Case Study: Term Project

Transcription

1 Case Study: Term Project Expectations for the term project An example of a previous term project U N I V E R S I T Y O F MARYLAND David L. Akin - All rights reserved Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

2 AAR Design Project Statement Perform a detailed design of a small astronaut assistance rover, emphasizing mobility systems Chassis systems (e.g., wheels, steering, suspension ) Support systems (e.g., energy storage) Navigation and guidance system (e.g., sensors, algorithms...) Design for Moon, then assess feasibility of systems for Mars, and conversion to Earth analogue rover This is not a hardware project - focus is on detailed design (but may be built later!) U N I V E R S I T Y O F MARYLAND 2 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

3 Objectives for Design Project (1) UMd SSL is proposing to do month-long simulations of lunar/mars science exploration missions to examine impact of robotics Primary missions would be held at HI-SEAS in Hawaii Rover design should facilitate shipping to/from Hawaii Minimal size and mass Modular construction for packing (ideally each less than 50 lbs with packaging) U N I V E R S I T Y O F MARYLAND 3 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

4 Objectives for Design Project (2) Multiple individual rovers One rover/crew Rover can carry two crew in contingency mode Both responsive and unresponsive transport Operation on volcanic soils and terrains Capable of bring brought through airlock for repair or servicing U N I V E R S I T Y O F MARYLAND 4 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

5 Level 1 Requirements (Performance) 1. Rover shall have a maximum operating speed of at least 15 km/hour on level, flat terrain 2. Rover shall be designed to accommodate a 0.3 meter obstacle at minimal velocity 3. Rover shall be designed to accommodate a 0.1 m obstacle at a velocity of 7.5 km/hour 4. Rover shall be designed to accommodate a 30 slope in any direction at a speed of at least 5 km/ hour with positive static and dynamic margins U N I V E R S I T Y O F MARYLAND 5 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

6 Level 1 Requirements (Payload) 5. Rover shall be be designed for an instrument payload with a mass of 50 kg and volume of 0.25 m 3 6. Rover shall also accommodate a Ranger-classs sample-collection manipulator system with a mass of 50kg 7. Rover shall be designed to nominally transport a 95 th percentile American male crew in full pressure suit 8. Rover shall be capable of carrying two 95 th U percentile N I V E R S I T crew Y O F in a contingency MARYLAND 6 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

7 Level 1 Requirements (GN&C) 9. Rover shall be be capable of being controlled directly, remotely, or automated 10.Rover shall be capable of following an astronaut, following an astronaut s path, or autonomous path planning between waypoints 11.Rover shall be capable of operating during any portion of the lunar day/night cycle and at any latitude U N I V E R S I T Y O F MARYLAND 7 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

8 Final Project Expectations Final design of rover Solid models of design Design evolution through as the analysis progressed Details of mass, power, etc. Trade studies (NOT an exhaustive list!) Number, size, configuration of wheels Diameter and width of wheels Size and number of grousers Suspension design Steering design Alternate design approaches (e.g., tracks, legs, hybrid) U N I V E R S I T Y O F MARYLAND 8 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

9 Final Design Expectations (2) Vehicle stability Slope (up, down, cross) Acceleration/deceleration Turning Combinations of above Terrain ability ( terrainability ) Weight transfer over obstacles Climbing/descending vertical or inclined planes Hang-up limit (e.g., high-centering, wheel capture) U N I V E R S I T Y O F MARYLAND 9 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

10 Final Design Expectations (3) Suspension dynamics Development of drive actuator requirements Detailed wheel-motor design Development of steering actuator requirements Detailed steering mechanism design Mass budget (with margin) Power budget (with margin) Other design aspects as included U N I V E R S I T Y O F MARYLAND 10 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

11 Final Project Presentations Tuesday, Dec. 6 and Thursday, Dec. 8 (dates corrected) Each final project will be presented in class Single-person projects: 15 minutes Double-person projects: 30 minutes Looking for volunteers to go on Tuesday Otherwise, I ll pick randomly on the day U N I V E R S I T Y O F MARYLAND 11 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

12 Final Project Submissions You should submit the slides you used for the presentation on Tuesday, December 6 (whether or not you present on that day) You should submit a comprehensive set of slides documenting your design by the posted final exam day for this class, Tuesday, December 20. If you feel your presentation is comprehensive, just send me an saying that there will be no further report Not looking for spreadsheets or Matlab code U N I V E R S I T Y O F MARYLAND 12 Case Study: Final Design Project ENAE 788X - Planetary Surface Robotics

13 Terrestrial Lunar Rover (TLR) ENAE788X Planetary Surface Robotics Design Project Team Members Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler

14 Overview Project Requirements and Objectives Concepts Explored TLR Design Overview Terramechanics and Energetics Stability and Breaking Steering Suspension system Chassis Motors and Gearing Track Wheel Hybrid Mobility Unit Details TLR Design Details Operations Sensors Mapping Command and Control Mass Budget Reliability and Fault Tolerance Earth Analog Considerations Possible Improvements to TLR ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 14

