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A question about a "megatruck" for a train.


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#1 Madcat2000

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Posted 30 April 2009 - 04:01 AM

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What it is is one of the four "megatrucks" used on the Dora and Gustav railway guns. The problem it the things under the normal three axel trucks might not allow them to turn enough for them to corner. I have a few pics from LDD to show you the problem. the reason this thing is being built in LDD is that I don't have the peices to build this thing in real bricks. I also need to know if a 6 or 4 long version of the peice is possable.

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Edited by TheBrickster, 02 May 2009 - 06:54 AM.


#2 Captain Zuloo

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Posted 30 April 2009 - 07:58 AM

I'm not entirely sure what you're asking. Could you please try and use more words to descibe your problem? And if you are only building it in LDD, what does it matter if it doesn't [i]really[i] turn?

EDIT: Are you asking if three wheeled bogies will go around standard L gauge curves? If so, the answer is yes. :pir-wink:

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#3 DaCheese

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Posted 30 April 2009 - 12:32 PM

A quick Google search after you mentioned Dora and Gustav the other day with no explanation as to what they were revealed that these things ran on two parallel tracks. That's not going to be practical with Lego trains unless you use flexible track for a curve of larger radius than the standard curve.

Like Captain Zuloo, I wouldn't worry about getting those bogies around corners. The wheelbase of each is short enough, and you'd be surprised how little articulation the coach you get with the Emerald Night needs to get around curves.

#4 Madcat2000

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Posted 02 May 2009 - 05:26 AM

Sorry if I wasn't clear with what I was asking. What I'm asking it will this work and still allow both of the trucks to turn.
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Or do I need to make the thing between the trucks smaller.

Also so you can better understand how this thing works ans it isn't accurate to the original guns(it will probably only vaguely resemble them when I'm done). What I did so that the thing could go around corners was make the "megatrucks"(normal train baseplates holding the smaller normal trucks.
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Here's a referance pic of a model of Dora
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Edited by Madcat2000, 02 May 2009 - 05:28 AM.


#5 SavaTheAggie

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Posted 02 May 2009 - 06:49 AM

Unfortunately, unless you use some of the new flex track, you won't have to worry about making turns with the cannon - LEGO only makes one radius of curve, and you'll need two to make it take any curves.  

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#6 Captain Zuloo

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Posted 02 May 2009 - 08:58 AM

View PostMadcat2000, on May 2 2009, 03:26 PM, said:

Sorry if I wasn't clear with what I was asking. What I'm asking it will this work and still allow both of the trucks to turn.
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Or do I need to make the thing between the trucks smaller.
No, I'm pretty certain that will turn. But that x 2 will be a little tricky. Mainly because you will need to use a mammoth ammount of Flexible Track to create a trackplan that suck a bizzarre train will run on.

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#7 Madcat2000

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Posted 02 May 2009 - 05:58 PM

If you look closely at the pic I posted of the whole structure you should be able to see the technic rods are in tight holders on the baseplate but normal hole holder where the main structure will be, this allows it to "stretch" when goung around corners. You probably didn't notice the turntables in the center on the train baseplates either this should allow it to turn, but I'm not entirely sure. Here's some pics to better explain it.

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#8 SavaTheAggie

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Posted 02 May 2009 - 06:59 PM

View PostMadcat2000, on May 2 2009, 11:58 AM, said:

If you look closely at the pic I posted of the whole structure you should be able to see the technic rods are in tight holders on the baseplate but normal hole holder where the main structure will be, this allows it to "stretch" when goung around corners. You probably didn't notice the turntables in the center on the train baseplates either this should allow it to turn, but I'm not entirely sure. Here's some pics to better explain it.

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That's awful slick, I don't see you haven't many issues at all, then.

--Tony

#9 Doctor Sinister

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Posted 03 May 2009 - 10:30 PM

Is this going to be powered?  If so, I can foresee some major problems:

1)  It will be heavy.  REALLY heavy.  My own railway cannon runs on one track and is already too heavy for one engine at sustained runs - I need a second.  If you are going to include the ammunition train behind the gun, plus that massive superstructure on top, you'll need two engines, possibly three PER TRACK.  I.E. between 4 and 6 engines.

