New 2.5 cc Model Diesel design and build.

[mu38&Bg#]

I spent two evenings trying to come up with figures that matched Ed's. I failed miserably. I then got in touch with Ed who confirmed that his figures could also be wrong.

https://www.rcgroups.com/forums/showpost.php?p=36347313&postcount=12246

 

[fishy-steve]

And the penny drops !
Thank you diesel pilot. A quick glance at the drawing you've linked to made me realise my school boy error.
I can now do the math using the cosine rule. :thumbup:

 

[edholly]

I have always been of the opinion that most home machined engines like the Holly Buddy do look a bit squared edged which detracts a bit from their aesthetics and in fact I designed the HB this way and encouraged those making one to customize their engines by softening this aspect of them.

Just prior to the HB came a small 0.5cc conventional engine and in fact a picture of it can be found on page 1 - it is the 2nd photo in this thread. That engine inspired the internals of the HB and it gives as good a power as any of the late 50's early 60s commercial .5cc motors. It has slightly softer lines but still has that square edged look. One way around that is to do a casting, but then the cost associated with that defeats the objective in my opinion. I have spoken to Steve Jenkinson who did the HB plans about doing CAD plans for the .5cc one, but somehow we never got past the talking about it stage ..

I have been playing around with an idea of inserting a tube in a tube and have done a mock up, albeit on a larger scale than this engine will have. But of course not not sure if it will work - only one way to find out I guess. A photo of this mock up is here alongside the HB and the .5cc little fella. This item is pressed together with Loctite and pinned with 4 x 1mm music wire as can be seen in the photo below. I am of the opinion that this will work in a tiny motor like this where the firing pressure forces are relatively small, an hydraulic lock on starting probably the worse it will experience.

For the next project I would like to design and make a 020 size diesel. To make it an easy handler - a longish stroke and a piston port induction is envisioned, a Mills .75 uses this type of porting for instance.

I want it to be a practical engine that can be used to power a small free flighter, or lightweight RC model. I love really small diesels.

I have started down the road of putting pencil to paper. The engine from necessity with the cylinder in a cylinder design will need quite some thread machining, which shouldn't be too difficult as I think it can be done in the primary machining process before removing the work from the lathe in the first instance.

Some rough measurements are 9/32" bore (.2813") and a 0.32 stroke. With tiny diesels a longer stroke and piston length I think will help with gas seal on the piston / cylinder walls. This gives a capacity of 0.0199 CI.

The Cox 020 is called a Pee Wee so what should we call this ? ... How about the Wee Dee ... for little diesel ?

I will start a new thread on this if there is any interest shown ...

Ed

 

[bollaero]

Good luck with it, any small engine demands precision fits and low friction to run at all, this is why DC abandoned the Bambi as it was too expensive to make consistently well, I guess Cox had very sophisticated machine tools so could overcome the difficulty of achieving tight tolerances.

I am working up to larger sizes, now have a 7.5cc diesel which flies a 7foot span plane well.

 

[edholly]

Thanks Bollaero - I will start another thread as I have started on the initial design phase. Yes fits will be very important and never considered friction - an easy build will minimize friction errors so will try to achieve that. Like your suggestion of Teeny D - but might stick with Wee Dee ... cheers

 

[Niels Abildgaard]

I am working up to larger sizes, now have a 7.5cc diesel which flies a 7foot span plane well.

Pictures or videos?
Please?

 

[edholly]

The current AeroModeller January 2019 magazine has a 4 page feature on the Holly Buddy written by Maris Dislers.

 

[stackerjack]

Have now put the crankcase parameters into the drawing and initial thoughts on crankshaft design within the crankcase.

Note the inlet transfer ports have been slimmed down to 6mm from 8mm. I think 8mm would slow the gas speed too much. Have also shown the exhaust ring with either a slitting saw cutting the apeture, or you could use a slotting drill to make them if you don't have a slitting saw. I've shown a 20mm diameter saw, but any smaller diameter one will do, just go in so that the length of the slit is about the same.

In this drawing you will see the crankdisc with the crankpins 5mm long drawn at tdc and bdc. The disc is 5mm thick relieved a bit to create a land for the 10 x 19 x 5 deep ball bearing, a pretty common and not expensive size that will run to over 30,000rpm on the NTN catalogue.

Now as I am writing this I realise that there is a problem - the housing for the bearing is going to block a major portion of the forward inlet transfer port, so in the design of the housing it will have to be relieved here to create a free passage for the gases.

The crankdisc will be 21.1 diameter (14.6+4.5+2)and the shaft size at the ball bearing will be 10mm.

Having said all this - with this cylinder design you are not limited where you rotate the cylinder, to have the ports 90/180/270/360 degrees to the engine or maybe better still 45/135/225/315, that way no blanking of one of the inlet transfer ports. Although for aesthetics I would like them 90/180/270/360 - but you can always experiment by turning them once it is running of course. although once assembled and run in not a good idea o disturb the hard won piston/cylinder finish.

