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Software Tools / Re: Playing with Blender For Artists (Bforartists) - Easier way to learn Blender?
« Last post by vtsteam on June 08, 2025, 08:27:42 PM »&pp
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Software Tools / Re: Playing with Blender For Artists (Bforartists) - Easier way to learn Blender?
« Last post by vtsteam on June 08, 2025, 08:22:57 PM »I ran into the same slight oddity of piston movement when researching Scotch yokes, recently. Apparently a Scotch yoke imparts a true sinusoidal movement to a connecting rod, but not so a conventional crank and conrod.
There's a nice animation somewhere online of two different color pens tracing these alternate versions of movement on top of each other so you can see the difference.
There's a nice animation somewhere online of two different color pens tracing these alternate versions of movement on top of each other so you can see the difference.
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Software Tools / Re: Playing with Blender For Artists (Bforartists) - Easier way to learn Blender?
« Last post by sorveltaja on June 08, 2025, 07:03:38 PM »Off-topic time again:
I remember trying out bones system back in the days in 3D studio max 2.5, but never really got it. In Blender, using bones doesn't seem to be any more straightforward either.
Rigging, or contacting the object(s) to bones or vice versa, and assigning IK (inverse kinematics) constraints when and where needed (like in some mechanisms to work as expected), is where I got totally lost.
In the meantime, this is as far as I got with bones:
No wonder that there are those (although only a few on Tube) who have looked for more easily approachable ways to get certain results by not using the bones system.
One such way is to use 'copy rotation/location'- and 'track to' constraints (not related to ones used with bones).
I've used the usual piston/piston rod/crankshaft combination - as it should have rather predictable behavior - to see how that works out, but stumbled on to one factor, that I never thought before - piston speed/velocity variation vs crankshaft rotation. Can't remember the exact search terms, but I looked on the net about it, and yes, it's a can of worms on its own, having plenty of equations to explain it.
I remember trying out bones system back in the days in 3D studio max 2.5, but never really got it. In Blender, using bones doesn't seem to be any more straightforward either.
Rigging, or contacting the object(s) to bones or vice versa, and assigning IK (inverse kinematics) constraints when and where needed (like in some mechanisms to work as expected), is where I got totally lost.
In the meantime, this is as far as I got with bones:
No wonder that there are those (although only a few on Tube) who have looked for more easily approachable ways to get certain results by not using the bones system.
One such way is to use 'copy rotation/location'- and 'track to' constraints (not related to ones used with bones).
I've used the usual piston/piston rod/crankshaft combination - as it should have rather predictable behavior - to see how that works out, but stumbled on to one factor, that I never thought before - piston speed/velocity variation vs crankshaft rotation. Can't remember the exact search terms, but I looked on the net about it, and yes, it's a can of worms on its own, having plenty of equations to explain it.
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Project Logs / Re: The Return of No. 83, a Hot Air Engine
« Last post by vtsteam on June 07, 2025, 02:59:51 PM »By comparison a new test today with cylinder #3 gave max RPM as 1254 while on the brake and maximum power as 0.489 Watts at 670 rpm. That makes cylinder #4 the winner.
But why? Not easily known, because there are two variables between them. #3 has a thick aluminum flange, and a copper end plate. Cylinder #4 has a thin steel flange and a stainless steel end plate.
As a guess though, the copper end plate has better heat transfer, so is probably not the problem for #3.
But the thicker aluminum flange likely does a better job of cooling the "cold" end of the displacer. I'm guessing that might be helpful with excessive heat from a furnace, but with only 100 watts going in to the furnace on the test rig. It may be doing too much cooling. Most small Stirling engine experiments use gas ring burners with far greater heat input.
The thick aluminum flange also effectively shortens the intermediate regenerative section of the displacer cylinder -- the no-man's land between hot end and cold end.
Well, just guesses.
But why? Not easily known, because there are two variables between them. #3 has a thick aluminum flange, and a copper end plate. Cylinder #4 has a thin steel flange and a stainless steel end plate.