2)  Assuming number 1 above is correct, you'll find that not all LEGO motors run at precisely the same speeds - and very soon you will end up in a bit of a mess with the thing going seriously out of alignment, especially if you are running 6 motors.

3)  To aim the original guns, German engineers had to shunt them back and forth along special semi-circular track laid just so they could angle the gun.  You might have to do the same to get some realism.  The alternative is to have the gun rotate, which would cause its own problems with blowing the train off the track every time it fired and possibly widen the superstructure even more to get a decent looking turntable.

4)  I'm not sure the friction in the technic axles will allow you to freely rotate as your picture indicates.

There's a very good reason these guns went at insanely slow speeds.

I wish you luck - but perhaps you could simply arm your railway cannon with nuclear tipped rocket assisted shells which would allow you to reduce the calibre, size of gun and save you LOTS of $$$.

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#10 Madcat2000

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Posted 03 May 2009 - 10:52 PM

View PostDoctor Sinister, on May 3 2009, 04:30 PM, said:

Is this going to be powered?  If so, I can foresee some major problems:

1)  It will be heavy.  REALLY heavy.  My own railway cannon runs on one track and is already too heavy for one engine at sustained runs - I need a second.  If you are going to include the ammunition train behind the gun, plus that massive superstructure on top, you'll need two engines, possibly three PER TRACK.  I.E. between 4 and 6 engines.

2)  Assuming number 1 above is correct, you'll find that not all LEGO motors run at precisely the same speeds - and very soon you will end up in a bit of a mess with the thing going seriously out of alignment, especially if you are running 6 motors.

3)  To aim the original guns, German engineers had to shunt them back and forth along special semi-circular track laid just so they could angle the gun.  You might have to do the same to get some realism.  The alternative is to have the gun rotate, which would cause its own problems with blowing the train off the track every time it fired and possibly widen the superstructure even more to get a decent looking turntable.

4)  I'm not sure the friction in the technic axles will allow you to freely rotate as your picture indicates.

There's a very good reason these guns went at insanely slow speeds.

I wish you luck - but perhaps you could simply arm your railway cannon with nuclear tipped rocket assisted shells which would allow you to reduce the calibre, size of gun and save you LOTS of $$$.

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1. Well what kind of motors were you using? I heard the thing the Emeral Night uses is pretty powerful but I don't think anyone knows about the normal PF train motor. If the PF steam engine setup is powerful I might make a pair of deisals that use stem engine wheels in a 4-8-4 setup.

2. I think PF fixed the variable speed between motors problem.

3. I'm using the original design just making it more modern looking.

4.I'm not sure what you mean. The mechanism is hard to understand through pictures.

#11 Doctor Sinister

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Posted 04 May 2009 - 12:56 AM

View PostMadcat2000, on May 3 2009, 11:52 PM, said:

1. Well what kind of motors were you using? I heard the thing the Emeral Night uses is pretty powerful but I don't think anyone knows about the normal PF train motor. If the PF steam engine setup is powerful I might make a pair of deisals that use stem engine wheels in a 4-8-4 setup.

I'm using an IR train motor.  A 9V might be more powerful but I've never tried it as all mine are tied up in my town.  However fellow AFOLs in my LUG will regularly run two train motors even on a 9V system on any rake of substantial length.  The problem here is not a rake of course but the sheer weight of the gun carriage which amounts to (more than) the same thing.  Your gun carriage is going to be spread across two parallel tracks with weight in between and a complicated steering mechanism for curves.  As I say, I fear you are going to need a heck of a lot of power to pull this thing along your double-track, even if it's just to get around those corners,  and you may end up having to co-ordinate up to 6 engines to get it moving.  For the sake of realism, I personally wouldn't just run the gun on its own you see, my own railway cannon has 7 carriages, only one of which is the actual weapon.  I've got troop carriages (Dora had 250 crew JUST to operate the gun, plus several thousand supporting troops to look after her), a flak carriage, the loading crane, ammunition storage.  You'd need some or all of that in tow as well.  Mind you, that would look REALLY cool.

