Model Engine Maker

Engines => Your Own Design => Topic started by: Plani on September 02, 2017, 08:18:48 PM

Title: Rocker V Stirling Engine
Post by: Plani on September 02, 2017, 08:18:48 PM
Hello all

This time I would like to introduce my Stirling engine Project. It is actually not my invention. This type of Stirling engine was was designed by Andy Ross who is in my opinion a real master of building Stirling engines. A while back I got in touch with him about some Stirling related questions an he kindly helped me and also provided copies of articles he wrote about his engines. And a couple days later I received a package containing two nice deep drawn stainless steel cups:

(https://s20.postimg.cc/g51spww8d/Rocker_V_00.jpg)

This was the starting point for this project. And since I made the drawings for it, I think it's ok to put it under my own design...

The Engine is an alpha Stirling. It incorporates a rocking compression piston and will be balanced like a 90 Vee twin. Therefore it's called a Rocker V. The swept volume is 9cc.

And this is how I think the whole thing should look like:
(https://s20.postimg.cc/x30tbr5m5/Rocker_V.jpg)

(https://s20.postimg.cc/s5n8qn3n1/Rocker_V_Cut.png)

Plani
Title: Re: Rocker V Stirling Engine
Post by: yogi on September 02, 2017, 09:32:26 PM
Very cool Plani!  8)
Looking forward to see the engine come to live.  :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Ye-Ole Steam Dude on September 02, 2017, 10:45:00 PM

Add me to the list of followers on this build.

Thomas
Title: Re: Rocker V Stirling Engine
Post by: Dave Otto on September 03, 2017, 12:30:32 AM
Looks like an interesting design, looking forward to seeing it take shape.


Dave
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on September 03, 2017, 12:57:04 AM
Nice looking design Plani.  A while back a friend gave me the casting pictured below and assorted parts including two drawn cups also. Maybe you know something about this engine as well. I do have some written plans but not a lot in the way of drawings.

Bill
Title: Re: Rocker V Stirling Engine
Post by: Jo on September 03, 2017, 07:37:08 AM
Nice, I still have to find a Stirling to add to my list of engine to build so I will be following along  :).

Jo
Title: Re: Rocker V Stirling Engine
Post by: Ian S C on September 03, 2017, 12:38:57 PM
Bill, that B 20 kit of Andy Ross's turns into a powerful little motor, although in his book "Making Stirling Engines" he does say that some people were having difficulties building the motor. If you have any problem, give him an E-mail, I hear he is more than happy to help.
Plani, this motor looks very interesting, I'll be watching this one.
Ian S C
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on September 03, 2017, 01:41:11 PM
Thanks Ian. Looks like I need to find the book and do some reading up on it.

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on September 03, 2017, 08:11:43 PM
Thank you all for the kind comments.

Bill, you are lucky! This is a B20 engine kit made by Andy Ross. Here is the one of Andy himself:
https://www.youtube.com/watch?v=402tNFGY23Q (https://www.youtube.com/watch?v=402tNFGY23Q)
The intention of these kits was to get people to do experiments and development work on small Stirling engines. But this turned out to be difficult and so the production of these kits was discontinued. 
As Ian said, it will make a powerful little Stirling engine. And if you have any particular questions about the kit, I think too Andy Ross will be helping you.

Plani
Title: Re: Rocker V Stirling Engine
Post by: Ye-Ole Steam Dude on September 03, 2017, 08:20:52 PM
Thank you all for the kind comments.

Bill, you are lucky! This is a B20 engine kit made by Andy Ross. Here is the one of Andy himself:
https://www.youtube.com/watch?v=402tNFGY23Q (https://www.youtube.com/watch?v=402tNFGY23Q)
The intention of these kits was to get people to do experiments and development work on small Stirling engines. But this turned out to be difficult and so the production of these kits was discontinued. 
As Ian said, it will make a powerful little Stirling engine. And if you have any particular questions about the kit, I think too Andy Ross will be helping you.


Plani


Just watched the video and it appears to be a very nice and powerful engine

Thomas
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on September 03, 2017, 09:52:50 PM
Thanks for that link Plani. I've had this thing sitting around for a while, maybe I need to pay it more attention :)

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on September 04, 2017, 07:57:24 PM
Yes Bill, I think you certainly should  ;)      :stickpoke:

Plani
Title: Re: Rocker V Stirling Engine
Post by: Plani on September 04, 2017, 08:16:28 PM
But now lets get started with making parts. I started with the flywheel. Luckily there was a disc of free cutting steel in the cutoffs bin of just about the right diameter. That made life really easy. Unfortunately I forgot to take a picture while turning the Flywheel  :facepalm:

So we start where the spokes are milled:
(https://s20.postimg.cc/6sxttd73h/Rocker_V_01.jpg)

The spokes where then rounded with a radius cutter:
(https://s20.postimg.cc/mbqocqq0d/Rocker_V_02.jpg)

Then the Flywheel was was chucked on its hub to drill and ream the center hole:
(https://s20.postimg.cc/98zn77p65/Rocker_V_03.jpg)

And this is the finished part:
(https://s20.postimg.cc/l86k0s5d9/Rocker_V_04.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on September 04, 2017, 08:45:58 PM
That certainly turned out well!! Very nicely done.

