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[andrewh]

Joe,

I'm in the midlands of the UK - about an hour north of London - yes we had a 5.3 Richter earthquake last night, centred deep in the boonies of Lincolnshire about 60 miles away.  I will check my chimneys tonight!

BFO - it had never ocurred to me that I can load the turbine (to prevent excess of rpm) with a resistor in the electrical circuit.
Thanks for that. 

andrew

[Capricorn]

I take it earthquakes are rare there?  We are pretty safe here, the nearest major fault being in Missouri, which has the potential of being serious because it's inactive for long periods of time and therefore hadn't been viewed as a threat at least until recently.

Hope turbine test goes well, how tight of a tolerance is there between the rotor and the housing, that's something I'm curious about, I see that as a potential difficulty if I build one from scratch.

Joe

[andrewh]

Joe,

Lots of tremors - few earthquakes.  The nearest plate edge is in mid-atlantic but they still can and do happen

Pic of the intended cuts attached.  Didn't happen last night - I stripped a Seagate drive with my son.  The motor is sweet, but uses the case as housing,  - this might be a GOOD thing if the concept works as it would be a built in support and housing!

Clearances with impulse turbines should not be critical, and they are using velocity, not pressure, to spin the rotor.  There needs to be enough clearance for the steam leaving the buckets to have a free way out and not interfere with the jet.

On clearance I would bow to John and people who have done it!
andrew

[Capricorn]

Andrew, 

It looks like you have it figured out, I was curious how you hold the motor while machining it.  I don't imagine you have a dividing head, I'd like to have one but they are minimum $500 for a cheapo one (I think) so not likely, I bet John has one.  I figure I can probably put something together for a specific spacing but may be just as well marking by hand with a protractor.

Anxious to hear the results.  (Hope your chimney held up)

I've been idle no news to report on the turbines.

Joe

[bogstandard]

Andrew,
Just a bit of info on how I do it.

I do use a rotary table, or a dividing head, just depends which one is handy.
I do it in one hit as set up like your 'x' picture. As shown in the first pic.

The nozzle is stepped down from 3.2mm (1/8" tube) inlet, to 1.5mm in steps, to increase the velocity of the either air or steam. You can see mine in the second pic.
The outer running clearance I set at 0.5mm (rotor diam of say 30mm, running in a chamber of 31mm diam). The tangential exhaust starts to strip the air or steam off at approx 90 degrees from the inlet nozzle impact point. You can just see the exhausts in the second pic.

John

[Capricorn]

John, Like Andrew said, masterly work.  Is that your original turbine or a new one?  That rotor must be 60 or 70mm or so isn't it? 

I should say I have 70mm propellers, opposite hand, three blade type D, that's about scale size but I'm nearly convinced they will be too small.  I'm not really very experienced with boats enough to know, although I've done some investigating, what do you all think?.  The ship is 10'6" long and should weigh somewhere between 100 and 125 lbs.  I think the props (raboesch, I can't spell it), are rated at 4,000 rpm or something around there, I'm not opposed to exceeding that, but I imagine it's efficiency as well as vibration, possible damage to the props and maybe cavitation at some point. 

I think I need to drop in the shafts and electric motors temporarily, get the weight up and test it before I'll know much, I'll work toward that.  I've got to seal the inside of the hull and glass or cover the outside, hopefully I can do that before spring. 

All the best.  Joe

[andrewh]

I located the article I remembered on steam turbines in Model Boats - September 1985.

I suspect it is not as relevant now, but I have uploaded it to Photobucket
http://s222.photobucket.com/albums/dd159/andrewh_photo/plansscans/

The second half of the article was published in October 1985  - but I don't have that edition - wonder if anyone else has?

John - thanks for that picture - it tells several thousand words - I see the exhausts leaving and the general quality.

If I have been a good boy, and led a clean life, I might finish up soon with a little Colchester lathe which is being disposed of at work - this would open things up a bit for me, but the steam turbine might be behind the pair of  1/10 scale 20hp Fowler ploughing engines!

Joe, thats a lot of boat!  I am not (ever) defeatist, but wonder if you have given some thought to a backup electric propulsion?  You might want to have a way of returning her to the bank anyway if anything should go pear-shaped on the water!

