Servo to analog range optimization

[papadako]

Some optimizations for servo DCs I have been working on and for which I would like some input

• Faster path to toAnalogRange
• Optional zero-crossing hysterisis to avoid pid chatter around 0
• sigma delta PWM dithering for sub-count resolution
• stiction kick when the motor is not moving or during direction change for a small window (helps in guiding)

[papadako]

Currently, I am thinking that the acceleration ramping during tracking is a bad idea. In the calibration code it was creating inconsistent results and I think it will be a good idea to remove it also from tracking / guiding. What do you think?

P.S. I have implemented it my local branches but unfortunately I can not test it right now due to clouds.

P.S.2 It leads to oscillations. We need some kind of ramping. I will experiment by increasing the acceleration value

[hjd1964]

I'll hang on to merge this until you do more testing. As for the "acceleration ramping during tracking" well this is an acceleration limiter and more about protecting motors/drive systems. At tracking rates it should be so darn fast (even instant as in one pass through the routine is enough to hit the rate change?) and its a setting that can be increased/decreased. I'm generally against that change.

[papadako]

Yes it is better to wait a bit. No ramping leads to oscillations so it is not the recommended route.

I have so many changes that I am testing and I am still experiencing some mechanical issues.

Maybe you can checkout the fast path e82a345 and

the Sigma-delta dithering
e82a345

[hjd1964]

Just now much has changed in OnStepX which regrettably had to break some of this work. One of the big changes is a new Analog class the attempts to deal with global and per-pin resolution and frequency capabilities as well is handling the odd pin38 hack semi-transparently. This also adds deadband support (all Servo child classes) and for DC servo drivers deadtime (on direction change) as runtime parameters.

[papadako]

I will try to check those out and adapt the code. Currently we have very bad skies and I did not have time to progress my work.

However, merging things after refactoring usually requires a lot of work. It would help me if we could evaluate/check proposals early.

[hjd1964]

The latest code has support for an inner velocity PI control loop with DC motors. The encoders have a blended velocity estimator (t/d and d/t.) Testing seemed to show it improves performance vs. operating without it. Disabling should be easy just set the vP and vI to zero or use it.

Example config:
`// using my "DcStick" and "ABStick", both of which are enabled with logic HIGH so the default LOW won't work
// the MaxESP4 has one enable pin connected to all four motor drivers
//#define SHARED_ENABLE_STATE HIGH

// using my "DcStick" and "ABStick", both of which are enabled with logic HIGH so the default LOW won't work
// the MaxPCB5 has per axis enable pins
#define AXIS1_ENABLE_STATE HIGH
#define AXIS3_ENABLE_STATE HIGH

#define ANALOG_WRITE_RANGE 4095 // 12 bit

// the MaxESP4 pinmap is designed to work with my "ABStick" module
// the module plugs into Axis3 or Axis4 and changes it from stepper driver outputs to encoder inputs
#define AXIS1_ENCODER AB

#define ENCODER_FILTER 200 // allow 200ns until next encoder edge detection to supress spurious signals
// See EncoderBase.h for more info, these are tuned a bit more aggressively that default
#define ENCODER_VELOCITY ON // enable the encoder subsystem blended velocity estimator and velocity control loop for DC motor servos
#define ENCODER_VEL_WINDOW_US 5000UL // default 10ms (10000UL)
#define ENCODER_VEL_STOP_US 100000UL // default 0.3s (300000UL) to detect a motionless state
#define ENCODER_VEL_BLEND_COUNTS 4.0F // default 4 counts (4.0F)

// the encoder direction must be correct, the motor direction can be changed at runtime to match if needed
#define AXIS1_ENCODER_REVERSE ON

#define PID_SAMPLE_TIME_US 2000 // normal sample time for the outside DualPID position loop is 10000us

// use 0 to immediately switch from the Tracking PID set (at 0% power) to the Slewing PID set when a slewing event occurs
// or use 10 (etc.) to scale smoothly from the Tracking PID set (at 0% power) to the Slewing PID set (at 10% power)
// for DC motors this smooth scaling method seems to work best
// for stepper motor based servos I just omit this setting (0 for immediate mode is the default)
#define AXIS1_PID_SENSITIVITY 20

// in arc-seconds to provide a little tolerance for the encoder not being EXACTLY on target
#define AXIS1_TARGET_TOLERANCE 60.0
`

[papadako]

That is a nice Christmas present! Thank you Howard!