So I'm working on a gatehouse/tower combo.

The idea is that the thing will have a mechanized portcullis and drawbridge. While making a drawbridge is quite easy and there are several methods I do seem to have trouble with making the portcullis go up and down. Obviously I don't want to have a rinky dinky portcullis on a winch. That's easy and not what I'm looking for.

What I want to achieve is a portcullis that has racks alongside and is winched up with a wormgear, to ensure that it goes up and down straight there will be an additional transaxle transferring the rotating motion to the other side of the cullis. This mechanism has a great benefit in that it's self locking (the wormgear ensures that). The downside is the gearing, since it requires a lot of revolutions but that's not an issue. As soon as the main mechanism is done I will transfer the operation under the landscaping into a shed or some other auxiliary building which will house a gearbox to gear it up.

So what's the problem you ask? Well, while such a construction is fairly easy to build using technic exclusively it's a bit harder to mount in System. The problem I face is that it's immensely hard to lock the portcullis in the vertical plane. The groove is either to narrow for the cullis + rack to fit in or it is to wide which means that it slips the gear.

Has anyone ever tried doing this? I've searched a lot of fora and websites on mechanizing castle features but I have to say that this is one topic that is quite poorly covered everywhere.

Any help or ideas are most welcome.

P.S. While writing this I came up with the idea to mount the portcullis on axles going through one of these little fellas:

Actually that sounds like neat idea, I'll get right to it. :DD Any input is still highly welcome though!!!

Thanx in advance!

Maybe this: http://www.bricklink.com/catalogItem.asp?P=2428

and this: http://www.bricklink.com/catalogItem.asp?P=2426

The rack is pretty stiff you may need to use XL motor to drive it if you don't use any gearing.

Wow. I never knew such a part existed!!!

I guess that a rack and pinion mechanism using this part could be made self locking by gearing down a low torque input. The pinion will require a lot of torque to allow the portcullis to fall and will to all intents 'lock' the portcullis in the up position. The downside is that in such a case I would really need to PF the mechanism since it will require a lot of turns to move the portcullis and my four year old might not want to turn the knob 30 times. ;)

The reason I was opting for a wormgear setup is that I could reverse the torque i.e. high(er) input torque and few revolutions would generate a low torque but a lot of spinning on the output. I figure that the low torque on the output should still be enough to raise the grate which isn't all that heavy. The advantage is that it will work fine with a manual setup and should I want to PF it, I just need to reverse the gearing.

I hope this is kind of clear and that I'm not missing something obvious here. :DD

The self-locking is an important feature to me. I don't want no ratchet-doohickeys locking the cogs for the little'un's sake and the space limitations rule out any form of a mechanical liftarm self-lock mechanism.

I know I'm being picky. :DDD

Anyway, thanks for the input!! I'll order some of these and will have a go at both.

1. Rack and pinion with the specialized piece

2. Wormgear on a frame as per my OP.

Will keep you guys posted, should anyone actually be interested. ;)

Edited May 21, 201212 yr by chelman

I would love to see it when you are done I just didn't know how to help you with your problem

Easy solution would be to build the whole gate sideways and then snot it upright against the wall with headlight bricks. There's nothing wrong with using technic either; just make sure you conceal is with system parts.

Lots of real world castles have facades and mechanisms that appear one way but are actually quite different when you look behind the build.

If you're trying to challenge yourself to build something entirely out of system that's great, but it's far more practical to use concealed gears and cogs for motorized action.

I would love to see a picture of what you have thus far - it would help clarify what you're trying to do a bit, as I'm new to all of this. However, from your description, I'm wondering if you could make the portcullis a bit wider than what's actually going to be seen. That way, you could build slots just wide enough to hold it in place horizontally, and then widen them just enough to hold the gear and rack. I'd give you a picture of a drawing, but I'm at work right now - I'll try some ASCII art :P

________

________|

......|_|

...O<=========

______| |

________|

Top down:

O is the gear,

< is the rack,

= is portcullis and

| | is a brick

... are empty space (empty spaces are trimmed after posting)

Obviously, this isn't going to be scale on what you want, but I think it gets the point I'm trying to make across.

I don't know if this is exactly what you want, but I hope I helped a bit. Oh, and if you're doing this the way I think you're doing this, it's an AWESOME method, and your kid is truly lucky.

Rawel

Edited June 13, 201212 yr by Rawel

I think everything about the mechanics depends on the portcullis. One I am currently working on is a 1x1 brick thick, whereas lego's are a bar. Not only thickness but area and weight are a big thing. I would love to share some ideas, or walk people through the construction if it would help.

So I guess, like many people have said, what do you have so far? From what I've read, I think you might be restricting yourself with the mechanism or by not using technic/bionicle.

Other potential mechanisms you might want to consider would be something like a ratchet. This can be placed either on the gear/crank box itself, or on the tracks the gate slides in. The effect could yield a couple things. My personal favorite is the spaced out clicks when the portcullis catch points reach the hinged track prongs. Then at the top, when the lever for the track prongs is released, it can slam shut. If the ratchet is placed at the reel, then it can act more like an on off switch that you hit whenever your finished cranking. This method still lets you have it slam shut when you want. (And of course "slam" is only as fast as your reel can unwind. If your using chains, it can be pretty quick and cool sounding.)

Lmk what you think, and if it would be helpful for a progressive MOC walkthrough. Otherwise we'll probably just post it when it's finished.

hoping to see a picture of your attempts and success , and nor did i now thode parts exsisted , (ordered already lol )

I found a solution to that problem in one of my own MOCs:

You can see that behind the portcullis is a line of teeth, which will move the gate up or down when the gear whose own teeth are in it is spun. Obviously this gearbox can be as complex as one would like - mine is simple for playability's sake - and the design is adaptable, but there's the basic idea! Hope it helped!

Cool! I'm definitely going to have to incorporate this idea in my next castle build.