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Author Topic: Bob's H.M.S. Polyphemus  (Read 208406 times)

derekwarner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #175 on: November 16, 2012, 08:09:30 pm »

Interestingly they appear to use toothed belts....but flat faced pulley wheels.... :o
Would they not get better grip if the belts were reversed ...flat face of belt to flat face of pulley? ....Derek
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Derek Warner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #176 on: November 16, 2012, 08:37:34 pm »


How weird    Perhaps they allow for slippage.


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Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #177 on: November 16, 2012, 08:45:52 pm »

My goodness !  Now that is a handsome piece of confined space engineering.  My new Conrad cogs look vast compared to that.  20 dia were the smallest they did with grub screws (ie: not free rolling).  Strange use of non-toothed pulley wheels too.  Probably the rubber belts are less likely to slip than my fine wire reinforced nylon belt.
I do like the simple nylon belt guides illustrated. I was going to construct tensioned idlers.
 
It is also strange that extensive searching on Google did not bring these up, or the HPC gears recently recommended.  Even with very specific sets of keywords Google loves throwing in tons of non relevant rubbish.
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #178 on: November 16, 2012, 09:25:07 pm »

I expect they do use toothed pullyeys on the shafts of the hydroplanes, but don't bother for the other end which just act as a tensioner.

derekwarner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #179 on: November 16, 2012, 11:45:41 pm »

Thanks Subculture...that would make sense O0 ...but from the images I cannot see how the rotational moment is created or applied to the driven pulley wheel......Derek
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #180 on: November 17, 2012, 11:07:00 am »

Yes it's tricky to work that one out. The way it works is thus- the resin pieces which are connected to the metal control rods in the picture latch onto the toothed belts. So as the control rods move in linear fashion the belt is pulled with it- make sense?

Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #181 on: November 17, 2012, 12:25:04 pm »

Please do not expect my belt geared twin bow rudders system to be that sophisticated  %%

Its just in a very restricted space, with multiple hull curves in all directions, and underneath a waterproof access hatch.  Upper platform mounts the three gear pinions.  Lower platform mounts the toothed belt drive and servo.
 
Getting the three shafts aligned will be fun.  I am aiming for a full +/- 45 degree rotation. 
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Bob K

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Re: H.M.S. Polyphemus, Bow Rudders Drive Train Installed
« Reply #182 on: November 22, 2012, 08:19:46 pm »

 
Bow Rudders Drive Train Installed

This 3D puzzle has been challenging as most of it is positionally critical to almost everything else, in a very restricted space. 
Here goes . . .

First stage was to build the servo sub frame exactly parallel to the waterline.  This was built up in blocks so I could get all the profiles right. 
Using this as a template I then made the ply platform to sit on it.

   

I next made up the upper platform that would support the pinion gears, and drilled it for the three brass bearing tubes.  Tacking everything in place I inserted the brass tubes.  Checking for verticals I marked through the rearmost tube onto the servo platform, and using this as datum I marked out the platform to drill the holes and servo cutout. 



Before fixing the platforms in (whilst I still had room to operate a Rotacraft flexi drive inside) I used a dab of paint on a satay skewer slid through the rudder tubes to mark the exit positions onto the fibreglass hull. 
Drilled hull, very carefully.  Opened vertical detents with conical diamond burr, then drilled through vertically.

   

The cog holes are 3.2, but the toothed wheels are 4.0 I/D.  This required three sizes of slide-together brass parts.  Dry assembly checks before the bearing tubes could be epoxied to the platforms and platforms to the hull.  Small blobs of Blu-Tack were inserted in tube ends during epoxy operation then pushed out with 1/8 rod to ensure epoxy did not get up the tubes.

Despite several assembly dry runs the actual gluing was fraught as tubes kept jamming whilst set time seconds ticked away. 
It was therefore necessary to open a couple of chilled beers afterwards, before assembling the drive components the next day. 
Hey.  It works  :-))



The rudders will be fairly straightforward.  Brass, silver soldered, with washers and O rings top and bottom.

 
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derekwarner

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #183 on: November 23, 2012, 05:27:10 am »

This looks the part Bob :-)) ...............I am sure those few cold beers helped....... <*<
1. Will you paint or preserve the timber support sections?................
2. Will you be using a programmable R/C setup?...... where you can limit/adjust servo travel in each direction & hence obtain optimal rudder movement
Derek
 
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Derek Warner

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Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #184 on: November 23, 2012, 08:13:50 am »

Thank you Derek.   By the time I had completed the epoxy sequence the beers were essential ( Tee hee !)

1)        The wooden parts will get protective varnish.  As the bulkheads frame structure and under decks are clear Lexan for maintainence visibility I am painting the rest of the insides white.

