PID DC Motor -myRIO

[ar38160]

Hi,

I'm currently tuning my 12V Geared DC Motor. I noticed whilst tuning my PID stuck to my setpoint (1 rev/s) in the counting up direction. However, when I changed the direction of the motor the motor doesn't stick to the set point and drops to around -1.2 rev/s. I think there's a mistake somwhere in the code but I've tried changing to constants but no luck.

[GerdW]

Hi ar,

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@ar38160 wrote:

I think there's a mistake somwhere in the code

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Yes, I think that's the reason, too!

Unfortunately you didn't attach any code. (Remember: we cannot run/edit/debug images with LabVIEW!)

[ar38160]

Hi,

I've attached the code below. I've been using the following PID gains: P = 0.400, I = 0.004, D =0.001

Thanks

[GerdW]

Hi ar,

I don't have hardware with me to test your VI, but can give some suggestions and questions:

• Why do you place a sequence frame? It doesn't serve any purpose…
• Why do you use local variables when the terminals are left unused?
• Why do you need a timed while loop - at 10Hz iteration rate? Use a simple loop with a wait statement…
• I prefer the PID-Advanced VI: it offers the options to switch between automatic and manual mode!
• What happens when you go to manual mode and set some duty cycles manually? Does the motor behave as expected?
• Can you (try to) reach a certain speed using the manual mode?
• How did you determine your PID gains?
• Why is the PID output range set to 0…100, when the "Duty" ExpressVI seems to expect values in the range of 0…1?
  Why do you calc "1 - PID_output"? What's the reason for this? What happens when the PID outputs values larger than 1? How does the motor handle a duty of, lets say, -50???