PID control loops - closed loop feedback

[Salik Syed]

I am planning to use PID on the arm for our end of year mini-game bot
(we make a mini game w/ the robotic class (sadly only 7 students one being a moderator) split into 2 teams w/ a 2X2X3'
80 lbs robot its really cool)
any ways for ours (i'm not sure if this will work)
I will basically just put a gyro on the arm and
compare the "wanted speed" to the real speed and
then just add a bit to the PWM (dependent on how close real is to wanted)
to calibrate it just move the gyro away from or closer to the joint!
to get the real speed i'm just going to multiply the accel*time/looptime + previous...that
should probly give me speed..
Will this work? Also i'm using the PBasic controller so i'll have to learn that a bit...
do i have to keep loop time constant or not...does it really matter that mucH?
This part really bugs me out because i read about everyone keeping loop times constant and
what not but on the Edubot controller I just wrote the code...heck to loop time and
everything worked (for our little autonomous gyro guidance thing)
IF it does matter a LOT
i might take a educontroller and connect it to the maincontroller so it can receive
gyro inputs and then simply output the amount to add to the PWM through dig_out which
plugs into dig in on the RC

Also can someone explain why it matters so much (in reality ) do the loop times really
vary by so much that it would greatly affect operation (i imagine if it loops so quickly
it wouldn't matter...the differences would be averaged out to a menial number??)

Thanks!