2)        Servo throw has been a concern.  The gearing and rudders will turn more than 90 degrees, plus the centre drive pinion has less teeth than the two rudder pinions.  Hopefully this will allow the servo to turn slightly more than +/- 45 with the rudders slightly less.

The part I cannot check until I wire it up is getting the rear rudder to work in unison with the bow rudders, using a Y lead.  If I have to reverse the linkage side on the rear rudder that may mean reversing the channel on the Tx.
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #185 on: November 23, 2012, 10:35:29 am »

Most servos can be made to move up to about 180 degrees throw. You just need a pulse stretcher, which are readily available, often described as servo extenders.

Beyond 180 degrees, they're usually mechanically limited by a stop which is moulded into the final output gears, although some servos don't have this. The feedback potentiometer on a servo will read up to about 270 degrees, so if you remove the mechanical stop (I file it off) you can get a large movement from your servos. A lot of the folk into robotics modifiy servos in this way.

Many digital servos are software limited to about 90 degrees of throw. Some of them can be programmed to move beyond this, but if you want a servo that is easy to modify the older analogue models are the easiest to tinker with.

Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #186 on: November 23, 2012, 11:02:08 am »

That is really useful to know.  However in this case I want the servo around 90 degress, 110 max.  I have three Sanwa SRM 102 3 Kg servos.  ( 2 for rudders + 1 for air pump / water valve).  The later will be run on a cam with a microswith for the pump and an arm for the valve.
 
My concern was possible overthrow damage to gears, after my experience with the special servos that Engel had specified for the 212A sub.  If I go beyond the mechanical limit I could strip the gears.  Data on these does not quote operating angle, but others I have had are around 90 degrees
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #187 on: November 23, 2012, 12:51:06 pm »

Standard opeartig angle is 90 degrees for the normal 1-2ms pulse that is squirted out by pretty much all radio systems. Servos are usually mechanically limites to 180 degrees, never encountered any limited to 90 degrees.

The limit is put in to protect the servos potentiometer.

Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #188 on: November 23, 2012, 01:26:01 pm »

A normal operating angle of 90 will do just fine.  I was referring to max left / right Tx stick operation, translated to actual servo angle generated through the on-board Rx.   Due to my bow gearing if I want to bow rudders to turn left when the stern rudder also turns left I may have to reverse that channel on the Tx.
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

Bob K

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Re: H.M.S. Polyphemus (1881), Progress on internals
« Reply #189 on: November 29, 2012, 11:13:30 pm »

Progress on Internals

Have I bitten off more than I can chew here?  A host of techniques and materials that are mostly new to me.  Had I opted for a safe but non-scale waterline and just fitted the shafts and motors etc this ship would be sailing by now.  Stiffness of joints precludes me from being able to kick myself. 
A partly submergible Victorian warship complete with funnel smoke and steam engine sound is my goal.

Stern Rudder Servo

Fairly conventional, a ply platform epoxied to the hull sides.  Care needed to ensure everything clears the nutserts beneath the clear underdeck. 
Lots of room underneath for ballast.



Motors Mounting

I had been advised not to rigidly fix the motors in to reduce vibration, so instead of standard motor mounts I built a wood cradle with rubber strips.  Bonus:  Easier to remove for maintenance.  When the epoxy has set I will fit a 12mm wide shaped brass retaining bar with rubber pads.



Bow Rudders Snag

I hit a snag on the drive train.  Tension in the belt was trying to wrench the toothed wheel forwards out of the servo.  A 3mm Lexan top bearing plate was added. 
At least the drive train now looks a bit like Victorian engineering.  {-)



Almost ready to fix the Lexan frame assembly into the hull.  Around 2m of watertight joints.   {:-{
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unbuiltnautilus

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #190 on: November 30, 2012, 09:25:26 am »

With the old Olympus Belt Drive units, you were advised not to tighten the belt fully and to allow a little slack, the benefits of a toothed transmission I believe. It may be worth easing the servo forward a millimetre or so.
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Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #191 on: November 30, 2012, 09:39:11 am »

That sounds sensible.  I was wondering if the 3kg servo could cope.
Moving the servo by half a fixing hole diameter could be interesting at this stage.  I will get my Bagpus hat on.
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #192 on: December 07, 2012, 06:27:15 pm »

Hi Bob


Following your build with great interest. I was skimming through some old books I bought a few years back and found these pictures which you might be interested in.














They are from a book called 'The Royal Navy in Old Photographs' by Wilfrid Pym Trotter. There are some very interesting pictures of RN warships but also of the crews and the equipment they used.
Hope this helps.
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #193 on: December 07, 2012, 06:30:39 pm »

Just realised that two of them are very similar to the others earlier in your thread, hope the third and fourth help! :embarrassed: :embarrassed:
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Bob K

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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #194 on: December 07, 2012, 09:06:26 pm »

Thank you Nick B:   Some of those photos I have, but not your third one showing her extreme low freeboard (far right).  A poor sea boat indeed, water drove over the focsle and along the main deck at speed, but as the fleet exercise proved she was highly effective at penetrating hostile harbours with little visible for shore batteries to fire at.    She broke the harbour boom. The bow rudders would have snagged if she tried to pass over it.

