utopian isotope

Plan 9 from outer phase again.. Is it possible to replace permanent magnet(s) (be it neodymium, ceramic, or whatever) with electromagnet(s)? I'm aware that it wouldn't be too practical and requires more coils, more work etc. What I have in my mind is to have some kind of "virtual"(instead of real one(s)) and an "adjustable" magnet(s). I guess that it wouldn't be too efficient, if using same current/voltage, that driver uses? Anyway... just a thought.

Hehee, same here. It's amazing how much material you can reuse. -------- Anyway, when looking for magnets, I found this site: http://www.supermagnete.de/eng/index.php?switch_lang=1. They have those tiny disc magnets, that could be used instead/with steel polepieces. Since those are neodymium magnets, maybe smaller size would be enough, to avoid excess string pull? There is also magnetisation strength grades, that are too much on theory side for me.

Again one possible way to make a bobbin... I dug my stuff, and found about 1mm thick plywood. It can be cut with scissors, filed and/or sanded. I did also cut 5mm pieces out of pickup polepieces, that were lying around. Here is result: No fancy tools or equipment required.

My addition to diy porn section... I made a mold out of candle wax, and poured epoxy glue to it. Slowly it goes.. as it takes 16 hours to cure. Candle wax might not be the ideal material to make a mold, as some epoxies could melt it. ---------------- For those, who wonder what I'm talking about, answer is simple; to find an easy way to make bobbin(s) of desired size for desired driver.

@psw: (Almost) perfect template can be made, if you have accurate reference(s). For example, I used four similar ball bearings when filing test piece. Ball bearings have an exact diameter and they are hardened, so they don't wear easily. Maybe that picture explains better what I mean: Ball bearings effectively keep you from filing too much. Takes some work, but resulting piece is most accurate, that you can make without cnc.

------------------ One possibility is to use polyester resin, but when cured, it can be too fragile, and needs fiberglass to support it. It also stinks awfully. Too much hardener heats resin so much that it starts to smoke... just result of my ancient testings. Even at present time, there doesn't seem to be available any liquid plastic, that allows easier molding. Or is there?

When workin with epoxy, I've noticed that by warming it with hot air makes it more liquid, so that bubbles disappear easier. Suitable amount of heat is when epoxy changes from blurry to more glossy. Maybe that works on casting too?

I've done some machining experiments on nylon, attempting to make bobbin templates out of it. Not worth an effort, since it is quite difficult material to work with, unless you have access to cnc. What I have in mind is to make a template, where you can wound coil(s), that has possibility to easily remove core(s), so that they can be re-used, when testing different coils. ---------------------------- @psw: What materials do you use to make bobbins? My suggestion is to use pc-board, since it isn't fragile as most plastics are. Solder pads are also much easier to make. One major disadvantage is that you must use carbide bits(more expensive) for tooling, as pc-boards contain fiberglass, that wears hss quite fast. Anyway, if there is other more suitable materials available for that purpose, let me know. ------------------------ In case of epoxy casting, mold(s) can be polished, so that it is easier to snap finished piece out of it. I have two packs of epoxy for testing. Addition to polishing mold, I might test cooking oil, vaseline and motor oil... But seriously taken, those who use polyester resin, use some kind of "removing liquid"(don't know the right phrase) for easier removal of finished piece out of mold. I once had bottle of that stuff, but it lost when I moved.

Here is another example how to use template to make multiple parts. Red part is ball bearing, that has same diameter as sanding drum. Template doesn't need to be that thick as in animation.

Thanks for reply! @psw: Machining nylon is tricky thing to do. Does your router have a speed adjustment? Too high rpm simply melts nylon, as you have experienced. No matter how sharp bit is in use. Higher rpm requires higher feed, so that nylon doesn't have time to melt. Under 5000 rpm is more suitable. But then again, lower the rpm, the more prone the working piece is to kick on your fingers. For example, on the mill I've used under 1000 rpm when machining nylon. Sanding/grinding is more forgiving, since it doesn't have only two or four teeth as routing/milling bits have. So that it allows you to do things more gently, little by little. Anyway, feel free to post to me, I'll be glad to help on those machining things. ---------------- Yes, I'll make some animations.

Totally OT again... One hint when rounding ends of the centerpiece(s) and bobbins/templates with sanding drum: Just a tip of an iceberg... If there is enough interest, I can make more animated stuff about it, as there is also some other things that can be done.. It really isn't beginner's project as it requires almost an extreme accuracy.

