Author Topic: Building the Minimag  (Read 33816 times)

Offline Bogstandard

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Re: Building the Minimag
« Reply #50 on: February 07, 2011, 02:07:39 PM »
Many thanks for all the good comments lads, I hope at least a couple of you have picked up a few tips.


Rob,

There a few way to fit it, and when the engine is built, the final decision will be made.

First off I could drive it from the main crank with say a 1/4" chain and sprocket, and reduce it down to half engine speed, that could be done from either side, and direction doesn't matter as it all depends on how it is magnetically timed, it can be driven either way.
But the favourite at this time is to take a 1 to 1 drive off the main engine valve cam, either directly mounted to, or what I am favouring at the moment, a drive gear or chain drive putting it to one side, and utilising the original points adjusting plate somehow, to allow me to easily adjust the ignition timing.

Basically putting it somewhere near where the original contact breaker points were to be. It all depends if I can squeeze it into the space.


John
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Offline John Stevenson

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Re: Building the Minimag
« Reply #51 on: February 07, 2011, 02:14:23 PM »
John, You need a gear drive like this to get it to give a right flick.



Here's it in action  :D

<a href="http://www.youtube.com/watch?v=zOmSrePm_UM" target="_blank" class="new_win">http://www.youtube.com/watch?v=zOmSrePm_UM</a>



John S.
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Offline Bogstandard

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Re: Building the Minimag
« Reply #52 on: February 07, 2011, 02:23:59 PM »
 :lol: :lol: :lol:

But I thought I could get away with a one tooth gear on each part  :bang:
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Offline Dean W

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Re: Building the Minimag
« Reply #53 on: February 07, 2011, 09:22:21 PM »
That gear setup would drive people loony, and they'd never notice the engine or mag it was running.  ; )

Bogs, it all turned out great!  It's a good looking little unit, and as always your work is very instructive.
Dean W.

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Offline madjackghengis

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Re: Building the Minimag
« Reply #54 on: February 09, 2011, 12:09:09 PM »
Well John, that is a very clean magneto, truly inspiring, and very neatly and solidly done.  I particularly like the points set up, out of the way, but easy to adjust, my question is regarding a condensor, is there one in circuit somewhere?  I have found a small magneto coil which looks about the same size or similar, on a weed eater engine, and I believe I can push the core, which is odd shaped, out, and push in a straight set of laminations, and try out building one using your demonstrated techniques on one which could fire nine cylinders, so I can use it on the radial build.  I looked at those two you put the link to, and they look to fit very well where they're at, and should be substantially better than batteries and such.  The aligator clip reminds me of the standard wire set up on all old cars, motorcycles and the like, with the end of the high tension lead having just a two pronged clip for connection to the plugs.  This has been a great build log, and if my mag experiment doesn't prove out, I will be ordering a minimag kit I expect.  Very nicely done, all around. :nrocks: :beer:cheers, mad jack

Offline Bogstandard

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Re: Building the Minimag
« Reply #55 on: February 09, 2011, 12:33:38 PM »
I am just in the process of finishing it off Jack, but my body has told me otherwise, as usual.

No condensor required, just take the red lead to the plug and if the main body is earthed to the engine, you will have spark.

Stew took me out to the scrappies this morning, and one of the first things I picked up was some sort of garden machine engine, a tiny little thing, and that had a magneto sitting on the front of it. No bigger than the one I have made here.


John
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Offline cfellows

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Re: Building the Minimag
« Reply #56 on: February 09, 2011, 02:52:33 PM »
Very nice project, John.  Nicely documented.  Thank you for the time and effort to share.

Chuck

Offline Stilldrillin

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Re: Building the Minimag
« Reply #57 on: February 09, 2011, 03:22:27 PM »
Nicely done..... Nicely shown, John.  :thumbup:

Yer said, don't say anything..... I didn't!   :wave:

Enjoyed the show. But, still got no meaningful comment.....  :scratch:

Thanks!