15 Project Requirements & Specifications Project Description Perform a detailed design of the mobility systems for a small pressurized rover Chassis systems (e.g., wheels, steering, suspension...) Navigation and guidance system (e.g., sensors, algorithms...) Design for moon, then assess feasibility of systems for Earth analogue rover The following are the level one requirements provided to impact our design: L1-1: Rover shall have a maximum operating speed of at least 15 km/hour on level, flat terrain L1-2:Rover shall be designed to accommodate a 0.5 meter obstacle at minimal velocity L1-3: Rover shall be designed to accommodate a 0.1 meter obstacle at a velocity of 7.5 km/hour L1-4: Rover shall be designed to accommodate a 20 slope in any direction at a speed of at least 5 km/hour with positive static and dynamic margins The following are the specifications provided to impact our design: L1-5: Rover shall be capable of supporting a mass (exclusive of chassis and mobility system) of at least 1000 kg L1-6: Rover shall be capable of accommodating a cylindrical pressurized cabin that is 1.80 meters in diameter and 1.83 meters long L1-7: Target overall vehicle mass shall be less than 1800 kg with positive margin ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 15

16 Project Requirements & Specifications The following are the Level 2 requirements derived to impact our design: L2-1: The vehicle shall be designed to be operational on the surface of the moon with the environmental constraints given in Table 1. L2-2: An analog test vehicle shall be designed to be operational on the surface of the earth with the environmental constraints given in Table 1. The following are the design goals derived to impact our design: G-1: Safety factors - at least 1.5 to 2.0 (this might be driven by the earth analog requirements) G-2: Fault tolerance - Every subsystem should be single fault tolerant G-3: Mobility degrees on the spot turns and movement G-4: Adaptability - Don't be limited to only this size payload (mass, weight etc) Table 1 Gravitational Acceleration Atmospheric Density Atmospheric Constituents Temperature Range Length of Day Earth Moon 9.8 m/s2 (1g) m/s2 (0.16g) pa (14.7 psi) - 78% N2 21% O2-120 F -100 F 250 F -250 F 24 Hr 28 Days ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 16

17 Concepts Explored ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 17

18 Concepts Explored ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 18

19 TLR Design Overview Each mobility unit is capable of rotating about the center of the large wheel Each large wheel houses two motors that are cross strapped to operate the wheel and the actuator to rotate the wheel connector bar Supported Payload Accommodates All Sensors and Avionics Aluminum Chassis Suspension System 4 Track-Wheel Hybrid Mobility Unit Wheel to Chassis Connection Tracks Wheel Connector Bar Large Wheel Driving Wheel Small Wheel Houses the Motors Free Running ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 19

20 Terramechanics and Energetics Trades Wheels Tracks Study Cases (for each trade above) Draw Bar Pull vs. Wheel Diameter vs. Wheel Width Grousers vs. No-Grousers Power vs. Wheel Diameter vs. Wheel Width Number of wheels vs. Wheel Diameter vs. Wheel Width Wheels vs. Tracks Wheel diameter varying from 0.3 to 1.0 m Wheel width varying from 0.1 to 0.6 m Large wheel diameter varying from 0.3 to 1.0 m Small wheel diameter 2/3 of the large wheel Flat terrain with 15km/hr velocity 20o slope with 5km/hr velocity 10 cm obstacle with 7.5km/hr (assuming all wheels encounter the obstacle at the same time) 50 cm obstacle at minimum velocity (assuming all wheels encounter the obstacle at the same time) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 20

21 Wheeled System Draw Bar Pull No Grousers Flat Terrain Wheel Wheel Wheel Wheel Diameter 0.30 m Diameter 0.50 m Diameter 0.70 m Diameter 0.90 m Draw Bar Pull (No Grausers) - DP - (N) Draw Bar Pull (No Grausers) - DP - (N) 4 wheels o Slope Turtle Performance is Highlighted Wheel Diameter 0.40 m Wheel Diameter 0.60 m Wheel Diameter 0.80 m Wheel Diameter 1.0 m Wheel Diameter 0.50 m Wheel Diameter 0.60 m Wheel Diameter 0.70 m Wheel Diameter 0.80 m Wheel Diameter 0.90 m Wheel Diameter 1.0 m Wheel Width - b - (m) Wheel Wheel Wheel Wheel Diameter 0.30 m Diameter 0.50 m Diameter 0.70 m Diameter 0.90 m Wheel Diameter 0.40 m Wheel Diameter 0.60 m Wheel Diameter 0.80 m Wheel Diameter 1.0 m 0.55 Draw Bar Pull (No Grausers) - DP - (N) Draw Bar Pull (No Grausers) - DP - (N) 0.55 Wheel Diameter 0.40 m wheels 0.50 Wheel Diameter 0.30 m Wheel Diameter 0.30 m Wheel Diameter 0.40 m Wheel Diameter 0.50 m Wheel Diameter 0.60 m Wheel Diameter 0.70 m Wheel Diameter 0.80 m Wheel Diameter 0.90 m Wheel Diameter 1.0 m Wheel Width - b - (m) Wheel Width - b - (m) Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 21

