actuators –57.5 degrees/second at 32 Nm torque –62.5 degrees/second at 16 Nm torque

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-12 ReductionReduction Two Stage Transmission Stage 1 - Planetary Gearhead –Integral Unit –4.8 to 1 reduction –1.3 deg no-load backlash –80% efficiency Stage 2 - Harmonic Drive –High reduction ratio with zero backlash –Low mass - high torque ratio –Efficiencies ranging from 70% to 80% CSF 2A-GR-14 Harmonic Drive

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-13 Motor Selection Motors Selection Criteria –Power Minimization –Mass –Available with integral encoder and planetary gearhead –Space relevance Maxon Motors –DC Graphite Brushed –Rated for 42 volts, operating at 30 volts –.340 kg –4800 rpm & 24 Nm output torque requires 48 watts

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-14 Joint Overview 3 Inline revolute (Size A) 2 Offset (Cantilever) revolute3 Inline revolute (Size B) 3 Axial revolute

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-15 Axial Revolute Joint Most Complicated Interface between F/T sensor and Gripper Mass 1.48 kg Shear key

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-16 Anatomy of a Joint Force Torque Interface Cap Force Torque Interface Bearing Secure Bearings Output Shaft Harmonic Housing Harmonic Drive Potentiometer Belt Feedback Drum Bearing Baseplate Gripper Interface Force Torque Closing Plate Potentiometer Pulley Potentiometer Motor/Planetary/ Encoder Package

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-17 Structure Overview High bending and torsional stiffness Weight minimization –Truss reduction Access via removable bottom plates –Also serve as internal attachment points Each link is unique –Little opportunity for modularity

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-18 GripperGripper

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-19 Gripper’s Force Analysis Clamping force needed to counteract effects of stride Maximum force required: 500N x y z Time (s) Force (N) Singularity in stride

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-20 ConceptConcept Dynamic gait requires a robust and fast gripping mechanism Robustness Simple Design - Single jaw actuated Low Power - Limited motor torque required Error Correction - Designed with mechanical allowance for imperfect approach Speed Fast Approach - Direct approach allowed by configuration Fast Mechanism - High speed advantage provided by linkage Fast Motor - High RPM attained with low torque requirement

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-21 MechanismMechanism Gripping Mechanism: “Vise Grip” Four bar linkage –Speed Advantage: Moving jaw adequately slowed at final closing –Force Advantage: Motor force multiplied at locking –Power Advantage: Zero power required when locked

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-22 CoatingCoating Potential for wear of aluminum gripping face mandated protective coating Stainless Steel Coating Reduced wear Increased coefficient of friction Thermally sprayed coating courtesy of the State University of New York at Stony Brook’s Center for Thermal Spray Research

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-23 Gravity Compensation Skyworker requires gravity compensation to operate properly Marionette style cable support counteracts the force of gravity Combination Active/Passive system –Vertical axis is passive –Horizontal axis are active Modify a heritage gravity compensation system

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-24 Robot Interface Modifications Four attachment points Sliding interface to allow transition between walking and manipulating postures Arc center located at CG

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-25 Feedback Controller Optical Angle Sensor Picture of shuttle with angle sensor board (to be taken w/ digital camera) Output voltages linear function of angles.

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-26 Feedback Controller Control Issues Gantry pendulum is a fourth order system Model as a second order system –Second order model sufficiently accurate over a small range of inputs. –Skyworker will only move over a small range of velocities. –Tune PID controller for good responses over these inputs. –Hack: Zero integral term with change of direction (faster response)

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-27 Skyworker: Power Electronics Power Budget: –Motors: 140W peak power required –Motor controllers, communications, sensors, digital electronics, CPU, and miscellaneous: +5, +10, -10 volt supplies, 60W maximum –Worst case: 200W –Mass Constraint:  4kg (batteries+converters) Skyworker must be capable of performing operations for a minimum of 20 minutes prior to recharging

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-28 Battery Technologies Batteries we considered: New high-rate discharge NiMH batteries will be used, because they provide a high power/weight ratio along with other desirable properties

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-29 Panasonic High Rate Discharge NiMH

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-30 Power System Two separate battery packs –Motor pack 30 cells 102 watt-hours –Electronics pack 20 cells 68 watt-hours Further optimization possible (to equalize run time) Powers three switching power supplies that produce +5V, +10V and –10V Safety System –E-stop switches located on robot and at control station –Power switching circuitry prevents simultaneous connection of multiple power sources

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-31 Testing Batteries

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-32 Battery and Tethered Operation Charging –Using external delta-V chargers to charge batteries without removing them from Skyworker Battery Monitoring System –Battery voltage monitoring circuitry will let Skyworker know that it’s batteries are nearly drained When Skyworker’s batteries are recharging, it can run off of a tether that supplies 36V and 24V to Skyworker’s motors and voltage regulators.

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-33 Electrical Wiring Diagram

The Next Step SPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-34 Joint Labeling Scheme