If you are still with me on this you can see there is a bit in just coming up with a simple design, sure wish I knew how to do CAD, as my penciling skills are pretty slow !

View attachment 84785

I've been using Autocad for about 5 years now and I find I can do a drawing in about the same time as it takes to draw one with a pencil. The advantages are: Mistakes don't show and I can copy it as many times as I want and print it exact size. I learned how to use it by borrowing 3 books from our local Library and going through them during one Winter. There are also tutorials on You-Tube.
In the UK, the Model Engineering Workshop Magazine is currently running an article on ALIBRE, another drawing tool. You can also download a FREE TRIAL of the sofwtare through the magazine.
Jack

 

[edholly]

I have been thinking for a long time about building a flat twin engine - but always got hung up on the need to use either spit big-ends or use a built up crankshaft. Well I have finally bit the bullet and decided to make a twin using a "sort of" built up crankshaft. It might not work, but I think it will and only one way to find out. The twin is based on the Holly Buddy and if you are interested the thread for it is at https://www.homemodelenginemachinist.com/threads/a-flat-twin-version-of-the-holly-buddy.31463/

regards to all ... Ed

 

[josodl1953]

Split big ends are a feasible option, see my flat twin at https://www.homemodelenginemachinist.com/threads/longest-project-ever.27251/ Only you may need very thin bolts to hold them together. In my flat twin I used m2 Allen bolts.

Jos

 

[edholly]

Been a while since l posted here - the Holly Buddy continues to run well and I have decided to try to make it a more normal looking engine with a rounded crankcase.

To that end ... here is the pattern to have some Holly Buddy crankcases cast by a local non-ferrous foundry. They have done work for me before for a 2.5cc TBR version of the Owen Mate and also a ED Baby. They can do rough sand cast or smooth - David Owen seen the castings and asked if he could take a cut on the ED Baby casting - and was very impressed with it, a tiny cut on his Hardinge lathe and the swarf came off like fairy floss. The castings were each heat treated before delivery and were a joy to machine. David had had work done by these people about 30 years prior and was disappointed back then but could see that this wasn't the case here - about 5 years ago now.

I have loaded a few photos - and ask for opinions - if you were having them cast would you go for rough or smooth ?

My intention is to get one cast - prove the work by building an engine and if ok then get maybe 10 cast up for anyone that wants to build the engine - and l will simply ask the cost of the casting and postage. I have made the pattern to use the Holly Buddy plans for the componentry to complete it so no redesign of the engine.

The first photo is the pattern - second the pattern with the machining extensions shown - third the Holly Buddy in front row and the 2.5 TBR Owen Mate back row - last is the ED Baby with smooth casting finish and the Owen Mate with the rough sand cast finish. I will do the proving casting smooth - as l want to see if there are any major blemishes that need to be removed ...

I would like to put an embossed motif on the outside but can't find anywhere on the web that says how to do this. Something along the lines of a circle with a H inside. No hurry for that - the proving casting doesn't need it.

Any opinions as to the rough v smooth would be appreciated as would anyone that wants a casting please let me know. I intend to start a new thread detailing the cast crankshaft engine build ...

 

[edholly]

For those interested in the pattern - it is made from Aluminium and the various bits were glued together and a bit of filler used to fillet various bits - then a coat of silver paint. Took about 10 hours to make maybe a bit more - but it will cut down the build time considerably, especialy for an engine with beam mounts.

 

[Ghosty]

I think the smooth looks better

 

[NickP]

I’d go for smooth too - just think it looks a little more ‘finished’ - I like rough castings for steam engines though

 

[SteveT]

Smooth also, and let me know when available.
I completed my first ever machining project a HB2.5 and it runs beautifully. Now in the middle of making a batch of 3 for friends.
If you ever intend to modify the basic engine, provisions for a silencer and throttle would be fantastic.
Many many thanks for designing the engine and making the plans available.
Steve T

 

[Cholchester]

I would like to put my name down for one. Any idea of the price yet? Smooth finish is the best.

 

[777engman]

I'd be very keen to acquire a few castings to mate, go for the smooth finish, looks way better and a lot more professional.
Regards
Dean

 

[edholly]

Dropped the pattern off to Camcast this morning - looks like $60 AU including heat treatment each .... which is not much more than they charged for the castings l had done about 5 years ago

Can you guys that have indicated you want one or more please email me ... edholly at optusnet dot com dot au ... makes it easier for me that way ...

It will probably take about 3 weeks before l get my one back to trial build with - then if that's ok then will get them done after that. Getting close to 20 castings requested so far ...

 

[Chris Murphy]

Ed-as per my reply on 'another' forum-put me down for one of each-the Buddy and the ED Baby (and should you be tempted to do another run of David Owen 'Mate' BB case castings-one of them as well..!

 

[777engman]

Ed-as per my reply on 'another' forum-put me down for one of each-the Buddy and the ED Baby (and should you be tempted to do another run of David Owen 'Mate' BB case castings-one of them as well..!

Yup, same for me for any other castings mate, emailed you already today.
Cheers mate thanks heaps
Dean