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on September 13, 2017, 08:19:21 PM
Thank you Bill  :cheers:

I went on with some con rods.

The conrod for the expansion piston was fixed on a piece of aluminum to get it it contoured:
(https://s20.postimg.cc/o4okrhhd9/Rocker_V_05.jpg)

The seat for the big end bearing milled:
(https://s20.postimg.cc/s3lsab60d/Rocker_V_06.jpg)

The finished part:
(https://s20.postimg.cc/t4m0zfmzx/Rocker_V_07.jpg)

The machining pictures of the short con rod didn't turn out usable :facepalm2:
But the part itself is ok  ;D:
(https://s20.postimg.cc/9isyphv71/Rocker_V_08.jpg)

(https://s20.postimg.cc/f8979t1d9/Rocker_V_09.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: tvoght on September 13, 2017, 09:33:17 PM
I am following along on the build of this interesting engine, Plani. Good work so far!

--Tim
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on September 14, 2017, 12:50:21 AM
More nice looking parts Plani. I am anxious to see things start going together and then running of course.

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on September 18, 2017, 07:57:19 PM
Thank you Tim and Bill  :cheers:

Bill, I'm anxious too. These Stirling engines tend to have some "personality" and sometimes it's hard to get them to run. Although on this one I'm pretty confident since it's a proven design to which I made only minor changes  :). So we shall see.....

I went on with the bell crank.
Some aluminum stock was milled to thickness:
(https://s20.postimg.cc/thmnkmwj1/Rocker_V_10.jpg)

Then the 3 holes were drilled and the piece was bolted down using some allen screws to mill the outer contour:
(https://s20.postimg.cc/pp354wh0t/Rocker_V_11.jpg)

In the same setup the relief for the web was milled:
(https://s20.postimg.cc/w4261knql/Rocker_V_12.jpg)

Since the holes are symmetric and only the contour of the web is uneven the same arrangement could be used to mill the relief on the second side:
(https://s20.postimg.cc/xs1bg81m5/Rocker_V_13.jpg)

Finished part:
(https://s20.postimg.cc/8aiwwmjvx/Rocker_V_14.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: yogi on September 19, 2017, 11:07:49 PM
Looking good!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Plani on September 25, 2017, 08:17:51 PM
Thank you Yogi :cheers:

Next up, The cylinder block:
It all started with some 50mm by 50mm EN AW 6082 aluminum stock which was surfaced first to get a proper datum:
(https://s20.postimg.cc/h87csigbx/Rocker_V_15.jpg)

Then the relief was milled using a disc cutter:
(https://s20.postimg.cc/apj3tbtil/Rocker_V_16.jpg)

Next the cylinder bores were roughed out, making them 1mm undersize:
(https://s20.postimg.cc/hh9iw6ii5/Rocker_V_17.jpg)

Then the contour of the backside was milled:
(https://s20.postimg.cc/62d1rk65p/Rocker_V_18.jpg)

And after milling the outer contour, the holes for the bearing stands and the bearing of the bell crank were drilled and tapped:
(https://s20.postimg.cc/yqpzus8bx/Rocker_V_19.jpg)

First side done:
(https://s20.postimg.cc/t155wqcrx/Rocker_V_20.jpg)

The part is then turned over and brought to its final hight:
(https://s20.postimg.cc/gwpwfqzvx/Rocker_V_21.jpg)

And then most of the aluminum is cut away to form the expansion cylinder:
(https://s20.postimg.cc/akar5wwtp/Rocker_V_22.jpg)

Going round and round a couple times to mill the spherical part of the cylinder after drilling and tapping the holes for the cooler:
(https://s20.postimg.cc/ff91hxkj1/Rocker_V_23.jpg)

And the last operation is to bore out the bores with a fine feed to get a straight and round bore with a good surface finish. Here the expansion bore is done the compression bore is still to go:
(https://s20.postimg.cc/xjc22ki7h/Rocker_V_24.jpg)

The finished part, ready to be shipped to a specialized company to have it hard coat anodized:
(https://s20.postimg.cc/yvtr4gfn1/Rocker_V_25.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: Dave Otto on September 26, 2017, 12:35:35 AM
Very nice!

