Robot Drifting

[steven114]

Originally Posted by Mark McLeod

Remember that constant doesn't have to be restricted to integers like 1,2,3,..
It can be a #define like "#define CONSTANT 150/100" to get a value of 1.5 without using floating point #'s.

Might I point out that 150/100 will evaluate to 1, not 1.5... there is no way to store a floating point number in an integer. You can hack around it by storing an exponent, but I don't believe setting myInt to 150/100 will store 1.5...

[Aignam]

I spent the entire day yesterday, and 2 hours today learning to stop our 2003 robot on a dime in a 30 by 36 box when driving from about 10 feet away. Yes, the robot drifts. Yes, it is really annoying to have to compensate for it. Yes, this is going to happen in real matches. Yes, I'm going to shut up and deal with it. Just have your driver prepare for it.

[Mark McLeod]

Originally Posted by steven114

Might I point out that 150/100 will evaluate to 1, not 1.5... there is no way to store a floating point number in an integer. You can hack around it by storing an exponent, but I don't believe setting myInt to 150/100 will store 1.5...

#define's don't evaluate expressions.
You don't evaluate (150/100). You evaluate (x * 150 / 100).
To get a floating point effect you do all your multiplication first, then all your division.

In integer math,e.g.,

x = 150/100 * 100 = 100
but
x = 100 * 150 / 100 = 150

Just be careful to type cast the expression to the largest size you need, e.g., using all char for the above will return an incorrect result.

[Phil_Lutz]

You Constant (#define) can be a floating point value.
but....
when you apply it in your program the result will be an int.
ie.

#define CONSTANT 1.5

int adjust_speed(int speed_in)
(
int speed_out;
speed_out = (speed_in/CONSTANT);
return speed_out; //sends back an int
)

[deltacoder1020]

Originally Posted by Phil_Lutz

You Constant (#define) can be a floating point value.
but....
when you apply it in your program the result will be an int.
ie.

#define CONSTANT 1.5

int adjust_speed(int speed_in)
(
int speed_out;
speed_out = (speed_in/CONSTANT);
return speed_out; //sends back an int
)

however, the floating-point constant forces the processor to do floating point math, which is slower. in this case, using

#define CONSTANT 3/2

is better, because the processor can use integer math, which is faster.