Wiimotes and Robots David Lippman Pierce College Ft Steilacoom

Real World What do we mean by this? Capturing data for analysis is cool, but Can we solve a problem, and see it in action?

Wiimotes Can connect over Bluetooth to computer 3-axis accelerometer Infrared camera with blob detection (4 pts)

Interacting with the Wiimote Low Level Wiiuse / WiiuseJ (C / Java) Wiimotelib (C#) High Level GlovePIE

Problem #1 Prereq: Algebra Problem: Wiimote returns dot values in the range x: , y: GlovePIE maps mouse position to a 0-1 scale in the x and y How do we map Wiimote position to a mouse position?

Prob #1 Soln Wiimote pointing left puts dots on the right, so need to invert x. Dont need to invert y since Mouse.y measures down from the top of the screen Mouse.x = 1 - wiimote.dot1x/1023 Mouse.y = wiimote.dot1y/767

Problem #2 Prereq: Trig Problem: Wiimote returns dot values in the range x: , y: 0-767, roll GlovePIE maps mouse position to a 0-1 scale in the x and y How do we map Wiimote position to a mouse position, compensating for roll?

Prob #2 Soln Angle = asin(Wiimote.gx/1) or use atan2 Angle is off horiz Find x camera, y camera Convert to polar Adjust for roll angle Convert back to Cartesian, map to mouse

Problem #3 Prereq: Algebra Problem: How do we determine 3D position of Wiimote in space? (using triangles) (Assume no roll for simplicity)

Prob #3 Soln Calculate distance between dots Distance from camera = 264/dot dist Dist at 1m = 0.1m real / 132 px camera X position: 1 m 200 px = 200*0.1/132 = m 4 m

Problem #4 Prereq: Trig Problem: How do we determine 3D position of Wiimote in space? (using trig) (Assume no roll for simplicity) Could we have done this with 2 Wiimotes and one dot?

Prob #4 Soln Camera FOV = about 45 degrees Pixels/degree = 1024/45 = px 8.8 deg 1 m 4 m

How different? Distance determination: Dist (m) Dot separation (pixels) Relative difference X-location determination: Pixel x actual x Relative difference

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Problem #5 Prereq: Linear Algebra Problem: Mark 4 points on a projected plane (projector image) that correspond to 4 points of a unit square (screen coordinates). Find the transformation that maps points on the projected plane to the unit square. u v x y

Prob #5 Soln Homogenous Coordinates: u v x y

Using 4 corner points, this gives: Reduces further using unit square for (u,v) Solve using Gaussian Elimination. To map back to (u,v), find inverse of the mapping matrix.

Problem #6 Prereq: Integral Calculus / DiffEq Problem: Use the accelerometer readings to estimate distance the Wiimote moves.

Prob #6 Soln Simplistic approach: s 0 = 0, v 0 = 0. Step: Δt =.05 sec Loop: v n = v n a s n = s n v n However, accelerometers are very noisy, so this is not very accurate. In fact, its so horrible Im not even going to show it!

Arduino Computer on a chip 14 digital I/O, w/ 6 pseudo analog out 6 analog inputs 16KB storage 1KB RAM Serial over USB Open hardware Open software

Problem #7 Prereq: Algebra Problem: Create a car backup alarm using distance sensor and LED light. Distance sensor can detect time (in microseconds) that a sound takes to echo back.

Prob #7 Soln dist = rate*time rate = experimentally determined, or speed of sound converted to appropriate units blink delay proportional to distance Does direct proportionality look good? Should it be quadratic? Logarithmic?

Problem #8 Prereq: Algebra Problem: Map Nunchuck joystick data (values -105 to 105) to PWM values (500 to 2500) for the Servos

Prob #8 Soln JoystickServo

Problem #9 Prereq: Trig Problem: Use the Pan/Tilt laser pointer to draw a circle

Prob #9 Soln Use parametric equations: t=0 Loop: x = cos(t) y = sin(t) map (x, y) to Servos t = t +.1 delay(20)

Problem #10 Prereq: Pre-algebra Problem: In a robot with differential drive, each wheel can turn at a different rate. If the wheels are 10cm apart and the outside wheel turns at full speed, at what fraction of full speed will the inside wheel need to turn to drive a circle with inner radius 50cm?

Prob #10 Soln 10cm 50cm C inside = 2π(50) cm C outside = 2π(50+10) cm Speed inside = (2π(50) cm)/unit time Speed outside = (2π(50+10) cm)/unit time Ratio of speeds = 50 / ( ) = 5/6

Problem #11 Prereq: Trig Problem: Ballistics trajectories. Experimentally determine initial velocity, then adjust launch angle to hit a target. Have a class competition to see who can come closest!

Prob #11 Soln

Advanced ideas Kalman filters Gesture recognition (hidden Markov model) Gesture recognition Augmented Reality

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Correlation doesn't imply causation, but it does waggle its eyebrows suggestively and gesture furtively while mouthing 'look over there'.