22 Wheeled System Draw Bar Pull With Grousers Flat Terrain Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) 4 wheels Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Wheel Diameter 0.08 m Wheel Diameter 0.03 m Wheel Diameter 0.05 m Wheel Diameter 0.07 m Wheel Diameter 0.09 m Wheel Diameter 1.0 m Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) wheels 0.30 Wheel Width - b - (m) Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Wheel Diameter 0.08 m Wheel Diameter 0.09 m Wheel Width - b - (m) Wheel Wheel Wheel Wheel Wheel Diameter 1.0 m Diameter Diameter Diameter Diameter 0.03 m 0.05 m 0.07 m 0.09 m Wheel Wheel Wheel Wheel Diameter Diameter Diameter Diameter 0.04 m 0.06 m 0.08 m 0.10 m Wheel Width - b - (m) 0.05 Wheel Diameter 0.04 m Wheel Diameter 0.06 m Wheel Diameter 0.08 m Wheel Diameter 0.10 m Wheel Diameter 0.09 m o Slope Turtle Performance is Highlighted Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 22

23 Wheeled System Obstacles Draw Bar Pull With Grousers 10 cm Obstacle Turtle Performance is Highlighted 50 cm Obstacle Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Wheel Diameter 0.08 m Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) 4 wheels Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Wheel Diameter 0.08 m Wheel Diameter 0.09 m Wheel Diameter 0.09 m Wheel Diameter 1.0 m Wheel Diameter 1.0 m Wheel Width - b - (m) Wheel Width - b - (m) Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m 0.55 Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) 6 wheels Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Wheel Diameter 0.08 m Wheel Diameter 0.08 m Wheel Diameter 0.09 m Wheel Diameter 0.09 m Wheel Diameter 1.0 m Wheel Diameter 1.0 m Wheel Width - b - (m) Wheel Diameter 0.07 m Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 23

24 Wheeled System Obstacles Draw Bar Pull With Grousers 50 cm Obstacle On All Wheels 50 cm Obstacle On Two wheels Wheel Diameter 1.0 m Wheel Diameter 1.1 m Wheel Diameter 1.2 m Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) 4 wheels Wheel Diameter 1.0 m Wheel Diameter 1.1 m Wheel Diameter 1.2 m Wheel Diameter 1.3 m Wheel Diameter 1.3 m Wheel Diameter 1.4 m Wheel Diameter 1.5 m Wheel Diameter 1.4 m Wheel Diameter 1.5 m Wheel Diameter 1.6 m Wheel Diameter 1.6 m Wheel Diameter 1.7 m Wheel Diameter 1.7 m Wheel Diameter 1.0 m Wheel Diameter 1.1 m Wheel Diameter 1.2 m Wheel Diameter 1.3 m Wheel Diameter 1.7 m Wheel Diameter 1.0 m Wheel Diameter 1.1 m Wheel Diameter 1.3 m Wheel Diameter 1.2 m Wheel Diameter 1.4 m Wheel Diameter 1.5 m Wheel Diameter 1.6 m Wheel Diameter 1.7 m Wheel Width - b - (m) Wheel Diameter 1.6 m Wheel Diameter 1.4 m Wheel Diameter 1.5 m 0.30 Wheel Width - b - (m) Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) 6 wheels Wheel Width - b - (m) Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 24

25 Wheeled System Power With Grousers Flat Terrain Wheel Diameter 0.30 m Wheel Diameter 0.40 m Wheel Diameter 0.60 m Wheel Diameter 0.80 m Wheel Diameter 0.90 m Wheel Diameter 1.0 m Wheel Diameter 0.30m Wheel Diameter 0.40m Wheel Diameter 0.50 m Wheel Diameter 0.50m Wheel Diameter 0.60m Wheel Diameter 0.70 m Wheel Diameter 0.70m Wheel Diameter 0.80m Wheel Diameter 0.90m Power Required - P - (W) Power Required - P - (W) wheels 20o Slope Turtle Performance is Highlighted Wheel Diameter 0.10m Wheel Width - b - (m) Wheel Diameter 0.30m Wheel Diameter 0.40 m Wheel Diameter 0.40m Wheel Diameter 0.50m Wheel Diameter 0.50 m Wheel Diameter 0.60 m Wheel Diameter 0.90 m Wheel Diameter 0.60m Wheel Diameter 0.80m Wheel Diameter 0.70m Wheel Diameter 0.70 m Wheel Diameter 0.80 m Wheel Diameter 0.90m Power Required - P - (W) Power Required - P - (W) 6 wheels 0.35 Wheel Diameter 0.30 m Wheel Diameter 1.0 m Wheel Diameter 0.10m Wheel Width - b - (m) 0.30 Wheel Width - b - (m) Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 25

26 Wheeled System Obstacles Power 10 cm Obstacle Wheel Diameter 0.30m Wheel Diameter 0.40m Wheel Diameter 0.50m Wheel Diameter 0.60m Wheel Diameter 0.70m Turtle Performance is Highlighted Wheel Diameter 0.80m Power Required - P - (W) 4 wheels Wheel Diameter 0.90m Wheel Diameter 1.0 m Wheel Diameter 0.40m Wheel Diameter 0.50m Wheel Diameter 0.60m wheels Wheel Width - b - (m) Power Required - P - (W) Wheel Diameter 0.30m Wheel Diameter 0.70m Wheel Diameter 0.80m Wheel Diameter 0.90m 0.50 Wheel Diameter 1.0 m Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 26