David D


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Still modifying bits of metal... Occasionally, making an improvement!

Offline Bogstandard

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Re: Building the Minimag
« Reply #58 on: February 09, 2011, 03:31:22 PM »
David, as long as you enjoyed reading it, that's all that matters and no comments needed. It is when no-one reads it is when the problems start.

Chuck,

I have sent you a PM.


John
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Offline John Stevenson

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Re: Building the Minimag
« Reply #59 on: February 09, 2011, 04:15:11 PM »


Stew took me out to the scrappies this morning, and one of the first things I picked up was some sort of garden machine engine, a tiny little thing, and that had a magneto sitting on the front of it. No bigger than the one I have made here.


John

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Offline Bogstandard

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Re: Building the Minimag
« Reply #60 on: February 09, 2011, 04:23:46 PM »
No gloat John, I chucked it back in the skip as I've already got one now. :lol: :lol:

Now I can gloat


John
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Offline NickG

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Re: Building the Minimag
« Reply #61 on: February 10, 2011, 05:29:03 AM »
Haha, didn't realise you meant literally you just "picked it up" !

Was that the sort of thing I talked about in the other thread John? Chainsaw or strimmer type engine. I'm going to get one and do some experiments with that when I start my i.c. build.

Nick
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Offline Bogstandard

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Re: Building the Minimag
« Reply #62 on: February 10, 2011, 06:41:12 AM »
That's right Nick.

The magnets were actually embedded in the cooling fan on the front of the engine.

It looked a little complicated to get things how they would need to be, as rather than mechanical points, it had some sort of electromumbo gizzmo firing the spark, so I think I will stick with what I've got.


John
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Offline madjackghengis

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Re: Building the Minimag
« Reply #63 on: February 10, 2011, 08:59:24 AM »
Hi John, that thing you chucked back sounds like exactly what I have in hand myself.  I assume you've glanced at my build of the radial engine, and in truth, I've been off it for some time, waiting on parts, but in part, waiting for inspiration, as I don't want a big wooden box full of electrical mess as you described, and yet it must be reliable.  I've planned on attempting a magneto from the start, but until your build log, wasn't sure I was going to be satisfied in the end.  I still have to put together a rotor, and test my theory, but I think I can build a mag that is smaller than the engine, using ideas gained from your build, and if a mag can fit on it without interfering with any rotating parts, I'd be satisfied with it.  With my background in radar and electronics, I expect to make use of the built in trigger mechanism, and if I can't, I will end up using at the least, a coil from the minimag, as it is the right size, regardless of anything else.  A points or electronic ignition is easily built, but only a maggie is stand alone, and I feel an engine ought to be complete in and of its self, and hate to see electrics which are twice the size of the engine they run.  I appreciate the fact you've picked up a mag like I'm talking about, and have given me a comparative size review, as that supports my idea of getting one working for my purposes.  Your build was altogether a fine learning experience, and well done. :beer: cheers, mad jack

Offline HS93

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Re: Building the Minimag
« Reply #64 on: February 10, 2011, 09:48:50 AM »
Hi John, that thing you chucked back sounds like exactly what I have in hand myself.  I assume you've glanced at my build of the radial engine, and in truth, I've been off it for some time, waiting on parts, but in part, waiting for inspiration, as I don't want a big wooden box full of electrical mess as you described, and yet it must be reliable.  I've planned on attempting a magneto from the start, but until your build log, wasn't sure I was going to be satisfied in the end.  I still have to put together a rotor, and test my theory, but I think I can build a mag that is smaller than the engine, using ideas gained from your build, and if a mag can fit on it without interfering with any rotating parts, I'd be satisfied with it.  With my background in radar and electronics, I expect to make use of the built in trigger mechanism, and if I can't, I will end up using at the least, a coil from the minimag, as it is the right size, regardless of anything else.  A points or electronic ignition is easily built, but only a maggie is stand alone, and I feel an engine ought to be complete in and of its self, and hate to see electrics which are twice the size of the engine they run.  I appreciate the fact you've picked up a mag like I'm talking about, and have given me a comparative size review, as that supports my idea of getting one working for my purposes.  Your build was altogether a fine learning experience, and well done. :beer: cheers, mad jack

