Author Topic: The Modular Tower Engine - a new, experimental design  (Read 1772 times)

Offline awake

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The Modular Tower Engine - a new, experimental design
« on: July 01, 2020, 09:59:09 PM »
With some fear and trepidation, I am introducing a model engine that I have designed, and which I am about half-way through building. The fear, of course, is that I have no idea yet if it will work! Attached are some CAD mockups of what it will look like. The first three pictures provide different angles on the fully assembled engine; the last picture has the ignition components removed so that you can see the details of the crank and cam gearing.

It may not be obvious at this point, but this design was inspired by Longboy's Side Shafter and Super Tee - though I hasten to say that he is not responsible for the gaffes and mistakes that I am no doubt making! The key element of Longboy's designs are the connection of multiple cylinders through gears rather than through a shared crankshaft. You may be thinking, "but this "modular tower" is a single cylinder design." Quite right ... but you may note that the design includes the placement of holes and features that will allow a second cylinder to be placed at the other end of the tower - at which point, the tower will be turned 90 degrees in a boxer configuration, but the cranks will be connected to each other via gearing with the cam shaft. Now you know why I call it the "modular" tower engine!

One major feature of the design is also the primary source of my fear and uncertainty about whether it will actually work: The main shaft, i.e. the shaft on which the flywheel resides, is actually the cam shaft rather than either of the crank shafts. I've never seen this done ... but I can't think of a reason it won't work. That may simply reflect my ignorance and inexperience! One issue could be the piston having to complete all four cycles for one revolution of the flywheel ... but then again, this is also true of the various Atkinson designs. I know the "Atkinson differential" is a beast to get running, but from what I can tell the "Atkinson cycle" seems to be reasonably easy to get running.

I welcome your comments and feedback, disparaging or encouraging alike! Stay tuned for the build ... I will provide pictures and plans as they become available.
Andy

Offline crueby

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Re: The Modular Tower Engine - a new, experimental design
« Reply #1 on: July 01, 2020, 10:24:34 PM »
Very interesting concept, hope it comes together well!

Offline Jasonb

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Re: The Modular Tower Engine - a new, experimental design
« Reply #2 on: July 02, 2020, 08:11:10 AM »
May need a heavier flywheel than would be usual for the size of engine a sit won't be turning as fast, other than that it's standard mechanicals so should run.

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #3 on: July 02, 2020, 07:33:42 PM »
Here's the first piece of the engine - the "tower," which functions as the foundation for everything else. Since there is nothing out of the ordinary in any of this, I did not take any pictures while machining - just the finished product.

A couple of notes. First, note that this is fully symmetrical - both ends, both sides, both faces are drilled/tapped/bored exactly the same way. This will allow the second cylinder to be added later one. Second, note that the bores are made to take the common-as-dirt 608 "skateboard" bearings - these will be used throughout to support the crank shaft and cam shaft ... which means that both shafts will be 8mm diameter.
« Last Edit: July 02, 2020, 08:28:52 PM by awake »
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #4 on: July 03, 2020, 07:01:21 PM »
May need a heavier flywheel than would be usual for the size of engine a sit won't be turning as fast, other than that it's standard mechanicals so should run.

Since the flywheel is under discussion, I'll go ahead and jump ahead to show that next. The pictures below show the finished flywheel and its tapered locking hub. The weight of the finished flywheel together with hub and screws comes out to 2.05 lbs. / 930g.
« Last Edit: July 03, 2020, 07:40:48 PM by awake »
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #5 on: July 03, 2020, 07:12:55 PM »
I haven't been taking pictures of making most of the parts for this engine, but I did take pictures of making the flywheel, since this was a new approach for me - the last flywheel I made used a key, but this one uses a tapered, split hub that tightens into the flywheel, and tightens onto the shaft at the same time. It uses 4 screws to attach the hub to the flywheel, and has two set screws to help push it out after it is tightened (the taper is gradual enough to lock). There is also an open hole in the hub that may be used for a starter mechanism - that is not yet worked out.

