DYNO eddy current brake. take 2!

HeadSmess

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right! the scrap yards open after the break, ive been paid for the last week of slavery, the pile of bills has shrunk, i can return to this project!

purchased, after much scavenging...one piece of brass (grrrrr, there wasnt any copper i could see that was suitable, alloy would have possibly been better anyway- and cheaper!) cut as a 8 " or so disc. there was a whole stack of them. i think theyre rejects because of the small nick in one edge (opposite my thumb) due to bad cutter programming...

also scored a nice 1:1 right angle drive :)

Photo0052.jpg

anyways! the plan!

bore hole in centre, trim edge, balance using a whipstick. (a long mandrel, held in chuck, disc at far end. mandrel rides in tailstock centre. spin it up with crayon held just off disc edge, back off tailstock centre just a touch, and disc will "wobble" and be marked at the heaviest point. drill out small spot of material, retest, repeat till perfect)

machine that alloy thingy as a hub with bearings. bolt to disc. probably better to balance it after all that, rather than just the disc. im planning on running this straight off the crank now :)

then get a steel plate, set it up on a bush so it can be slide back and forth along the shaft. cover the thing in neo magnets and by decreasing clearance between magnets and disc...achieve adjustable eddy current braking.

may end up silver soldering some brass strips to the back, to make a rudimentary fan. possibly two discs with the strips in between for a "slotted" rotor... getting too far ahead of myself now!

the disc with the magnets will be the stationary "torque" member.


yay. lenz law :)


now where to find some big neo magnets that are fairly cheap...

wow. a 4" X 1 " disc has 262 kg of pull! and costs about that much too! (oh yeah... one place i worked at, a client bought in his "fishing" magnets. they needed a permit because they CAN KILL YOU! "fishing" as in fishing out the auger that just fell apart 2 km down in a sand and water filled hole)

or a 12x5mm with 4kg of pull...20 pack for $42 :) sounds betterer...thats 240 kg or so of pull for $120 :)
 
one place i worked at, a client bought in his "fishing" magnets. they needed a permit because they CAN KILL YOU! "fishing" as in fishing out the auger that just fell apart 2 km down in a sand and water filled hole)

HeadSmess, can you please expand on that story. It sounds """SO""" 'Dr Evil'
 
well, if you think that not many people can curl 100kg, let alone 240 kg concentrated in a 100mm diameter area... get that on your chest, and suddenly you discover that;

big powerful magnets are DEADLY.

thats basically it :) the ones this guy had were 100 mm cubes! i think they were rated at around 1 tonne of pull! even need special delivery drivers and all that stuff. nasty things! credit cards? wiped from 2 metres :)

oh, and horizontal boring rigs are also deadly when something goes wrong :)

in this case, it was just the auger/reamer fell apart near the end of a hole. theres only one way to keep drilling to finish the job. get all those diamond insert filled lumps of steel out of the muck! a single blade weighed in around 150kg, so you needed something pretty good to drag them out of what was basically quicksand. well, big multi million dollar lawsuit and someone was fired... not me! id already walked by that point :)

guys on the oil rigs hate broken tips too....they have to lift kilometres of pipe VERTICALLY! can take months to clear a broken head...
 
wiki would answer all that. all i know is that neo loses its power at a very low temperature...that could be a problem for what im doing what with radiant heat. meh. theres other types of magnets and i dont really think it will be an issue anyway. seems to be about 70c...

this guy was only able to transport his so freely cus they were already stuck to something... still powerful, but clinging like barnacles to a rock... kept clean as supplied and they jump to anything magnetic that gets too close. hence the danger. hmmm. barnacle cannon :wacko:

most magnets are sintered out of some collection of ground up goop. ferrite is basically cast iron, alnico is aluminium cobalt and nickel, neo is another weird collection again... pretty interesting how they build the super powerful magnets that make the superconductors look wimpy... a superconductor is used mainly because once the field is established it persists as long as its kept cold. while they do make strong magnetic fields...they arent the strongest.

dont ask me what makes a magnet do its thing but. bit like gravity and time, noone really knows...
 
money=progress.

25 magnets coming my way. 6.1kg pull each, or...4,200 gauss.

gives me about 100,000 gauss in total.


some spreadsheet calculator came up with figures of 400 amps in a 30cm conductor spinning at 5000rpm... 270 ft/lbs of force on a conductor carrying 400 amps in a 100,000 gauss field... . . . . . . . . . . . .

im pretty sure this will work? otherwise, i got some good fridge magnets...

http://www.ndfeb-info.com/neodymium_magnets_made.aspx
 
25 neo magnets are freaking STRONG! without a good grip, theres no chance of pulling 6kg directly off a steel bench.


so, havent pulled the cover off the lathe yet, just played with magnets all last night...

the quick "swipe" past the previously pictured brass disc encountered serious resistance, with just one magnet... its why lenz law is a law...its always going to do it. and as ill be trying to do it with 25 magnets, at quite a few more RPM...

so. i guess i have to do some machining now!
 
yay. i return, at last.

i finally machined up the disc. quite tricky really. involved shrink fits and mandrels and its good to practise such things.

so. i found a (dodgy) camera that works. has a pathetic mic. when i got it from fleabay it didnt work at all! maybe leaving them for a year helps? they have to ripen or something... :giggle:

oh!

dodgy vid! ignore the date...

[video] http://youtu.be/-1g8bDLXNAQ[/video]

here you can see it does stop rather quickly. yes, its not safe yet! i can feel the braking force, iunno if the video shows it too well... but basically my hand stopping the magnets will be replaced with a set of scales and a torque arm... me will will be replaced with a bench, and a safety shield. be spinning it at crank speed! just a felixibke...wtf? flexible!! coupling:giggle: between it and engine under test.

gotta find bearings with a larger ID, these are just old crank bearings... larger shaft, then find that PERFECT 10mm thick steel disc off the back of a speaker that i cant find... grrrr.... this is what happens :) i lose stuff :) too much junk! anyway. steel disc, ill machine with evenly spaced pockets to take the magnets. for now, a faceplate is good enough and just happens to slide on the shaft i have ;)

length of runs will be determined by how hot the disc gets!

also buy a few hundred magnets perhaps...? they took up a lot less space than i expected...


need to experiment with the polarity of the magnets... alternating or monopole?

but.


it works :) neat-o :)
 
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