Adjust phase when close to target, allow read_position to work while in closed loop mode #41
Conversation
Currently the PID loop always uses either + or - maximum phase advance. This means that when the PID output value is 0, there is no torque applied. This causes the motor to zoom past the setpoint if there is no external friction to stop it, which in turn causes a lot of oscillations. This commit adjusts the phase angle when PID output is close to zero, which acts to brake the motor and allows it to stop accurately between steps also.
|
|
||
| if (u > -deadband && u < deadband) | ||
| { | ||
| pa = PA * abs(u) / deadband; |
There was a problem hiding this comment.
This is a really nice idea, I was thinking of implementing like this myself, but It looks like you beat me to it.
It might be a good idea calculate inverse of deadband once where its defined, and multiply by this inversion. I think doing an expensive division every interrupt is not good practice (Armv6 doesn't have division instruction).
There was a problem hiding this comment.
Possibly true, but it is a float division so a float multiplication is only slightly faster.
There was a problem hiding this comment.
Sorry you are correct, I forgot about the lack of floating point hardware. Out of curiosity I will try both approaches and time the results.
There was a problem hiding this comment.
Sorry you are correct, I forgot about the lack of floating point hardware. Out of curiosity I will try both approaches and time the results.
I just had some time to test, your approach took 20uS, the inverted multiplication 12uS. The code seemed to work fine.
This pull request has two small improvements:
Adjustable deadband in PID output, which works so that the phase angle is adjusted with output value is close to 0. This reduces oscillations when motor friction is low, especially in position control mode.
Allow read position command to work when closed loop mode is active. Instead of calling
readEncoder()directly, use the latest value read by interrupt.