I first roughed out the blank for the flywheel (not shown). Then I set it aside and worked on the hub. This began as a slightly oversized blank with an 8mm / .315 hole bored through (attachment 1). Next I mounted this blank on an 8mm (.314+) arbor that was made between centers, affixing it with Loctite (attachment 2). I mounted this between centers in the lathe and finalized the size of the flange; then I put it in the mill vise, located the center, and drilled the various holes into the flange. I also tapped the two 6-32 holes that will hold setscrews to use to push the hub out after the taper locks (attachment 3). I put the arbor back between centers, set the compound to 4, and cut the taper (attachment 4).

With the hub finished (all except slitting the slot), I continued working on the flywheel. I left the compound set at the 4, mounted the flywheel, faced it off, and drilled it at 5/16". Then I began boring, using the compound still set at the same 4, until the hub just fit (attachment 5). Unfortunately, there was a bit more spring in the boring bar than I thought, so after the final spring passes, the hub fit loosely (attachment 6). :( Fortunately, there was a ready solution. I went ahead and cut the inset on the face of the flywheel, then faced off the middle hub area shorter until the taper fit snugly as desired (attachment 7).

Once the hub fit securely, I removed the flywheel and began to work on finishing the other side and the rim of the flywheel. I tried to do this with an arbor between centers, but to get access to the face, I would have needed a very long arbor ... and at 8mm diameter, a long arbor was too flexible. So instead I prepared an arbor using a piece of scrap stock in the lathe, cutting a 4 taper until I got the fit I wanted. I drilled and tapped for a central screw to secure it. I neglected to take pictures of this, but it worked well, allowing me to finish the turning of the flywheel. The final step was to mount it in the mill vise, locate the center, then drill and tap for the four 6-32 screws that attach the hub to the flywheel (attachment 8 ).

I also neglected to take pictures of the final operation on the hub - with it still loctited to the arbor, I put mounted one end of the arbor in a spin indexer and secured the other end with a center. I positioned it to the right orientation and used a 1mm slitting saw to cut the slot through. Then I heated the hub and arbor to break the loctite bond, pressed out the arbor, and cleaned it all up.

The previous post has pictures of the final results. I made the 8mm cam shaft and tried it out - the tapered hub tightens up and locks tightly. I spun it up to 2000 rpm in the lathe, and it seems to be free of vibration.

On to the next part ...
Andy

Offline crueby

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Re: The Modular Tower Engine - a new, experimental design
« Reply #6 on: July 03, 2020, 07:37:58 PM »
Great progress!  I love the taper-lock style hub, use it whenever I can make it fit the model, very stable and true.
 :popcorn: :popcorn: :popcorn:

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #7 on: July 03, 2020, 07:41:49 PM »
Great progress!  I love the taper-lock style hub, use it whenever I can make it fit the model, very stable and true.
 :popcorn: :popcorn: :popcorn:

Thanks! I just realized I forgot to include the plans for the flywheel - I added them to the post with the pictures of the finished part above.
Andy

Offline Art K

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Re: The Modular Tower Engine - a new, experimental design
« Reply #8 on: July 04, 2020, 02:59:07 AM »
I used the taper lock setup on my Upshur engine. Now I need to modify it so I can use the same starter on both of my engines and can dispense with the drill and hockey puck.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #9 on: July 05, 2020, 07:06:59 PM »
Next up for your viewing pleasure, the cylinder. No pictures of the making process - nothing unusual involved - so just the finished pictures. I notice that it has got a bit of rust on it - I had the garage door open the other day when it was raining, and I've been paying for it ever since. :(
« Last Edit: July 05, 2020, 10:30:07 PM by awake »
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #10 on: July 13, 2020, 12:08:57 AM »
Work has been rather demanding, so this is my first chance to get the next part finished. Attached are the plans and pictures of (most of) the crankshaft - I just realized I still need to make and fix the crank pin, but that will be a relatively simple operation.

