Rapid Prototyping of Dynamic Robots
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The document discusses the rapid prototyping of dynamic robots, focusing on tools, sensors, and case studies like the Switchblade UGV. It outlines challenges in robotics, including mobility and manipulation, and highlights the importance of using modern fabrication techniques such as 3D printing. The conclusions offer humorous rules for robotics that emphasize practical engineering considerations.
![Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 -
Simulation Case Study
Backlash Modeling
• Backlash can be modeled as a
switched system
• Derive coupled and uncoupled
dynamics and conditions for
coupling and uncoupling
if coupledOld == 0 % uncoupled
% if gap is >= backlash and relative speed is same sign as gap, couple
if (abs(gap) >= delta) && (sign(relVelocity) == sign(gap)) % +'ve or -'ve engagement
coupled = sign(gap);
resetVel = ( J2*x(6) + Jg*x(7) )/(Jg+J2);
resetPos = [x(1); x(3)+sign(gap)*delta; x(3); x(4); x(5); resetVel; resetVel; x(8)];
else % stay uncoupled
coupled = 0;
end
else % coupled
% if relative acceleration is opposite sign as gap, uncouple
if sign(relativeAcceleration) == -sign(gap) % accelerating to open gap, uncouple
coupled = 0;
else % stay coupled
coupled = coupledOld;
end
end
2δ
Motor Load
γ α
11](https://image.slidesharecdn.com/webinarmorozovsky-161004190536/85/Rapid-Prototyping-of-Dynamic-Robots-11-320.jpg)
Rapid Prototyping of Dynamic Robots
- 1. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Engineering Tomorrow’s Robots and Drones Today Rapid Prototyping of Dynamic Robots Nick Morozovsky, PhD Co-Founder, Accel Robotics @DrNickMo October 4, 2016 1
- 2. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Outline • Introduction • Tools for Rapid Prototyping • Sensors • Simulation Case Study • Conclusions 2
- 3. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Introduction Robotics Challenges MobilityPerception Manipulation “Go get me a beer from the fridge” Stairs Opening a door Sand, eggs, clothes Unstructured terrain Where to grasp object Localization Mapping 3
- 4. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Introduction Robotics Landscape Cost ($) Functionality Toys Service 102 106103 104 Cleaners 101 Medical Manufacturing Military Consumer Commercial Industrial 4 105
- 5. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Tools for Rapid Prototyping Paradigm Shift • Digitally fabricated custom mechanical structure • Ecosystem of off-the-shelf single board computers and sensors • Powerful open-source software available • Trade-off between optimizing for rapid prototyping and production • Trend: 3D printing for production, niche/custom parts that aren’t cost-effective to tool up 5 racewaredirect.co
- 6. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Tools for Rapid Prototyping 3D Printer vs. Laser Cutter 6 3D Printer Laser Cutter Speed Slow Fast Dimensions 3D 2D Material Selection Limited, but growing Diverse Limitations Anisotropic, Surface Finish Flat Design Tips Print Orientation Selection, Captive Nuts Tab & Slot, T-Slot, Living Hinge, Kerf Cost $300+ $3,000+
- 7. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Sensors • Cost reduction driven by smartphone development • Accelerometers, gyroscopes, magnetometers, light sensors, cameras, GPS, WiFi, Bluetooth, etc. • Be smarter than the sensor • Filters: low-pass, high-pass, moving average, median • Calibration: use estimator (Kalman filter) for bias and drift • Redundancy: decrease noise, add robustness 7
- 8. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Sensors Complementary Filter • MEMS accelerometer can measure absolute angle of gravity vector • Susceptible to high frequency noise and body accelerations • MEMS gyroscope can be integrated to measure incremental angle • Susceptible to thermal drift and integration error • Use complementary filter to combine accelerometer and gyroscope measurements atan2 1/s Low Pass High Pass s Accelerometer Gyroscope Encoder + + ++ ++ ˙ ˙✓ ✓ µGHP = 1/!c 1/!c + h , µALP = h 1/!c + h θ LC r mC mW x y ϕ 8
