Robotics Midterm
Why does a compass heading reading need to be tilt-compensated?
Because it reads 3-Axis
What does the term "autonomous" mean?
Can sense its environment, and can act on it to achieve some goals
You are steering a robot using a compass sensor as input and servo motors (driving differential wheels) as outputs. What types of errors/"noise" might cause inaccuracies in your steering?
Compass might not be calibrated. Compass may have interference. Wheels may not be calibrated correctly. Turns may not be aligned correctly.
A proportional-only controller is being used for compass bearing control in a robot. A step change is introduced into the system, and the following response occurs. What might be causing this? How might you fix it?
It seems that there is a large gain causing unstable oscillations
What is the role of each of P, I, D, in PID Control?
Proportional: Instantaneous error Integral: Error over time Derivative: Difference between errors
ActivityBOT: What drive speed command should be issued such that the robot turns clockwise along an approx.. 3ft radius of curvature at an average (tangential) speed of 10ft/minute?
ROC=3ft=36in v=10ft/min=2in/s=w=v/ROC V(left)=w*[ROC-(d/2)]=1.88in/s V(right)=w*[ROC+(d/2)]=2.12in/s
Explain why robotic servomotors are generally geared motors.
Reduces RPM and increases torque
For compass bearing control of steering, what limits how large an output response can be from a PID controller?
Saturation
A 270-degree positioning servomotor utilizes PWM as its control input with a 20ms cycle and 1-2ms pulse width. Assume 90 degrees is the neutral position (with 125 degrees rotation from there in either direction). a. What pulse width is needed to move the servo to 90 degrees? b. What pulse width is needed to move the servo to 200 degrees? c. Write the code needed to move one of the ActivityBOT servos to its center position.
a) 1.5 ms b) 1.907ms c) pwm_start(20000) pwm_set(X,X,1500)
A automated guided vehicle (AGV), a simple cart like robot used in manufacturing facilities to move parts from one machining center to another along a path (typically a painted line or embedded wire in the floor), needs to be able to detect obstacles in the path in front of it (such as people, other carts, etc.). The AGV moves at no more than 2 mph, and can stop within a few feet. What kind of sensor would you recommend? Identify pros/cons/issues of your selection.
(Example) an IR sensor can work in this situation. It would follow the yellow path and correct when it gets off path. The problem with this would be if the lighting changed from one part of the facility to another.
What is the difference between stepper and servo motors?
Stepper: No feedback hardware required Their control is directly compatible with digital technology They can be operated open loop by counting steps, with an accuracy of +/- 1 step. They can be used as holding devices, since they exhibit a high holding torque when the rotor is stationary. Control of rotational speed and angle control, very low speed / high angular precision (angular resolutions of < 1deg) is possible without reduction gearing by using many rotor teeth. Brushless. Disadvantages: Typically no feedback, but can add encoders to enable feedback control (it is possible to "lose" steps under high load conditions). Servo: More advanced servo drives can also control for torque, or for hybrids of torque, position, and speed.
In control, what is "deadzone" mean?
The +/- region about an input that will result in no actuator movement
What is hexadecimal 4AC3 in decimal? In binary?
hex 19139 binary 100101011000011
For the Parallax Board (ActivityBOT), give the code needed to: • Read the current input value I/O pin 6 into an integer variable. • Output "True" (1) to pin 5 • Output a 1000hz tone to a buzzer on pin 8 for 1 second. • Write to the value of variables X and Y (both integers) on a single line, separated by a comma, to the SimpleIDE terminal window.
int x=input(6); high(5); freqout(8,1000,10000); print("%d,%d,",x,y)
A motor encoder has 60 slots around its perimeter (or 120 slot / not-slot transitions). If the motor is directly driving a 4" diameter wheel, how far does the wheel advance along the ground in 1 "tick"? (ignoring slippage)
360/120=3 degrees/slot (3/360)*pi*d=.1047 in
"Smart sensors" - such as compass and gyro sensors - have their own microcontrollers. What standards are used to communicate from the robot microcontroller to sensors such as these? Identify some differences between the standards.
2-way digital communication more complex sensors data needs to be processed where as for simple sensors it can just shoot out a voltage
What is decimal 9345 in hexadecimal?
2481
What is binary 100011011 in decimal?
283
What type of sensor would a quadcopter use outdoors to determine its location? Heading?
Accelerometer Gyroscope
The infrared distance sensors we used with the ActivityBOT are binary devices - they return either 0 or 1. How can they be turned into analog sensors?
DA converter on the activity bot
What is the difference between external and internal state for a robot?
External: location, weather, time of day, what's present Sensed using robot's sensors Internal: Internal maps and planned paths; planned tasks; current position, orientation, velocity Stored (remembered)
A line-following robot tracks a line using two infrared sensors (one on each side). When the line "disappears" from one sensor, it applies a fixed rate of turn back towards the line. What type of control algorithm is this? (name only)
Feedback
What type of sensor would I use to insure my robotic gripper is not crushing the object it is picking up?
Force Sensor
How does a quadcopter moving north turn to move east?
Increase speed of the left motor and with use of a compass
What does IMU stand for? What does an IMU include? What is it used for?