27 Wheeled Terramechanics and Energetics Conclusions There is substantial amount of gain from using grousers. There is not a substantial difference between different grouser heights It is possible to achieve a positive draw bar pull for all wheel sizes and diameters on flat terrain, on a slope, and going over 10cm obstacle with all wheels. A large amount of power is required to overcome the resistance from these cases It is not possible to achieve enough drawbar pull to go over a 50 cm obstacle, assuming all wheels will encounter the obstacle at the same time, for reasonable size wheels. A wheeled system is not a good option FOR THIS APPLICATION unless: A Lunar Monster Truck is created or A system with more than 4 wheels and the same number of actuators (increased mass and complexity) is produced or An inefficiency in mobility is accepted or An inefficiency in power consumption, hence operation time is accepted Therefore; need to look at: Tracked vehicles to achieve larger drawbar pull and lower resistance (less power use) Clever concepts that would help overcome 50cm obstacles instead of large wheels ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 27

28 Track-Wheel Hybrid System Terramechanics and Energetics Four two-wheel track system Large wheel is attached to chassis and drives the system Small wheel is free running and is ran by tracks. It is connected to the large wheel by two beams (one on each Side) The small wheel can be rotated about the center of the large wheel. Grouser height used = 0.01m for all calculations 10% of the total resistance has been added to all calculations as internal resistance to accommodate for possible unknowns Rotate 360o Wheel m Wheel 1 ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 28

29 Track-Wheel Hybrid System Draw Bar Pull With Grousers Flat Terrain 20o Slope TLR Performance is Highlighted Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) Wheel 1 Diameter 0.03 m Wheel 1 Diameter 0.04 m Wheel 1 Diameter 0.05 m Wheel 1 Diameter 0.06 m Wheel 1 Diameter 0.07 m Wheel 1 Diameter 0.03 m Wheel 1 Diameter 0.04 m Wheel 1 Diameter 0.05 m Wheel 1 Diameter 0.06 m Wheel 1 Diameter 0.07 m Wheel 1 Diameter 0.08 m Wheel 1 Diameter 0.08 m Wheel 1 Diameter 0.09 m Wheel 1 Diameter 0.09 m Wheel 1 Diameter 1.0 m Wheel 1 Diameter 1.0 m Wheel Width - b - (m) Wheel Width - b - (m) cm Obstacle Draw Bar Pull (With Grousers) - DPg - (N) Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.08 m Wheel Diameter 0.07 m Wheel Diameter 0.09 m Wheel Diameter 1.0 m Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 29

30 Track-Wheel Hybrid Draw Bar Pull With Grousers 50 cm Obstacle TLR Performance is Highlighted Thrust Capacity Tc Resistance R Tc R Both Small and the Large Wheel Acting on the Obstacle Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Wheel Diameter 0.08 m Wheel Diameter 0.09 m Wheel Width - b - (m) 0.25 Only the Small Wheel Acting on the Obstacle Draw Bar Pull (With Grousers) - DPg - (N) Draw Bar Pull (With Grousers) - DPg - (N) Wheel Diameter 1.0 m Wheel Diameter 0.03 m Wheel Diameter 0.04 m Wheel Diameter 0.05 m Wheel Diameter 0.06 m Wheel Diameter 0.07 m Thrust Capacity Resistance Wheel Diameter 0.08 m Wheel Diameter 0.09 m Wheel Diameter 1.0 m Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 30

31 Track-Wheel Hybrid System Power With Grousers Flat Terrain 20o Slope TLR Performance is Highlighted Wheel 1 Diameter 0.30 m Wheel 1 Diameter 0.40 m Wheel 1 Diameter 0.30 m Wheel 1 Diameter 0.40 m Wheel 1 Diameter 0.50 m Wheel 1 Diameter 0.50 m Wheel 1 Diameter 0.60 m Wheel 1 Diameter 0.60 m Wheel 1 Diameter 0.70 m Wheel 1 Diameter 0.70 m Wheel 1 Diameter 0.80 m Wheel 1 Diameter 1.0 m Wheel 1 Diameter 1.0 m Wheel 1 Diameter 0.80 m Wheel 1 Diameter 0.90 m Wheel 1 Diameter 0.90 m Power Required - P - (W) Power Required - P - (W) Wheel Width - b - (m) Wheel Width - b - (m) Wheel Diameter 0.30 m Wheel Diameter 0.40 m Wheel Diameter 0.50 m Wheel Diameter 0.60 m 10 cm Obstacle Power Required - P - (W) Wheel Diameter 0.70 m Wheel Diameter 0.80 m Wheel Diameter 0.90 m Wheel Diameter 1.0 m Wheel Width - b - (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 31

32 Wheel-Track Hybrid Terramechanics and Energetics Conclusions Wheel-Track hybrid is superior in all cases to a wheeled system Wheel-Track hybrid system provides positive drawbar pull for all four cases. Wheel-Track hybrid system requires significantly less power. Wheel-Track hybrid system power requirements meet the Turtle average and maximum power draw requirements for all three cases The 50 cm obstacle is overcome by the design choice and implementation: Rotating the small wheel at an optimum angle to place on the 50cm obstacle and driving over it Leveraging the vehicle on front wheel to go over the obstacle or Riding on the small wheel and rolling over the obstacle with the large ones ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 32

