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My first little PID: please comment

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This has been one of the better PID discussions here.

While experimenting I have found that outputting several of the PID input and output parameters useful and almost necessary to determine the PID loop response and for tuning the PID coefficients.
For this I use the u-controllers UART and send the data to a PC for collection and analysis. On my Bot I use XBees in transparent mode as a wireless serial line.

Data includes:
 1- Wheel speed (I use hardware timer counts between encoder ticks, The smaller the count the faster the wheel speed)
 2- The PWM duty cycle (actually the timer count that produces the pulse width)
 3- the three error terms in the PID.

Once collected on the PC I then import the data into Excel and plot the data on a graph. This gives a nice visual of how the PID loop is responding.
Do this for several physical conditions:
 1- steady state, running with no acceleration, turns.
 2- Starting and stopping.
 3- load changes due to slight inclines
 4- extreme load changes like when Bot runs into a non-detected object

Currently I am devoting a good chunk of CPU time to outputting trace data.
Nothing structured enough though that I could import into Excel (that would make sense).

I have my PID experiment on hold at this moment while I'm combating some strange 'crashes' of my car.


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