As a guess though, the copper end plate has better heat transfer, so is probably not the problem for #3.
But the thicker aluminum flange likely does a better job of cooling the "cold" end of the displacer. I'm guessing that might be helpful with excessive heat from a furnace, but with only 100 watts going in to the furnace on the test rig. It may be doing too much cooling. Most small Stirling engine experiments use gas ring burners with far greater heat input.
The thick aluminum flange also effectively shortens the intermediate regenerative section of the displacer cylinder -- the no-man's land between hot end and cold end.
Well, just guesses.
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Project Logs / Re: The Return of No. 83, a Hot Air Engine
« Last post by vtsteam on June 07, 2025, 01:15:18 PM »I've finished making the test rig, and here's a photo of it, now all fastened down to a base. The electric furnace is trimmed down a little squarer and clamped. The engine is clamped, and the tachometer and scale are blocked up and screwed in place.
[ You are not allowed to view attachments ]
I did an initial test of No. 83 with displacer cylinder #4 and 100 watts input to the furnace and got a max RPM of 1300, and maximum power output of 0.575 watts at about 800 RPM.
Maximum free running RPM is probably higher, as the brake, even when loosened, weighs something. And that probably means the max power is also slightly under-represented. But it's good to have this initial set of figures anyway as a start on more accurate comparisons than I've done in the past.
[ You are not allowed to view attachments ]
I did an initial test of No. 83 with displacer cylinder #4 and 100 watts input to the furnace and got a max RPM of 1300, and maximum power output of 0.575 watts at about 800 RPM.
Maximum free running RPM is probably higher, as the brake, even when loosened, weighs something. And that probably means the max power is also slightly under-represented. But it's good to have this initial set of figures anyway as a start on more accurate comparisons than I've done in the past.
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Member Videos / OKMO Harley-Davidson Panhead V-Twin Engine Model R30
« Last post by Jim Dobson on June 05, 2025, 09:34:15 PM »OKMO Harley-Davidson Panhead V-Twin Engine Model R30
An absolute delightful (gasoline) petrol engine from OKMO Microcosm the level of detail in the engine is incredible for the size,
This is a miniaturised version of the Harley - Davidson Panhead engine, it is scaled down by 1:5, and the details of each part are truly representative.
The engine is 120MM long, 90MM wide, 110MM high and 1.1kg in weight and the displacement is 4.2ML.
The engine cylinder diameters are 13MM, and the stroke is 16MM. The fuel is petrol with oil added (gasoline). The igniter for the spark plugs uses three 1.5V small batteries (4.5V) for power supply.
This is a rather complex model, which is made of aluminum alloy, brass and stainless steel CNC.
This one of the most complex engines that OKMO Microcosm produce and manufacture. This is a very representative V-type dual-cylinder engine with an included angle of 45 degrees.
Panhead (1948~1965) The 1948 FL was unveiled with a new "Bontou" engine and the nickname Panhead which comes from the engine cylinder head (rocker covers) resembled cooking pans.
An absolute delightful (gasoline) petrol engine from OKMO Microcosm the level of detail in the engine is incredible for the size,
This is a miniaturised version of the Harley - Davidson Panhead engine, it is scaled down by 1:5, and the details of each part are truly representative.
The engine is 120MM long, 90MM wide, 110MM high and 1.1kg in weight and the displacement is 4.2ML.
The engine cylinder diameters are 13MM, and the stroke is 16MM. The fuel is petrol with oil added (gasoline). The igniter for the spark plugs uses three 1.5V small batteries (4.5V) for power supply.
This is a rather complex model, which is made of aluminum alloy, brass and stainless steel CNC.
This one of the most complex engines that OKMO Microcosm produce and manufacture. This is a very representative V-type dual-cylinder engine with an included angle of 45 degrees.
Panhead (1948~1965) The 1948 FL was unveiled with a new "Bontou" engine and the nickname Panhead which comes from the engine cylinder head (rocker covers) resembled cooking pans.