Is it possible that certain amount of opposite winding has the effect similar to bifilar coil? Cancelling some part of the signal? -------------------------- I have a small "3 in 1". Means lathe, mill and drill in the same machine. One disadvantage of using mill is, that cutter(s) has to be razor sharp, when machining nylon(aka Polyamide/Ertalon). Most challenging part is the centerpiece. It can be made without mill, if you have any kind of grinding/sanding machine available. Even with humble power drill and sanding drum, it can be made. But the nylon blank needs to be attached firmly to... -- shame on me as I don't know how to explain it in english. Have to make some animated gif's to clarify the idea.

That got me thinking - what about some sort of U section plastic strip of some kind - you could use it to make something with reasonable structural rigidity, it would be slightly thicker due to some overlap, but I think that will only be important if your trying to build a piggy-back driver. A refinement if this kind of idea might do the trick ? cheers Col

String? Do you mean steel sheet that I used for cores? The DC resistance of the coils is not the key factor - whats is important is the impedance over the systems frequency range. If you're building a dual core driver, then it depends if you are going to wire the coils in series or parallel. If series, then each coil should have half the impedance it would for a single core driver. If parallel, then each should have twice the impedance... If you were looking at simple DC resistances, then it would be 4 & 4 for series or 16 & 16 for parallel. If you're going for a slightly higher inductance, you will probably be best looking at a lower total DC resistance (probably best not to go much below 4ohm unless you're going to install a heatsink.... even then, I'm not sure what the consequences might be). Yes, I'm building dual core driver, so that both coils have separated inputs. That way I can test them in series and parallel, in phase,and out of phase. Maybe I wind 16 ohms coil around those cores also. That means six wires... and lot of testing possibilities. I have no clue about theory, and how that works with sustainer, but for me there is only one way to find out... For my next driver I will be going for dual core in parallel config with a total DC resistance of 4ohm. I will work out what the maximum inductance would be so that the driver still functions at what I consider to be a high enough frequency. This will involve building a dummy coil on my intended core and measuring the inductance, then calculating from that how many turns of wire I need to get that inductance... then finally working out what gauge of wire is required for that number of turns to give the desired DC resistance of 16 Ohm per coil. Then when it's built I will measure the actual specs to see how far off they are to guide the next effort. And then of course, test the thing out - I should find out pretty quickly the answers to the questions I still have as to how running coils in parallel effects the field that is generated. I also want to have some bobbins that allow the core to be removed, so I can compare parallel and series versions with the same overall inductance, impedance and resistance... Some kind of plug-in system would be great. So that core(s) and coil(s) and also whole driver could be removed or replaced without hassle. Just need to get an inductance meter, some suitable magnets and a few other bits and pieces - probably will happen in a couple of months. Not sure how that would work? Would it not mess up the balance of the field dramatically, change the phase response and cause some hefty inefficiency in the load to the amp ? better to have two coils with different specs - basically a 'woofer' for the low strings and a 'tweeter' for the high strings. Has been suggested a few times, but its still a valid idea, and still hasn't been tried... hmmm... its certainly a possibility for a bi-lateral driver - another reason t ohave a standardized bobbin and removable core for comparison testing. That's what I'm after, since wound strings seem to be somewhat slower in response when compared to plain strings. That slowness might be one cause of fizz. ----------------------- BTW, I took stick of wood (about 35 cm), and wound 10 rounds of coil wire to it. Then measured resistance, and did some simple calculations. Certain amount of rounds gives about 8 ohms, twice that gives about 16 ohms etc, so that I can cut 4, 8 or 16 ohm amount of wire for future drivers. Don't know if that method is already in use, but no more guessing when winding.

How do you guys laminate the core? I have disassembled small transformer, and tried to make core(s) of "I" pieces. I found it quite hard to align the pieces properly. Maybe it is the superglue that I'm using. It cures way too fast. Using epoxy could be one solution, but when you apply that to pieces, and clamp them together, they tend to slide away. Lazy as I am, I took 0,8 mm steel sheet(maybe Fe37), and cut two 4mm x 210mm pieces out of it with plate shears. Then rolled them so that they form about 4mm x 5mm x 30mm pieces of mild steel each. I'm sure that eddy current(s) will occur with this, as there is no isolation between sheet rolls. Anyway, I got two cores ready to winding as soon as I make bobbin(s) out of plastic. Should the twin coils have 4 or 8 ohms each? What I have in mind is to use a pot to adjust balance between wounded and plain strings.