You use linear_extrude() to make the blade.  What if you created a
 profile for the top of the blade and one for the bottom,
 separately, and then used hull() to connect them.  Then the base
 could be broader than the top.  In fact, the base could be the top
 just scaled by 2.


 On 6/7/2017 5:12 PM, Alexey Finkel wrote:

 The blades actually taper veeery slightly toward the outer edge,
 but indeed do not include any real buttressing. Because of the
 complicated shape of the hub, I am really not sure how to even go
 about putting something like that in place. I could mess with the
 arc that generates the blade surface to make the taper more
 pronounced, but that's not quite the same thing, of course.

 Excel does not, as far as I know, come with an animation package,
 so I think I would lose out on the visual appeal part of the
 market for the calculators.

 On Wed, Jun 7, 2017 at 10:09 AM, jon <jon@jonbondy.com
 <mailto:jon@jonbondy.com>> wrote:

     Preview rendered instantly here, although trying to
     manipulate the view screen in any way causes OpenSCAD to hang
     (which may be what you meant).  I worry that the blades are
     of uniform thickness, which means their attachment point at
     the base is fairly narrow.  My intuition says that they will
     snap off without some broadening at the base

     I wrote some Stirling Engine simulators which were very
     naive, but I included animations.  It was to help my
     intuition. I had quite a few requests for them, even though
     they were ... stupid.

     :)


     On 6/7/2017 8:08 AM, Alexey Finkel wrote:

     I will ponder on the question of the Discussion group until
     Sunday, but as my comment on the meetup page suggests, I
     think putting the whole thing on hold while it is not
     working so great for you has a substantial risk associated
     with it.

     Without knowing much of anything about how to use a DSP
     unit, I will nevertheless venture a guess that "stunning"
     difference may live in a very small and remote corner of
     available parameter space; a corner that is difficult to
     find unless one has either much insight knowledge, or
     preternatural intuitive talent. But that's just a guess.

     Of course real engineers have much, *much* more complete and
     sophisticated software packages for turbomachinery design.
     My spreadsheets are naive child's drivel by comparison.
     Their primary purpose is really to give me the illusion of
     knowing that I knew what I was doing when choosing some
     basic design parameters. It may be an intermediate stage
     between completely seat-of-the-pants design and real-life
     engineering work, but I have to wonder how big a market
     there is for such a beast. At any rate, if we ever built
     something based on those calculators, and it worked in any
     sense of the word, I would probably make the calculators
     available online for free.

     It looks like I sent you the wrong version of the new blade
     design. This may be for the best, because I developed it
     into a proof-of-concept compressor rotor design by now. The
     result is attached. Be sure to disable preview before
     opening it though! The thing is very high-polygon, and
     pretty much kills my SCAD dead if it tries to preview it.
     The rotor has a radius of 50 mm, so if you wished, you could
     use it as a test. However, I recall you mentioned that the
     resin is not cheap, so I wonder if a scaled-down version
     would be a more practical way to go. Or, you could cut out a
     cylinder or a cone from the rotor hub, at least if
     unsolidified resin can be recovered and reused. Also, I used
     lower values of $fn that I might for a "final" version to
     save computation time. If you were interested to see how
     smooth we can get the surfaces, maybe increasing $fn to 100
     or even 200 everywhere would help put the printer through
     its paces.

     On Tue, Jun 6, 2017 at 8:36 AM, jon <jon@jonbondy.com
     <mailto:jon@jonbondy.com>> wrote:

         The new/larger resin printer is assembled, but not
         tested, so the timing is good (I hope).

         Your spreadsheets are interesting.  I wonder if they
         could become a commercial product (or, better yet, they
         could be re-coded to produce a commercial product).  I
         know that the Big Guys would not want/need them, but DIY
         folks might.

         The new 5' tall speakers are interesting.  The sound is
         OK but not stunning in the frequency-response sense, but
         the "sound field" that I had assumed was just BS turns
         out to be palpable. You can walk behind the speakers
         without losing much of the sound.  It seems to just fill
         the room.  So, from the perspective of wanting to
         experience something new, it is a success.  The $700 DSP
         unit produces detectable differences in system response,
         but not stunning differences.

