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Author Topic: Norwegian Tjeld class MTB  (Read 44073 times)

Shipmate60

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Re: Norwegian Tjeld class MTB
« Reply #75 on: June 20, 2010, 01:24:13 PM »

Do you have access to an ammeter to check the current draw of the motors.
Mechanical misalignment or a tight bearing can put excess load on the motor.
What voltage are you running her on?

Bob
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #76 on: June 20, 2010, 01:30:22 PM »

I did check the current at each motor before I fitted the deck, and when they were attached to the shafts and spinning the propellers (out of the water), they were well within what was written in their specs. Can't remember exactly how much, though. However, now that you mention it, a good ide might be to test this again, and see if there is a difference between the starboard and the port side engine.

Spinning the propeller and shafts when they are connected to the engines, I can't feel any heavy load, and no significant difference between the port and starboard side. In addition, I think 30 A is a ridiculous amount of current for one engine to draw - they should draw no more than 18 according to their specs.

The batteries fitted are 12 volts.
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John W E

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Re: Norwegian Tjeld class MTB
« Reply #77 on: June 20, 2010, 02:51:14 PM »

hi ya there Sin Win

I noticed on your sketch that you have your 2 batteries connected together.  Now, some speed controllers do not like a shared voltage between 2 batteries or a single battery.  This is due to a curcuit which is built into them which creates a form of negative loop.   In other words, one speed controller can supply the other one and also it interacts with it, causing the electrics inside it to short.  Try running one speed controller off one battery.   See what the amperage draw is.   This may be the problem.

aye
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #78 on: June 20, 2010, 03:47:54 PM »

Is that so? I never knew! I will have to test that as soon as possible. Thanks a lot!

I really hope that is the problem, so that I can go on with more interesting tasks than cheching the electronics over and over again for months!
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #79 on: July 17, 2010, 09:15:35 PM »

In order to test the engines and electronics, I need the propellers to run in water. The nearest pond is not so far away, but it is both slippery slopes and a highly trafficated road to cross before you get there, so to walk back and forth just for a little test is not that fun when everything works for just two seconds...

Well - we have a large garden here, so a small part of it has now been converted to a small pool to test model boats. I just built it from some old plaking we have, and will fit some plastic etc. inside it tomorrow to keep the water in, before i can go on with the testing.

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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #80 on: July 18, 2010, 10:36:59 PM »

I may have found a solution! Or, perhaps, a workaround.



Having fitted the pool with plastic and filled it with water, I ran the engines for a long time today, in order to find out what is going wrong. After having blown several fuses, I gave up - but looked briefly through the manual for the Graupner MX 12 transmitter that I use. There I found something called servo travel (I think), which basically gives an adjustable travel range of servos from 0-150 %. I set this to 80 % for both engines, and tried again: the 25 A fuses did not blow, and I was able to run for a long time without any blown fuses.

Success! At least I hope so.

A few blown fuses from the testing...

The rest of the day was spent on painting details, and working on the mechanics for the turnable 40 mm gun.


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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #81 on: July 20, 2010, 09:23:40 PM »

I had to go to work yesterday (I'm currently on a holiday, but a crisis emerged), but it was all right, as I then had access to a laser engraver/cutter. With that, I cut out the supports for the torpedo tubes. I'm afraid they're not 100 % accurate, but based on blurry and small photos and the single drawing I have, it was the best I could manage.


4 mm acrylic parts glued together.


.. and with the torpedo tube fitted.

And now, the whole boat looks like this, with the superstructure and 40 mm loosely fitted:

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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #82 on: July 21, 2010, 01:26:18 AM »

Hi sinwin, This site contains a lot of detail/photographs  of  American PTF 'Nasty Class' survivors which might be useful, although torpedo tubes were'nt  fitted.  :-)

. http://www.ptfnasty.com/
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #83 on: July 21, 2010, 10:23:53 AM »

Thank you! I've glanced over the site, and it's gallery, but found few pictures of the torpedo tubes, since, as you say, they weren't fitted to the american models.

