When is 200 really 200?

[Zesty_Lykle]

Hi all,
Is there a way to measure the actual speed a nozzle is making while printing?

The reason I ask is that we posted a video of what was supposed to be approx 300 mm/sec. At least, that is what the slicer and firmware told us.
But comparing it to other videos, it seems to be a lot slower.

I did a similar test, here is a little clip of that.

https://youtu.be/IcLxbGk9-iA

After this video I found my acceleration values in the firmware to be very low, so I upped them and it does seem faster. But still not 200 mm/sec.

2 questions for you guru's:

1 Any idea what else is causing the slow down? (all settings in S3D are at 100%, as on the firmware)
2 I still need to measure actual nozzle speed. Any idea how?

Thanks in advance.
Lykle

[Turpinator]

For measuring, id resort to video, and then analyzing it with some physics tracking type program.

Ive used Tracker before, free, open source, cross platform. http://physlets.org/tracker/
Logger Pro is also another option, except its not free. But, it does have a 30 day demo, it looks like.

Doing it this way would require placing the camera directly above, directly in front of your X axis (But, you can only track X axis speed), or directly in front of the Y axis, again, only Y axis speed can be determined. Above would be your best option, in my opinion.


You could also get some accelerometers and put those on, but that seems like a lot of work.

Another idea, again, much harder and more time consuming and only gets you 1 axis...
Place a camera on the effector, pointing at an object, then record video, analyze object size to get distance, and in turn, speed. Of course, this wont work, as youre adding weight onto the effector area.


Also, the nimble looks awesome. Probably going to have to get one of those.

[IMBoring25]

What are your jerk and acceleration values and what size is the part? The acceleration and deceleration phases are definitely dominating my perception of the speed in that video. It's only about 0.60 seconds total per segment.

You would probably get a better sense of top speed on a large circular perimeter because the accelerations involved would be less limiting, but if you're still running a Rambo, the kinematics of such a move would probably overwhelm its processing power.

[Polygonhell]

Acceleration/Jerk and minimum layer times becomes dominant really quickly.
KissSlicer has a place to type in the acceleration, to improve it's print time estimates, you can set that and try fiddling with the speed Slider to see how it changes the print times, you'll be surprised how little the print times improve with even large speed changes after about 60mm/s especially if you don't use linear infill.
The Acceleration settings on the RM are pretty conservative, but I wouldn't try and boost Jerk much above where it is.

[IMBoring25]

Interesting thought on the minimum layer time. It's a big enough layer I wouldn't normally consider that a factor, but 200 is a really high print speed that could also generate significant difference between actual and calculated layer times due to jerk and acceleration. It would be interesting to dig into the generated g-code and see if there are actually any G1 commands with positive E parameters and an F parameter of 12000.

[nebbian]

When I was seeing how fast my printers were capable of going, I did a 100mm Z move down from the home position. I bumped up the speed in Repetier host until it sounded like it had hit the limit (the sound didn't increase in pitch any more). Then I used a phone in movie mode, and recorded the move.

Then in movie editing software I could measure the time taken to make the move.

This turned out to be about 125 mm/s at my current settings. This seemed fast enough for me, I don't feel the need to lower the microsteps to get faster speeds. Maybe this method can help.

Note that your firmware will limit your top speed when it hits the maximum number of toggles of the step pin per second. I think this was about 25 khz for me, driving all three motors at the same time. If you want to go faster then you need to lower the number of microsteps, and obviously your steps per mm value.