DYNO eddy current brake. take 2!

Discussion in 'Performance Mods' started by HeadSmess, Jan 19, 2014.

  1. HeadSmess

    HeadSmess Well-Known Member

    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 :)


    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 :)

  2. Fabian

    Fabian Well-Known Member

    HeadSmess, can you please expand on that story. It sounds """SO""" 'Dr Evil'
  3. HeadSmess

    HeadSmess Well-Known Member

    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...
  4. Fabian

    Fabian Well-Known Member

    That's an unfathomable amount of magnetic attraction.
    More interesting is how such magnets are made?
  5. HeadSmess

    HeadSmess Well-Known Member

    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...
  6. HeadSmess

    HeadSmess Well-Known Member


    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...

  7. HeadSmess

    HeadSmess Well-Known Member

    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!
  8. Fabian

    Fabian Well-Known Member

    Still reading and still got my bag of popcorn beside me.
  9. HeadSmess

    HeadSmess Well-Known Member

    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... :jester:


    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:jester: 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?


    it works :) neat-o :)
  10. Fabian

    Fabian Well-Known Member

    The link does not work.
  11. HeadSmess

    HeadSmess Well-Known Member

    :confused: dont ask me...

    only "better" bearing...6003 rather than 6202.. 17mm ID :)

    hmmm....crank bearings huh?
    Last edited by a moderator: Dec 15, 2015
  12. HeadSmess

    HeadSmess Well-Known Member

    i dont forget about things and i dont give up... i simply stop and ruminate for a while. life keeps getting in the way :)

    found my lump of steel. just wanted to use it cus its nice and soft...magnetically and machining wise.

    magnet disc...


    fresh off the mill. obviously 24 neo magnets will sit in them there pockets. no need for glue. im never getting the one i stuck in so far back out!

    ive decided the whole thing works better when the magnets are alternating in polarity. much better.

    this just makes me realise how time can fly past...

    tried writing a code so they would slowly spiral in rather than just be on the circumference, but other than rewrite a few thousand lines by hand, i had to put up with it. wont affect anything.
    Last edited: Apr 27, 2014
  13. 074KU

    074KU Member

    Looking very nice, I hope one day my machine work looks that good. I have been keeping an eye on this thread for a while now and can hardly wait to see the finished product in action. :cool:
  14. HeadSmess

    HeadSmess Well-Known Member

    cheers. tis the machine, but i take credit for using it :) and it took me a while to set it up.

    next mill/lathe i buy, im getting a surface plate and doing some scraping. makes the world of difference on cheap chinese muck :)

    you got me in the mood to go take pics of what i just made...

    back. phone camera sucks :)


    just the hub. very small spigot to centralise on. what you cant see is its 50mm of 90mm round bar at the back...(life getting in the way...set of carbide tools i bought were 2mm too high, so i decided i would machine all 50 at once...now i got all these lathe tools i can use :). but i had to do at least one for this job:rolleyes:) now for some holes on a pcd, some countersunk screws, and all i need is the shaft and adjuster doodad. that gets things to the rotating/loading point...

    then some v block type clamp to hold the shaft steady. scales... grrrr. scales.

    brrr. getting cold. meh. go rug up and drill some holes :)
  15. 074KU

    074KU Member

    Sounds like you have it all planned out. I humbly volunteer to risk my ride for the sake of testing her when its all together :jester:
    I think Fabian is going to be pounding on your door to give this little beaut a go. :grin5:
    All joking aside I imagine it will be a very solid well built Dyno if your brake is anything to go by, Thank you for keeping us updated with all that sexy metal.

    I think I am going to have to drag the wood heater into the workshop myself in the next few days, not enough light or warmth to keep up with my desire to mess about in the workshop, Women don't understand our sacrifices.
  16. HeadSmess

    HeadSmess Well-Known Member


    as the title says, today was boring, literally.

    the part ive been dreading...the part i knew would take all day...9am to...its 4pm ish now :)

    the spindle.

    how to bore a 25mm hole 150mm deep? my 22mm drill bit has only 120mm of flute to use!

    once that was over, the rest was easy. just wasting time with a finishing tool, nice slow feed whilst turning slow with a funny tool...


