Mega Y expansion idea....

[Cameron]

OK so I am so glad that I got the 12x12" model as there are times where I am trying to print stuff that I have to even run diagonally to get a little bit more out of it. I do lots of prints that are super wide but not too high up the Z axis....

I was loafing around the OpenBuilds site and was looking at their Linear actuator kits with the leadscrew with the C -beam
Using one of the 1000mm kits with some other 20x40 extrusions and a new build plate and a few other things, I could expand my capacity to 12x12x24! Imagine the possibilities.
I could add one more heater plate from MF and a new glass. I could really use the extra real estate.

I have a new power supply that could handle to 2 beds OK. So I think from a high level I would need:
1000mm linear actuator kit $150
2 more 1000mm 20x40 extrusions $30
12x24" aluminum plate $35
Custom cutting for plate $30
Wheels and gantry plate stuff $60
New 12x24" PEI $35
Other.. $30 (including an improved stepper driver for the actuator)

All the dollar amounts are approximate, but this upgrade would be ~350-375 or so.
I could do it cheaper without the C-Beam actuator, but I think this could work.

OK so any thoughts on this idea? I think it wouldn't be too hard to modify the base to handle this.

Cons would be bed leveling, space taken up... cost.

Thanks!

Cameron

[printbus]

Deleted.

I likely just don't know what I'm talking about.

[Cameron]

Hey saw your post before you deleted it

OK. Yeah the new actuator has a nema 23 motor that I think can drive that leadscrew with enough power for the bed.... When I was first thinking of the design I was thinking about changing from a Nema 17 to 23 and adding the GT3 belt instead to handle the extra weight.

One other thing I need to look into is backlash on that openbuilds actuator kit and how fast it can actually move.
There are still some things that I haven't figured out from a high level such as how I would want to do the end stop etc....

Also heat bed control might be a little bit weird since I have two that are running at the same time. I might need to change to a higher capacity solid state relay too...

[printbus]

I deleted the post after I looked at the long linear actuators. They're intriguing. In addition to the Y-bed & large object weight concern I had mentioned in the deleted post, I've always figured using lead screws for XY would lead to slower movements than with the belt. In the Marlin motion parameters thread, I think I concluded 5 revs/sec was about the best I could get on the NEMA17s. The lead screws I think OpenBuilds uses are 8mm lead per rotation, so doesn't that leave you with a maximum print and movement speed of 5 rev/sec * 8 mm/rev or 40 mm/sec? Set up your current printer for that and see what you think. Maybe a large bed like that would require the slow speed anyway. One concern I'd have is how slicers tend to move around on a layer for touchup fill or whatever. That'd waste a lot of time if a 24-inch print has to repeatedly move from one end to the other.

Hopefully adamfilip can chime in with at least his experiences in using lead screws on Z. He'll have to clarify whether his are 2-start or 4-start. I don't remember what he gets for lead out of each rotation.

[Cameron]

Good point on the speed. Can't you change the steps from 1/16 down to 1/4 with jumpers under the stepper driver on the ramps board? Then it could go pretty fast. 40mm sounds pretty painful. That is definitely something to look into!

[printbus]

Good point on the speed. Can't you change the steps from 1/16 down to 1/4 with jumpers under the stepper driver on the ramps board? Then it could go pretty fast. 40mm sounds pretty painful. That is definitely something to look into!

Yeah, it would be 14 or 15 seconds to go from one end to the other on a 24-inch bed at a 40mm/sec rate, not factoring acceleration. Of course, it's unfortunate that Marlin and slicers don't let you set X and Y independently. If Y has to be set slow, X is forced to run that slow too. Before investing this kind of money, I'd ask OpenBuilds if they have suggested Marlin settings to use with the linear actuator. Will they give you a spec sheet for the motor or at least a part number for the motor that could be pursued for detail? Even then, I'd personally start by only purchasing the linear actuator for some experimenting. You'd probably be able to learn a lot with it being driven by itself with different weights fastened to the actuator plate.

Keep in mind that I'm not an expert in all this. Those that understand it all either have better things to do with their time or like to sit back and laugh at those of us trying to piece together what we can figure out. Perhaps there's a reprap forum on it, or the reprap IRC might be place to ask for references. Details that follow come from my pursuit of knowledge last year in the thread Marlin Motion Related Configuration.h Settings for MakerFarm i3v. That effort was based on Marlin as of the becdac fork in October 2014. I have no idea whether any of these fundamentals have changed in the recent updates to Marlin.

