Magnetically Sprung Wobbler

[Ken I]

A simple double acting wobbler.

Basically a single cylinder version of my V4

Based on an idea by "spudevans" it uses a magnet rather than a spring.




Year: 2015

View attachment wobble1.dwg

View attachment wobble1.dxf

View attachment wobble1.pdf

View attachment wobble1-388.zip

 

[Anatol]

Ken
the magnet idea is interesting, how does it work in practice? I'm interested I these kinds of solutions - using materials, like high power magnets, that didn't exist 100 years ago.
"Basically a single cylinder version of my V4"
Where is the thread on your V4? Its double acting 4cyl, right? What is the advantage of so many cylinders? Does it outweigh the extra work in making them? This is a serious question, I'm interested in designs which maximize both efficiency and simplicity.
thanks!

 

[TonyM]

The one downside of this that I can see is that the magnet will attract and retain any steel particles / contamination and may eventually result in premature failure

 

[Ken I]

The V4 is there in the downloads - just keep going.
https://www.homemodelenginemachinist.com/threads/v4-oscillator-motor.29069/
The magnet is not in a position to attract bits and has not proven in the least troublesome.
The V4 is self starting and revesible - see added throttle.
Regards, Ken

 

[Ken I]

Just got round to making a video of the single - easier to understand what's going on - a dead simple engine - all metal to metal no seals - not even a piston ring.



Edit - for some stupid reason my voiceover starts by incorrectly calling it a single acting - its double acting.

Regards, Ken

 

[ACHiPo]

This is great. Thanks for sharing!

 

[ACHiPo]

Ken I (and others),
I've decided to tackle this over the coming weeks. I started by putting together a bill of materials and tool list for shopping, as while I have some basic things on hand, I'll need to pick up some stock and tools to finish the wobbler. About half way through the list I gave up on converting to imperial and embraced metric. Being in the US I'm much better tooled and instrumented in imperial than metric, but am a bit paranoid about making a conversion mistake, so will likely just buy the requisite metric tools as an early Christmas present to myself.

Here's the BOM I came up with. Do you see anything obviously missing? I'm planning to make the cylinder out of cast iron rather than Aluminum Bronze, so will use bronze for the piston. I'll be using drill rod (I think that's equivalent to silver steel?) I have some nicely figured wood, so plan to use that as the base instead of aluminum.

1​	3.25" x 1.75" x 3/8" mild steel plate (or aluminum?)	Body
1​	13/32" od x 2" phos bronze rod (or oilite?)	Bushings
1​	1" x 1" x 0.25" brass plate	Crankshaft weight
1​	1" x 1" x 0.25" brass plate	Rod gland
1​	1" x 1" x 0.25" brass plate	Cylinder head
1​	10 mm x 14 mm (bronze, brass, delrin)	Piston
1​	3/8" x 3/8" OD silver steel rod	attractor trunion
1​	1/2" x 1/2" x 1/4" thick brass plate	Big end bearing
1​	4 mm Silver Steel rod	Piston rod
1​	5 mm silver steel rod	Crank pin
1​	6 mm silver steel rod	Crankshaft
1​	2.25" x 2.25" x 3/4" thick brass plate	Flywheel
1​	8mm dia x 5mm rare earth magnet
1​	pneumatic air fitting
	M4 SHCS	Mounting bolts
	M3 set screws	Pneumatic plugs
	M2.5 set screws	Pneumatic plugs
	M2 x 7 mm SHCS	Pneumatic plugs
	M4 set screw	Flywheel

Is there a technical reason for the body to be mild steel? It seems 6061 aluminum would be easier to machine.


These are the required tools I don't already have:

1​	6.0 mm reamer
1​	8.0 mm reamer
2​	2 mm drills
2​	long 2 mm drills
2​	M2 taps
2​	M3 taps
2​	m2.5 taps
2​	1.5 mm drill
2​	1.8 mm drill
1​	M4 tap

Thanks!
Evan

 

[ACHiPo]

Oh, one other question. The drawing shows the bushings bored to 6.0 mm and 8.0 mm. It seems there ought to be a little clearance between the shafts and the bushing, especially if oilite is not used as bushing material?

 

[Ken I]

Evan, I used the reamed size - drill rod typically fits that very well but I turned the trunnion to suit. The magnets seem to be made 8mm but the Nickle plate makes them a tad over which pressed firmly into place and haven't moved since - but you can always locktite them in.
Aluminium will work fine for the body but probably won't be as durable - but given the amount of use may be of no consequence.

Never look up at mountain - just keep digging !

I like to work from a set of plans - usually my own - even when using others I normally redraw them as part of the process of getting the model "into my head" it also helps in understanding how errors may stack up / can be corrected etc. etc.

Make one part at a time and before you know it, its finished ! (having said that the odd catastrophe can be very disheartening)

Regards, Ken

 

[ACHiPo]

Off to the races!

Well, Merry Christmas to me! After multi-tasking on DrillsandCutters, McMaster-Carr, and Ebay between meetings, I've dropped close to $300 on this little endeavor. Of course I'll have enough material to make the 4 cylinder or something else should I choose to, plus I have the basic metric drills, taps, and die that can be used for other model making stuff from across the pond.

I decided to use 1/4"-20 bolts to secure the engine to the base, and a 1/4"-20 set screw for the flywheel. All the other fasteners will be metric. For the magnet I have a couple choices of what I already have--either 2@3/8" x 1/8" N42 or 1@1/4"x1/4". I think either option should provide a strong-enough pull to seal adequately, but would appreciate feedback.