33 Wheel-Track Hybrid Power Use Requirements: Average power for Turtle driving system is kw Defined as operations over 3 days Maximum power draw for Turtle driving system is 6.19 kw Allocated power for the driving system is 0.86 kw Allocated power for the avionics is 0.59 kw in use, 0.2 kw in standby mode Based on the power calculations for a 1m diameter, 0.30m width wheel: Turtle could support only ~6 hours of drive time a day on average (driving half the time over 10cm obstacles half the time on flat terrain). Tack Wheel Hybrid System: Nominal power usage: for flat terrain ~0.9 kw Maximum power usage: for 10 cm obstacle is ~1.6 kw Power usage for 20o slope is ~1.7 kw Based on the power calculations: Track-Wheel hybrid system can support ~16 hours of drive time a day on average (driving half the time over 10cm obstacles half the time on flat terrain or half time on slope) and almost continuously on flat terrain. This would allow for more autonomous applications and a larger range of operations from a base. The avionics power use is well below the 0.59 kw There is 10% margin on all calculations for drawbar pull & power to account for internal resistance or other unknownns ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 33

34 Track-Wheel Hybrid Mobility Unit - Details Wheel: The wheel well is made out of titanium Houses the in-hub motor Interior is protected by a flexible cover to avoid dust collection on critical components Tire: Modified Lunar Rover wheel construction: Thicker woven flexible steel mesh tires with titanium track engagement threads. Track: Same construction as the tires. Thicker woven flexible steel mash with titanium grousers on the outer surface and titanium wheel engagement threads on the inner surface * No CTE mismatch between tracks, tires, wheel wells, and the wheel connector bar * Tire can operate without the track in place in emergencies * Easily maintained - installed/removed, replaced - tracks Small supporting rollers to distribute pressure evenly on the tracks between the wheels (not shown) Steel Woven Mesh Track Titanium wheels Titanium Grousers Flexible Cover on both wheels Steel Woven Mash Tires Titanium Track Engagement Threads ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 34

35 Stability CG Nominal CG (x, y, z): (1.2, 1.3, 0.73) meters Fluctuation (x, y, z): (±0.2, ±0.1, ±0) meters Critical slope: 48 x y z z cg x z cg y TRADES Cg height versus length of vehicle (flat terrain and 20 slope) Vehicle width versus cg height, turning radius, and velocity (flat terrain and 20 slope) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 35

36 Stability Flat Terrain CG Location vs. Vehicle Length CG Height off of the Ground (m) TLR Limit Vehicle Length Vehicle Length Needed for Stability for flat terrain ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 36

37 Stability Slope CG Location vs. Vehicle Length CG Height off of the Ground (m) TLR Limit Vehicle Length Vehicle Length Needed for Stability for a 20 Degree Slope (m ) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 37

38 Turning Radius: 2 m Turning Radius: 4 m 7m Vehicle Width = 2.37 Turning Radius: 6 m Turning Radius: 8 m CG Height off of the Ground (m) Stability Flat Terrain Vehicle Width vs. Turning Radius and CG Height Vehicle Width Needed for Stability, Velocity = m/s ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 38

39 Turning Radius: 2 m Turning Radius: 4 m Turning Radius: 6 m Turning Radius: 8 m 0.00 CG Height off of the Ground (m) Stability Slope Vehicle Width vs. Turning Radius and CG Height Vehicle Width Needed for Stability, Velocity = m/s ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 39

40 Breaking Main breaks: Disk breaks within each wheel. Back up: Slow or stop the motor to come to a gradual stop. Stop the motor and lock the tracks to come to a halt. Max Deceleration rate Flat Terrain: 2.66 m/s2 20 slope: 1.94 m/s2 Stopping distance (flat terrain and 20 slope) Flat Terrain: 3.3 m 20 slope: 0.50 m Stability Stopping time (flat terrain and 20 slope) Flat Terrain: 1.57 s 20 slope: 0.72 s ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 40

41 Stability Going Over Obstacles Rover Overturn Due to Collision With Immovable Obstacle 15 Rover Speed [km/hr] Level Terrain 5 deg slope 10 deg slope 15 deg slope 20 deg slope Level Terrain 5 deg slope 10 deg slope 15 deg slope 20 deg slope Obstacle Height [m] Solid lines assume 5% energy lost at impact * Solid line denotes 5% **energy dissipated at impact; dashed line denotes 25% Dashed lines assume 25% energy lost at impact Low CG and wide base contribute to stability in handling obstacles. ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 41

42 Steering Flat Terrain 20o Slope Steerability Steerability Wheel 1 Diameter 0.03 m Wheel 1 Diameter 0.04 m Wheel 1 Diameter 0.05 m Wheel 1 Diameter 0.07 m Wheel 1 Diameter 0.09 m Wheel 1 Diameter 0.03 m Wheel 1 Diameter 0.04 m Wheel 1 Diameter 0.05 m Wheel 1 Diameter 0.08 m Wheel 1 Diameter 0.06 m Wheel 1 Diameter 0.06 m Wheel 1 Diameter 0.07 m Wheel 1 Diameter 0.08 m Wheel 1 Diameter 1.0 m Wheel 1 Diameter 0.09 m Wheel 1 Diameter 1.0 m Wheel Width - b - (m) Skid Steering The larger the track width the better the performance Extra mass and complexity for actuators to steer is avoided Zero turning radius at rest Steerability Criteria: Fo c b l +(w tan(φ))/2 Wheel Width - b - (m) V1 V V2 Steerability = (c b l +(w tan(φ))/2) - Fo ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 42