         I seem to have run out of steam for the Discussion
         group.  In the past, topics just leapt to mind, but now
         my mind heads in other directions.  I'm not sure what to
         do about that.

         :)



         On 6/6/2017 6:36 AM, Alexey Finkel wrote:

             It seems I haven't said anything on the subject in a
             while, but the last couple of weeks have been a
             relatively productive time on the turbine front, so
             I thought I'd give a bit of an update on the state
             of things.

             Both the compressor and turbine calculators are
             coming along. Both pass the basic sanity checks I've
             put into them and give believable results. However,
             I keep adding bits to them, and finding other bits
             that can be done better, so I would not risk saying
             that they are "done" just yet (or ever, really). One
             conclusion is that going from 30-mm radius to 50-mm
             rotors makes a huge difference in power, as well as
             a significant, but less dramatic one in compressor
             pressure. Kilowatt-level output seems feasible with
             50-mm rotors without going to ludicrous rpm.

             I think this means that we could tentatively answer
             one question from the long list as follows: if the
             100-mm resin printer is going to be available, we
             should be able to print high-precision and smooth
             moulds, and cast a ceramic rotor (or rotors).
             Whether this works in practice, and whether a stator
             made from a plastic printer cast can be made usable
             remain open questions, of course.

             I've also tried to match a compressor to one
             possible version cold-air turbine, and found that it
             is sort of possible even with the very low flow rate
             available, if a number of adaptations and
             concessions are made. Still, as I think I mentioned
             ,if we can get higher flow rate even at the cost of
             pressure, it would be a lot better.

             However, I have not tried to assemble a full
             compressor-diffuser-combustor-turbine calculator yet
             because my rudimentary combustor calculator is
             giving me unrealistically high combustion
             temperatures, and because useful data on even the
             simplest kind of radial-flow diffusers is proving
             tricky to track down.

             On the other hand, I came up with a new way of
             generating blade geometries in SCAD. It uses linear
             extrudes with twists instead of hull, thus getting
             around the convexity issues I had before. A sample
             is attached, but be warned: it also uses differences
             of high-polygon objects, so it *really* doesn't like
             to run in preview mode. On the plus side, it seems
             to compile and render pretty quickly for me.

             Proceeding with diffuser design may be slow for a
             while, as it looks like I am going to have to do
             some more serious reading, but I will try to keep
             myself entertained by modeling other parts and
             pondering how to fit them together.

             How are your projects going by the way? Do you have
             more speaker cabinets than you know what to do with
             yet? Or did you see the light and opt for the
             magical "blue diamond" sound-improver?

