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Author Topic: Using a pump for bow thruster - advice wanted!  (Read 6683 times)

Colin Bishop

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Using a pump for bow thruster - advice wanted!
« on: June 03, 2010, 10:33:49 AM »

A while back I bought the Revell Queen Mary 2 plastic kit with a view to motorising it. The late lamented Richard Webb wrote a review on doing this in Model Boats and said he used a Halfords windscreen washer pump Ref: HWP21 to use for the bow thruster. He didn't make it clear just how he had fitted it though. I have bought the pump - photo below - and it has two washer tube connectors plus a big hole in the back where it is intended to mate to the car washer bottle. I'm not at all clear just how this is supposed to work in the boat!
 
My setup has a washer tube fitted to each side of the bow of the model and I had assumed that it would be possible to suck water from one side and push it out the other and vice versa but this pump doesn't seem to lend itself to this configuration. Richard refers to sucking water from the underside of the hull and squirting it out of the bow thruster holes but I'm not at all clear how he did this if using this pump.
 
Any ideas anyone, or are there alternative pumps which could be used as this one seems a bit heavy for the model and is of course 12v.

Colin

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6705russell

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Re: Using a pump for bow thruster - advice wanted!
« Reply #1 on: June 03, 2010, 12:01:29 PM »

Hi Colin

You need the other type of washer pump, one inlet and one outlet or use the two pumps you have and close off one of the outlets, ideally you will need the inlet pipe tubing to the underneath of the hull...

Russ
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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #2 on: June 03, 2010, 12:19:10 PM »

Hi Ross, thanks. What are those natty litle pumps you are using there? They look like what I'm after.

Colin
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Martin [Admin]

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cos918

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Re: Using a pump for bow thruster - advice wanted!
« Reply #4 on: June 03, 2010, 02:38:15 PM »

Hi Colin
Here is a QM2 build worth looking at.

John


http://www.rcgroups.com/forums/showthread.php?t=1179184
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Patrick Henry

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Re: Using a pump for bow thruster - advice wanted!
« Reply #5 on: June 03, 2010, 03:19:54 PM »

Try this, Colin...Halfords screenwash pump, about 15.00 or maybe less, I can't remember exactly how much it was. Sucks water in one side, blows it out of the other...microswitch control, or use an esc if you have room.


Rich

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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #6 on: June 03, 2010, 04:55:07 PM »

Martin, thanks but those pumps all look a bit big - not much room/available payload in the hull so eveything has to be small.

John, hadn't seen that build. Mine would be far less ambitious. I have some cheap plastic windup speedboats with outboard drives which can be taken apart and converted to pods. The idea is to put vertical shafts on them and drive them via horizontal pulleys within the hull. It may even work!

Rich, that looks like the pump I should have bought...

Thanks for all the info so far.

Colin
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Umi_Ryuzuki

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Re: Using a pump for bow thruster - advice wanted!
« Reply #7 on: June 03, 2010, 06:33:10 PM »

Check out how Audrey is working this out...

http://www.rcgroups.com/forums/showthread.php?t=1179184&page=2

 8)
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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #8 on: June 03, 2010, 06:44:29 PM »

Yes Umi, I've seen that. Vast overkill for me I'm afraid!

I find it a bit puzzling that someone would devote so much expertise and skill into modifying a kit when it could be applied to building a model from scratch which would then be all your own work. But whatever floats your boat I suppose!

My QM2 build is really just a diversion for my own amusement rather than a serious project as such.

Colin
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Umi_Ryuzuki

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Re: Using a pump for bow thruster - advice wanted!
« Reply #9 on: June 03, 2010, 07:06:21 PM »

He's almost local, so if we can get Audrey to a meet in Seattle or Portland, we'll work on
getting him to build bigger...  O0
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Subculture

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Re: Using a pump for bow thruster - advice wanted!
« Reply #10 on: June 04, 2010, 07:51:28 AM »

A very simple and inexpensive solution is to use two very small motors with equally tiny props set into a small tube running from port to starboard. Mount the motors each side, and set them up with a small esc or microswitches.

Source of these motors and props? Look on ebay for those tiny little speedboat toys you can pick up for a couple of pounds or one of the tiny little R/C submarines. Most of these motors are designed to run off about 3 volts, so you could run them off a separate supply or add a 3.3 volt voltage regulator if you're electronically inclined.

Another idea is to use some small motors (got any knackered servos?) and twist some small two bladed props up out of some thin tin sheet or brass and just solder or epoxy them on the end of the motr shaft.

portside II

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Re: Using a pump for bow thruster - advice wanted!
« Reply #11 on: June 04, 2010, 09:13:03 AM »

I did that on a 8 foot tanker using two props , very effective .
The reversable fuel pump idea is good as the size of the model would allow the pump to be efficient.
A slightly cheaper option based on your original idea using a washer pump ,
http://cgi.ebay.co.uk/TWIN-OUTLET-WINDSCREEN-WASHER-PUMP-Opel-Astra-G-Estate-_W0QQitemZ300425295055QQcmdZViewItem?rvr_id=&rvr_id=&cguid=d7026dca1250a0e201920ba2fbf49c09
but use the pump off a astra estate which is reversable bit the inlet is smaller and neater ,
it can be fitted into the hull bottom with a grommit and removed easly, these pumps are more than enough for a boat of that size.
Hope this helps.
daz
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Patrick Henry

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Re: Using a pump for bow thruster - advice wanted!
« Reply #12 on: June 04, 2010, 10:02:00 AM »

Favourite IF you can find one, is an old 6volt VW Beetle screenwash pump. All the modern ones need 12volts to pump efficiently.  6v Beetles are as rare as hen's teeth nowadays though...