The plans are in attachments 1 & 2; the finished parts can be seen in attachment 3; the full assembly in attachments 4 & 5; and assembled in place on the "tower" in attachments 6 & 7.

Finally, a picture showing things to come in attachment 8 - here it is with the camshaft (mostly done), tappet cage, and flywheel in place. The action of the gears is very smooth, with very little backlash.

Hopefully I will get some time this week to finish up another part or two ...
Andy

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #11 on: July 13, 2020, 12:40:07 AM »
I'm mostly not doing pictorials of the make - unless there is something noteworthy in terms of procedure. I'm not sure if this is altogether noteworthy, but I thought it might be helpful to show one way of handling the fixturing of the web. Attachment 1 shows the key idea in a nutshell, but obviously there has already been some work to get to this point.

First I stacked two plates, tacked the edges with a few quick bursts from the TIG welder, and machined them to a square just a bit larger than the OD of the web. I then located the center and drilled and bored to .500". I moved over .500" from the center and drilled the .201" hole for the crank pins. While I was at it, I also drilled 1/4" holes that represented the inside corners of the final shape - this made it a bit easier to handle the milling later on.

I then prepared a mandrel with a .499" stub and loctited the blanks in place. After the loctite set, I turned the blank round and to the final 1.496" OD. After removing the blanks from the mandrel and separating them, I had the two blanks shown in the foreground of the picture above. Unfortunately, I neglected to take any pictures of preparing the blanks up to this point.

With the blanks prepared, I needed a way to hold them securely and aligned along an axis in the mill. The answer was to put a piece of scrap stock into the mill, locate the center, drill and tap for 3/8-24", then move over .500" and drill and tap for 10-24. On the lathe, I used some more scrap to turn pins that screwed down into these holes, one with a .499" OD and one with a .200" OD. When I made the larger pin, I also drilled and tapped it for 1/4-20. Both pins were turned just a bit shorter than the total height of the stacked blanks. The results are shown in attachment 2. A button-head socket screw and a washer secured the blanks in the jig (attachment 3).

Now the milling could begin - with the help of the DRO, it was a relatively simple matter to rough out the cut-away parts, then come back for a final smoothing pass (attachments 4 & 5).

A bit of file work shaped the corners and eased the edges. Finally I needed to drill through the center of the larger part of the web for set screws; to secure the blanks in the mill vise, I put a scrap piece of .499" round through to align the blanks, and a couple of parallels to lift them up to clear the rounded inside corners (attachment 6).

Then it was a simple matter to find the center, locate the edges, drill the relief hole, and drill the tap drill through. I then loctited the hubs/gears in place, in which I had already cut the keyways, lining up the keyways as per the plans. After the loctite set up, I put the hubs back in the mill vise and finished drilling through and then tapping 6-32.

Next up ... maybe the cam shaft.
Andy

Offline Roger B

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Re: The Modular Tower Engine - a new, experimental design
« Reply #12 on: July 13, 2020, 11:00:37 AM »
Just catching up on this build  :ThumbsUp:  :ThumbsUp:  :wine1: I think that one of Jan Ridders designs had a geared down flywheel.
Best regards

Roger

Offline awake

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Re: The Modular Tower Engine - a new, experimental design
« Reply #13 on: July 13, 2020, 03:02:23 PM »
Thanks, Roger. If you happen to stumble across it, I'd be curious. Someone on HMEM pointed out an aircraft engine (by Continental) that had the propeller mounted on the crankshaft, so that gives me some hope that it will work. (Apparently the design worked, but commercially it didn't sell well.)
Andy

Offline Roger B

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Re: The Modular Tower Engine - a new, experimental design
« Reply #14 on: July 14, 2020, 12:11:37 PM »
This is the engine I had in mind. It featured, with the plans, in Maschinen im Modellbau. Jan's site has it in English:

http://www.ridders.nu/Webpaginas/pagina_1-cilinder_glas_4takt/1cil_glas_frameset.htm

He has quite a lot of fun designs  :)
Best regards

Roger