             Alexey

Can I share this code with the OpenSCAD group? Or do you wish to? OpenSCAD general discussion <discuss@lists.openscad.org> I think you have to join and until then your questions get flagged in some way. Might be easier for me to do. OpenSCAD is not a programming language. It is a language to define geometry. And the geometry is static. So all named values are in fact constants, not variables. Thus your confusion about summation. EVERY OpenSCAD user goes through this moment of WTF. You are correct, of course, about using hull(). I think there is a way to use various sweep libraries to create the shape you need. As I recall the sweep libraries call a function to generate a cross section and another function to generate a path through space. Does the attached demo help at all? Jon On 6/8/2017 12:30 AM, Alexey Finkel wrote: > Blade shape is somewhat more complicated than may at first appear. If > you comment out the rotor generation, and uncomment "blade_prim();" at > the end, you will see how it is supposed to curve more clearly. The > generic design I sent you uses a fairly narrow sliver of the whole > shape, but does require that it curve in multiple directions. That is > not something that hull() does well, as I learned during my last > venture into SCAD. For one, it makes a straight line on the back of > the cord, filling in the concavity. It will also not give a different > angle of attack at the top vs. the bottom of the rotor unless I build > it out of straight-line segments like before, which would again be > computationally intensive and also prevent me from using "backsweep" > (and backsweep is supposed to be good for both flow stability and > compressor efficiency, I am told). > > Attached is a version of the design with thicker, more visibly tapered > (but still not buttressed) blades. > > The 3Dsweep library that you suggested a while ago may be able to > handle it, but I do not know how to generate the NACA airfoil profiles > that it uses, or even if those can be adopted to centrifugal blade > profiles. Reading the code, I also could not see right away how to set > the curve between the beginning and ending profiles. Still, may be > worth another look. > > By the way, I had a moment of profound bewilderment when I realized > that the only way OpenSCDA can do summation is through recursive > functions. What sort of a respectable language would do that?! > > My search for diffuser guidelines is not proving fruitful, so I am > going to forge ahead with what I hope is a relatively safe, if not the > most effective design. If I aim my efforts towards a test rig, then we > will soon need to do some scheming to figure out how the driver > turbine with its plumbing, the compressor with its, and the > throttleable instrumentation pipe can all be made to "coexist > peacefully together". Speaking of which: did any information on > possible compressor options come to light? > > > > On Wed, Jun 7, 2017 at 9:35 PM, jon <jon@jonbondy.com > <mailto:jon@jonbondy.com>> wrote: > > You use linear_extrude() to make the blade. What if you created a > profile for the top of the blade and one for the bottom, > separately, and then used hull() to connect them. Then the base > could be broader than the top. In fact, the base could be the top > just scaled by 2. > > > On 6/7/2017 5:12 PM, Alexey Finkel wrote: >> The blades actually taper veeery slightly toward the outer edge, >> but indeed do not include any real buttressing. Because of the >> complicated shape of the hub, I am really not sure how to even go >> about putting something like that in place. I could mess with the >> arc that generates the blade surface to make the taper more >> pronounced, but that's not quite the same thing, of course. >> >> Excel does not, as far as I know, come with an animation package, >> so I think I would lose out on the visual appeal part of the >> market for the calculators. >> >> On Wed, Jun 7, 2017 at 10:09 AM, jon <jon@jonbondy.com >> <mailto:jon@jonbondy.com>> wrote: >> >> Preview rendered instantly here, although trying to >> manipulate the view screen in any way causes OpenSCAD to hang >> (which may be what you meant). I worry that the blades are >> of uniform thickness, which means their attachment point at >> the base is fairly narrow. My intuition says that they will >> snap off without some broadening at the base >> >> I wrote some Stirling Engine simulators which were very >> naive, but I included animations. It was to help my >> intuition. I had quite a few requests for them, even though >> they were ... stupid. >> >> :) >> >> >> On 6/7/2017 8:08 AM, Alexey Finkel wrote: >>> I will ponder on the question of the Discussion group until >>> Sunday, but as my comment on the meetup page suggests, I >>> think putting the whole thing on hold while it is not >>> working so great for you has a substantial risk associated >>> with it. >>> >>> Without knowing much of anything about how to use a DSP >>> unit, I will nevertheless venture a guess that "stunning" >>> difference may live in a very small and remote corner of >>> available parameter space; a corner that is difficult to >>> find unless one has either much insight knowledge, or >>> preternatural intuitive talent. But that's just a guess. >>> >>> Of course real engineers have much, *much* more complete and >>> sophisticated software packages for turbomachinery design. >>> My spreadsheets are naive child's drivel by comparison. >>> Their primary purpose is really to give me the illusion of >>> knowing that I knew what I was