Your props and thinking sound quite sensible, but at this size I think you would be amazed how efficient the hull and props are (compared with smaller boats)

I have been following a build of a STAGGERING Yamato about twice as big, I think (sorry, havn't got the link to it here)  The builder is using 4 DC motors off a pump assembly that must be available in the US - I'll post the link when I find it, if that would hepl give you assurance about the props'revs/etc.

andrew 

[Capricorn]

Andrew, Thanks for finding the article! I haven't read it yet but will.

I have planned to have auxiluary electric motors, I'm not sure exactly how I'll get them connected in.  Now that you mention it if I figured out how I want to mount them now that could be a permanent installation, the only thing is I'm not sure that the aux motors will be adequate for testing the max speed etc. ???  The aux motors I'll probably use for that are surplus motors from allelectronics (pretty nice for $3.50 ea), see photo.  I thought scooter motors for testing the hull, bigger, high powered ones.

I'll look for the the huge yamato, I find the big ones fascinating, thought I was nuts at first until I saw some really big ones, have you seen the Arizona that is about 40' long a fella is building in his backyard?  There are some aircraft carriers that the pilot rides inside, driven by a small outboard motor.  Here on MBM Martin was starting a 1:35 scale Hood, but I haven't seen much on it for a while.

I tend to agree on your propeller opinion, I haven't given up hope on the small props, just haven't got the know how to be sure they'll do it.

Thanks for all the input, great help.  Joe

[Capricorn]

Andrew,

I read the article, still very valid I think, it confirms the high rpm recommendation.  I keep hoping to get by dropping the rpm but keep hearing it's not the point on turbines so it's good to hear again.  1,000 rps is up there, (hopefully half that works), fortunately these days halfway decent gears are relatively cheap, just have to remember to get spares. etc.  Hope you and your son get chance to test turbine soon, am waiting to hear, and John you must get busy again, help excersize you arm. 
Joe

[andrewh]

1/96 Yamato build

Interesting not only in the speed, precision and compotent home-engineering of the whole thing, but it might help with drive train, power ideas

http://www.wmunderway.8m.com/cgi/yabb/YaBB.cgi?board=BuildB;action=display;num=1200112206;start=15

Fwiw - I see that new hard disc drive use fluid bearings - It will be interesting to see if these are any use to us!

I havn't cut pockets yet, but have the device fitted to a backplate - its a start!
andrew

[bogstandard]

Andrew,

The new hard drives are now running at 10k rather than 7.2k. Don't believe all you hear about bearings and hard drives.
I used to be on the ground floor making protos of the damned things, and I can tell you now, they might sound all singing all dancing, but they will be the cheapest thing that they can get hold of to keep the price down, they have most probably done away with the balls completely and stuck in a chamber of oil, and called it some super duper thingymajig name to make it sound great, designed to run so many hours and then fail, just enough to get them thru the warranty period.

Caps,

I have had a total rethink on the turbine and have designed one in my head that puts all rotors together as one unit, I thought that seperate units would cause a balancing problem at such high speed. But it does mean that machining tolerances will have to be fairly tight (about 0.002" rotor to case clearance) also the exhausts will start to scrape much earlier (about 45 deg after inlet). Easier to make, more compact and only two bearings, both on the outside, so will have a better chance of keeping cool.

Your props will hopefully need about 400 to 500 rpm top wack, so a gear ratio of say 100 to 1 reduction would be the most that would be required. Need to see the speed output by the turbine before that is needed.

I have already geared up the making on a model engine site that I use, it will be after I have finished my latest project, and should take about a week if my health holds up. Then we should see if it comes up to expectations. The difficult bit will be making the throttle/reverse unit for it, but again the idea is locked in my brain at the moment, but it should work. As you know, I make on the run, piccies are for those who don't know what they want to do.

John

[Capricorn]

Interesting that you've rethought it.  Am anxious to see it but I assume I won't see any piccie's for a while.  I read the article from Andrew by Terry Burnett, his sounds like a successful turbine but a bit beyond my means to construct, also chapter 12 on turbines and centifugal pumps, that turbine I might be able to make, and I can make it big enough too.

Will have to look into the fluid bearings, I imagine John is correct about their being as cheap as possible but they must rack up the revolutions by the time their life is over (be it with little load on them).  Interesting you mentioned Seagate hard drives, they put them together here in the twin cities and one of my coworkers was there last week to review their roof for another bridge crane.  They have rather intense security, he couldn't bring anything but a pad of paper and pencil inside (so not likely to come out with secrets or anything else :'().