43 Suspension Human Factors Frequency (Hz) Motion sickness, peak incidence occurs at ~0.17 Hz 1 3 Side-to-side and fore-and-aft bending resonances of the unsupported spine Strong Vertical resonance in the vertebra of the neck and lower lumbar spine Up to 80 Hz Effect Resonances in the trunk Resonances between head and shoulders Localised resonances of tissues and smaller bones ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 43

44 Suspension Trade Type Description Examples Advantages Disadvantages Dependant Movement of wheel on one side of the vehicle affects the movement of wheel on the other side of the axle. Commonly used on commercial and off road vehicles. Hotchkiss (leaf springs) Trailing arms Leaf spring 4-bar Simple to design Low cost Low mass Negatively affects ride and handling compared to independent systems Semidependant Beam that can bend and flex Trailing twist axle Simple to design Design flexibility Independent Widely used today in the commercial vehicle industry Macpherson Strut Double Wishbone A-arm Multi-link Better drive and handling over independent passive suspensions. Design flexibility Better reliability than active/ semi-active. Better cost and mass over active/semi-active Semi-Active Suspension dynamics change continuously but is not electronically monitored Hydropneumatic Hydrolastic Hydragas Continuous improvements to road handling and ride Cost and design maturity Active Electronic monitoring of vehicle conditions, coupled with the means to impact vehicle suspension. Bose Suspension Active body control Continuous monitoring of vehicle motion for improved bounce, roll, pitch and wrap modes. Increase in cost and mass, negative affects to reliability, and design maturity ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 44

45 Suspension Analysis Mass of Body Natural Frequency of the Suspension versus Spring Diameter Coil Diameter = 0.06m Coil Diameter = 0.08m Coil Diameter = 0.10m Coil Diameter = 0.12m Coil Diameter = 0.14m Natural Frequency (Hz) MODEL Natural Frequency (Hz) Natural Frequency of the Wheel versus Spring Diameter Coil Diameter = 0.06m Coil Diameter = 0.08m Coil Diameter = 0.10m Coil Diameter = 0.12m Coil Diameter = 0.14m Spring Diameter (m) Mass of Wheel Coil Diameter = 0.06m Coil Diameter = 0.08m Coil Diameter = 0.10m Coil Diameter = 0.12m Coil Diameter = 0.14m Spring Diameter (m) Critical Distance of the Wheel versus Spring Diameter Critical Distance (m) Critical Distance (m) Critical Distance of the Suspension versus Spring Diameter Spring Diameter (m) Coil Diameter = 0.06m Coil Diameter = 0.08m Coil Diameter = 0.10m Coil Diameter = 0.12m Coil Diameter = 0.14m Spring Diameter (m) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 45

46 Suspension Macpherson Strut Material: 2014-T6 Density = 2800 kg/m3 Modulus of Elasticity = 72.4 GPa Poisson's Ratio = 0.33 Bulk Modulus = 27.2 GPa Number of Coils: 7 Coil diameter = m Spring diameter = 0.1 m Length = 0.24 m Ks = 40 N/m ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 46

47 Chassis Analysis Material: AL 6061-T6 Density: 2700 kg/m3 Yield Strength: 310 Mpa Ultimate Strength: 27 Mpa Youngs Modulus (E): 69 Gpa Poisson s Ratio: 0.33 Axial Launch Load 6g Area Moment of Inertia (m): 8.33E-7 Critical Axial Load (N/m2): 1.52E+5 Safety Factor: 2.88 Margin: % Static Loads: 1g Lateral Launch Load: 2g Area Moment of Inertia: 8.33E-7 Area Moment of Inertia: 8.33E-7 Maximum Deflection (m): Maximum Deflection (m): Stress in Beam (N/m2): 2.05E+7 Stress in Beam (N/m2): 2.46E+8 Max Sheer Stress (N/m2): 1.42E+3 Max Sheer Stress (N/m2): 1.70E+4 Safety Factor: Safety Factor: 1.12 Margin: % Margin: 11.61% ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 47

48 Chassis Dimensions Mass: 90 kg 0.02 m 1.93 m 0.08 m 0.08 m 0.08 m 1.9 m ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 48

49 Track-Wheel Hybrid Mobility Unit Wheel Connector Beam Wheel 1 Diameter: 0.6 m Wheel 2 Diameter: 0.4 m Material: Titanium (6% Al, 4% V) Yield Strength: 1.05x1011 Beam Thickness: m Beam Width: 0.06 m Load Applied: ~ 734 N Rotate 360o 0o point 0.4 m 0.6 m 0.2 m Length of beam (m) Maximum Deflection - Y (m) Mass of Beam (kg) Maximum Stress in Beam (N/m2) ~ E+08 Desirable Angle Optimum Angle Safety to the 50 cm to the 10 cm Factor (SF) Obstacle Obstacle ~ o ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 0.00o 49