How about one of these, cheap simple and I think they do them for more cylinders as well.
peter
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10996

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9906
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Offline NickG

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Re: Building the Minimag
« Reply #65 on: February 10, 2011, 09:57:48 AM »
Yeah you're right John, I don't think it'd be a simple task to modify it. It'd have to be hidden away under a box I think too, don't think it'd look pretty.

Peter, the point of this is, it is self sufficient i.e. doesn't need anything else to make it run other than fuel and authentic!
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Offline HS93

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Re: Building the Minimag
« Reply #66 on: February 10, 2011, 10:02:33 AM »
It was realy just to see if it would help madjackghengis from the post above mine. I prefer the mag as well for older engines, but some members also build more modern engines as well.

Peter
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Offline kvom

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Re: Building the Minimag
« Reply #67 on: February 10, 2011, 11:17:10 AM »
As someone who failed his electricity classes, can someone confirm my understanding of this?

The shaft of the minimag is connected to the shaft(?) of the IC engine and acts as a generator to provide energy to the engine's spark plugs.

I haven't attempted an IC engine yet, and won't likely do so for a while, but I enjoyed following along with the build.

Offline Bogstandard

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Re: Building the Minimag
« Reply #68 on: February 10, 2011, 01:07:11 PM »
Kvom,

You are quite correct.

The shaft thru the Minimag should be driven at half engine speed for a 4 stroke, either thru gears or chain from the engine crank or direct from the camshaft, which runs at half engine speed. But having said that, you could run it at crankshaft speed and use the 'wasted spark' method of ignition. For a two stroke engine, you run it direct from the crankshaft.

As the magnetic rotor turns inside the soft iron laminations, it produces energy which is stored in the coil. As the mechanical points on the magneto open, the charge inside the coil is released to the positive lead (red), which, if connected to a spark plug with the outside of it earthed to the magneto, a spark will be fired across the gap in the plug.

But if you hold onto the bare wired red lead with your fingers, and turn the rotor with your other hand, you end up with a curly haircut and brown trousers, as up to 10,000 volts is produced, and your body reacts to this high voltage with the previously mentioned symptoms.

Basically, it is a stand alone unit, driven by the engine, and produces it's own power to fire the spark plug, with nothing else required at all. Turn the engine, spark plug fires, engine continues running until it runs out of fuel, or the line to the spark plug is broken.

John

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Offline madjackghengis

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Re: Building the Minimag
« Reply #69 on: February 11, 2011, 10:06:49 AM »
John, Nick, Kvom, Peter and all, I've built Harleys for a living my whole life, as a side job most of it, with two decades in the Marines on active duty, and the single factor which most often causes breakdowns is batteries and electrical problems.  I've run magnetos on every bike I've had, as well as every kind of ignition available, and having the ignition in its own, dedicated package, is as close to getting a gas engine self-sufficient as a diesel is, as is practicable.  I can very easily make the points distributor or the electronic ignition distributor with hall effect parts, that are both in the engine's plans, but as John says, that leaves a battery in a box, and electronics in the box, and I want the reliability and stand alone capacity of a weedeater.  While a magneto on a full sized radial engine is perhaps shoe box sized for each of two, on an engine six or seven feet in diameter, and I'll be lucky if I can get the mag under half the size of the engine its self, simply being self standing is important to me, because it more closely matches reality.  In truth, I could use glow plugs and just eliminate the sparks, but then it would not be a timed, well running engine.  The engine which I use for my icon, is a 103 cu in Harley engine, with both an electronic distributor, and a centrifugally advanced magneto, and it has dual plugs, one set fired by electronics, the other pair fired by the distributor.  The electronics is a high tech bought piece of equipment, while the magneto set up is custom built into the engine, designed and built by myself, to match the specs of the electronics for timing and advance.  I don't know at this point, if I will be successful in my endeavor to build a nine cylinder magneto, but John's build has given me high hopes for the first time since I started the radial engine three or so years ago.  I have perhaps fifteen or twenty different kinds of magnetos on my shelves, dating from turn of the last century to brand new on engines, all working, and except for the very new ones, all doing it exactly the same way, with the new ones using a hall effect pickup built in to eliminate the points.  John's build shows me it's possible, so I will pursue it until it fires my engine, or I give up in failure, and put a distributor on the engine.  The magneto was among the greatest advances in i/c engine design, to this day, IMNHO, and it remains almost unchanged and equally effective more than a hundred years after it made its debut.  I like them, they fit my ideals:  "KISS, or keep it simple, stupid" and it looks possible.  What more could a model engineer ask for? :nrocks: :headbang: :beer: cheers, mad jack

