Acceleration commands effecting speed

[gnydick]

I have a print running with very specific speed controls dialed in. No more than 70mm/sec.

It's a 2 tool print. I noticed that the acceleration was quite low, probably a scripting or slicer error of mine, so I turned it back up to what it should be.

M204 T8000 P4000

Immediately, the movements were much, much too fast.

I've witnessed thousands of tool changes and I know exactly what the motion should look like and sound like.

These movements during the tool change were FLYING.

The print itself was also FLYING. I had to turn it down to 50% speed just so I wasn't going faster than the filament can handle.

This isn't a matter of suddenly being able to reach higher speeds over small distances. These moves are hundreds of mm long.

This isn't the first time I've noticed this since at least the 3.0 release, IIRC. It's been years.

[dc42]

@gnydick what acceleration was set before you changed it?

[gnydick]

@dc42 1500/1500.

I should also add, that if I cancel the print and start again, everything goes back to normal, even with fixing the acceleration again.

[dc42]

@gnydick with that acceleration, a 200mm long move would only reach about 173mm/sec at the mid point. If your M203 speed limit and the requested speed of the move are higher than that, then of course increasing acceleration will increase the speed that is reached.

You can watch the Requested Speed and Top Speed readouts in DWC to help you understand what is going on.

[gnydick]

@dc42 sure, I understand that. But the moves aren't supposed to be fast. But they ARE fast, when they shouldn't be.

[mrehorstdmd]

@gnydick speed is modal- if the previous move was at high speed and you don't specify a new speed for the next move, that next move will occur at the last used speed. Maybe that's the problem...

[gnydick]

@mrehorstdmd , thanks, I understand that.