50 Motors and Gearing Design Space Multi-Staged/ Combinations Harmonic Drives Planetary Gear Systems ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 50

51 Motors and Gearing Motors Trade Space Type Advantages Brushless DC Electric Motor Long lifespan Low maintenance High efficiency Brushed DC Electric Motor Disadvantages Typical Application Typical Drive Hard drives CD/DVD players Electric vehicles Multiphase DC Low initial cost High maintenance Simple speed control (brushes) Low lifespan (Dynamo) Treadmill Exercisers Automotive starters Direct (PWM) AC Induction (Shaded Pole) Least expensive Long life High power Rotation slips from frequency Low starting torque Fans Uni/Poly-phase AC AC Induction (Split-Phase Capacitor) High power High starting torque Rotation slips from frequency Appliances Uni/Poly-phase AC AC Synchronous Rotation in-sync with freq Long-life (alternator) More expensive Clocks Audio turntables Tape drives Uni/Poly-phase AC Stepper DC Precision positioning High holding torque Slow speed Requires a controller Positioning in printers and floppy drives Multiphase DC High initial cost Requires a controller Motor Comparison, Circuit Cellar Magazine, July 2008, Issue 216, Bachiochi, p.78 ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 51

52 Motors and Gearing Legacy and Future Rovers Mars Exploration Rover (180 kg) Motors Gearing Independently driven wheels; 28 VDC brushed motors Identical motors used for steering front and rear wheels. Two-stage planetary gearbox powers a harmonic drive. (1500:1) Apollo Lunar Roving Vehicle (210 kg) Mars Science Laboratory (900 kg) Independently driven wheels; 36 Selected brushless DC motor; low VDC brushed motors temperature/low-mass gearbox. A failure in testing of the proposed dry lubrication to support motor actuator Harmonic drive (80:1) operations at very cold temperatures is contributing to MSL project delays. Motors/Gearing for TLR will likely require significant R&D. Legacy and Future rovers provide a starting point for design/analysis. ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 52

53 Motors and Gearing TLR Motors The design for the drive system consists of tracks independently driven by brushless DC motors. BluWav Systems has a line of DC brushless motors that show promise, though further R&D would be necessary. The brushless DC motors were chosen for: Low maintenance High efficiency (>95%) High reliability High controller TRL (SAE J1939; RS-232/485) These areas would need further R&D: Gearing options (planetary vs. harmonic) Lower power requirements Minimum operating temperature range* * Note: a low-temperature failure in testing of the brushless DC motors is contributing to MSL project delays BluWav In-Hub Motor ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 53

54 Motors Lifting the Vehicle About Small Wheels Use the in-hub motor to raise the small wheel while driving and to pivot about the small wheel to lift the vehicle Gearing ratio and Torque Required: Assuming even distribution of the weight over the four tracks Each motor has to lift ~734 kg of mass Moment arm about the small wheel = 0.7m Torque required to lift wheel about the small wheel = ~514 Nm Main motor torque = ~85 Nm Gear ratio used = 8:1 Torque generated = 680 Nm to lift the vehicle W 4 Rotate small wheel about large wheel to change angle of approach W 4 W 4 W 4 Rotate about small wheel to lift vehicle ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 54

55 Design Details Dimensions 0.30 m 2.1 m 0.40 m 0.60 m 1.87 m 0.3 m 1.9 m 2.6 m 1.93 m 3.1 m y z x ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 55

56 Design Details Dimensions 2.7 m 0.9 m 2.47 m 3.67 m 0.07 m ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 56

57 Design Details Mobility Configurations Nominal Driving Configuration All four tracks flat on ground Front and rear tracks at same configuration: Large rear and small front wheel Drive on Flat Terrain Drive on slope Easily avoid nosing in Other possible Configurations Rear wheels can be rotated 180 from nominal condition to increase foot print Front wheels can be rotated 180 from nominal condition to decrease foot print This would be the launch configuration Jamming is easily avoided in every configuration ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 57

58 Design Details Mobility Configuration Other Possible Configurations Each track can be adjusted to take on a different size obstacle at optimum angle of attack Can adjust wheels to provide a level chassis in all directions up to 18.7o slope Used mainly for obstacles. Main configuration to overcome the 50cm obstacle. θ All tracks can be configured to drive on the small wheel only. This method can be used to approach 50cm obstacle. After the approach the vehicle can roll over it while rotating the small wheels in the X direction. Easily avoid bottoming out on obstacles less than 0.9m tall ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 58

59 Operations Logic Diagram Use Sensors and Imaging to Generate Map Initialize Operations Nominal Driving Condition Tracks are flat to ground Every 15 seconds Detect Obstacles Detect Slopes Calculate Path Categorize obstacle height Categorize slope angle Compare to previous 1 1 No Obstacle in Path No Slopes in Path 2 Obstacle in Path Obstacle > 50cm Re-plan path to Avoid Obstacle 3 Obstacle in Path Obstacle 10cm Lower Speed to 7.5 km/hr 4 Obstacle in Path Increase Speed to 15 km/hr Operate on Flat Terrain 10 cm Obstacle < 30cm Lower Speed to 5 km/hr Change Angle of Approach Change Angle of Approach ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 59