John, when you say top wack do you mean max rpm's?  I wouldn't think 400 or 500 rpms would be enough, I'd like a bow wave up to the deck if possible, but that's probably only 7 to 10 knots actual speed, which isn't slow but I was expecting to run those props pretty hard. 

Cap

[bogstandard]

Cap,
As far as I can remember, Rabo props are a built up design (rather than cast) and had a fair pitch on them. On the full sized ship they were most probably only turning just over 100 rpm. I don't think my calcs are far out for the size and speed required. but easy enough to rectify if wrong. My Clyde puffer weighed about 120lbs in the water, that was pushed along fairly rapid by a Rabo 4" prop running at 150rpm., and that was a bluff bowed hull with a lot of displacement, unlike yours which will be a lot sleeker in the water. The probs with running larger built up props at high speed, the blades tend to flex or come off.

If I can get this new design running somewhere between 35 & 40k (loaded) in forwards and about 25k in reverse and still have a good power output I will be more than pleased. Just depends how much pressure will be needed to get there. Won't know until it is tried, but going by what I have noticed with my larger version, I hope that it will be below 40 PSI, just depends on the volume then, whether a normal boiler can keep up with it.

John

[Capricorn]

John,  You remember correctly, they are not cast.  I put one on a shaft with the 12v motor, and if I remember correctly (which I may not) it ran around 3,000 rpm with no load, at 7.2v it runs 2,200 rpm and it doesn't make a noise (obviously those figures have nothing to do with the prop).  I ran it in the tub with 7.2v and it moved a heck of a lot of water around (that's not a very precise description of the prop performance either).  At least in my case I likely won't be steaming it around a lot, but I sure wouldn't want the blades to flex off.

I don't know but I think one way or another I'll be able to get enough steam for it, like I said I have what seems to me to be a lot of room if needed.

I hope your arm is doing better John, do you know yet if it's going to be better than before? 

Cap 

[bogstandard]

Cap,

I thought I would let you know that I have made a tentative start on the proto on an engine build site, here are a couple of pics, the first shows a quickie sketch of what the engine should look like and the second is a pic of the raw materials.






This proto engine will be about 3" long x 2" high x 2 1/2" wide (excluding shaft length)

I hope to make a start on the rotor tomorrow.

My arm by the way is right back to square one, so now working again with one and a bit arms.

I will keep you posted on the progress.

John

[Capricorn]

I'm sorry to hear about your arm, wish it had turned out better, but you've still got your mind and that's more important as you get older.

Great that you've got the materials, looks substantial, but I imagine a lot of it ends up as shavings.  That's your special valve on the side and the exhaust on top it looks like.

I've ordered some epoxy coating for the inside, paint essentially, hope it's not too stinky, I've used 5 minute epoxy, it's strong smelling but not too bad in small quantities.  We'll see what this is like.  Then decide what goes on the outside regular fiberglass cloth and epoxy or paper or just paint?  I think it will crack on the plank joint without reinforcing.  Hopefully I can get it ready for a putt around the lake come late April when the ice goes out around here (usually, it's been a cold late winter here though).

Andrew, have you made progress on the turbine?     Cap

[bogstandard]

To totally seal your plank on frame hull, the best solution is to glass tissue the whole of the outside, when dry, pour glass resin on the inside and slosh it about so that everywhere is covered. Doing it that way, the hull ends up as a totally bonded and sealed unit. When it is all dry, fill and flat the outside. The underside of the deck also needs the same resin treatment. People tend to forget that and wonder after a while why all the planking is lifting and the deck warping, especially with the damp atmosphere caused by steam.

John

[andrewh]

Cap,

I would suggest (humbly) a one-word mod to John's suggestion for the outside of the hull, and that would be cloth rather than tissue.  Both will finish up doing the same job but you will curse less with the right cloth! 

My favourite for a  hull is twill-weave cloth (this is what the females in your life will descride as bias-cut)  Goes/drapes round curves better than mat/tissue or plain weave cloth.

My favourite resin is epoxy (though I dislike the chemical)  - probably since a friend gave me 3 US galls of the stuff! 5-min epoxy is the worst (imho) for smell and function.  Slow cure versions and the 2-part paints are much less objectionable.