Dave
Title: Re: Rocker V Stirling Engine
Post by: Plani on October 09, 2017, 10:40:07 AM
Thank you, Dave  :cheers:

The next substantial part of the engine is the cooler. It's made from the same bar stock as the cylinder block.

First it was faced and the outer contour was milled:
(https://s20.postimg.cc/hm9nieast/Rocker_V_26.jpg)

The holes for the hot cap spotted and drilled. They will be tapped later:
(https://s20.postimg.cc/i98k7x7ot/Rocker_V_27.jpg)

Some material from the bore removed:
(https://s20.postimg.cc/g5y5097vx/Rocker_V_28.jpg)

Roughing out the contour of the cooler:
(https://s20.postimg.cc/5my5b357x/Rocker_V_29.jpg)

Since I didn't have a suitable t-slot cutter at hand, I made a fly cutter to machine the cooling fins:
(https://s20.postimg.cc/6uc33avcd/Rocker_V_30.jpg)

First side done:
(https://s20.postimg.cc/t7jtq3wa5/Rocker_V_31.jpg)

The part turned over and removing excess stock:
(https://s20.postimg.cc/oj3tux73h/Rocker_V_32.jpg)

The cylindric part of the bore machined:
(https://s20.postimg.cc/tcnkzs3l9/Rocker_V_33.jpg)

The spheric part of the bore was milled using a ball end mill:
(https://s20.postimg.cc/xkmym9uel/Rocker_V_34.jpg)

And finally, the o-ring groove and the port was milled and the holes for the bolts drilled:
(https://s20.postimg.cc/zdpvalfl9/Rocker_V_35.jpg)

Finished part:
(https://s20.postimg.cc/85ofpigbx/Rocker_V_36.jpg)

The edges of the port will be rounded, to allow for a good gas flow:
(https://s20.postimg.cc/xczbprjfx/Rocker_V_37.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: cfellows on October 09, 2017, 06:24:09 PM
Wow, that was some heavy machining.  The result sure turned out nice!

Chuck
Title: Re: Rocker V Stirling Engine
Post by: Perry on October 09, 2017, 07:44:27 PM
WOW.. I'm watching this too.. That will be quite powerful stirling. Does it take long time to program your cnc to do this? Now with almost zero free time I sometimes wish for a benchtop cnc.. Keep on good work!
Title: Re: Rocker V Stirling Engine
Post by: Ian S C on October 10, 2017, 02:50:34 AM
with everthing else OK, the part that I find will hold up starting is the fit of the piston in it's bore, and now days i seem to get that fairly right, I used to make the fit too close, and it took a bit of running in to get it free enough to over cme friction, then a few hours running with heat to get full power, but once up to full power there is little or no wear to the bore or piston for the life of the motor. Friction is the killer of these motors, followed by air leaks.
Ian S C
Title: Re: Rocker V Stirling Engine
Post by: Hugh Currin on October 10, 2017, 04:18:07 AM
Plani:

Beautiful machining. Thanks for the build thread.

with everthing else OK, the part that I find will hold up starting is the fit of the piston in it's bore, and now days i seem to get that fairly right, I used to make the fit too close, and it took a bit of running in to get it free enough to over cme friction, then a few hours running with heat to get full power, but once up to full power there is little or no wear to the bore or piston for the life of the motor. Friction is the killer of these motors, followed by air leaks.
Ian S C

Ian:

Is it then feasible to lap the piston to the bore? I've thought this would give too much space and leakage. But from what you said....

Thanks.

Hugh
Title: Re: Rocker V Stirling Engine
Post by: Ian S C on October 10, 2017, 11:27:06 AM
After lapping the cylinder, I lap the piston out of the cylinder until it just fits the cylinder, and when it will slide through the cylinder, (I usually add the weight of the con rod) under it's own weight, then all but stop when the end of the cylinder is blocked off, it then should be about right. I find the final fit is more by feel than measurement.
Ian S C
Title: Re: Rocker V Stirling Engine
Post by: Hugh Currin on October 10, 2017, 03:00:28 PM
After lapping the cylinder, I lap the piston out of the cylinder until it just fits the cylinder..........

Thanks Ian.

Hugh
Title: Re: Rocker V Stirling Engine
Post by: Plani on October 10, 2017, 08:11:27 PM
Thank you gentlemen for the kind comments! It's very much appreciated!  :cheers:

Perry, I have a CAM program on my shop-computer. So when I'm lucky enough to hit the right buttons, it actually doesen't take very long to make a program for the mill. In this case I imported the solid model from the CAD and made the program from there.