Keeping the waterline realistic is why I am spending so much effort into watertight compartments and water ballasting trim-down system.  This will be fun to sail  %%

In the next few days I hope to have the next photo chapter of this build.  All going well so far.
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HMS Skirmisher (1905), HMS Amazon (1906), HMS K9 (1915), Type 212A (2002), HMS Polyphemus (1881), Descartes (1897), Iggle Piggle boat (CBBC), HMS Royal Marine (1943), HMS Marshall Soult, HMS Agincourt (1912)

Bob K

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Re: H.M.S. Polyphemus (1881), frame assembly
« Reply #195 on: December 09, 2012, 09:18:22 pm »

More Internals

Servos

Thanks for the tip to leave more slack in the toothed belt to reduce axial force twisting the servo gear. 
It took some rework to move the installed servo mountings by only 2 mm. 

Jump Leads set up

Not wanting to wait until I can get the Futaba F14 working I ran some long servo leads from the Rx in one of my other ships to set up the two rudder servos. 
Both operate nicely.  Stern linkage set up and checked.  Bow servo toothed belt operation now feels a lot better.

Set in Sealant

Now I can get the bulkheads frame assembly in.  I marked the positions of the seating edges onto the hull in pencil, then applied a bead of white Silkaflex 221 sealant along each of the joins.  Seated in the frame, adding some temporary weights, and left to set off.



When set I filled each frame compartment one at a time with water to check for leaks.

Fitting and sealing the clear Lexan underdeck will be interesting.  This has to seal the two ballast tanks and keep water out of the frame compartments. 
Next instalment coming soon !
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #196 on: December 09, 2012, 09:23:01 pm »

looking good bob !

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Re: H.M.S. Polyphemus (1881), under-deck
« Reply #197 on: December 10, 2012, 09:04:05 pm »

Thanks Guy. 

Under-deck

This stage has perhaps my greatest potential for messing up, as everything up to this point depends upon the under-deck fitting exactly with some 4 metres of sealed joints all doing their job.  Once set in place opportunities for remedial corrections become limited.

Seating planes

The open top frame assembly is in, with compartments seeming reasonably watertight.  Additional hard wood strips were next epoxied to the hull edges in sections, taking care to check each was level with the Lexan frame top edges. 



Extending the sealing edges beyond the frame towards the stern used temporary alignment strips to maintain a consistent parallel supporting surface. 



Fitting the under-deck

Using more Silkaflex 221 white sealant I carefully applied beads of just enough sealant to make sure it was waterproof, but without having too much unsightly excess oozing out beyond the joints.  I would rather err on the side of a little ooze than incomplete joints.

Not so easy using a two foot long mastic gun.  Any leaks, especially on the top faces of the ballast tanks, could be terminal. 
This was a single stage apply glue and fit deck operation.



Hopefully, after checking integrity of joints, I can now start fitting out the electrics and running gear
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Re: H.M.S. Polyphemus (1881), el momento de verdad
« Reply #198 on: December 14, 2012, 12:20:18 pm »

 
El momento de verdad

The moment of truth.  Preliminary tests pouring water into individual compartments looked good.  Now was the long awaited bath test to see how the ship held up under fully loaded water pressure.  It was also the time to see how my mass distribution calculations panned out in practice.

Mounting trays were made up and fitted for the key items such as the big 6V battery and Mister.  Three other smaller battery packs, air pump, P94 and motors were loose fitted in their intended positions.  Boy, is this a lot heavier than my previous boats, and almost fills the length of the bath!
 


The good news

Seems to float on a reasonably level keel, and not far off what was intended.  As expected the SLA battery has its centre of mass offset to the side opposite the terminals.

The bad news

Water pressure under displaced loading forces the levels in the ballast tanks to rise a third the way up the tanks.  More than I had expected.  Water is not compressible, but air is.  She thus floats lower than anticipated.  I am having second thoughts on how effective the ballast blow and fill system will be.

After several minutes there was slight water ingress into three of the six compartments, one of which was the bow rudder chamber, so  I need to better seal off the rudder tubes exits, no problem.  More worrying was a slow water ingress into the SLA and mister chambers.  This will be a little more tricky to fix.

More work to do.     O0
 
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Re: H.M.S. Polyphemus (1881), not quite a submarine
« Reply #199 on: December 14, 2012, 12:29:04 pm »

Just use the pump to put a little extra air pressure into the tanks
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