Paddleducks
Paddler Modelling => Kits & Hulls => Topic started by: ihughes on July 28, 2005, 11:46:21 PM
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Hi everyone
I'm a Paddleducks newbie.
I've been building a Richard Webb Princess Elizabeth kit for about 12 months now. I've built it as a wartime armed minesweeper which in fact the real Princess Elizabeth became during WW II.
My reasons for building it this way was that I met someone who had completed the standard pleasure cruiser version just after I started building the hull and they explained that they had real problems with the COG as all the super-structure weight was biased towards the stern. To overcome this they had installed the main battery pack in the bow section but still had problems.
I intended to build the civilian version with lots of figures seated and standing on the rear deck area and thought this would only make COG matters worse.
So, managed to find some photos of a naval version and off I went!
I have also used very light weight etched brass rail posts to try and keep top weight down to a minimum.
I had one frustrating attempt at building the paddle wheels to Richard Webb's design, and then converted some plastic reels I had which used to contain sticky lead strip for making leaded windows. These were slightly bigger than planned but I have modified the tops of the paddle boxes to compensate.
I will post some photos of the current state of build as soon as I can.
I'm pondering about the drive system and was planning to go down the single motor/rudder route but reading some of the postings I'm now seriously considering two motors.
I'd be interested in hearing from anyone building a Princess Elizabeth, or happy to help anyone else with the benefit of my experiences so far.
Ian
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Nice to have you with us Ian - Looking forward to the photos of the Princess Elizabeth...
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I have posted a few photos of my Princess Elizabeth Minesweeper in the gallery.
Ian
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Hello Ian, what a fantastic craft you have made she really looks the part. I'm surprised that you have managed to make the ship to this point without having any motors installed. Am I right with this assumption? It'll look absolutely wonderful on the water and may I congratulate you for the out of the norm thinking. :clap2
cheers
Jim
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Thanks for the photos Ian - she certainly looks nice! As Jim said above, it makes a nice change to see one of the armed minesweepers modelled rather than a passenger vessel.
Do you have any photos taken during the build? I always like to see how things come together during construction.
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No photos during construction I'm afraid.
I deliberately haven't fitted motors or sorted out battery positions until I've finished the superstructure (especially the railings) because of predicted COG and balance problems. Also, installing motor/shaft mounts in plasticard is a doddle with solvent welding!
I've purchased Richard Webb's recommended single motor set-up from Model Motors Direct. However, this is a geared Buhler motor that runs at 18+ volts. I'm now thinking of two smaller geared motors running at 6v.
I'm also assuming that I may have to split the batteries into different sections of the hull with the possibility of biasing the weight towards the bow if necessary.
Anyone got any practical experience of motors and battery combinations in the Princess Elizabeth?
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Super project, Ian...congratulations on a fine model. However, NOW the fun begins!
Everything you do from now is predicated by the following which can only really be determined in a test tank (aka the bath!):
1) How much displacement exists already or, in other words, where does the model float ABOVE her sponson deck line or the paddle blades dip in the water.
2) Is there any list to port or starboard or as you have already stated a pitch to bow or stern?
3) Where is the COG of the model in it's current stage or how stable is the vessel when you roll it in the water? Does it feel "stiff" or does it "wobble" from side to side, i.e has what we call "top hamper"?
Having determined all these possible problem areas, you now have to set about completing the model in order to bring the final COG down to a level where the model is stable, wheels have the correct "dip" for maximum thrust and she floats evenly at her waterline without any list or for and aft pitch.
First thing to do is to absolutely determine how much displacement you have to play with i.e. how much weight do you still have available to you for control and propulsion systems. Get a bunch of small ziploc plastic bags anf fill them accurately with pre weighed amounts of any small grain material (rice works quite well and water even better except it's a bit unwieldy.) With the model in the water SANS removable superstructure start distributing these bags throughout the ship until you have it sitting exactly where you want the sponson deck to clear with the paddle blades 75% immersed. (Mind you that's open to debate too!).