Ian/Hugh, the cylinders of this engine will be hard coat anodized. The aluminum oxide which is formed on the surface in this process is very hard and a little porous. These pores will be treated (by the company who does the anodizing) with ptfe in order to get a surface with very low friction. And therefore I don't want to do any more machining on these surfaces except for maybe a little bit of honing in order to get the ptfe to the surface.
The piston skirt of the expansion piston will be made from cast iron and the goal is to machine it 0.01mm smaller than the bore...we shall see..... Because as Ian pointed out, the fit of the piston should be so that the piston under its own weight doesen't go anywhere when the cylinder is blocked off, but when open it should fall right through.
And the compression piston will get a lip seal consisting of some plastic bearing material which is also supposed to have a very low coefficient of friction.
I haven't done this before, and I'm really curious to see how that will work...

Plani
Title: Re: Rocker V Stirling Engine
Post by: 10KPete on October 10, 2017, 09:39:09 PM
Remember that Anodizing aluminum is an additive process in that the oxide is 'grown' on the surface of the aluminum.

Talk with your plater about time/thickness for your parts so get the proper fit after Anodizing.

Pete
Title: Re: Rocker V Stirling Engine
Post by: Ian S C on October 11, 2017, 03:48:08 AM
You could drop an e-mail to Andy Ross in the states, he's been there and done that as far as coatings and anodizing of cylinders and pistons.
I just keep away from aluminium on these parts, and try to stick to cast iron for both bore and piston, although if the size is right I use the tube from inside a shock absorber, because this is round, parallel, and highly polished.
Ian S C
Title: Re: Rocker V Stirling Engine
Post by: Plani on October 11, 2017, 08:13:29 PM
Thank you for the input Pete. I'm aware or this fact, actually I had to specify the thickness of the oxide layer (in micrometers :o) to the company who is doing this. So I think this will be done quite accurately. And also for this reason I will fit the piston to the cylinder, so it doesn't really matter if the bore is a little bit smaller.

Ian, I was in touch with  Andy Ross. He provided the articles he wrote about these engines.

Plani
Title: Re: Rocker V Stirling Engine
Post by: 10KPete on October 11, 2017, 10:48:36 PM
 :ThumbsUp: :ThumbsUp:

Pete
Title: Re: Rocker V Stirling Engine
Post by: Plani on October 24, 2017, 02:23:00 PM
This time I made the ring to which the hot cap will be soldered later.

Some mild steel was faced and drilled:
(https://s20.postimg.cc/eu1yvdrrx/Rocker_V_38.jpg)

The hole was then opened up, including the step for the hot cap:
(https://s20.postimg.cc/7e2p9lji5/Rocker_V_39.jpg)

Then the other side was faced and the diameter turned as well as a groove for the O-ring:
(https://s20.postimg.cc/rzhh0x8ml/Rocker_V_40.jpg)

Finally the part was taken to the mill to drill the holes for the bolts:
(https://s20.postimg.cc/am76m25lp/Rocker_V_41.jpg)

Done:
(https://s20.postimg.cc/z1fenowz1/Rocker_V_42.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: Plani on November 04, 2017, 04:24:09 PM
Just a very brief update. That's what the cylinder looks like hard coat anodized. I actually think, it looks ok.
(https://s20.postimg.cc/vnjf5sabx/Rocker_V_43.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on November 04, 2017, 05:01:49 PM
Looks cert good to me plani. Did you have it done commercially?

Bill
Title: Re: Rocker V Stirling Engine
Post by: crueby on November 04, 2017, 05:27:44 PM
That looks fantastic. Does the anodizing hold up on the interior of the cylinder okay? (is that the 'hard coat' part of the name? )
Title: Re: Rocker V Stirling Engine
Post by: Plani on November 05, 2017, 08:43:58 AM
Bill, as far as I know there are some nasty chemicals involved in this process as well as very high electrical currents. Therefore I had the anodizing done by a specalized company.

crueby, time will tell....although I'm optimistic since half of the aluminum oxide layer grows into the surface and the other half is added on top of the surface. So this should hold up quite well. But we will see once the engine is running...

Plani
Title: Re: Rocker V Stirling Engine
Post by: yogi on November 05, 2017, 09:10:23 PM
Beautiful looking part Plani!!!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Plani on December 17, 2017, 04:39:02 PM
Thank you Yogi  :cheers:

With the cylinders finished I could now move on to the Pistons. I usually do it in this order, because it's easier to fit the piston to the cylinder than the other way around.
The compression piston on this engine consists of three parts. I started with the body of the piston:
(https://s20.postimg.cc/voqvtvpr1/Rocker_V_44.jpg)

After turning the first side, the part was left on the stock and a slot was cut for the bell crank:
(https://s20.postimg.cc/6ipxn11bh/Rocker_V_45.jpg)

Then the first side was faced, the hole for the pin was drilled and reamed and the outer contour was milled:
(https://s20.postimg.cc/9pkh6nth9/Rocker_V_46.jpg)

