Greetings Donal (and other readers), I agree that the extrusion process is much less well understood than making an X/Y/Z positioner, so there are numerous research projects that can be based on improving understanding of how the plastic melts/flows/adheres/solidifies. Note that these poorly-understood processes are not confined to the extruder itself. So, analysis, modeling/simulation, instrby Larry_Pfeffer - General
Greetings all, I think the motor for the solarbotics GM3 is the same size as those used in 1/32 scale slot cars (they agree to a couple thou when I measure them, and the shaft diameter is dead on.) Slot cars use 12 Volts (in the U.S. I don't even know if slot cars are much of interest elsewhere....) I suspect that the torque/Amp is as good as the GM3 motor, but I haven't checked that. So, 1by Larry_Pfeffer - Mechanics
Another thought re inter-module comms: Use dedicated arbitration hardware: Instead of attempting to resolve contention entirely in band (that is, on the data lines themselves), would it not be easier to adopt a (stripped-down) version of (one of the many) bus request/grant schemes? These typically used a geographically-ordered priority to handle the simultaneous-request problem, and used dedby Larry_Pfeffer - Controllers
Greetings all, A question from out of the blue (and not meant to disparage the considerable amount of thinking on this matter), apart from using a differential pair for the signalling, wouldn't an inter-module comm system built upon the SNAP protocol again serve adequately for reprap? I realize that the last SNAP-based reprap design was implemented in PIC firmware (which I never built; I haveby Larry_Pfeffer - Controllers
Greetings Viktor, Corwin, et all, I've thought a fair bit about closed-chain linkages, Stewart/Gough platforms and related mechanisms, originally in the context of robot manipulators, and then (after Viktor's first post on the subject) for use in repRapping. The software for controlling a closed-chain (or parallel) mechanism is "non-trivial" -- a polite way of saying it's a major pain -- exceby Larry_Pfeffer - Delta Machines
Freds, et al, First off, a couple questions: Is this a model airplane, or an airplane with people aboard? Is this signal you're reading/writing at all critical to flight safety? (I'm a great fan of experimentation, but not when it might cause an accident. So please use all due caution!) IMHO, an instrumentation amplifier is a good way to change a small differential signal into aby Larry_Pfeffer - Controllers
Fred, et al, If you want this chip with a bootloader pre-installed, you might look at the RBFK644 from it comes with a few other components (and probably costs more than the unprogrammed avr), but it's apparently in stock. I have no experience with this Co., yet -- but they did answer my question re stock status very promptly. I may order another sanguino or shield from them, since they haveby Larry_Pfeffer - Controllers
fenn Wrote: ------------------------------------------------------- > I can't seem to find anything equivalent on all > the usual sites (digikey, jameco) but mouser did > have something similar: I think digikey does carry these. I put "RWM" into digikey's search, and seemed to come up with the same (Vishay, up to 450 deg C.) resistors the digikey p/n is RWMB-6.8CT-ND the mfgr's p/nby Larry_Pfeffer - Controllers
aka47 Wrote: > > Back on topic the observations re your experiences > of harmonic drives I think I understand. Can you > explain what you experienced as softer stifness > around zero torque ?? Andy, Pretty much any mechanical transmission has a finite stiffness and a finite mass. Together these limit the frequency of vibration that the transmission can transmit. Some transmisby Larry_Pfeffer - Mechanics
Greetings all, In my experience (built a robot wrist with them in grad-school), harmonic-drive mechanisms don't exactly have backlash, but they have something similar -- nonlinear stiffness, with significantly lower (softer) stiffness around zero torque. This can cause control-loop problems if not handled correctly. However, having said that, they're still useful for getting big reduction ratiby Larry_Pfeffer - Mechanics
Jeff, No worries about questions. If you look at the schematic, specifically in the subsection labelled "POWER SUPPLY" you'll see that the "VIN" (wired to the barrel jack) has a diode (to protect against reversed polarity) and then a regulator (7805) to regulate down to +5 VDC. The intention is that you could provide this terminal unregulated DC from a wall-wart or similar to power your sanby Larry_Pfeffer - Controllers
Greetings all, Interesting notion. Let me toss in a Blue-sky idea regarding "valving" for melted plastic: If we could design this extruder such that the auger-to-piston channel was thermally isolated from the rest, then we could heat just that channel when we wanted flow (from the auger into the piston's chamber), and let it cool off otherwise. This wouldn't be instantaneous, but small thinby Larry_Pfeffer - Mechanics
Greetings Alex, In case you haven't seen it yet, there's a forum specifically for French speaking/writing reprappers, see If you don't turn up collaborators among the art community, you might look for collaborators among the tech/engineering community. For myself (a techie, certainly no artist!) , I've found tech/artist interactions to be interesting and productive. Best regards,by Larry_Pfeffer - Reprappers
Greetings all, IMHO, this is a dangerous way to do lathe cutting. Nothing you're going to make is worth a hand or an eye! If the drillpress's chuck comes loose from the side loads, it could cause *serious* personal injury! -- Larry PS: The comments on that page (by "Hands Without Shadows") are IMHO quite correct: Drill press bearings are not built for any kind of side load. This willby Larry_Pfeffer - General
Annirak Wrote: ------------------------------------------------------- > I'm building a toolhead controller for my extruder > experiments > 1xGPIO(commited)--Toolhead dock detect > 4xGPIO(commited)--Dock ID Annirak, et al, It seems to me that you can do this with fewer GPI pins -- or have more dock IDs for the same Npins: Determine the logic level when disconnected (probablyby Larry_Pfeffer - Controllers