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Software Tools / Re: Playing with Blender For Artists (Bforartists) - Easier way to learn Blender?
« Last post by sorveltaja on June 05, 2025, 10:34:42 AM »I've experimented a bit with rebuilding meshes in Blender, as imported ones are not necessarily that easy to edit. For example, selecting vertex/edge/face loops or rings is usually impossible with such objects.
Comparison of imported mesh object (2800 vertices) vs rebuilt one (360 vertices):
[ You are not allowed to view attachments ]
Imported objects appear to have their origin points at 0,0,0 location (yellow dot on the left):
[ You are not allowed to view attachments ]
One way to set object's origin or pivot point to a desired location is to select a set of vertices/edges/faces in edit mode. 3D cursor (which acts as a temporary reference point) is then moved to the center/middle of those elements by Shift S → cursor to selected.
Next in the object mode right-click → set origin → origin to 3D cursor:
[ You are not allowed to view attachments ]
Some parts of imported mesh may not have so regular structure, though:
[ You are not allowed to view attachments ]
In this case, another way is to use a circular primitive object like UV sphere, which is scaled and moved to find approximate center point:
[ You are not allowed to view attachments ]
Comparison of imported mesh object (2800 vertices) vs rebuilt one (360 vertices):
[ You are not allowed to view attachments ]
Imported objects appear to have their origin points at 0,0,0 location (yellow dot on the left):
[ You are not allowed to view attachments ]
One way to set object's origin or pivot point to a desired location is to select a set of vertices/edges/faces in edit mode. 3D cursor (which acts as a temporary reference point) is then moved to the center/middle of those elements by Shift S → cursor to selected.
Next in the object mode right-click → set origin → origin to 3D cursor:
[ You are not allowed to view attachments ]
Some parts of imported mesh may not have so regular structure, though:
[ You are not allowed to view attachments ]
In this case, another way is to use a circular primitive object like UV sphere, which is scaled and moved to find approximate center point:
[ You are not allowed to view attachments ]
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Project Logs / Re: The Return of No. 83, a Hot Air Engine
« Last post by vtsteam on June 02, 2025, 08:05:49 PM »Have thought a lot the past day about the Scotch yoke. I like it okay on its own, but what is giving me pause is the need for some kind of sliding support to keep it from flopping sideways.
It seems there are twenty animated examples of simplified Scotch yokes online, to every one photo of an actual physical working version. In practically all of the animations, the authors haven't bothered to restrain the yoke with a guide. So almost none are practical.
I think the guide is where the real friction is going to be. I've come up with a limited number of choices for guides:
1.) the crank pin, or pin and roller, bearing would need side rims to keep the yoke trapped between them.
2.) the yoke is grooved and a pin bearing rides in the groove
3.) the yoke is constrained between rubbing guides on either side, or a grooved guide at the bottom.
4.) the pushrod is flattened or square sectioned with a bushing to fit
5.) an additional pushrod above or below the active one is used as a second guide
6.) a pivot at the bottom of the yoke and a pivoting connection to the pushrod restrains the yoke (actually, this is technically a quick return linkage, not a Scotch yoke.) It is non linear in stroke speed. Hence the name.
I don't know. The #6 appeals to me because of the elimination sliding guides, but would the non-linear stroke be an advantage or disadvantage? And should it be favor the slower motion toward the hot or cold end of the displacer cylinder?
It seems there are twenty animated examples of simplified Scotch yokes online, to every one photo of an actual physical working version. In practically all of the animations, the authors haven't bothered to restrain the yoke with a guide. So almost none are practical.
I think the guide is where the real friction is going to be. I've come up with a limited number of choices for guides:
1.) the crank pin, or pin and roller, bearing would need side rims to keep the yoke trapped between them.
2.) the yoke is grooved and a pin bearing rides in the groove
3.) the yoke is constrained between rubbing guides on either side, or a grooved guide at the bottom.
4.) the pushrod is flattened or square sectioned with a bushing to fit
5.) an additional pushrod above or below the active one is used as a second guide
6.) a pivot at the bottom of the yoke and a pivoting connection to the pushrod restrains the yoke (actually, this is technically a quick return linkage, not a Scotch yoke.) It is non linear in stroke speed. Hence the name.
I don't know. The #6 appeals to me because of the elimination sliding guides, but would the non-linear stroke be an advantage or disadvantage? And should it be favor the slower motion toward the hot or cold end of the displacer cylinder?
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Metal Stuff / Re: How Not to Hate Casting Aluminum
« Last post by vtsteam on June 01, 2025, 03:21:49 PM »I did a little research online, and I believe that the extrusion which created the worst muffin ingots was called an 8020 1515 linear rail, and it seems these are typically 6063 -T6 alloy. Good to know in general.
My guess at the alloy from the bell housing that made the best looking, very low shrinkage muffins is either AlSi12, aka A413 (US)and D6 (GB), also used for pistons. Or AlSi18 aka A390, which has the lowest shrinkage I can find, of the aluminum casting alloys.
6063 has a thermal elongation coefficient of 23, A413 is 21, and A390 is 18. (I'm leaving out units here, but you get the idea.
This is all of interest to me presently because I'm considering trying a cast iron piston in an aluminum cylinder, and thermal behavior is what I think will make or break that combo.
My guess at the alloy from the bell housing that made the best looking, very low shrinkage muffins is either AlSi12, aka A413 (US)and D6 (GB), also used for pistons. Or AlSi18 aka A390, which has the lowest shrinkage I can find, of the aluminum casting alloys.
6063 has a thermal elongation coefficient of 23, A413 is 21, and A390 is 18. (I'm leaving out units here, but you get the idea.
This is all of interest to me presently because I'm considering trying a cast iron piston in an aluminum cylinder, and thermal behavior is what I think will make or break that combo.
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Project Logs / Re: The Return of No. 83, a Hot Air Engine
« Last post by vtsteam on June 01, 2025, 03:09:29 PM »I'm seeing some wear again in the displacer rod/bushing. I feel that the bushing is too short, compared with what I'd now like. Or at least with the side forces on it, considering the shortish connecting rod I now have for its throw.
However, increasing the bushing length isn't possible without major reconfiguration of the engine. I'd have to move the crankshaft, supports, bearings, and flywheel aft, and remake all of the rods. I also don't really want to increase the length of the engine for other reasons.
Instead, I'm considering a few more compact linkage systems to reduce the side forces on the displacer pushrod. Also making a Teflon displacer bushing. Among possible alternative linkages used on hot air engines are the Scotch yoke, the pivoted Scotch yoke, and the Ross linkage. I can probably add at least one of these without moving the crankshaft, and they might also allow a longer bushing and pushrod as well as reduced side forces.
The penalty is more friction and more moving mass. But I think it's a trade-off I want to make, because in future I'd like to try an axial regenerator in the displacer cylinder. That would require very accurate linear motion. Though presently working fine, I think there's too much play now in the bushing to fit anything in the small clearance space around the displacer without interference.
However, increasing the bushing length isn't possible without major reconfiguration of the engine. I'd have to move the crankshaft, supports, bearings, and flywheel aft, and remake all of the rods. I also don't really want to increase the length of the engine for other reasons.
Instead, I'm considering a few more compact linkage systems to reduce the side forces on the displacer pushrod. Also making a Teflon displacer bushing. Among possible alternative linkages used on hot air engines are the Scotch yoke, the pivoted Scotch yoke, and the Ross linkage. I can probably add at least one of these without moving the crankshaft, and they might also allow a longer bushing and pushrod as well as reduced side forces.
The penalty is more friction and more moving mass. But I think it's a trade-off I want to make, because in future I'd like to try an axial regenerator in the displacer cylinder. That would require very accurate linear motion. Though presently working fine, I think there's too much play now in the bushing to fit anything in the small clearance space around the displacer without interference.