Interesting system, but I think your idea for mechanical simplicity is a false impression.
I think trying to use line for control arms is going to be the biggest problem. Line (and belts) stretch, and in this case, you aren't simply driving something with it, you are actively trying to control something only with string. Even one slightly loose belt on a Delta can cause alignment issues and slack, on this, it means your extruder may not even sit straight. Ultimately, I think the filament is going to be a serious nightmare and something you will never get stabilized enough for any consistency, and this is before you even extrude any plastic.
Hi Brandon. That's an interesting setup from a decade ago. Printer's a laid out a little differently to keep the lines from hitting the print. With the three string setup, I don't understand how hot end would stay perpendicular to the base. I must be missing something.
Yeah, I think 6 strings and motors is perfectly constrained. If instead of a stick, you have a triangular effector on each end the strings will also constrain rotation. The challenge will be getting the initial tension and home position repeatably. Can't wait to see this working.
--
You received this message because you are subscribed to a topic in the Google Groups "Delta robot 3D printers" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/deltabot/-r8AKjQz0oQ/unsubscribe.
To unsubscribe from this group and all its topics, send an email to deltabot+u...@googlegroups.com.
To post to this group, send email to delt...@googlegroups.com.
Visit this group at http://groups.google.com/group/deltabot.
For more options, visit https://groups.google.com/groups/opt_out.
Hi Anatoly.I've made a little bit of progress between work, travel and family visits:
- I have a fairly stock version of smoothieware running on a controller (NXP LPC1768 MiniDK2) This is an ARM cortex3 board.
- Derived the arm solution required for the motors. Coded and unit tested it against test vectors on the host. (More on this later.)
- Made 6 motor mods to smoothieware (coded & compiled, haven't started debug yet.)
- Cerberus drive spools _finally_ arrived (vendor had some delays - no gripes there, life happens and he kept me well informed.) Now that I have them in hand, the thread spacing (lead) is way too tight (.5 mm) to expect them to work off axis running directly to the spike. I suspect an M16-2 or M16-1.5 spool might work, but I lack the setup to make these accurately. So my backup plan is to use those and run the line over some small V pulleys that I just got in, which look like they will handle the +-25 degrees I'm looking for.
- I banged together a sturdy (AKA probably overbuilt) chassis
- I think a hall rotary position sensor might function homing, if I first get the spike near the home position. (Plan on parking it in a "parking spot")
So lots and lots left to do:
- Make some motor/pulley mounting brackets (don't like the first ones I tried - machining at midnight is a bad idea.) A printer would be handy for that!
- Wiring up the stepper drive boards to the controller and motors (missing some headers at the moment)
- Debug of the 6 motor mods
- Integration
- Haven't even started the hot end design or mount - thought I'd see how the other bits go first.
- Haven't worked out the tension measurement
A word on the arm solution. Having coded it up - in my opinion, there's too many coefficents to measure/enter (or mismeasure/mistype). So my new plan is now that I know what the solution terms are, manually position the head at a few points and run a regression to produce the coefficients.
Very cool - that's a ton of progress. Definitely keep this group in the loop - I'd love to see pics as it develops. I'm interested in the motor mount design, and I have spools & spare motors to try out ideas.
This is genius in its simplicity - thanks for posting! Of course there are potential practical concerns like tensioning and getting the line lengths exactly right, plus possibly needing bearing mounts on motors to avoid needing eyelets. Feels like synchromesh would be a perfect fit here - with a small pulley, the side to side line twist as the extruder moves might be negligible.
Also, take a look at the Simpson design, which has a similar need for concentric bearings on its effector. My hunch is that by modeling the string mounting offsets on the effector in the position-control math, these can be avoided..
Interesting system, but I think your idea for mechanical simplicity is a false impression.
I think trying to use line for control arms is going to be the biggest problem. Line (and belts) stretch, and in this case, you aren't simply driving something with it, you are actively trying to control something only with string. Even one slightly loose belt on a Delta can cause alignment issues and slack, on this, it means your extruder may not even sit straight. Ultimately, I think the filament is going to be a serious nightmare and something you will never get stabilized enough for any consistency, and this is before you even extrude any plastic.
variable gain - - - this is not an analog system
To unsubscribe from this group and all its topics, send an email to deltabot+unsubscribe@googlegroups.com.
... Could you please share the code for the above pictures?