John,
Nice sketch of the turbine concept - I see what you mean about the bearings held in cartridges outside.
With a shaft each side it could drive paddlewheels on each end.
<<straight face>>
Are paddle wheels Ok at 50 to 70,000 rpm?#

I have several steam boats with non-self-starting oscillators, and often want an electric drive to motor them back to the bank if the engine stops.  Adding another prop and shaft is easy, but not what I really want. 
My solution (though I have not done it yet) is a friction drive 385 motor swung into contact with the flywheel by another servo (I have spare channels)

How many shafts would your DD have in real life, Joe?  2? or More?
Presumably it would be possible to use a heli clutch or similar to clutch in an electric drive to the existing props (actually since heli clutches are centrifugal it might be a better idea to clutch in the steam turbine drive) 
There are beautiful cousins of roller bearings called sprag clutches which grip in one direction but are completely free in the other - I don'y know how small they are made but I wonder if they would help.

No progress on the trial turbine - I'm rigging my Brig now

Sorry to hear about your arm, John.  From your sketch you are a right-hander, hope this isn't the one with the problems.

andrew

[Capricorn]

Well thank you both, I got some input on RCgroups too, it's much the same, I haven't used paper or cloth so it will be interesting.  We'll see how many yards I need, probably cost a small fortune, the epoxy for the inside is 25$ a qt, plus the hardener.

Great point John on the bottom of the deck, I may have forgotten that too, total seal is what I'm shooting for, dolphinite in all the screw holes too.

The destroyer is a Fletcher (at 1/35 scale), I haven't done like many and picked a specific named boat, for one thing it isn't an accurate copy of the hull, it's squared off on the bottom, doesn't have the secondary keels etc so I'll probably leave it at "destroyer".  It has two props, apparently on the real ones they prop shafts weren't symetric, one was tipped up more and offset maybe?  Not sure why, although I read it, I doubt I'll do that.

A clutch of some sort is what I'd probably look at first, Pops is building 1/48 scale Fletcher (clayt.com) and he used the same type of contact wheel that you mention above Andrew, for his anchor chain winch, I'd probably think about that type as well.  I'll look at the heli's and roller type.

Cap

[andrewh]

Cap

For when you get back from work
http://www.renold.com/Products/SpragClutchFreewheels/Sprag_Clutch_Index.asp

My brig is here under scale sail (for the adventurous) and on RC groups (brig Volante)
andrew

[bogstandard]

Andrew,
What you call a sprag clutch, we call a one way bearing. I have been using them for years and have many in my stock of bearings. The main problem with them is when in the 'freewheel' mode, they don't like the shaft spinning inside them going too fast.

There is a fairly easy way of having an emergency motor, and it only comes into contact with the gear on the shaft when it is energised.
When the motor is spun, the idler gear is thrown over to come into contact with the drive gear on the shaft and the action of the electric motor shaft still turning keeps it in contact with the propshaft gear and so drives it. When the prop shaft is turning, it automatically throws the idler gear out of engagement. You do have to make sure the electric motor is turning the right way and is on the correct side of the shaft. This is a system used by ic engine boats to restart the motor in the middle of the lake, but it will work for an emergency return to the bank.



John

[andrewh]

John,

Thanks for the sketch - I love your involutes - an automatic system with no drag when its disengaged

My cunning plan was similar, and used friction drive onto the flywheel

While trying to think of a controllable clutch, I realised that the tank drive systems must have servo-operated clutches  - I know that Tamiya sell them as loose systems - must have a look for interest.
andrew

[bogstandard]

Here is where the rotor is up to. It is made from PB1 and is to the stage of being ready to cut the pockets.




John

[Capricorn]

Wow John, that looks great, really.  I've got to find out about getting it from you when it's ready, I'll send you a secret message.  That is assuming you'll be willing to give it up or make another (or two   )

I appreciate the input from you guys on the clutch but haven't done much on it, was hoping the epoxy would arrive, but probably Monday.  I've got to go back and read all the posts etc on finishing with fiberglass and epoxy etc, but John you mentioned finishing the outside first then the inside, I'm sure it makes sense, but do you think it would be a mistake to do the inside first?  I was sort of hoping the coating on the inside would key the planks together so I could give it a good sanding on the outside.  If I sand the outside now some planks are "free" from rib to rib and may not stay sanded down if you know what I mean.  I could "sprinkle" a bunch of CA in it to key them I suppose.  If the epoxy coating isn't too thin I don't think it will leak though, I haven't got very wide cracks or anything.  Andrew, you seem to have some knowledge on this too what do you think.

Thanks,  Cap

[bogstandard]

After many hours, this is what the rotor looks like. It still requires balancing.



John