Hi,

I am trying to determine the sample rate for a new hobby project (digital control of a quad-rotor flying robot). The few references
I've found seem to suggest there are no rigorous calculations
available to decide the sample rate. They suggested the following
"rules of thumb":

I don't have an actual vehicle, nor do I have a model (yet). I've seen data on the web that indicates the (open loop) step response of rotor thrust has a rise time of 0.1 sec, which implies a bandwidth of 3.5 Hz or so (I'm presuming the inertia of the frame will only increase the rise time). So it seems that I could get away with 35-100 Hz sampling rate (per the 4th rule)

Does anyone have any better rules or calculation procedure? What if the un-augmented system is unstable? Are there rules of thumb or calculations to select the closed loop bandwidth?

Thanks in advance, Roy

I am trying to determine the sample rate for a new hobby project (digital control of a quad-rotor flying robot). The few references

*** Use ten times the rate suggested by Shannonâ€™s sampling theorem. ***Make sure that there are four to ten samples per rise time of the closed loop system.*** Make sure that there are 15 to 45 samples per period of the oscillating closed loop system. ***Sampling frequency should be 10 to 30 times the bandwidth.*** Choose Ï‰cTs to be 0.15 to 0.5, where Ï‰c is the crossover frequency and Ts is the sampling time. ***Choose the sampling time in such a manner that the decrease in phase margin of the discretized system is not more than 5 to 15 degrees of the margin in the continuous time system.I don't have an actual vehicle, nor do I have a model (yet). I've seen data on the web that indicates the (open loop) step response of rotor thrust has a rise time of 0.1 sec, which implies a bandwidth of 3.5 Hz or so (I'm presuming the inertia of the frame will only increase the rise time). So it seems that I could get away with 35-100 Hz sampling rate (per the 4th rule)

Does anyone have any better rules or calculation procedure? What if the un-augmented system is unstable? Are there rules of thumb or calculations to select the closed loop bandwidth?

Thanks in advance, Roy