Greetings all, I just received a packet from SCphotog (Charles) with three samples of the Ebony Star laminate, along with bonus LEDs (UV and a high-brightness) and resistors. I'm very much looking forward to experimenting with all of these (and my kids want to see what minerals we can make fluoresce with the UV LED.) Again, I'd like to encourage reprappers to post regarding things to swap likby Larry_Pfeffer - General
Wade Wrote: ------------------------------------------------------- > > I wonder, does anyone make a sort of instrumented > bolt for a reasonable price? The extruder mount > could use a pair of bolts with strain gauges, and > you could watch the change in bolt tension when > you run into something. Probably cost as much as > the RepRap. If all that's wanted is a (binaby Larry_Pfeffer - General
Wade Wrote: ------------------------------------------------------- > I wonder, does anyone make a sort of instrumented > bolt for a reasonable price? The extruder mount > could use a pair of bolts with strain gauges, and > you could watch the change in bolt tension when > you run into something. Probably cost as much as > the RepRap. Wade, et al, If we had such a sensoby Larry_Pfeffer - General
aka47 Wrote: ------------------------------------------------------- > Rather than going for restricted proprietary IP > and limited distribution cores do a search on the > Open Cores Project. > > You will find cores for AVR, PIC and ARM Unfortunately(with respect to ARM), if you look at the processors at opencores , and look at the ones that are obviously ARMish: (Gutsby Larry_Pfeffer - Controllers
Cris, et al, IMHO, if you want to avoid creep, design in a generous safety factor, to keep the strain down. So you could over-estimate now, and get started. Another thing to consider about plastic structure is its relatively large thermal coef. of expansion. Even heating would cause linear expansion, but uneven temperatures could cause significant bending/warping -- not a good thing for a macby Larry_Pfeffer - General
Nop, Believe me when I tell you that my initial run-in with fiberglass insulation was *painful!* I was ~12 years old, working on roofing cabins at a summer camp (and poorly supervised.) The first day, I was lying on the !@#$% stuff, without a shirt (hot summer day), as I nailed on the replacement roofing. The ensuing 24 hours were *not* fun, though they sure taught me a lesson. Sometimes Iby Larry_Pfeffer - General
Nop, I am *not* and expert on this, but my impression is that the danger from asbestos (and similar fibers) is from inhaling small (e.g. broken off) fibers. I don't recall any special safety instructions included with my order, but I'll look in the box again. Meanwhile, I treat it gently (don't crush it or crease it) and keep the rest in a plastic bag. I did wipe my tin snips and my work surby Larry_Pfeffer - General
Charles, Thanks for your kind words; you're most welcome. Sharing a few small/light parts by mail is easy, so why not? I was merely trying (on a smaller scale) to follow Wade's exemplary action -- a full set of extruded reprap parts for a case of beer strikes me as very generous, even for primo beer (which I hope it was!) Another reprapper was kind enough to send me some flexible mica, askiby Larry_Pfeffer - General
Grael wrote: > I've been looking at using the STM arm-cortex-m3 for an all in one PCB, A couple of us are looking at ARM and/or Cortex chips. (The STM32 cortex chips have a 12bit A2D, which I like.) Similarly he Fab@home project uses an NXP arm chip LPC2xxx on an olimex/sparkfun board. These are a nice bit of bang/(currency of choice) -- though (as I've said) I don't want to tax mainstby Larry_Pfeffer - Controllers
Brendan, et al, First off, if the shipping cost is an issue, let me know and I can help out with that. (Certainly don't let shipping cost constrain the sample size -- get as much as you can!) I did a bit of searching, and I *think* I understand the odd units given for conductivity. I think this value is a surface resistance -- the value of ohms/square, based on an unspecified (to us, at leastby Larry_Pfeffer - Controllers
Greetings all, From what I've read about it, many solder alloys are eutectic, to get the lowest melting point possible. However, being eutectic apparently implies that the solidus and liquidus temperatures are the same; thus there is really no plastic behavior at all for eutectic alloys. For controlled extrusion, we want plastic behavior (e.g. betwwen solidus and liquidus), where the viscositby Larry_Pfeffer - Plastic Extruder Working Group
cptwinder Wrote: ------------------------------------------------------- > So the other night I was messing around with a > stepper motor controller on a bread board when my > brother-in-law asked me to explain to him what > everything did. Turns out he really wants to learn > electronics and how to design his own circuits > from scratch. I'm in no position to teach it to > hby Larry_Pfeffer - Controllers
Wade Wrote: ------------------------------------------------------- > Just a heads up for anyone building a Sanguino - > when I fired mine up, I wasn't getting any > flashing on the red debug led at all, which led me > to believe that the bootloader wasn't installed. > I ordered two of them (as I tend to let the magic > smoke out of semiconductors on occasion), and > neitherby Larry_Pfeffer - Controllers
Ian, I'm glad to hear that this offering (RapMan)is a marketing/support channel for Ian's work! Unimatic's webpage mentions both polycarbonate and UPVC in their list of extrudable polymers. Have you/they had success with these? If so, could you please give some detail about the extrusion temperatures used? Breakdown of UPVC into toxics is a concern, IMHO. Thanks much,by Larry_Pfeffer - General
Fred et al, IMHO, some sort of workholding (e.g. a vise) is a good idea, for safety if nothing else. A bench vise can be used with the hand drill to rig an Afghan lathe, or just to hold a part still. If drill presses don't come with a vise, I hope users get ahold of one, to prevent personal injury. Craigslist or freecycle are the hobbiests' friend, in my experience. When others move (or uby Larry_Pfeffer - General