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dda.c: more notes on rampup_steps calculation.

This commit is contained in:
Markus Hitter 2013-10-20 18:23:06 +02:00
parent a97c65b940
commit 3343cfc753
1 changed files with 9 additions and 6 deletions
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15
dda.c
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@ -305,12 +305,7 @@ void dda_create(DDA *dda, TARGET *target, DDA *prev_dda) {
dda->c_min = (move_duration / target->F) << 8; dda->c_min = (move_duration / target->F) << 8;
if (dda->c_min < c_limit) if (dda->c_min < c_limit)
dda->c_min = c_limit; dda->c_min = c_limit;
// This section is plain wrong, like in it's only half of what we need. This factor 960000 is dependant on STEPS_PER_MM.
// overflows at target->F > 65535; factor 16. found by try-and-error; will overshoot target speed a bit
//dda->rampup_steps = target->F * target->F / (uint32_t)(STEPS_PER_M_X * ACCELERATION / 960000.);
//sersendf_P(PSTR("rampup calc %lu\n"), dda->rampup_steps);
//dda->rampup_steps = 100000; // replace mis-calculation by a safe value
// End of wrong section.
/** /**
Assuming: F is in mm/min, STEPS_PER_M_X is in steps/m, ACCELERATION is in mm/s² Assuming: F is in mm/min, STEPS_PER_M_X is in steps/m, ACCELERATION is in mm/s²
Given: Given:
@ -329,6 +324,14 @@ void dda_create(DDA *dda, TARGET *target, DDA *prev_dda) {
Note 4: Anyone trying to run their machine at 65535 mm/min > 1m/s is nuts Note 4: Anyone trying to run their machine at 65535 mm/min > 1m/s is nuts
*/ */
if (target->F > 65534) target->F = 65534; if (target->F > 65534) target->F = 65534;
// Note: this is inaccurate for several reasons:
// - target->F isn't reverse-calculated from c_limit, so speed
// reductions due to slow axes are ignored.
// - target->F means the speed of all axes combined, not the speed
// of the fast axis, which is taken into account here.
// The good thing: taking target->F means rampup_steps is always
// equal or larger than the number of steps required for acceleration,
// so we can use it when also limiting max speed according to c_limit.
dda->rampup_steps = ACCELERATE_RAMP_LEN(target->F); dda->rampup_steps = ACCELERATE_RAMP_LEN(target->F);
// Quick hack: we do not do Z move joins as jerk on the Z axis is undesirable; // Quick hack: we do not do Z move joins as jerk on the Z axis is undesirable;
// as the ramp length is calculated for XY, its incorrect for Z: apply the original // as the ramp length is calculated for XY, its incorrect for Z: apply the original