Joysticks

[Mike Soukup]

Originally Posted by Andy A.

The work around is to calibrate your Victors to each joystick. The process is pretty simple, and can do wonders for drivabilty. Basically what happens is that the victor looks at the outputs from the joystick as you move it from physical stop to stop, and then scales its (the victors) outputs to match. It accomplishes the same thing that your programmer may have done, but in a much simpler manner.

No, the workaround is as Sven stated, fix the range in software. All you need to do is determine the min & max values of each joystick axis and create a function that linearly maps the smaller joystick range to the full 0-254 range. Just make sure you have two mapping functions, one for below 127 and one for above. Then calibrate your speed controllers for the full 0-254 range. We've been using this method for at least 3 years.

The reason to fix this in software instead of the speed controller is in the cases of autonomous or feedback control. If the speed controllers that handle your arm joint are calibrated for a smaller range of 30-245 (typical values I've seen for the y-axis) then your feedback code is only effective over that range. Any numbers outside the range will not make the arm drive faster, and if your feedback routine wants to drive the arm slightly slower than full reverse (say a pwm value of 20) it will still be going full reverse.

[billbo911]

Originally Posted by Mike Soukup

No, the workaround is as Sven stated, fix the range in software. All you need to do is determine the min & max values of each joystick axis and create a function that linearly maps the smaller joystick range to the full 0-254 range. Just make sure you have two mapping functions, one for below 127 and one for above. Then calibrate your speed controllers for the full 0-254 range. We've been using this method for at least 3 years.

I've often wondered how I could linearize a range of values to another range of values, such as 137-235 linearized to 137-254. But, not being a software guru, yet, I am not certain how to do this without several "if, if else, else" statements turning the output into a multi stepped scale. Something like:
if (P2y > 135 && P2Y <= 145)
PWM02 = 140
if else (P2Y > 145 && P2y <= 155)
PWM02 =150
etc. etc. etc.

As you can see, not too smooth a response. So the question is, what code would you use to linearly map one range to another?

[Alan Anderson]

Originally Posted by billbo911

I've often wondered how I could linearize a range of values to another range of values, such as 137-235 linearized to 137-254...So the question is, what code would you use to linearly map one range to another?

Use the equation for a line, y = mx + b.
Take the input value x, multiply it by a factor m, and add an offset b to yield the output value y. The factor can be a floating point value, or to save time you can multiply by an integer and divide by another integer.
To determine the m and b constants, use algebra to solve the pair of equations for the known input and output values.

[billbo911]

Originally Posted by Alan Anderson

Use the equation for a line, y = mx + b.
Take the input value x, multiply it by a factor m, and add an offset b to yield the output value y. The factor can be a floating point value, or to save time you can multiply by an integer and divide by another integer.
To determine the m and b constants, use algebra to solve the pair of equations for the known input and output values.

Thank You Alan

I knew it would be a relatively simple solution.
My years removed from Algebra are many, too many in fact, so some portions of my memory need a little refresh. This will help tremendously.