www.amazon.com will find books that include that
competition in their descriptions of robot
It is not essential to use only analog data input
for your PID algorithms. However, PID is analog, so
you will have to use many digital (yes/no) type
sensors to simulate an analog spread of input data.
My advice to you with respect to designing a
Micromouse competition robot is to look at You Tube
videos and hunt those robots down on the ‘net. Find
out how their designers solved their problems. There
are many commonly used algorithms that have been
tried and proposed — some of them are truly
fantastic! There is nothing in the competition rules
that says that this is an easy task! Robotics is an
inherently difficult subject to deal with, and there
are very few masters of this genre of engineering.
Best of luck!
Q. Is there a formula to plug in the value from a Sharp IR range finder and get the actual range out? I’ve been estimating based upon the values,
but that just doesn’t seem “scientific” enough.
Figure 4. The originally measured data points.
A. Yes, there is; www.acroname.com has a great article about just this type of calculation at www.acroname.com/robotics/info/articles/
Sharp starts by telling us that V = 1/(R + k). Doing
some algebra to work our range (R) as the result of the
voltage from the y = mx +b form (you do remember your
college algebra, right?), we get the form R = (m’/(V + b’)) –
k where m’ = 1/m and b’ = b/m. Don’t worry, you can get
Excel to do this for you.
A friend of mine, read this and came up with an Excel
spreadsheet that handles all of the calculations. You just
plug in the numbers that you read from your IR range finder
at carefully measured ranges and fiddle with the k constant
until your line is straight. The secret is in the division of the
voltage values and finding a k constant that will give a
straight line. In Figure 1 and Figure 2, I show the Excel
curve of the measured voltage related to the actual range
to the object and the final linearized (pardon me for
inventing a verb) curve after I found a good k constant.
This is all nice, but what do I get out? Figure 3 and
Figure 4 show the calculated ranges vs. the actual ranges
read from the device. Those curves look very similar! It turned
out that for this sensor, k = 2. This constant will be different
for every sensor model, and will have some small variance
between individuals of a particular model, but not much.
The key to success here is to take very careful
measurements and spend some time working to find a
good k constant. This approach works well if you round
your constants to whole numbers. It works even better if
you have the ability to use floating point math. Now that
I’ve tantalized you with a spreadsheet so that you don’t
have to work all this math out by hand, I suppose that I
should give it to you. You can download this spreadsheet
from www.servomagazine.com under Mr. Roboto as
STEER WINNING ROBOTS
Perform proportional speed, direction, and steering with only two Radio/Control channels for vehicles using two
separate brush-type electric motors mounted right and left
with our mixing RDFR dual speed control. Used in many
successful competitive robots. Single joystick operation: up
goes straight ahead, down is reverse. Pure right or left twirls
vehicle as motors turn opposite directions. In between stick
positions completely proportional. Plugs in like a servo to
your Futaba, JR, Hitec, or similar radio. Compatible with gyro
steering stabilization. Various volt and amp sizes available.
The RDFR47E 55V 75A per motor unit pictured above.
SERVO 02.2012 15