    erm. boring the hole. custom boring bar using a lump of old HSS endmill as a cutter :)


    then we started getting all the rust off the outside...note the mandrel in the chuck for concentricity :)


    old lord poobah here decided he wanted a nice smooth finish so made a funky tool... well, taking 4mm off in one pass with HSS is always ugly :)

    first finin pass.


    there is no final pass!

    but... there is a finished...semi finished product :)


    so. a long brass plug goes down the hole. it has a hole bored through it, tapped to M14x1 (just cus i have that size handy, saves doing an internal thread) and another hole at right angles at the far end.

    this spindle i made needs the small hole tapped, firstly, to retain the disc.

    then its getting a slotted hole down near the end.

    the hole in the brass plug should line up with this slot.

    the previously posted magnet disc, will have a bolt through it, engaging with the brass plug.

    then a lead screw is stuffed down the end of it, threading into the brass plug.

    so when i turn the handle, the magnet disc assembly will move towards or away from the rotor.

    a whole freakin day...im going out and getting something to eat...
  17. HeadSmess

    HeadSmess Well-Known Member

    some number crunching, showing how easy this is in theory...

    If torque and angular speed are known, the power may be calculated. The relationship when using a coherent system of units (such as SI) is simply

    P = \tau \omega
    where P is power, \tau is torque, and \omega is angular speed. But when using other units or if the speed is in revolutions per unit time rather than radians, a conversion factor has to be included. When torque is in pound-foot units, rotational speed (f) is in rpm and power is required in horsepower:

    P \text{(hp)} = {\tau \text{(ft} {\cdot} \text{lbf)} \times f \text{(rpm)} \over 5252}
    The constant 5252 is the rounded value of (33,000 ft·lbf/min)/(2π rad/rev).

    When torque is in inch pounds:

    P \text{(hp)} = {\tau \text{(in} {\cdot} \text{lbf)} \times f \text{(rpm)} \over 63{,}025}
    The constant 63,025 is the rounded value of (33,000 ft·lbf/min) × (12 in/ft)/(2π rad/rev).

    seee if that posts properly, otherwise...



    lets say i have a foot long reaction arm. of course i will!

    and my scales, in pounds, reads 10 when i load the thing down at 5000rpm....

    so, take the equation...



    rotational speed, measured torque...hp :) seasy :)

    3.6 lb at 6500rpm? 4.45 hp...etc etc...

    now, my only thinking bit at the moment is mounting this spindle...

    so, i need the torque reaction from the magnet disc. i guess the easy way is to just make the slot slightly oversize and let the thing spin slightly on the shaft, is how ive been picturing it so far. other option is to mount the spindle itself on bearings, the slot is tight with minimal play, and the reaction arm is clamped to the spindle... lets me use plain old spring scales but i think a proper load cell is on the horizon...
  18. Fabian

    Fabian Well-Known Member

    I like how you've sexed up your post with a bit of maths.
  19. HeadSmess

    HeadSmess Well-Known Member

    well, its there, it works. hmm. i gotta mount it on the lathe and take a video. anyways.

    i was browsing just now and came across this...


    now, it might sound impossible, dyno an engine with just a microphone?

    the explanation makes it clear. engine produces a given frequency at given rpm.

    it takes so much power to accelerate a given weight to a given speed.

    knowing the gear ratio and mass being moved, and the rpm, one can deduce the power required...

    not catering in wind resistance which complicates the issue but hey...

    stuck on a bench, testing the magnetos signal, rather than a mic...and just a heavy weight being accelerated, like an inertia dyno. one knows the mass, one knows the rpm, one knows the change in speed per second or acceleration...

    so whyd i make this thing anyway? lol :)
  20. 074KU

    074KU Member

    I like the look of that program, The wind resistance thing seems a bit of a pain.. Maybe just mount the rear wheel on some sort of freewheeling drum and strap the bike down with a load equal to riders weight and input 0 for the Cd value?

    The rest of it seems fairly straight forward to produce, bit of veroboard, few components from Jaycar or the like, maybe a couple of spade terminals wired into the parallel with the CDI to allow quick and easy hookup if you felt like doing further dyno work.

    Mount a Bicycle computer to the rear wheel, multiple magnets for more accurate reading as suggested..

    May not be 100% accurate that way but should at least give enough information to determine if change X is "good" or "bad".

    I dunno, I am just spitballing here.

    All that being said I am still very keen to see how your project is panning out. :eek:16:
    May have to stick the bike on the ferry and come give it a whirl :laugh2: