Sun-Planet Engine

I thought about it and for the system to work, the sun and planet gears must be a 1: 1 ratio. Anything else will bind. If there was a ring gear, then different gear ratios are possible. The ring gear would constrain the planet and then the connecting rod wouldn't need to be "fixed" relative to the planet.

I wanted the sun-planet gearing to be on the side of the engine, prominently displayed. The gearing in the middle is where I'm not thrilled where it's going. I'm not done, it just needs for design work.

...Ved.

Hi Verdestein,
I probably didn't explain my suggestion clearly.
First, whatever the ratio of the sun and planet gears, the crank rotataes once for each complete cycle of the piston. My suggestion is to fix the cam directly to the crank.
Second, I think you can have any ratio you like between the sun and planet gears. A large planet gear and a small sun gear will give you more shaft and flywheel speed. There should be only one rotational constraint between the crank and the shaft, so there is no reason why the system should bind.

Peter Twissell said:

There should be only one rotational constraint between the crank and the shaft, so there is no reason why the system should bind.

Click to expand...

True. But what I think you're missing Peter is that in Watt's design the big end of the connecting rod doesn't rotate relative to the planet gear. Re-watch the video of the 1785 engine. Notice that the planet gear doesn't rotate on its axis. It rotates around the sun, but relative to the con-rod, it doesn't rotate. If the two gears were different sizes this "fixed" relationship fails and a constraint would need removed.

Removing the constraint between the con-rod and the planet would then allow the system to freewheel and depending on the internal forces may or may not transfer the torque to the flywheel or it just may go to top or bottom dead center and get stuck. The addition of a ring gear on the outside would eliminate the freewheeling and still allow for the planet to rotate on its axis relative to the con-rod, but I don't have the tooling (or any desire) to make a ring gear.

I built this a few years ago, so I have some insight on actually working with sun-planet gearing systems.



It's been some years since I got my mechanical engineering degree, but I did specialize in kinematics when I was there. I believe your half way there. I just think there's one part you're missing that would prevent the system from working. (Or perhaps vise-versa and there's something I over analyzing.)

...Ved

To take your example: If the planet gear is freed from the connecting rod, the shaft and flywheel can spin freely while the rod stays fixed and the planet gear spins on its axis. This remains true for any ratio between the sun and planet gearss. If the planet gear is constrained to anything (whether it be the rod or a ring gear) then it will drive the sun gear.
I never completed a degree, but I'm not concerned with who is qualified or who is right. If any of us arrives at the correct answer, we all benefit from the knowledge.

After some consideration, I thought that inverting the engine would make it more visually appealing.

After also making the engine single acting (no crosshead) it looks much better. So at this point it's not a design to be junked (yet).

Looks good Ved! It looks much better this way. Do you think you still need to support the outboard shaft of the flywheel though?
How big/small is this going to be?

John

Looks good that way up.
Presumably, with the planet gears fixed to the connecting rod and the rod motion, the motion of the piston will be somewhat non sinusoidal at constant flywheel speed. This might give an advantage in changing motion ratio, smoothing the output torque.

johnmcc69 said:

Do you think you still need to support the outboard shaft of the flywheel though?
How big/small is this going to be?

Click to expand...

John,

I already thought about the flywheel. The flywheel (about 5" diameter) is huge for this engine. The reasoning for such a large flywheel is explained below about having enough energy to exhaust the gasses. The crankshaft is only 1/4" diameter. I could have gone bigger if I had a different set of gear cutters, but the only set I have is MOD 0.8 which is a 0.8mm gear pitch. You cannot see it from the picture/video, but there is an outboard ball bearing to support the flywheel. Also on the cam end, there are two ball bearings pressed into the same housing. That's why the bearing housing are thicker than they really need to be.

Currently the engine has a 1-1/8" bore and a 24mm stroke, making it a bit over square. The stroke is more or less set (again due to the gear cutters I have). The bore is still under consideration. I think if I make the bore under square, the relative longer stroke will give more "time" (percent volume vs percent of stroke) per stroke to let the gasses out.

On my last single acting engine, (https://www.homemodelenginemachinist.com/attachments/dsc01970-jpg.95019/) I made the inlet/exhaust porting too small. The engine would run, but much of the energy put into the engine was wasted getting the exhaust out. I don't want to make that mistake here.

Bore to stroke is a balancing act though. If I make the bore much smaller, the connecting rod will interfere with the frame and/or cylinder bore.

It's all part of design.

...Ved.

davidyat said:

Just let me know when the plans are ready. I need a new project after I finished with the Camgine.

Click to expand...

David,

As always, I highly suggest one waits until I actually build the first one. I have a book of Rudy Kouhoupt designed engine plans I can loan you if you're looking for a proven design. This way you can have a project and can wait the three to six months it will take me to build this engine. There's always changes I make on the fly and ideas that looked good on a computer screen suck in actuality.

The single piston on the Camgine! is an example. After I actually built it, I realized no matter how careful I was, there was no way I wasn't going to have the thing bind up. Hence I came up with the three piece piston. Also the plate on the back of the spherical bearing was added that wasn't in the original design.

I expect some issues with this design here.

If you really want the first issue of the design, I can send you the files outside of this forum (email or in person). Since we only live six miles apart, we can discover the design problems together! The choice is yours.

As usual with my designs, I'll post them here to the forum after I build the prototype for no charge.

BTW: (I think it's going to be named Contessa in tribute to my mother in law, Connie)

...Ved

I think I got the design more or less figured out. The cylinder turned into a casting, but that's ok with me.

The spool valving on Camgine! worked well, so I'm using a modified version of it here.

Next up is drawing set and bill of materials creation. But I'll do that another day.

...Ved.

I've been quiet on this project for a while. I've been working on it, but I'm not doing to build thread. (Not worth the considerable effort).

I have made progress though:

...Ved.

Ved,
I guess I'll just wait til you say it's a go. We'll swap out castings when I'm ready to start.
Grasshopper

Prior to starting the valve gear, I was analyzing the valve action and realized a simple eccentric cam wouldn't work. If it would it would work quite poorly.

This is because the pressure and exhaust ports would be open to the piston equal amounts on the stroke. The only way to make the system work would be to have the pressure and exhaust ports both open at the same time during a portion of the piston stroke which would be very wasteful.

I opened up my design from Camgine! and realized that the shape of the roller cam was essential. So I revised my simple eccentric to a vee shaped cam. This works out much better on the valve timing. I hope that the cam isn't too severe though.

Video is below...

https://www.youtube.com/pPFGxwVAd4Q

I still have to paint the engine, but I have a running engine. After it's painted, I'll post about it in the Showing Off section. But for now, in the next few posts, I submit the finished design files, drawings, etc....

PDF Drawing Set for the Sun-Planet Engine

More PDF Design Files (I can only attach 10 files per post)...

Here's the STL Files for the cylinder casting mold. Also attached is the 3D CAD model of the entire engine.

Enjoy...

Ved.

vederstein said:

Around 1770 or so when Watt was attempting to modify his pumping steam engine for rotary motion, the jerk (and he was an uber a-hole if you read some history...) couldn't get around an existing patent on the slider crank. So instead of paying royalties, he invented the sun and planet gearset to translate reciprocating motion into rotary motion.

After the slider crank patent expired, the sun and planet mechanism for this purpose died as well. I always thought it looked kind of neat.

So after my last failure, it's time to try another failure. I'm starting a design of a small steam engine with a sun and planet gearset.

Here's my first inital concept. It needs a lot more design, but it shows where I'm going...

Comments?

...Ved.

View attachment 113354

Click to expand...

HA ha haww! I laft out loud about your comment on Watt. Yes, I found out he was a thief like the scumbag edison. He took the inventions of his workers and called them his own. There are so many scumbags that do that, we all need to be very careful of those kinds of peeps. I tell my son to never give his ideas away to anyone who might take them. It's better to let good ideas die than allow scumbags to steal them. There are THOUSANDS of good people's inventions stolen by such people. I've workt for companies where the managers demanded that I give them some idea but when I ask what do I get out of it? (It IS MY work after all and I'm not being paid as an engineer, and I didn't do the thimking on company time), they angrily stalked away. Of course, they always get the bonus and credit for whatever. So to hell with them, I get the credit and the bonus or I won't give up MY ideas.

vederstein said:

True. But what I think you're missing Peter is that in Watt's design the big end of the connecting rod doesn't rotate relative to the planet gear. Re-watch the video of the 1785 engine. Notice that the planet gear doesn't rotate on its axis. It rotates around the sun, but relative to the con-rod, it doesn't rotate. If the two gears were different sizes this "fixed" relationship fails and a constraint would need removed.

Removing the constraint between the con-rod and the planet would then allow the system to freewheel and depending on the internal forces may or may not transfer the torque to the flywheel or it just may go to top or bottom dead center and get stuck. The addition of a ring gear on the outside would eliminate the freewheeling and still allow for the planet to rotate on its axis relative to the con-rod, but I don't have the tooling (or any desire) to make a ring gear.

I built this a few years ago, so I have some insight on actually working with sun-planet gearing systems.



It's been some years since I got my mechanical engineering degree, but I did specialize in kinematics when I was there. I believe your half way there. I just think there's one part you're missing that would prevent the system from working. (Or perhaps vise-versa and there's something I over analyzing.)

...Ved

Click to expand...

Is your bubble machine a piece of art or does it actually do something? Either way it is absolutely BEAUTIFUL! Thanx for showing it. I'd like to build one, do you have plans? I love that you are running it with a steam engine!