Inertial measurement units Accelerometers, Gyroscopes, Magnetometers Reports velocity, orientation and gravitational forces.
Name 3 types of sensors that can be used for detecting obstacles in a robot path. Identify differences in range, application, and price between them.
Infrared: Expensive most complex most usage same range as ping Touch: Cheapest simple applications only right next to it Ping: Moderate price medium complexity. Similar range to infrared.
A PID compass bearing controller has a steady-state error (it is always off-target slightly with no oscillations). a. What component of PID would you examine first to correct this, and why? b. If that didn't work, what are possible additional causes for the steady-state error?
Integral. Because Integral pertains to the steady state. Incorrect tolerances
A PID level controller for a quadcopter is maintaining level but the quadcopter looks "jittery" (oscillating slightly around the level). What PID factor would you examine first to correct this, and why?
Integral. Because if it is continuously jittering it would be an issue with the steady state error. could be backlash as well
A PID controller is being used for bearing control in a robot. A step change is introduced into the system, and the following response occurs. What might be causing this? How might you fix it?
It may not be properly damped So increase gain constants
Do stepper motors need encoders? Why or why not?
No but you can add encoders to enable feedback control
What drive systems allow a robot to move sideways?
Omnidirectional
A robot is using an Ackerman drive for its front tires, and a fixed axle for its back tires. The distance between left and right tires is 3ft, and between front and back axles is 7ft. The right wheel is turned -20 degrees (i.e., in counterclockwise direction) with respect to the forward direction of the car. a. What is the robots radius of curvature? b. How long will it take to turn 90 degrees if the car is moving at 100ft/minute?
See Image
A gearhead PMDC motor "M" (see diagram below) has a free speed of 200 RPM. Output torque decreases linearly from 4 in-lbs at 0 RPM to 0 in-lbs at the free speed. It will be used to power a winch-based crane on a robot that extends 6" out from the robot and can lift an object 2' into the air. The winch drum is 3" in diameter, turned directly by the motor. It must be able to lift at a rate of 100 inches per minute. Assume the winch system has 80% efficiency in transmitting torque. Assume the robot is heavy enough to counterbalance the lift. • What is the largest weight object "O" that the winch system could lift using this motor? <OR> • If need to be able to lift an object "O" of up to 2lbs, is this motor up to the task? (show work supporting conclusion).
See Work
What are the key components of a robot?
Sensors, Actuators, Effectors, Power and power control, Communications, Human Machine Interfaces
I have an electronic parts pick and place robot. The robot needs to move the manipulator straight horizontally left and right to position the part on the board. What type of actuator should I use for this?
Servomotor
For a snake robot, what gait would be most effective for inspecting a storm drain?
Side Winding
What changes have occurred in robotics in the past 20 years?
Significant advances in low-cost, low power computing capabilities; miniaturization in electronics, mechanical devices, and sensors; and improvements in materials leads to renewed interest in robotics and rapid advances.
I need my robot to determine if it is climbing too steep of a hill. Recommend a sensor.
Tilt Sensor measures the inclination
I need my robot to detect when it has come into physical contact with an object anywhere on its perimeter. Recommendation?
Touch Sensor
An analog light sensor outputs 0.1 to 4 volts corresponding to 0 to 50000 lux. It is read by a A/D input with 6 bits resolution, a 0..5v range, and no gain (i.e., gain=1). a. What is Vres (smallest input voltage difference that can be discerned? b. What is the resolution in lux? c. A values of 745 is read from the A/D input. What voltage does that correspond to? What Lux level does that correspond to? • See hw#1 for additional problems like this
a) Vres = (highest voltage in range)/(2^n) n = bits ans: .078V b) Lres = (highest Lux in range)/(2^n) 781.25V c) Vadc = (Vmin + x*Vres)/gain X = read A/D input Vadc = 58.20 V
The following gait is proposed for an octopod (8 legged) robot (the diagram indicates when leg is lifted up from ground or down on the ground). The robot's COG is also noted. Is the gait statically stable? Explain why or why not. Legs are labeled L/R (left/right) and numbered 1..4 from front to back (e.g., L1 is front left leg).
case 1, 2, and 5 are stable case 2 and 4 are unstable because the COG is out of the legs (eligible)
What is an encoder? What determines its positional accuracy?
converts information from one format or code to another, for the purposes of standardization, speed or compression. Position determined by magnetic/optical encoders, some form of evenly spaced fins are mounted on the shaft, and read with a proximity sensor (such as an inductive proximity switches for).
How can a microcontroller turn on and off a motor running at 24 volts DC and drawing up to 3 amps?
drive_goto(L,R) : set movement in ticks drive_speed(L,R) : set servo speed
What are 3 different types of artificial muscle actuators? What are the differences between them (in terms of application)?
pneumatic- light weight, flexible (prosthesis) shape memory alloy- thermal movement (small devices) electroactive polymers- change shape when electrically stimulated, high toughness, emulate bio muscles
ActivityBOT/Parallax Board: Write the code needed to output 2.5volts to analog output 0.
void dac_ctrl ( 26,0,193.93) 26=port 0 0= process dacValue = (int) (V / 0.012890625) 193.93= 2.5/.01289 other info: 27 = port 1
