Desensitizing Joysticks

[Ryan M.]

You could use low pass filter. I'm at school right now and don't have access to what I've written, but I'll try to post it when I get home.

[WillyC]

This is what I love about programming...there are so many different ways to solve the same problem. All of these are nest ideas. Good luck everyone!

[Ryan M.]

I've posted the low pass filter on the white pages. It's called low pass filter. (Duh! )

An example usage:

...
pwm01 = rampPWM(pwm01, where_we_want_it, 6, 5);
...

Basically, you call this function with what your current speed is, where you want it to be, how fast you want it to get there (higher numbers are faster), and how large you want the dead zone to be (i.e. if the joystick is at 129, you probably want to be at 127. You can set how far from 127 it will be corrected with this param.). It returns what value you should set the PWM to next.

By calling this function multiple times you get a nice gradual increase in output values, so if you move the joystick as fast as you can in circles, very little of that will be picked up. How sensitive it is to input is set by you. The exact equation for finding what to set sensitivity to:
255
-------------- = t
(1000/26.2)*s

t is time in this equation. deterimine what time (in seconds) you think is best for it to be able to go from full reverse to full forward and plug that equation. Solve and use that as your input to the function, ignoring any decimal portion. For instance, if t = 1 sec, then s = 6.

Note that the equation assumes it is being called every 26.2 ms.

Post again if you have any questions about the code or if you'd like to comment on it.

PS I had to re-write it because somebody took my disk that I had that on, so it hasn't been complied. It should be right, though.

[Chris Hibner]

Beware of low pass filters. We used an LPF on the joystick once and we decided that we didn't like using it. Under acceleration, it's fine, but under stopping, it's not so good. To make the story short, it will cause you to overshoot (because it ramps down your input just like it ramps it up). You can try some funky "if increasing do this, if decreasing do that" logic, but I really don't think it's worth it.

Also, the deadbands that have been described here are discontinuous deadbands, which are generally considered "hack" deadbands in the controls world (due to their abrupt change at the deadzone point). For a continuous deadzone (more commonly used), do this:

DeadZone = 15; // Calibration parameter
if (Joy > (127-DeadZone) && Joy < (127+DeadZone)) Joy = 127;
else if (Joy <= (127-DeadZone)) Joy += DeadZone;
else Joy -= DeadZone;

[Ryan M.]

Thanks for the warnings.