60 Operations Logic Diagram Use Sensors and Imaging to Generate Map Operating on Flat Terrain Nominal Driving Condition Tracks are flat to ground 15 km/hr velocity Detect Obstacles Detect Slopes Calculate Path Every 15 seconds Categorize obstacle height Categorize slope angle Compare to previous 1 5 Obstacle in Path 30 cm Obstacle 50cm A Change Angle of Approach Climb and Drive Over the Obstacle B Change Angle of Approach Place Small Wheels Onto the Obstacle C Lift Vehicle onto Small Wheels Approach Obstacle Come to a Stop A B C Lift Vehicle, Level off, and Drive Forward Roll Large Wheels Onto the Obstacle Rotate Small Wheels Back Drive Over the Obstacle with Large Wheels in Front Small Wheels in Back ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 60

61 Operations Logic Diagram Use Sensors and Imaging to Generate Map Operating on Flat Terrain Nominal Driving Condition Tracks are flat to ground 15 km/hr velocity Detect Obstacles Detect Slopes Calculate Path Every 15 seconds Categorize obstacle height Categorize slope angle Compare to previous 1 6 Slope in Path Slope > 20o 7 Slope in Path Slope 20o A Keep Nominal Driving Condition B Keep Nominal Driving Condition Lower Speed to 5 km/hr Re-plan path to Avoid Slope A B Lift Vehicle Onto Small Wheels Partially to Keep Vehicle Level Approach Slope And Start Climb θ Approach Slope and Climb θ ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 61

62 Sensors Obstacle Detection and Avoidance The scanning LIDAR (Light Detection And Ranging) will be the rover s obstacle detection system. It is a rotating unit which utilized multiple LIDAR sensors. All of the sensors measure the distance to surrounding objects and altitude of terrain while rotating. This scan will be done once every 15 seconds so that the rover will stay updated on passable paths. TLR will also employ cameras for remote control applications Some benefits of the scanning LIDAR are: 360 degree field of view (compared to RADAR and Stereo vision which have only 10 and 90 degrees field of view) Maps output to navigation computers which generate drive and steering commands to go around obstacles (necessary for rover requirements) Capable of operating at night and permanent shadowed regions (many on lunar surface) ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 62

63 Sensors Odometry System Dead Reckoning Deduce position after moving for a known time at a known direction with a known velocity β(p) We want to obtain position P+1 from the position at P d(p) P The difference x(p) = x(p+1) x(p) may be deduced from d(p), β(p) P+1 Forward Motion: d(p) = fd( d1(p),, dn(p), β1(p),, βn(p)) Angular Motion: β(p) = fβ( d1(p),, dn(p), β1(p),, βn(p)) where n = number of wheels ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 63

64 Sensors Angular Positioning Sensors β(p) r d(p) Forward motion may be measured by a sensor by multiplying wheel radius r by angular motion The transversal angle of angular motion may be measured with a sensor (for wheels and robotic arm) Sensor options for angular positioning are: Sensor Advantage Disadvantage Potentiometer Low cost and simple interface Easily dirty and sensible to noise Synchros/Resolvers Easily mounted, can withstand extreme environments Require AC signal source, heavy Optical encoders Higher resolution, digital High cost, not very robust * Incremental optical encoders will be used for TLR s angular positioning sensors ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 64

65 Sensors Guidance Sensors Odometry is not very reliable TLR also is equipped with sensors: To detect heading Orientation Inclination. TLR will employ rate sensors, gyroscopes and accelerometers integrated into an Inertial Measurement Unit (IMU) will cover this. Yaw IMU provides attitude and acceleration information during surface operations and convert to outputs used by vehicle control systems for guidance Roll Pitch ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 65

66 Mapping Local map will be created using fixed decomposition with LIDAR system. Position and ranging will be updated with 75 meter range accuracy. Continuous representation method not preferred for lunar exploration due to 3D surface obstacle and slope concerns. (only good for 2D representation) Occupancy grid will be updated using Bayesian method. P(A not B) = P(not B A)P(A) P(not B A)P(A)+P(not B not A)P(not A) Since Lidar scan will occur every 15 seconds it is safe and effective to update map using this technique. ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 66

67 Command and Control 3 RAD750 radiation hardened single board computers will be used to: Format and process navigation data for output Process path commands from the autonomous driving computer Command the rover through passable paths Build and output range maps to the autonomous driving computer. BAE Systems RAD750 * A maximum of 5 watts of power are required for each 133 mhz RAD750 computer 1 SCS750 high space-qualified super computers will be used to: Rover s autonomous driving computer Used to compute passable paths for rover to follow * A maximum of 20 watts of power are required for each 800 mhz SCS750 computer Maxwell Technologies SCS750 * Maximum of 35 watts processing for entire rover computer system ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 67

68 Command and Control IMU LIDAR Optical Encoders Attitude and Acceleration Obstacle Ranging Angular Position COMPUTING SCS750 Motor Commands based off possible paths Path Commands Range Maps RAD750 Motor Controllers IMU, optical encoders, and Lidar sensors will provide computers with position information. Computing will be programmed based off rover surface requirements. Motor controllers will be updated based off computer processing. ENAE-788X Cagatay Aymergen Jignasha Patel Syed Hasan John Tritschler 68