I have painted the torpedo tubes grey, but I'm not entirely sure that is correct. From the few colour pictures I have found, they appear grey, but might also be green - I've also seen both variants on model boats.
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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #84 on: July 21, 2010, 12:17:11 PM »

Hi Sinwin, The Tjeld's  torpedo tubes may be WW2 surplus from the Allies. Can you post best original photo? (They are unlikely to be Soviet  %). )  :}
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #85 on: July 21, 2010, 03:24:01 PM »

The Tjeld class used 533 mm ex german G7a T1 torpedoes. I guess a lot of torpedoes were left in Norway after the German capitulation, and G7a torpedoes were used on many vessels, and at several coastal forts - up until 1999/2000. I don't know exactly when, but some modifications were made to some of the torpedoes to make them steerable via cable, these were called T1 mod 1.

They might have used some allied torpedoes as well, so long as they were 21''.

The pictures I have found showing the torpedo tubes are these:
http://arkitekturnytt.no/uploaded_images/tjeld_MTB-747193.jpg
http://upload.wikimedia.org/wikipedia/commons/a/a0/Norwegian_MTB_Nasty.jpg
http://img377.imageshack.us/i/knmgeirhf7.jpg/

Not very much to go on, but I don't think I am very much off in my modelling - though it could certainly have been better.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #86 on: July 22, 2010, 03:39:58 PM »

The electronics certainly works! I went for a test run today, not only in the small pool I constructed, but in the pond close to the house.

After blowing one fuse on the starboard engine, I adjusted the servo travel on the transmitter to 70 %, after which I was able to run the boat for 15-20 minutes without any trouble at all.

At last!

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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #87 on: July 22, 2010, 06:05:21 PM »

Hi sindre, It might be worth laying both batteries down on their sides to help lower the boats's c of g (centre of gravity). This may improve stability/reduce roll, especially in fast turns. Have you tried running the hull with the batteries in tandem (one behind the other).These heavy batteries can be mounted on 'velcro' or thin rubber mat to prevent slipping during running trials to trim for the boat. Although this is a big hull with a large 'wet area', it's worth moving these heavy batteries around/experiment to find best placement.  :-) 
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #88 on: July 22, 2010, 06:29:46 PM »

Hi! Thanks for the tip. I have experimented quite a lot with the placement of the batteries, but never in tandem. However, I feel the boat is much more stable now, after removing one of the originally three batteries, and she makes a turn rather well, although some speed is lost (which is quite normal, though). Of course, the overall top speed is greatly reduced when I have to reduce the power given to the engines by 20 %, but as that seems to be the only thing that works, I guess I shall have to live with it.

I think I'll have to glue all the superstructure and deck details in place before I can experiment more with the placement of the batteries - but I will sure look into it!

Thanks a lot for your comment, though!
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HelgeBe

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Re: Norwegian Tjeld class MTB
« Reply #89 on: August 04, 2010, 12:51:28 PM »

Hello SinWin

Maybe these pictures can be of some help. They where taken by a clubmember whos has planned to build the same model but has not statred yet. I used them to build similar torpedotubes for the Norwegian Elco class MTB's

HelgeBe
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #90 on: August 04, 2010, 12:56:08 PM »

Wow, that is fantastic! These are by far the best photos I've seen of the Tjeld class, thank you so very much! Now that I'm going to make the details on the deck etc, this is a great help! It also, at last, allows me to see which parts should be which colour!

Again, thank you - this is a really great help!
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #91 on: August 26, 2010, 07:31:13 PM »

I've received even more photos of the Tjeld class, and now I see several details that I've either missed or modelled wrongly. There is still a lot of deck fittings to model, though, so I guess it will look better when I make those.

Anyway, I have now fitted the superstructure, torpedo tubes and fitted a servo to turn the 40 mm gun. I have also mounted two antennas on the side of the superstructure.

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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #92 on: August 27, 2010, 11:09:11 AM »

Really, this is not fun anymore! I went for a test drive yesterday, and after a few minutes, the port speed controller failed, and now only allows the engine to run backwards. This is the exact same fault as I had with the original speed controllers, and a problem that I had hoped was solved. The fuse (25 A) did not burst. What on earth could be wrong?