In order to get the second side square to the others, a parallel was stuck into the slot and indicated:
(https://s20.postimg.cc/l1x2off0t/Rocker_V_47.jpg)

The part was then cut off the stock and the second side was machined using a square collet:
(https://s20.postimg.cc/7l045kzkd/Rocker_V_48.jpg)

Piston body completed:
(https://s20.postimg.cc/4pn0za0vh/Rocker_V_49.jpg)

To hold the lip seal on the body a disc was turned:
(https://s20.postimg.cc/6u7e0da7x/Rocker_V_50.jpg)

Then the lip seal was made. For this I used IGUS W300 which is a plastic bearing material which is supposed to have a little coefficient of friction and also little wear:
(https://s20.postimg.cc/ebglezzkt/Rocker_V_51.jpg)

I first turned the outside diameter of the seal cylindrical and 0.05mm bigger than the bore. Then a 8 taper was machined on the inside and the outside with a wall thickness of 0.25mm. And finally the seal was parted off:
(https://s20.postimg.cc/8naao55j1/Rocker_V_52.jpg)

The assembled compression Piston:
(https://s20.postimg.cc/t7f4mmdkd/Rocker_V_53.jpg)

By sticking it into the cylinder and moving it by hand, it seems to be a little "stiff". Maybe the 0.05mm oversize was a bit much. I will reevaluate this once the whole mechanism is in place an I can see how it runs.

Plani
Title: Re: Rocker V Stirling Engine
Post by: yogi on December 20, 2017, 04:12:52 AM
Fascinating!!!
This is so cool! Looking forward to see your next installment...  :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on December 20, 2017, 11:56:05 AM
Still following along as well Plani. The piston assembly looks great  :ThumbsUp:

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on January 10, 2018, 08:21:53 PM
Thank you for the kind comments Yogi and Bill  :cheers:

Next I made the bearing posts. Therefore some aluminum stock was cut off:
(https://s20.postimg.cc/wbl0pq34d/Rocker_V_54.jpg)

The parts were milled to a T-shape:
(https://s20.postimg.cc/cgyz3lvml/Rocker_V_55.jpg)

Then the inner contour was milled:
(https://s20.postimg.cc/o62yrjrq5/Rocker_V_56.jpg)

And finally the parts were bolted to some scrap aluminum bar to mill the outer contour:
(https://s20.postimg.cc/639w0cbb1/Rocker_V_57.jpg)

Done:
(https://s20.postimg.cc/vytmjj5f1/Rocker_V_58.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: PJPickard on January 11, 2018, 10:54:15 AM
Excellent work on this and yes Mr. Ross knows his Stirling engines! He has a couple on youtube that I would love to get the plans for.
Title: Re: Rocker V Stirling Engine
Post by: Perry on January 13, 2018, 08:31:45 PM
Very interesting engine and build log, I especially like the lip seal type piston. Lots of inspiration  :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Plani on January 21, 2018, 08:17:37 PM
Thank you guys for the kind comments! It's very much appreciated!  :cheers:

A short update about the bearing block of the bell crank today.
The upper contour was milled from bar stock. The slot was also milled in this position, using an endmill going back and forth:
(https://s20.postimg.cc/irop7qye5/Rocker_V_59.jpg)

While still on the stock, the part was tilted to its side to its side to mill the radius and drill and ream the hole for the pin:
(https://s20.postimg.cc/zfg7a98l9/Rocker_V_60.jpg)

It was the cut off the stock to mill the final thickness and the recess on the backside:
(https://s20.postimg.cc/ypxexw0bx/Rocker_V_61.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: Plani on February 01, 2018, 09:12:32 AM
Next part to make was the center piece of the expansion piston.
This is the drawing I made for this:
(https://s20.postimg.cc/v5aq66skd/Rocker_V_62.jpg)

On the left side will be the displacer dome installed and on the right side the piston skirt. It was actually pretty easy to design it like this, but it would been rather difficult to make it and there would also be no way to fit the pin of the small end once the piston skirt is installed. So I decided to make two parts. First The center piece:
(https://s20.postimg.cc/kigx0rs4t/Rocker_V_63.jpg)

And then the small end bearing:
(https://s20.postimg.cc/964bizyvh/Rocker_V_64.jpg)

The two pieces will be bolted together using a M3 allen screw which will be loctided into the center piece:
(https://s20.postimg.cc/yownw0app/Rocker_V_65.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: yogi on February 01, 2018, 11:17:22 AM
You got some good looking parts there Plani!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
I had to go back to your first post to look at the sectioned cad model to see how the parts fit together.  :thinking:
Cool stuff!
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on February 01, 2018, 12:18:52 PM
More nice progress Plani. As I see it the  power piston will seal only on that ring around the middle of the piston...is that correct?