I found a 2.75" diameter x 4" long hunk of 360 brass for a good price delivered on Ebay which should make many flywheels. I also found Al plate for the body and 5/8" x 12" 360 brass for the piston (although I may use the oil-filled 841 bronze that I bought for the bushings instead--again feedback would be appreciated).

I found a few errors in my original BOM and tool list. Here's what I ultimately ended up buying...

BOM
1	3/8" x 6" x 12" 6061 plate	Body
1	1" dia x 12" grey cast iron	Cylinder
	1/2" dia x 6.5" oilite rod	Bushings
1	1/4" T x 1.25"W x 24"L brass plate	Crankshaft weight
Rod gland
Cylinder head
Big end bearing
1	5/8" x 12" 360 brass rod	Piston	Sintered bronze instead?
1	4 mm drill rod A2	Piston rod
1	5 mm drill rod A2	Crank pin
1	6 mm drill rod A2	Crankshaft
1	8 mm drill rod A2	attractor trunion
1	2.25" dia x 4"L brass rod	Flywheel
1	Rare earth magnet--Either use 2x3/8 x 1/8" or 1/4" x 1/4"?
1	M3 pneumatic fitting
1	M3 needle valve		M3 thumbscrew
	M4 SHCS	Mounting bolts	Replace with 1/4-20
	M3 set screws	Pneumatic plugs	M3-0.5 x 4 mm black oxide
	M2.5 set screws	Pneumatic plugs	M2.5-0.45 x 4mm black oxide
	M2 x 7 mm SHCS	Cylinder head screws	M2x8 mm SS machine to length
	M4 set screw	Flywheel	Replace with 1/4-20
Tool List
1	6.0 mm reamer
1	8.0 mm reamer
1	10.0 reamer
12	2 mm drills
3	M2-0.4 taps	Taper, plug, and bottoming set
3	M3-0.5 taps	Taper, plug, and bottoming set
3	M2.5-0.45 taps	Taper, plug, and bottoming set
2	1.5 mm drill
2	1.8 mm drill
1	M3 die

Nothing succeeds like excess!

 

[ACHiPo]

PS let me know if I should start a separate thread to track the build, or if you're ok with me updating this one.

Thanks!

 

[Ken I]

Evan, The oil filled bronze is even better for the application.

Please continue with this thread - at least its got it off the ground for now.

Regards, Ken

 

[ACHiPo]

Evan, The oil filled bronze is even better for the application.

Please continue with this thread - at least its got it off the ground for now.

Regards, Ken

Ken,
The oil-filled bronze would be good for friction, but not sure if loctite will stick? It may be like HDPE or Delrin in that regard?

I'm also re-thinking using aluminum for the body. I realized during the night (while I was noodling on oil-filled bronze and loctite) the wear area around the port.

Oh well, it's good to have options!
Evan

 

[ACHiPo]

The materials arrived from McMaster-Carr yesterday, the tools from DrillsandCutters today. Still waiting on the big brass and aluminum chunks off Ebay. Should be here by Friday.

Off to the races!

 

[ACHiPo]

Let the games begin. Won't make too much progress today thru Sat, but hope to start in earnest Sunday.

 

[Ken I]

Merry Xmas Evan and good luck with your build.

Regards, Ken

 

[johnmcc69]

Looking forward to the build! Ken's designs & plans are very well done, complete, & easy to understand. I've recreated a couple of them in 3D (Just for fun). Of course I had to model this one up, it's a very cool little engine. Attached are assembly drawings with BOM (Bill Of Materials), approved & with Ken's blessings. I hope they help. When you finish this one, there is always the V4...

Let the chips fly!

John

 

[ACHiPo]

Looking forward to the build! Ken's designs & plans are very well done, complete, & easy to understand. I've recreated a couple of them in 3D (Just for fun). Of course I had to model this one up, it's a very cool little engine. Attached are assembly drawings with BOM (Bill Of Materials), approved & with Ken's blessings. I hope they help. When you finish this one, there is always the V4...

Let the chips fly!

John

John,
The model is great. I was struggling to print the DWG drawing large enough on my black and white laser printer. Your pdf prints perfectly.

I got started today...

...and get to start over tomorrow. I was so excited not to break 2.05 mm drills or the 2.5mm tap that I neglected to notice that the ports and oil hole are not on the center line.

The scribe marks show where the manifold and oil holes should be centered. You can also see an apprentice mark 0.100" from where the center drill should be (yeah, I have a 0.200" edge finder).

I also discovered I don't have an allen key for a 2.5mm set screw.

 

[ACHiPo]

Slightly better day today. Only slightly. All the holes are in the right location, but I misplaced my 2 mm drills. Figured I'd drill for the M3 set screws as deep as my stubby #40 (2.09 mm) would go then finish with a 1.8mm drill which promptly snapped. I was able to dig it out with a carbide burr and Dremel, backfilling with JB Weld. Not ideal, but as this is my "learner" model engine, I want to get all the way through it as I'm sure I'll screw more stuff up before I'm done.

After all the drama I found my 2 mm drills that I'd bought for the project--evidently they fell into the drawer when I put away the super glue I bought around the same time, as they were right there in the glue drawer with the JB Weld.

 

[johnmcc69]

I wouldn't scrap the first block. Put a plug where the oil hole would be & re-drill your air feed hole through it. You could move the oil feed hole, or not..
(You can always shoot a little oil at the bushing)

Guess what? Anybody who has built "anything", has broken taps, drills, & unfortunately, skin. Be careful!

You're doing fine. Keep going!

John