It all started with the following YT comment.
"I want a small back pack hobby grade machine to get stuff cut for rc plane making. (With BLDC motor as spindle perhaps).
…such a machine will keep the maker in me alive.
Just rig it up on a table and you can cut balsa or some hardwood. Put two of these on parallel and run a nichrome wire through them and you got a 4 axis hot wire foam cutter.
Controlled from the board on the gondola itself. Just put the sd card in and off you go."
Maslow itself replied, “I love it! That is a brilliant idea. If you have questions when you build it check out our forums.”
So here I am.
I have based my design on the stringent plotter:
The two sides would just mirror each other. (JPEG attached for reference)
I have made the motor mount plates for laser cutting. Although it still needs to fix a place for the crossing of the cables. The file, nevertheless, retains the original stringent arrangement. I might be able to fix that subsequently.
However, I have no idea about programming. If anyone can help me with that, it would be useful.
spool wheel.stl (459.8 KB)
string junction.stl (32.2 KB)
(Open the file below in tinkercad and export it as a svg for the laser cutting file. The design is for 2mm mdf or acrylic. Needless to say it will be a multi-level gondola where the motor mount will sit on the middle level, the electronics on the top level and the bottom level will act like a stabaliser.)
stringent 4 axis.stl (273.9 KB)
Maslow can’t talk quite yet, just me…but I’m open to working on Alexa integration if people want it
I really do love the idea of a super compact version. My two thoughts are that we’ve found that for accuracy to be good it is very important that the belts are anchored so that they rotate around the spindle like this:
Also if you would like to be able to do automatic calibration it is important to use servo motors with drivers which can measure the current so that you can sense the tension in the belts. For a smaller machine you could get away without automatic calibration maybe because it wouldn’t be so hard to build the frame to precise dimensions.
so you want to make a Maslow 4, but use string instead of belts so it can be even more compact? Why not just modify the maslow 4 to use a smaller spindle motor? and 3d print smaller armatures? the maslow 4 is pretty dang small and can fit in most backpacks already?
Yes, I made a note of that Idea. Here are the two iterations
One junctions all cables at one point. Its downside I guess is the free wobble in the rest of the plate.
The other design uses a thick set of nuts and bolts to loop around the cables (one can even use the nuts as guides, or simply use the threads as cable guides)
It is based on the second idea, I plan to find a large enough, hollow in the middle, threaded attachment (grooved pvc??) to loop the cables and fit a small bldc router.
(Disclaimer: I don’t know engineering)
No, your suggested router is also a bit too large. This is going to be a barebones project.
Also not sure if the source code of the M4 is out yet.
This project might have some ideas worth borrowing: Hangprinter - Wikipedia
Yes. I am also looking at the hang printer for the stepper control.
Meanwhile, I had an idea about a dual cable axis like the one below, looped at the corners of their quadrant adjacent to the wheel.
(only two axes are shown)
The spikes are just vertical bolts to guide the cable.
Very interesting! I think it has potential
Two more iterations for the previous design.
The entire assembly is put inside a tube. The cable sets are colourcoded for reference.
Just a question, though.
What are the advantages/issues for a) routing the two cables from one place at 45* degree angle on one quadrant, or b) routing the two cables separately, closer to the 90* degrees, on two ends of a quadrant.
I will then make the laser cut parts and move to fabrication.
on the maslow 4 the belts do not go out at fixed angles, each motor/belt is on an arm that swivels around the router.
This is because trying to do the math to handle the case where the belts can apply torque to the sled (causing it to pivot, and therefor change the position of the anchors) is REALLY hard and we were not able to get anywhere close to making it work.
the chain maslow solved this by having the chains go to a ring (or other mechanism) so that if you draw a line from the anchor down the ring, it would continue to where the bit is. The maslow 4 does this with swiveling arms.
fixed anchor points can work for drawing where it doesn’t matter if you are off by a bit, but it won’t work for cutting parts that need to fit together
but note that the pen plotter you show pictures of above also has the lines on pivots so that they can swivel and always be lined up with the pen.
If you manage to make a breakthrough in the math and/or programming that can solve this, it would be fantastic. But we have been trying for years.
My set-up stands as follows. Pardon me if I am missing out on something.
My last design achives the swivling motion by using two cables for each axis. They wrap around the tubular structure of the gondola and give a virtual arm like function. The router/marker can then sit at the centre of this circle.
For the math, I am a little more uncertain. I am still basing myself on the stringent plotter set-up where the lower axes would just mirror the above ones. Thus, instead of relying on the cable pressure, this would rely on keeping the setup straight between the top and bottom axes (for both left and right side). In the stringent plotter, this was done by gravity, which will be replaced by the the bottom axis anchor in this setup.
You are getting a little bit beyond what I’ve tested, but that is exciting! I think that the wrapping the strings around the can idea is very interesting. I think that the only way to truly see how it works is to try it!
Question: where can I get a sturdy enough 6" cylindrical thing?
How sturdy are we talking? Would like thin wall pipe work? Thin wall stainless is super strong and reasonably light (compared to cast pipe or something like that), but if plastic is strong enough then plastic pipe is probably the way to go. It’s pretty universally available and light.
Sttled on a lasercut design. Realised that just the way I had created the pullies, same way can work for the whole gondola.
Here are the laser cut files for 3mm mdf (you can also just cut the base plate with 3mm and the rest with 1/2mm mdf). Only the circles need to be cut. Rest are to be engraved. The 45* degree markers are also engraved to align and stacc the cut parts. After gluing them, drill holes for the cable at the 45* degree markers, then secure those holes with an eyelet.
The mounting holes are fit for the 28BYJ steppers as used on the stringent plotter. Rest of the electronics follow from them. There is a large hole in the centre to mount the z-axis/z-actuator for a pen-plotter, needle cutter or a bldc router. One can pick any suitable design from thingiverse for this.
NOW, if anyone could volunteer with the code then I would be grateful. That area, at present, marks the end of my thinking capacity. Plus, I will be flying out on 6th so there might be a chance that the parts may not arrive on time. If anyone can volunteer to assemble a prototype (I will pay to see it come alive, no worries). I guess we are close.
4axis groove mount with 90 degree marks
4 axis groove mount 2 with 90 degree marks
corrected 4axis motor gondola mount with 90 degree marks
4 axis groove 2 with 90 degree marks.stl (27.0 KB)
4 axis groove with 90 degree marks.stl (27.0 KB)
4 axis gondola with 90 degree marks.stl (240.2 KB)
(If you cannot download the SVG files from here then open the STL files on TinkerCAD and export as an SVG file)
Also, does a retractable clothes line spark anyone’s interest?
Any ideas on lasercut cable tensioners for the steppers? I thought of using the mk8 extruder assembly but it is more suited for NEMA 17. Any reccomendations for BYJ48 steppers?
Or any other simpler method to control the cable?
Good News: The prototype has taken shape and looks workable.
The not so good news: I will have to leave it for my flight. Baggage allowance has exceeded.
Any volunteers who would like to see it come to life?
The files are as follows:
involute_gear 23 teeth.dxf
involute_gear 34 teeth.dxf
Great work! That’s awesome to see it as a real thing.