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Change servo defaults to safer defaults (#7023)

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* The default timings were chosen vastly outside specification. On COTS servos, this causes much confusion for the user, because a wide range of angle starting from 0 degress, and a just a large range of angle leading up to 180 degrees, is dead - in fact, the servo doesn't move at all, from any position.

Not investigated further for obvious reasons, as this may have also destroyed servos that ran hot trying to abide by the PWM signal but could not mechanically!

* Change timing limits to safe values. With previous default timings and safety limits, popular servos

could force against internal physical endstops, which could overload and destroy them.

* Review action: revert changes to hard boundary for min/max duty cycle timings. Internal review, fix/drop legacy comments.

* A Servo on each available ESP8266 GPIO (D0-D8), no observed interference.

* Remove possible jerk due to force-cancelling duty cycle.

* Overload attach: can specify initial angle for servo, too.

* Stricter checks for configured, and default, bounded timings.

* Missed the min/max in a comment.

* Default microsecond lower bound of 1000 causes confusing behavior - 200 is minimum enforced elsewhere, so use it here too as nearest multiple of 100 from 180.

* Comment rationale for changed defaults of min/max pulse widths.

Comment rationale for changed defaults of min/max pulse widths.
This commit is contained in:
Dirk O. Kaar
2020-11-14 08:59:14 +01:00
committed by GitHub
parent c5c9f845d1
commit 9b437d7c5e
2 changed files with 44 additions and 27 deletions
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35
libraries/Servo/src/Servo.cpp
View File

@ -27,15 +27,15 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
uint32_t Servo::_servoMap = 0;
// similiar to map but will have increased accuracy that provides a more
// symetric api (call it and use result to reverse will provide the original value)
// symmetrical api (call it and use result to reverse will provide the original value)
int improved_map(int value, int minIn, int maxIn, int minOut, int maxOut)
{
const int rangeIn = maxIn - minIn;
const int rangeOut = maxOut - minOut;
const int deltaIn = value - minIn;
// fixed point math constants to improve accurancy of divide and rounding
const int fixedHalfDecimal = 1;
const int fixedDecimal = fixedHalfDecimal * 2;
constexpr int fixedHalfDecimal = 1;
constexpr int fixedDecimal = fixedHalfDecimal * 2;
return ((deltaIn * rangeOut * fixedDecimal) / (rangeIn) + fixedHalfDecimal) / fixedDecimal + minOut;
}
@ -46,9 +46,9 @@ int improved_map(int value, int minIn, int maxIn, int minOut, int maxOut)
Servo::Servo()
{
_attached = false;
_valueUs = DEFAULT_PULSE_WIDTH;
_minUs = MIN_PULSE_WIDTH;
_maxUs = MAX_PULSE_WIDTH;
_valueUs = DEFAULT_NEUTRAL_PULSE_WIDTH;
_minUs = DEFAULT_MIN_PULSE_WIDTH;
_maxUs = DEFAULT_MAX_PULSE_WIDTH;
}
Servo::~Servo() {
@ -58,10 +58,15 @@ Servo::~Servo() {
uint8_t Servo::attach(int pin)
{
return attach(pin, MIN_PULSE_WIDTH, MAX_PULSE_WIDTH);
return attach(pin, DEFAULT_MIN_PULSE_WIDTH, DEFAULT_MAX_PULSE_WIDTH);
}
uint8_t Servo::attach(int pin, uint16_t minUs, uint16_t maxUs)
{
return attach(pin, minUs, maxUs, _valueUs);
}
uint8_t Servo::attach(int pin, uint16_t minUs, uint16_t maxUs, int value)
{
if (!_attached) {
digitalWrite(pin, LOW);
@ -76,7 +81,7 @@ uint8_t Servo::attach(int pin, uint16_t minUs, uint16_t maxUs)
_maxUs = max((uint16_t)250, min((uint16_t)3000, maxUs));
_minUs = max((uint16_t)200, min(_maxUs, minUs));
write(_valueUs);
write(value);
return pin;
}
@ -85,20 +90,20 @@ void Servo::detach()
{
if (_attached) {
_servoMap &= ~(1 << _pin);
startWaveform(_pin, 0, REFRESH_INTERVAL, 1);
delay(REFRESH_INTERVAL / 1000); // long enough to complete active period under all circumstances.
stopWaveform(_pin);
_attached = false;
digitalWrite(_pin, LOW);
_valueUs = DEFAULT_NEUTRAL_PULSE_WIDTH;
}
}
void Servo::write(int value)
{
// treat values less than 544 as angles in degrees (valid values in microseconds are handled as microseconds)
if (value < _minUs) {
// treat any value less than 200 as angle in degrees (values equal or larger are handled as microseconds)
if (value < 200) {
// assumed to be 0-180 degrees servo
value = constrain(value, 0, 180);
// writeMicroseconds will contrain the calculated value for us
// for any user defined min and max, but we must use default min max
value = improved_map(value, 0, 180, _minUs, _maxUs);
}
writeMicroseconds(value);
@ -106,6 +111,7 @@ void Servo::write(int value)
void Servo::writeMicroseconds(int value)
{
value = constrain(value, _minUs, _maxUs);
_valueUs = value;
if (_attached) {
_servoMap &= ~(1 << _pin);
@ -117,8 +123,7 @@ void Servo::writeMicroseconds(int value)
int Servo::read() // return the value as degrees
{
// read returns the angle for an assumed 0-180, so we calculate using
// the normal min/max constants and not user defined ones
// read returns the angle for an assumed 0-180
return improved_map(readMicroseconds(), _minUs, _maxUs, 0, 180);
}