doing when choosing some >>> basic design parameters. It may be an intermediate stage >>> between completely seat-of-the-pants design and real-life >>> engineering work, but I have to wonder how big a market >>> there is for such a beast. At any rate, if we ever built >>> something based on those calculators, and it worked in any >>> sense of the word, I would probably make the calculators >>> available online for free. >>> >>> It looks like I sent you the wrong version of the new blade >>> design. This may be for the best, because I developed it >>> into a proof-of-concept compressor rotor design by now. The >>> result is attached. Be sure to disable preview before >>> opening it though! The thing is very high-polygon, and >>> pretty much kills my SCAD dead if it tries to preview it. >>> The rotor has a radius of 50 mm, so if you wished, you could >>> use it as a test. However, I recall you mentioned that the >>> resin is not cheap, so I wonder if a scaled-down version >>> would be a more practical way to go. Or, you could cut out a >>> cylinder or a cone from the rotor hub, at least if >>> unsolidified resin can be recovered and reused. Also, I used >>> lower values of $fn that I might for a "final" version to >>> save computation time. If you were interested to see how >>> smooth we can get the surfaces, maybe increasing $fn to 100 >>> or even 200 everywhere would help put the printer through >>> its paces. >>> >>> On Tue, Jun 6, 2017 at 8:36 AM, jon <jon@jonbondy.com >>> <mailto:jon@jonbondy.com>> wrote: >>> >>> The new/larger resin printer is assembled, but not >>> tested, so the timing is good (I hope). >>> >>> Your spreadsheets are interesting. I wonder if they >>> could become a commercial product (or, better yet, they >>> could be re-coded to produce a commercial product). I >>> know that the Big Guys would not want/need them, but DIY >>> folks might. >>> >>> The new 5' tall speakers are interesting. The sound is >>> OK but not stunning in the frequency-response sense, but >>> the "sound field" that I had assumed was just BS turns >>> out to be palpable. You can walk behind the speakers >>> without losing much of the sound. It seems to just fill >>> the room. So, from the perspective of wanting to >>> experience something new, it is a success. The $700 DSP >>> unit produces detectable differences in system response, >>> but not stunning differences. >>> >>> I seem to have run out of steam for the Discussion >>> group. In the past, topics just leapt to mind, but now >>> my mind heads in other directions. I'm not sure what to >>> do about that. >>> >>> :) >>> >>> >>> >>> On 6/6/2017 6:36 AM, Alexey Finkel wrote: >>> >>> It seems I haven't said anything on the subject in a >>> while, but the last couple of weeks have been a >>> relatively productive time on the turbine front, so >>> I thought I'd give a bit of an update on the state >>> of things. >>> >>> Both the compressor and turbine calculators are >>> coming along. Both pass the basic sanity checks I've >>> put into them and give believable results. However, >>> I keep adding bits to them, and finding other bits >>> that can be done better, so I would not risk saying >>> that they are "done" just yet (or ever, really). One >>> conclusion is that going from 30-mm radius to 50-mm >>> rotors makes a huge difference in power, as well as >>> a significant, but less dramatic one in compressor >>> pressure. Kilowatt-level output seems feasible with >>> 50-mm rotors without going to ludicrous rpm. >>> >>> I think this means that we could tentatively answer >>> one question from the long list as follows: if the >>> 100-mm resin printer is going to be available, we >>> should be able to print high-precision and smooth >>> moulds, and cast a ceramic rotor (or rotors). >>> Whether this works in practice, and whether a stator >>> made from a plastic printer cast can be made usable >>> remain open questions, of course. >>> >>> I've also tried to match a compressor to one >>> possible version cold-air turbine, and found that it >>> is sort of possible even with the very low flow rate >>> available, if a number of adaptations and >>> concessions are made. Still, as I think I mentioned >>> ,if we can get higher flow rate even at the cost of >>> pressure, it would be a lot better. >>> >>> However, I have not tried to assemble a full >>> compressor-diffuser-combustor-turbine calculator yet >>> because my rudimentary combustor calculator is >>> giving me unrealistically high combustion >>> temperatures, and because useful data on even the >>> simplest kind of radial-flow diffusers is proving >>> tricky to track down. >>> >>> On the other hand, I came up with a new way of >>> generating blade geometries in SCAD. It uses linear >>> extrudes with twists instead of hull, thus getting >>> around the convexity issues I had before. A sample >>> is attached, but be warned: it also uses differences >>> of high-polygon objects, so it *really* doesn't like >>> to run in preview mode. On the plus side, it seems >>> to compile and render pretty quickly for me. >>> >>> Proceeding with diffuser design may be slow for a >>> while, as it looks like I am going to have to do >>> some more serious reading, but I will try to keep >>> myself entertained by modeling other parts and >>> pondering how to fit them together. >>> >>> How are your projects going by the way? Do you have >>> more speaker cabinets than you know what to do with >>> yet? Or did you see the light and opt for the >>> magical "blue diamond" sound-improver? >>> >>> Alexey >>> >>> >>> >> >> > >