I learned Marlin has a limit on how fast it can generate step pulses. The upper limit is 40,000 steps per second. Sounds high. I believe this is total across all movements. It also uses a 10 kHz interval to "packetize" motor steps. As I understand it, Marlin will generate one step per interval up to 10,000 steps per second. After that, it puts two or four pulses in each interval in order to achieve the maximum step rate of 40,000 steps per second. Some feel, however, that the combining of steps per interval can lead to movement jitter since all steps aren't evenly spaced. After all, moving one pulse at a time is different than moving two or four steps rapid steps at spaced intervals. Because of this, I read some people suggesting 10,000 steps per second is a better limit than 40,000.

Let's go with 10,000. Start with the stepper driver configured for no microstepping. Most motors are 200 full steps per rev, so in theory (so far) you could achieve 50 revs/sec. 1/16 microstepping would give just over 3 revs/sec. OK, no microstepping sounds good. But that sacrifices position accuracy, so let's look at that. The 4-start, 2mm pitch ACME screws have a lead of 8 mm/rev. A normal stepper motor without microstepping is 1.8 degrees per step, or 200 steps per rev. Combining the two, this equates to 0.04mm linear movement per full step. Is that resolution OK? For comparison, the 20-tooth OEM pulleys in the MakerFarm design provide an XY axis resolution of 0.0125mm per step at 1/16 microstepping. Going with 1/4 microstepping with the linear actuators would get you back to that ballpark. 1/4 microstepping at the 10,000 step rate would give you 12.5 revs/sec, or 100mm/sec. Tempting, at least compared to 40mm/sec. That'd get you down to 6 seconds full-length travel time on a 24-inch Y-bed.

Ah, but the motor likely complicates this. I know that the data sheet for the Kysan 1124090 NEMA17 motors I use includes a graph showing pull-out torque vs step frequency. The pull-out torque reduces pretty linearly with the step frequency. So, the faster you want to go, the less torque you have to reliably work with. Scanning back through the Marlin Motion thread, I mention in post 12 that I was able to drive the Kysan with 1/4 microstepping at what should have been 10 revs/sec (8000 microsteps/sec), but only with minimal loading. In the Z-axis application, I could only achieve less than half that when attempting to lift the shared weight of the x-axis assembly.

Again, I'd start with purchasing the linear actuator by itself and play with it. If you go that route, there are non-printing gcode snippets in the Marlin motion settings thread that might be instrumental in helping you observe how the actuator performs zipping back and forth with different microstepping, acceleration, and movement rate settings.

It'd be a fun project.

[Cameron]

Good advice.
OK I'm looking at their site....
Here is the spec sheet on their Nema 23 stepper. They have a graphic of a torque curve that is really hard to read on my machine...
http://openbuildspartstore.com/nema-23-stepper-motor/

I think I might have to get a beefier stepper driver for the ramps board for this nema 23 as well.
This seems like something that would be really fun to try and if it worked, it would be so awesome! If the actuator didn't work out for this project, I know I could use it for something else.

I'm not good at interpreting torque curves for stepper motor specs though so not sure if that Nema 23 sounds better than the 17. I would imagine that it would, but what do I know?

[printbus]

For comparison, here's the datasheet with torque curve for the NEMA17 1124090 Kysan motors that I'm using. The vertical scales differ by 1000, but at 2000 pps, the NEMA23 would be about 0.900 N*M and the NEMA17's down around 0.500.

http://www.kysanelectronics.com/Prod...?recordID=7850

[Cameron]

Alright. Did some more research on those linear actuators....
I don't think it will work well. Since we will be going at high speeds, I read that the 8m Acme rod wobbles a ton with a 1000mm length.

So now I'm thinking that I might have to go back to a belt design (which will probably save some money).
I'm thinking that at that length I might need to go to a GT3 belt and a Nema 23 motor to drive it.

I would then need to upgrade (I think) my driver board for that stepper with the beefier model out there.

Does anybody know a good source for those 12x24" silicone heating mats? I think that might be better than putting two makerfarm 12" heaters end to end....