Lab6_Haptics

Lab 6 HAPTICS

The goal of this lab is to introduce some simple one-dimensional active force-feedback using a motor and encoder. We start with a small knob but invite you to attach other physical "handles" like a larger knob, a lever, etc. Each haptic effect can be coupled to a sound by sending OSC to Pd. Different haptic effects suggest different sounds; different sounds suggest different effects. What are the most interesting mappings. Which are appropriate, controllable, even "expressive". Try each sound control with and without the motor turned on. Are there some that simply cannot be played without haptics?

PROFILES - First we compute forces as a function of just position: for every encoder position, there is a specific force. Think of it as a profile or landscape -- a resisting force feels like pushing something up a slope, as the force increases, the slope increases. Think of the spring-centering of motortest.c is a "valley", wall.c has no force until you reach the wall, bumps.c and detents.c are all variations of force as "slope". Textures can be rendered as series of bumps. Stability: A very stiff wall is hard to make "stable": first, the encoder and force values are discrete making for "stair steps" or "zippers" and the calculations in fixed-point reducing resolution, more importantly the update rate must be high. You can explore various resolutions and rates.

TIME - Forces that vary in time can be pre-programmed (tick.c). A short positive then negative force, if it is quick enough feels like a click. When pressing against a spring, a click simulates a contact being made.

DYNAMICS - We can increase the apparent "mass" - giving the knob a twist, gets it going. You can simulate simple mass-spring oscilators (think of it as a pendulum). Without measuring force (we only measure position) we cannot reduce the "mass" or "damping". The human hand acts as a "damper" stabilizing an oterwise oscillating system; the hand can also be a spring-mass coupled with the virtual spring-mass just like a drum stick bouncing on a snare.

FRICTION - can be simulated with a combination of texture, dynamics and even pre-programmed

0. Set up

    a. wire Motor power (twisted pair) to MotorBoard screw terminals (+ to A+, - to A-)
    b. wire encoder (grey cable) to Protoboard 8-pin connector (which should already be connected Green to C0, White to D2)
    c. use 15v wall supply and make sure it goes from solderless bread board to MotorBoard (GND, +POWER)
    d. unplug speaker (Blue) from D5 if it is not already
    e. jumper AVR ten-pin (PORTD) to MotorBoard (PORT X)
    f. plug in LCD display
    g. load Lab6 on to your 250a directory
    ~> cd
    ~> cp -r /usr/ccrma/web/html/courses/250a/lab6/programs 250a/lab6

1. motortest (spring-centering)

    a. run "motortest.c" (cd ~/250a/motortest then make load).
    ~>cd ~/250a/lab6/programs/motortest
    ~>make load
    b. The LCD should display Encoder: and Duty
        i) Try moving the knob left and right.
        ii) What is the maximum duty?

2. wall

    a. run "wall.c"
    ~>cd ~/250a/lab6/programs/wall
    ~>make load
    b. Look at the code for wall.c.
        i) Make the wall "stiffer"; what if it's too stiff?
       ii) Make the walls further appart or closer together.

3. wallbang (sending osc message to pd)

    a. run "wallbang.c"
    ~>cd ~/250a/lab6/programs/wallbang
    ~/250a/lab6/wallbang>make load
    b. run "wallbang.pd"
    ~/250a/lab6/wallbang>pd wallbang.pd
    c. Look at the code for wallbang.c.
        i) How might you send the amplitude (e.g. send "duty" to become "frequency")?
       ii) By varying the wall stiffness can you get an intentional bounce?

4. bumps and detents. plucks and friction.

    A "bump" is a slope up to a round top and a slope down on the other side.
    A "pluck" is a slope up like a wall but followed by an abrupt drop in force at the top.
    Stick-slip "friction" is many small plucks in a row.

    a. run "detent", "detents" and "pluck".
    b. can you make a "bump" instead of a "detent"?
    c. think of sending some OSC messages at the right time/positions.
    d. vary W, D, S to match the sounds from Pd.

detent

5. tick

    a. run "tick.c"
    ~>cd ~/250a/lab6/programs/tick
    ~/250a/lab6/tick>make load
    b. Look at the code for tick.c
        i) Make the ticks longer, larger, more frequent.

6. walltick

    a. run "walltick.c"
    ~>cd ~/250a/lab6/programs/walltick
    ~/250a/lab6/walltick>make load
    b. run "snare.pd"
    ~/250a/lab6/wallbang>pd Snare.pd
    c. what is the "right" place (distance into the wall), magnitude, etc.
    d. try matching the wall stiffness and the tick to different sounds.

7. pendulum

8. spring, mass and damping

references:
<~/avrlib/ccrma/osc.h>
<~/avrlib/ccrma/osc.c>
not included in <~/avrlib/docs/>

see schematics and manual for MotorBoard on Pascal's site: AVR boards
motor data sheet: <~/Lab6/RelianceMotor.jpg>