- 9. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Sensors Encoder Velocity Estimation • Limited by encoder and clock resolution • Quadrature sub-periods are not equal • Measure four separate periods • Average multiple periods when possible (M ≥ 2) • Bound low speed by time since last edge (M < 1) • Mount encoder before gearbox for increased resolution A ARF B AFR BFR BRF AR BR BR AF AF BF BF AR ARR BFF M = 2!h CPR ⇡ 9
- 10. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Simulation Case Study Switchblade UGV • Tread assemblies can pivot w.r.t. the central chassis • Significantly changes the center of mass • Different modes of locomotion • Applications: search & rescue, border patrol, mine exploration, toy/entertainment • Patent pending 10
- 11. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Simulation Case Study Backlash Modeling • Backlash can be modeled as a switched system • Derive coupled and uncoupled dynamics and conditions for coupling and uncoupling if coupledOld == 0 % uncoupled % if gap is >= backlash and relative speed is same sign as gap, couple if (abs(gap) >= delta) && (sign(relVelocity) == sign(gap)) % +'ve or -'ve engagement coupled = sign(gap); resetVel = ( J2*x(6) + Jg*x(7) )/(Jg+J2); resetPos = [x(1); x(3)+sign(gap)*delta; x(3); x(4); x(5); resetVel; resetVel; x(8)]; else % stay uncoupled coupled = 0; end else % coupled % if relative acceleration is opposite sign as gap, uncouple if sign(relativeAcceleration) == -sign(gap) % accelerating to open gap, uncouple coupled = 0; else % stay coupled coupled = coupledOld; end end 2δ Motor Load γ α 11
- 12. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - θ α ϕ x Simulation Case Study Results: Simulation vs. Experiment 0 1 2 3 4 5 6 −500 0 500 t(s) φ(deg.) 0 1 2 3 4 5 6 −50 0 50 100 t(s) α(deg.) Simulation Experimental 0 1 2 3 4 5 6 −50 0 50 t(s) θ(deg.) ) ) d = , r ) d s s , d , ) at unity magnitude. An important finding is that simply running the con- troller from certain statically stable positions (e.g. the tread assembly horizontal ↵ = 90 and the chassis just past vertical ✓ = 15 ) is sufficient to upright and stabilize the robot, see Fig. 4. Given these initial conditions, the center of mass is near the end of the treads by the chassis (Fig. 4a), and the control law derived from LQR will drive the treads backwards (Fig. 4b), which will cause the robot to tip forwards leaving only the tread sprocket in contact with the ground (Fig. 4c). Simultaneously, the V-angle is reduced by actuation of the motors between the chassis and tread assemblies (Fig. 4d) and the treads are driven until the sprocket is back in the original position (Fig. 4e). (a) (b) (c) (d) (e) Fig. 4: Maneuver for uprighting into V-balance mode with LQR control with center of mass indicated. 12
- 13. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - 13
- 14. Rapid Prototyping of Dynamic Robots - Nick Morozovsky - Oct 4, 2016 - Conclusions Rules of Robotics 1. Never disassemble a working robot. 2. If it works the first time, you’re testing it wrong. 3. When in doubt, lubricate. 4. Never underestimate the estimation problem. 5. If specs for a part are listed differently in two places, they’re both wrong. 6. Glue, tape, and zip-ties are not engineering solutions (though they might work in a pinch). 7. Do not leave lithium polymer batteries charging unattended. 8. Always have a complete CAD model, including screws and fasteners, before constructing your robot. 9. Avoid using slip rings if at all possible. 10.Clamping collars are always better than set screws. If you have to use set screws (e.g. for cost reasons), use a driving flat and an appropriate thread-locking agent. 11.Always check polarity before plugging a component into a power source. 14