Weigh the superstructure and calculate the total weight of bags you've placed in the model. Subtract the former from the latter and that will tell you EXACTLY how much weight you have available for the drive and control systems. You CANNOT exceed this total weight and you must select all your components and weight them individually. You then have to use the bags again to determine exactly WHAT weight (batteries etc) to place where in the hull. Everything has to be as low in the hull as you can get it. Remember the COG has to be WAY down low in a model paddler otherwise you'll get all kinds of nasty surprises on the water. The blades have to dip at the right height.
Ok when that's all done you now have to determine your propulsion system. I've seen people spend all kinds of money on expensive gear head motors and they often end up in the parts bin because theyr'e either too heavy or rotate too slow. Your ideal model paddle wheel rotation is about 120 RPM but up to 160 if you have tiny blades. Never direct drive your wheels but select a workable ratio depending on the revs of your engine(s). now that's a whole other subject!!! Select your gearing method (geared, belt, or chain...or even friction which I have STILL not experimented with). If you use gears, build a gearbox to deaden the sound as it's horrid to hear a lovely model grinding it's way across the pond!)
Simply, 12v volt systems are ideal for big models although 6v systems work fine and even one paddler I made with a 3v system was excellent! It's the batteries that make up lots of the weight and you can treat them as friend or foe depending on how you select and distribute them. I'm very interested in some of the new Li-Poly battery technology although you'll probably be much safer with conventional gel-cells. To overcome trim problems, you can even distribute smaller battery packs throughout the ship and wire them in series to your required voltage.
Phew, you may say!!! Well it's not that difficult if you don't mind breaking your back over the bathtub and going through a few hundred gallons of water...no you can't get IN the bath with your model I'm afraid! The secret is CONSTANT testing every time you make an alteration to the model and determining floating characteristics BEFORE you select and add each piece of equipment. (BTW..NEVER glue any mechanics or control systems permanently in a model paddler. Thrust tests to determine most efficient size of blades and wheel rotation are best done in a pond, although you can get a good idea in the bath by "feeling" the thrust with your hand and looking at the paddle wake.
I'm going to stop right now, 'coz I don't want to give you info overload (and I also have to go to work!!) But there's LOTS on this subject in the PD archives which Eddy spent dozens of hours copying from the old Yahoo site.
Good luck, keep us posted and holler if there's ANY help you need from now on with the most ctirical part of achieving a well behaved paddler on the water!!!
Regards
PJ
Victoria, BC Canada
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Wow, thanks PJ.
Sounds like I have adopted the right strategy with my building sequence and your advice is most helpful. Thanks for taking the time for such a good reply. One change of plan I will definitely be making as a result is to follow your suggestions on establishing how much additional weight I have to play with before making any further purchases of running gear and batteries. I have to admit I probably wouldn't have been that careful otherwise!
Ian
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Hi Ian,
There are a couple of photos of my Princess Elizabeth (See topic below this and my post) I currently have Richard's drive system installed, but am not happy with it and am planning to replace it with two geared motors from Greenweld - probably not until winter. My Hitec 3 channel RC has mixing built in so I will use that for steering. I may leave the rudder just for show, or I guess I could use a Y lead.
I do have some problems of stability, and need to address that. At the moment I have a speaker under the funnel for a steam whistle effect, but its not very good so can be removed. I don't think there is a problem of access to get the motors and batteries in. I currently have 2 x 6v 1.2AH SLA batteries in series to give 12 v, mounted under the fore deck. There is no problem with getting the correct water line, just a little lead needed, but she does roll into turns. Certainly keeping the superstructure weight down is a good start! My decks are ply, the rest plastic. You will see some figures are included, I have more but ran out of inspiration for the painting!
I haven't read PJs reply above yet, its late and I'm trying to catch on many things after a week away, but will certainly be doing so when I get chance. If you want more pics, let me know.
Barrie