The printer head doesn't move at full speed everywhere. Printers have "acceleration" and "jerk" specified in the firmware to control the head as it approaches a direction change or stop point. If you were to plot the speed of the head as it approaches a stop point, it would appear as a ramp function. Coast works more like a square wave function, where it just stop the extrusion and the residual pressure in the nozzle provides the extrusion force. It would be great if there was an enhanced coast feature that decelerated the extrusion rate for some specified distance as the printer head slowed down before stopping it completely. There would be some "tapering" coasting distance where the extrusion rate goes from 100% to XX% over X.XXmm, then it could have a traditional coasting distance where the extrusion is stopped fully if needed. I think this strategy could allow more refined tweaks on perimeters to get a seamless start/stop point. Right now, I always have either a slight over- or under-extrusion at my start/stop points and can never get it perfect.
Thanks for considering this feature,
Sean
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fudgefactor
- Posts: 15
- Joined: Tue Aug 17, 2021 2:14 pm
Re: Tapered Coasting
Have you tried Linear Advance (Marlin)/Pressure Advance (RepRap)? These features advance or retard the extruder based on toolhead acceleration, to mitigate just the sorts of issues you have described.
Re: Tapered Coasting
Unfortunately, Linear Advance is an update to Marlin firmware. The newer versions that contains it are not supported by some older printers. My Makergear MG2 for one... 
Re: Tapered Coasting
Swap that old board with a Duet - you get all kinds of fancy features (like Pressure Advance - AKA Linear Advance), plus a lot of flexibility for customizing without having to compile firmware.
Re: Tapered Coasting
I've considered it, but I just don't have the time to take on a major retrofit project like that. I've pinged Makergear to see if they have any plans to update the Marlin firmware to to latest version, but I suspect it's a low priority. Someone on the Makergear forum has done the firmware upgrade from scratch, but I'd prefer to go with a supported (and thoroughly tested) release from the manufacturer.
Re: Tapered Coasting
IMHO, trying to implement something like Linear Advance in G-Code isn't likely to work well because it doesn't support ramps. It's all just steps so to get your tapered coasting it would have to break the coast segment into itty-bitty pieces with each one reducing the amount of extrusion to the next step. This would be a burden for an old 8-bit control board and would likely cause stuttering and make more of a mess than enhancing print quality.
That's where the smarter boards have the advantage - 32-bit processing and this sort of feature build into firmware so it takes the basic G-Code command and makes something better out of it.
That's where the smarter boards have the advantage - 32-bit processing and this sort of feature build into firmware so it takes the basic G-Code command and makes something better out of it.
Re: Tapered Coasting
Unfortunately, I have an older Type A Machines Series 1 printer. They bit the dust a while ago. So there is no support or updated firmware. I love the printer and it makes great prints. I tweaked the firmware myself a while back to reduce the acceleration and jerk and it improved the print quality. I might look at the firmware of another machine to see if I can implement some of the newer features.
Re: Tapered Coasting
While a board change takes a little time, if you have the right tools it's really not a big deal. I highly recommend the Duet boards as they are an all-in-one solution, and provide total flexibility in the configuration so you can make your machine what you want it to be.
If you have a machine you like and the mechanicals are sound, investing $200 in a new control board can breath new life into an old printer. The online support with Duet is awesome. The guys who write the code are online and respond directly to inquiries on the Duet forums.
I'm no programming wiz and there were a few aspects of the config files that I struggled with - but with their support I got through it easy enough and my machines are far better than they were before.
Web interface built into the board - get it connected to your network and you can control it from any web browser.
If you have a machine you like and the mechanicals are sound, investing $200 in a new control board can breath new life into an old printer. The online support with Duet is awesome. The guys who write the code are online and respond directly to inquiries on the Duet forums.
I'm no programming wiz and there were a few aspects of the config files that I struggled with - but with their support I got through it easy enough and my machines are far better than they were before.
Web interface built into the board - get it connected to your network and you can control it from any web browser.