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on February 01, 2018, 08:23:39 PM
Thank you, Yogi  :cheers:

Bill, that's exactly how it's intended to work. The lip seal on the compression piston will touch the cylinder only on a very thin line. This needs to be so because the piston is not moving in a straight line but is slightly rocking (that's also where the name of the engine comes from). The rocking motion comes because the piston is driven directly by the bell crank. So to keep tight, the seal has to go out of its round shape and become slightly ellipticall through each stroke. I'm really curious if this will work :headscratch:....

Plani
Title: Re: Rocker V Stirling Engine
Post by: Plani on March 10, 2018, 10:20:22 AM
Bill, there might been a misunderstanding...
The aluminum part from the last post won't touch the cylinder at all. This is only the center part on which on one side the displacer (deep drawn cup) and on the other side the piston skirt will be glued.

This piston skirt is the next part I made. It's basically only a pipe made of cast iron:
(https://s20.postimg.cc/nnte70x65/Rocker_V_66.jpg)

The inner diameter is finished first, then the outer diameter is turned to a close sliding fit in the cylinder:
(https://s20.postimg.cc/fv2qf1ywt/Rocker_V_67.jpg)

And finally parting off:
(https://s20.postimg.cc/ynelin30t/Rocker_V_68.jpg)

At first all looked good, but after parting off I noticed that the part was slightly out of round.  :headscratch: That means it wasn't moving freely in the cylinder. I didn't expect this to happen with cast iron  :headscratch: :headscratch:
So I had to do it over, this time taking lighter cuts on the finishing passes. That solved the problem. On the next piston of this type, I will either use ductile cast iron or design the wall thickness slightly thicker...

Plani
Title: Re: Rocker V Stirling Engine
Post by: Doc on March 10, 2018, 02:31:16 PM
Things are looking pretty nice. That fly wheel looks super nice job. I just noticed this build and am watching on the side line.
 :ThumbsUp: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Plani on March 21, 2018, 02:57:37 PM
Thank you Doc  :cheers:

One of the few remaining things left to build is the crankshaft.
The webs were squared and then drilled and reamde together in order to get the whole thing running true:
(https://s20.postimg.cc/nrgf1gwel/Rocker_V_69.jpg)

I then insterted two pins to keep everithing aligned while drilling:
(https://s20.postimg.cc/wz8ni761p/Rocker_V_70.jpg)

...and tapping:
(https://s20.postimg.cc/w9pv5tan1/Rocker_V_71.jpg)

And finally the slots were cut to get the clamping to work:
(https://s20.postimg.cc/xorfujyvh/Rocker_V_72.jpg)

That's what it looks like with no bolts installed yet:
(https://s20.postimg.cc/6qxist6il/Rocker_V_73.jpg)

For the counter weights a steel disc was turned, cut in half and then cleanded up, drilled and counterbored:
(https://s20.postimg.cc/4z4jxwffx/Rocker_V_74.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: Craig DeShong on March 25, 2018, 11:45:16 PM
I just caught up with this thread.  Incredible work,  I'll be following  :happyreader: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Plani on April 01, 2018, 12:36:31 PM
Thank you, Craig.

Closing in on the homestretch  :)
The hot cap was soldered to it's base:
(https://s20.postimg.cc/ghsosjgx9/Rocker_V_75.jpg)

Some brass bushings for several links were made:
(https://s20.postimg.cc/t96uz13jx/Rocker_V_76.jpg)

Preassembly of the main conrod:
(https://s20.postimg.cc/miqdpl8od/Rocker_V_77.jpg)

Assembly of the engine started. Don't mind the base, I took what was lying around for a temporary base. A proper board will be made once everything is in place and the burner is sorted out:
(https://s20.postimg.cc/ppkx98g9p/Rocker_V_78.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on April 01, 2018, 01:29:12 PM
More beautiful work on this one Plani. Looking forward to seeing how it all comes together.

Bill
Title: Re: Rocker V Stirling Engine
Post by: Ian S C on April 01, 2018, 01:50:59 PM
Like the hot cap, is it stainless.
Ian S C
Title: Re: Rocker V Stirling Engine
Post by: Plani on April 03, 2018, 07:56:08 PM
Thank you guys!

Ian, yes the hot cap is a deep drawn cup made from stainless steel.