Argh. I am sick and tired of buying new speed controllers, tweaking and fixing the propultion...
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Martin [Admin]

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Re: Norwegian Tjeld class MTB
« Reply #93 on: August 27, 2010, 12:28:44 PM »


1. What speed controller(s) were you using?
2. What size motor?
3. What size prop?
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #94 on: August 27, 2010, 01:55:47 PM »

First of all, editing my own post: fixing the propulsion*

And then: thanks for your reply. To answer your questions:

1. I'm using two speed controllers, "Graupner Profi 40 7,2-12V BEC". Each one drives one engine, and now draws current from one battery each. I have also cut the positive wire from one of the controllers to the receiver, to eliminate the risk of the two BECs interfering with each other.

2. The engines are two Graupner Speed 700 Turbo C 9,6V. They are mounted as shown in some pictures at the first page of this thread. As shown, the caps of the motors are in connection with each other, electrically speaking, but should that be a problem?

3. The propellers are two Raboesch "C"-type propellers, 45 mm in diameter.

On each positive wire leading from the speed controllers to the engines, there are one 25 A fuse. Because these fuses constantly burst, I have set the "servo travel" function on my transmitter to 70 % for both channels driving the speed controllers/engines. This worked fine a few weeks ago, when I ran the boat for two hours. The instability puzzles me.

Now that it seems I'll have to change a speed controller again, I might as well buy some completely new ones of another kind or brand, but I don't know if that will help (ref. the fact that I've already changed from one kind to another). I have also bought a brand new receiver, and installed it, in case there was something wrong with it - but to no avail.
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Martin [Admin]

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Re: Norwegian Tjeld class MTB
« Reply #95 on: August 27, 2010, 02:27:05 PM »

With this kind of spec. and they didn't blow the 25Amp fuses, I would say you have a very good case of getting your money back!

Graupner SPEED PROFI 40R BEC:
Overheating guard Specification
Operating voltage: 7.2 ... 12 V Cell count: 6 ... 10 NiCd, NiMH
Peak current: 200 A Cont. current, forward: 40 A
Pulse frequency: 1 kHz BEC: 5 V / 1 A
BEC current, peak: 1.5 A
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marmoi

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Re: Norwegian Tjeld class MTB
« Reply #96 on: August 27, 2010, 02:33:02 PM »

Try connecting an ammeter into the motor side of the circuit and then run the boat up to full power while in your test tank (This can make you very wet, so cover the electrics).

Just by looking at your equipment specification I think with those motors and large props you are probably pulling a lot of current under load. It may not immediately damage the controller, but fuses will be stressed and fail after a short period if you keep loading the controller with high loads, it could also fail.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #97 on: August 27, 2010, 02:34:28 PM »

That is my thought as well! However, since this happens over and over again (this is the fourth speed controller I (or something else) break) with different speed controllers (first two Graupner Navy V30R, then one profi, and now the second profi) I am really wondering where the problem really is!

In addition, before I adjusted the servo travel function, I constantly blew both 25 and 30 A fuses when travelling at no more than two thirds speed.

And, for the record, I am using lead acid batteries - would that be a problem? They are 12 V, 7,2 Ah.


I would love to be able to measure the correct amount of current drawn by the motors, but I have no measuring equipment that is rated for more than about 10 A.
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marmoi

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Re: Norwegian Tjeld class MTB
« Reply #98 on: August 27, 2010, 02:42:36 PM »

The C type propellors will put quite a strain on the motors when run at great speed, I have never tried them on an MTB before, but have used them on a destroyer and they were very current hungry on that.

I think it maybe worth your while investing in a meter that can measure a higher current or look at different prop configurations.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #99 on: August 27, 2010, 04:59:23 PM »

So I can imagine. The thing is that I had just the same problem with the type A-propellers, which I had installed before the C-type. Those propellers pushed the boat forwards all right, but much of the energy was used up in cavitation and nothing else. However, the fuses blew at higher speeds and I destroyed the first set of speed controllers with the A-type propellers.


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