Rich
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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #13 on: June 04, 2010, 10:17:22 AM »

Thanks for the suggestions guys but remember this is a very small model, all up displacement around 1.5kg, a high CG and an equipment payload including batteries, radio and motors of about 1kg!

Colin
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Patrick Henry

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Re: Using a pump for bow thruster - advice wanted!
« Reply #14 on: June 04, 2010, 10:21:57 AM »

You'll need to be very careful Colin, with the weight distribution. Enterprise is just over a metre in length, and I found I'd overdone it with all the stuff I installed in her, ended up removing most of it, much to my annoyance.

I wish you well with your project...


Rich
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Martin [Admin]

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Patrick Henry

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Re: Using a pump for bow thruster - advice wanted!
« Reply #16 on: June 04, 2010, 10:59:17 AM »

BA will probably want to borrow that back...   O0
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Umi_Ryuzuki

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Re: Using a pump for bow thruster - advice wanted!
« Reply #17 on: June 11, 2010, 03:31:12 AM »

Rich,

I like the look of the Halfords screenwasher pump

And you say it runs both ways, just reverse the current?

 :-)

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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #18 on: June 11, 2010, 06:07:30 PM »

Umi,

Yes, I have now got around to testing it in the kitchen sink! The water of course is drawn in through the body of the pump and then expelled via either one of the two outlets depending on polarity. It gives a healthy stream at 12v but is very weak at 6v. 9v might be OK for my plastic model project but I will have to rig up that voltage to try it. The pump weighs just under 200g.

As a windscreen (windshield) washer pump one has to assume that it is not rated for continuous running at 12v though.

Colin
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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #19 on: June 14, 2010, 06:49:32 PM »

The pump seems to work quite well on 9.6v. I have been playing around with weights and was rather surprised that all the plastic parts on the sprues, (omitting the stand) weigh just on 1kg. It's difficult to estimate what their net weight on the model is likely to be 0.9kg maybe? When you add the weights for the motors, batteries, running gear etc the hull floats around 7mm deeper than the indicated waterline and that makes no allowance for a possible external keel for stability. The only obvious place to save weight seems to be to use a LiPo battery but then you are talking expensive chargers.

My original idea was to use an 8 or 9 cell 2200NiMh pack which would run the pump direct with a 6v output regulator to supply the RX and 3-6v main motors.

Not sure if this is a practical working project really. Not at an economic cost anyway. The weight of all the plastic is the killer, almost 1.5kg for hull and parts. Shaving bits off here and there isn't going to make much of an inroad into that.

Colin
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Re: Using a pump for bow thruster - advice wanted!
« Reply #20 on: June 14, 2010, 07:05:35 PM »

The only obvious place to save weight seems to be to use a LiPo battery but then you are talking expensive chargers.

Colin

Depends where you get them from and what level of sophistication you need-

http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6507

cos918

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Re: Using a pump for bow thruster - advice wanted!
« Reply #21 on: June 14, 2010, 10:33:03 PM »

Colin
I have a made up model of the Revell QM2,no motors or any RC. She clocks in at 933 grams.
I have got the same problem with some of my plastic kit models. I have started using LIPO batterys. Got a IMAX B6 charger on Ebay for 10+10p/p. it is a realy good charger it can do lipo, life, nimh, nicad ,pb, etc batterys
John
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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #22 on: June 14, 2010, 10:38:34 PM »

Thanks guys that is helpful. Looks like the net weight of the parts is not as much as I had feared. I don't mind the waterline being a bit on the high side as when the model is afloat on a rippled surface it won't be noticeable. I just don't want to spend a lot of money and then find it doesn't work!

Colin
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malcolmfrary

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Re: Using a pump for bow thruster - advice wanted!
« Reply #23 on: June 15, 2010, 01:24:51 PM »

If the batteries you considered are AA size, You might want to consider AAA NiMH cells.  Granted not as much capacity therefore a shorter run time, but I get well over an hour on my Tuna boat.  I don't need a special charger, either.  Making up your own sausage string of cells gives you the opportunity to plant their weight anywhere you need to, rather than being dictated to by the size/shape of a pack. 
Losing excess plastic from the decks inside the superstructure saves some weight, but more importantly saves it where you really need to lose it, upstairs.  If you then wind up with surplus buoyancy, you get the chance to use bits of flat lead in the bottom of the hull, which further helps with marginal stability.
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Colin Bishop

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Re: Using a pump for bow thruster - advice wanted!
« Reply #24 on: June 21, 2010, 07:28:08 PM »

I've been playing around with the other end of the boat. I had high hopes of being able to use the drive section of some wind up outboard motors from a cheap plastic toy. The drive leg is not much bigger than the propulsion pods in the kit. This would have involved a wonderful Heath Robinson system using lots of horizontal pulleys and drive belts, rotating inner pods and vertically mounted motors. Mechanically it is quite feasible but when I did a test with an adapted drive unit it was apparent that the tiny teeth on the nylon bevel gears would rapidly wear out. Back to the drawing board. I think I will just have to pinch the idea from another converter of using conventional twin screws with the props mounted just behind the inner pods which can be adapted to act as rudders. The actual propulsion will be reasonably well hidden. It's not a very serious project so I will just keep on dabbling.

Colin

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