The engine almost finished, still on its temporary base:
(https://s20.postimg.cc/6khnzhh19/Rocker_V_79.jpg)

In the meantime a proper board was made to have a clean base for the Engine.
(https://s20.postimg.cc/4sop4ld3x/Rocker_V_81.jpg)

And yes, it's a runner  :cartwheel:

Ha0UfpSFHag
The balance of the engine is really nice. Most of the noise is actually amplified by the table.
Plani
Title: Re: Rocker V Stirling Engine
Post by: Perry on April 03, 2018, 08:38:36 PM
Wow! Great achievement, what a stirling motor! Where can such hot cap be sourced from?
Perry
Title: Re: Rocker V Stirling Engine
Post by: yogi on April 03, 2018, 09:45:01 PM
Beautiful running engine Plani! Well done!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Rocker V Stirling Engine
Post by: Admiral_dk on April 03, 2018, 10:21:44 PM
Wow - not only good looking design and execution, but it runs fast enough to produce real power, very good for a Sterling Engine - I'm officially impressed  :NotWorthy:

Best wishes

Per
Title: Re: Rocker V Stirling Engine
Post by: Craig DeShong on April 03, 2018, 10:26:32 PM
Very nice, and it's not dancing around all over the table !
Title: Re: Rocker V Stirling Engine
Post by: Dave Otto on April 04, 2018, 12:28:39 AM
Very nice Plani!

The speed is amazing, have you put a tach on it?


Dave
Title: Re: Rocker V Stirling Engine
Post by: Zephyrin on April 04, 2018, 08:59:53 AM
Congratulations, great runner, and no vibrations!
According to the sound track, speed is 1740 rpm...nice results !
Title: Re: Rocker V Stirling Engine
Post by: Ian S C on April 04, 2018, 12:45:06 PM
Plani, have you had a tacho on the motor, it sounds to me that its getting to 2000rpm at least, that's a very good motor.
When Andy Ross was producing kits for hot air engines he had a source stainless cups for displacers and hot caps.
The case of a C size NiCad battery is a similar size to the hot cap on this motor.  If anyone goes this way, be careful digging the inside  out of these things, and use a dead battery.  I don't know exactly what these battery cases are made of, but they seem to work ok.
Ian S C
Title: Re: Rocker V Stirling Engine
Post by: Plani on April 04, 2018, 05:29:56 PM
Thanks everyone for the compliments!!! It is very much appreciated!  :cheers:

Perry, the hot cap as well as the displacer are deep drawn cups which are made for electronics housings. I don't know exactly where to get them, since I got mine from Andy Ross.

When making the video, I dinn't measure the speed of the engine. But I think Zephyrin is spot on.
I did take some measurements on another occasion thoug  ;D:

(https://s20.postimg.cc/za4jw3xvx/Rocker_V_82.jpg)

Plani
Title: Re: Rocker V Stirling Engine
Post by: tvoght on April 04, 2018, 07:01:36 PM
I can only repeat what others have said about the beauty and smoothness of your engine, Plani. Bravo!


--Tim
Title: Re: Rocker V Stirling Engine
Post by: Art K on April 05, 2018, 02:58:15 AM
Plani,
Ditto on what everyone else is saying. It runs great.
Art
Title: Re: Rocker V Stirling Engine
Post by: Plani on July 07, 2018, 08:47:00 PM
Oh wow, time is really going fast!
Anyway, today I got finally around to measure the Power of the little Stirling.
But before that, two little modifications had to be done: The engine got a heat deflector, to keep the radiant heat from the flame better away from the engine block. And then the lantern type wick of the alcohol burner was changed for some 70 mesh wire screen. This is to get a more consistent heat input, since the wire mesh won't change its shape and it's not burning either:
(https://s20.postimg.cc/pk9gbzhzh/Rocker_V_83.jpg)

The engine was then connected to the eddy-current-prony-brake-dynamometer ;D:
(https://s20.postimg.cc/lnw4g04pp/Rocker_V_84.jpg)

The engine working hard:
-LOJx8JhG_k
And the power curve:
(https://s20.postimg.cc/86z5x4eyl/Rocker_V_85.jpg)

Mechanical power output peaked just shy of 0.8W at roughly 1000rpm. I think for a Stirling engine of this size and with this kind of heater, this is not too bad.

Plani
Title: Re: Rocker V Stirling Engine
Post by: MJM460 on July 08, 2018, 08:28:02 AM
Hi Plani, that is pretty impressive performance for a little wick powered engine.  It should be able to power something, perhaps a small paddler, obviously not a steamer.

 Did you try and measure the fuel consumption so you can calculate the efficiency?  I suspect that it will be better than most similar powered steam engines.

The eddy current brake looks great.  Is it a published design?  I can't ever get my head around how they work, but I would like to build one of those.

MJM460

Title: Re: Rocker V Stirling Engine
Post by: Zephyrin on July 08, 2018, 10:04:58 AM
Great work with the power measures, very interesting, such data are scarce with ours little engines...