Offline Bogstandard

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Re: Building the Minimag
« Reply #70 on: February 13, 2011, 07:18:41 AM »
Sorry this final post has taken so long, I had done a little bit too much , so I just took a nice steady rest.


The plate that covers the rotor was made to drawings, and as you can see, it had to have a big hole in it to give the rotor somewhere to stick out into.  I still thought it wasn't really swarf proof, so I turned up a disc with a very shallow spigot on it to fit into the hole and duly soft soldered it in.




Unfortunately, I had to a bit of bling as well. So my trademark of concentric circles and a bit of playing about with my latest digital toy, my rotary table, I came up with this.




The cable strain reliefs were made and fitted, just to stop the cable from flopping about all over the place due to vibration, and maybe later on causing a breakdown due to fracturing of the inner strands.

The test rig was then made up and the Minimag given a turning over. I tried to get a vid of it showing the sparks on the plug, but underneath the lights you couldn't see them hardly at all, and in the pitch black my camera wouldn't work, so my word will have to do.




So the unit has been built and tested, I will just have to wait until my big engine is built to see if it works OK on that.

I'm sorry I can't go into more detail, but this post has over run by over a week, so I must now get back to the flamelicker project, otherwise that will end up in a box somewhere.

I hope you have enjoyed the journey.


Bogs

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Offline John Stevenson

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Re: Building the Minimag
« Reply #71 on: February 13, 2011, 08:28:36 AM »
Grab hold of the plug lead, give it a whirl and get Mo to get a video of you dancing about.

Unless you do this we won't believe you  :poke:

John S.
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Offline NickG

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Re: Building the Minimag
« Reply #72 on: February 13, 2011, 10:35:34 AM »
 :lol:  You should have put a disclaimer on there John S in case bogs tries it and it all goes wrong!  :palm:
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Offline HS93

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Re: Building the Minimag
« Reply #73 on: February 13, 2011, 11:02:37 AM »
Tie a chew stick to the handle and bandit will turn it for you, that way you can hold the plug and camera :lol: :lol:

 :worthless:

    :ddb: :ddb: peter  :ddb: :ddb:
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Offline madjackghengis

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Re: Building the Minimag
« Reply #74 on: February 13, 2011, 11:35:27 AM »
Great close to a fine build log, your bit of "bling" looks good, and I'm willing to take your word on the spark, at the same time, I will echo John S.'s comments, and Nick's as well.  Is it possible for you to extrapolate some on how you found the "sweet spot" to set the points break at, and comment on the apparent lack of a condensor?  I have long assumed the condensor for these modern maggies with electronic control, are embedded in that part of the magneto, but that has been an assumption, because I didn't want to tear apart a working magneto and find out.  All the other magnetos I've worked on have had a condensor, and a bad one will definitely disable a working magneto.  I would also say your test rig for the magneto is very good and something I will have to emulate, not having at least three hands myself.  Thanks much for this very clear presentation.  :nrocks: :beer: cheers, mad jack