View PostMadcat2000, on May 3 2009, 11:52 PM, said:

2. I think PF fixed the variable speed between motors problem.

I'm not so sure it did - I'm not talking about a specific LEGO problem here, every motor is unique, it's impossible to get two motors no matter how similar they might be running at precisely identical speeds.  Even a difference of more than a few RPM is going to cause problems over a period of time.

View PostMadcat2000, on May 3 2009, 11:52 PM, said:

3. I'm using the original design just making it more modern looking.

OK, so then to aim it you're going to need that semi-circle of track to shunt it back and forth.

View PostMadcat2000, on May 3 2009, 11:52 PM, said:

4.I'm not sure what you mean. The mechanism is hard to understand through pictures.

As I understand it, you have two turntable mechanisms attached by a cross-beam.  The cross-beam has a variable width through the use of a technic axle down the middle.  It looks very cool, but given that you explicitly want the two carriages on each parallel track to stay together, you must have that axle secured tightly on both sides or they will drift apart.  Securing them tightly with the technic axle will make it very difficult for the widening mechanism to work - the friction will likely tear one side from the carriage as it tries to lengthen and/or push one carriage off the track as it tries to shorten.  To get around that you'll have to make one side loose, in which case you're back to the issue of the two sides going their separate ways.

Unless I've misunderstood of course and there's something clever going on underneath.  I suppose if you had plates on top and a technic bush on one end of an otherwise free-floating axle it would create a stop-point for the movement, but it might be a bit rickety during movement.

AND the other problem that your setup presents is that the entire weight of the gun will be carried on the top of your cross-beams. Given that the weight is down the centre and not directly above the carriages, they might just decide to angle apart anyway.

I'll give this some thought as I'd love to see your MOC take shape - although it could be pricey.

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#12 Madcat2000

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Posted 04 May 2009 - 05:23 AM

I think I'll put the support cars on a pair of seperate armored trains that run ahead to clear any resistance. That should alleviate a fair amount of weight. The actual dora and gustav used steam engines over long distances and once they got close to the site and assembled it would be moved by a pair if oil engine so the enemy couldn't see the smoke of a steam train. So most likely it will at first be pulled by a pair of Emerald Nights, until I can build more suitable engines. Also just so you know the RC engines are notoriously bad for pulling power and quality,which if I read right is what you used :laugh: , I heard of a guy whose RC passenger train could barely pull itself in normal configureation. If that is the case a pair of ENs should be enough for the gun atleast. Thanks for mentioning that the technic beams might not be able to support it, I'll try to double it or find a way to make it work.

#13 Doctor Sinister

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Posted 04 May 2009 - 01:48 PM

View PostMadcat2000, on May 4 2009, 06:23 AM, said:

I think I'll put the support cars on a pair of seperate armored trains that run ahead to clear any resistance. That should alleviate a fair amount of weight. The actual dora and gustav used steam engines over long distances and once they got close to the site and assembled it would be moved by a pair if oil engine so the enemy couldn't see the smoke of a steam train. So most likely it will at first be pulled by a pair of Emerald Nights, until I can build more suitable engines. Also just so you know the RC engines are notoriously bad for pulling power and quality,which if I read right is what you used :laugh: , I heard of a guy whose RC passenger train could barely pull itself in normal configureation. If that is the case a pair of ENs should be enough for the gun atleast. Thanks for mentioning that the technic beams might not be able to support it, I'll try to double it or find a way to make it work.

Cool, I'll eagerly await your updates!

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#14 DaCheese

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Posted 04 May 2009 - 11:37 PM

I'm struggling to work out how the original gun would've gone around corners on parallel tracks, because the outside line on a curve will always be slightly longer than the inside one. With your design surely there's not just a problem with varying loco or motor unit speeds causing the whole thing to go out of alignment, if you're not going to use flexible track for outer bends there'll be a pretty big difference between both tracks. This will also cause the whole thing to go pear shaped...

Anyway, good luck.

#15 Madcat2000

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Posted 06 May 2009 - 11:20 PM

Would it be possably to move the turntables back to the back of the train baseplate to allow more room on the front of it or would cause problems like puting all the weight on the back truck and mabey causing the front end to even rise up a little?




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