With Audacity, amongst the analysis tools, there is a frequency spectrum analysis, a fast Fourier transform, that gives (with good recordings )a clear peak  of the fundamental frequency, and with the first video, a sharp peak at  29 Hz clearly emerges and other peaks at 58 (x2) 87(x3) etc. hence the 1750 rpm.
and in the video with the brake, the peak at 16 Hz and 960rpm, is obvious as visible on the picture.

but as it analyses the sound only, this could be misleading, ie for a 4st engine, it gives half speed  !

https://sourceforge.net/projects/audacity/
Title: Re: Rocker V Stirling Engine
Post by: b.lindsey on July 08, 2018, 06:17:04 PM
Beautiful engine Plani and what an impressive runner!!!

Bill
Title: Re: Rocker V Stirling Engine
Post by: Plani on July 08, 2018, 08:46:09 PM
Thank you, Bill  :cheers:

Zephyrin, thank you very much for the link provided. That's a nice tool to have in the toolbox to do such investigations  :cheers:

MJM460, I was thinking about some freestyle G-Scale loco for this engine. I think power would be sufficient.
Good point about the fuel consumption. I actually didn't bother to measure it during this run. I will do another run and then the burner will get weighted before and after to determine the burn rate and thereof the power of the flame. Any guess about the efficiency  ;)?

The Dyno is my design. The working principle is actually pretty simple. On one side of the pivot arm there is a strong magnet in front of the aluminum disc. When the disc is moving, the magnet induces eddy currents into the disc. These currents produce a magnetic field, which in turn act as a force on the magnet (just try once to slide a strong magnet down some aluminum sheet, or dropping it through an aluminum pipe). This dragging force is then picked up by a load cell which is place at a certain distance from the pivot. So from that we get the torque. The magnet sits at the end of a thread, so the torque can be adjusted by placing the magnet closer to the disc. There is as well an optical sensor to measure the speed of the disc and the the electronics just calculate Speed x Torque = Power.
(https://s20.postimg.cc/dqfy2mk4t/Brake.jpg)

Inside the Pivot there are 4 ball bearings in order to measure the drag of the disc bearings too:
(https://s20.postimg.cc/3t4x9k4t9/Brake_II.jpg)

I think to measure such small powers this is necessary, but the design is not optimal. Because of these four bearings in line, the disc tends to vibrate and this makes the measurement noisy. In a next version I would stick to the principle, but I would choose another set up of the bearings to get more stiffness.

Plani
Title: Re: Rocker V Stirling Engine
Post by: MJM460 on July 10, 2018, 12:43:04 PM
Hi Plani,

I think I can cope with that.  I assume you used a Tecscan force sensor or something similar with operational amps and an Arduino.  Or did you program a micro controller as a stand alone?  I think It could be done with Picaxe, which would be my choice, or Arduino if necessary.

Any requirements for the thickness of the disk?  I will keep thinking about that spindle system, but no really my area. 

By noisy signal, do you mean the torque fluctuation inherent in the engine, or physical noise?  It might be possible to smoothe the force signal fluctuation with a resistor-capacitor arrangement as a filter/averager.

No idea of the efficiency, but I think it could be a lot higher than my little oscillating steam engines, as you don't have to evaporate the water then throw away the latent heat in the exhaust, and it is a very high proportion of the total burner output.  I will be interested to learn how much fuel you burn per minute.

MJM460


Title: Re: Rocker V Stirling Engine
Post by: Plani on July 10, 2018, 08:41:44 PM
Hi MJM460

I just used some load cell from China. It was set up with a instrument amplifier to get some reasonable output. This is then read by an analog input of the micro controller. I'm using one of the same family as the arduinos, bur with another programming environment.

The thickness of the disk is not critical. It has to run true and for greater loads it has to be able to absorb the power in form of heat.

By noisy signal, I meant erratic readings of the load cell because the whole apparatus started vibrating. Some averaging is done in software to get a smooth reading.

So, and in the meantime I did another run with the Engine and I recorded the fuel consumption: During a run of 10 minutes the burner used 2.3 grams of burning alcohol. Wikipedia states the heating value of ethanol to be 26.78MJ/kg.
If I've done the calculations right, that means that the little flame has a power of 103W.
Follows the gross efficiency from fuel input to mechanical output of 0.78%

Plani
Title: Re: Rocker V Stirling Engine
Post by: MJM460 on July 11, 2018, 10:40:46 AM
Hi Plani, 103 watts seems about the right order of magnitude for that single wick compared with what I use for my oscillating engines.  I suspect that efficiency is way higher than the steam engines are achieving, though to make a real measurement is the reason for my interest in your dynamometer.  So far I have done the adiabatic calculations which give a limit for an ideal engine, but I have no idea how much power is lost in friction and so on.

I need to make that dyno.

MJM460