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New Turntable Design

Thursday, July 19th, 2012

The difficulty with large turntables made of LEGO parts is making them strong enough and stiff enough to withstand the large loads and moments that get applied to them. I’ve made many turntables through the years and I’ve noticed a lot of them have suffered from wanting to pry apart under load.

A solution to this is to make a sandwich of roller bearings; basically a self-contained stack of rings separated by bearings. It’s difficult to put into words, so hopefully this diagram will help:

This is the design currently used in my latest crane. The model is meant to be a tower crane with a luffing boom, but it is also a test bed for some new ideas that I’ve had.

I built the turntable for this years ago. I intended to use it to make a hammerhead style tower crane, but decided later to turn it into a slightly different style with a luffing boom.

The turntable uses the same roller bearing ring as used on my 4×4 offroad crane.

Crane Project Updated

Wednesday, April 27th, 2011

Earlier this month I uploaded the final photos and descriptions for the crane project.

click to view Crane Project page

I finished the project a long time ago. I just recently got around to fully dismantling the pieces.

Custom Battery Power for the Power Functions System

Tuesday, April 5th, 2011

There has always been a trick to getting a custom battery box to work with PF (power functions) components. The issue is basically that there are 4 wires used in the PF cables, and depending on where you are in the circuit, the outer set or the inner set can be used (but not at the same time).

The system is mapped out in detail here: Many, many thanks to Philo for this diagram.

Implementing this information to make a custom PF battery box is what I’ve figured out recently. I wanted to make a custom (non-LEGO) battery holder that would take 8x rechargeable AA batteries. That would give me a total of 9.6 volts (rechargeable AA batteries are typically 1.2 V per cell as compared to traditional alkaline batteries that are 1.5 V each) and essentially more and longer lasting power for my models (in comparison to using a standard LEGO battery holder that only takes 6x AA batteries).

Below is a schematic showing the set-up for a custom battery box.

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You can find off the shelf non-LEGO battery holders in a variety of sizes and capacities. For AA batteries, I’ve found holders that take 4 each and also 8. In my example below, I’ve used two 4x AA holders and wired them together in series.

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This is for my UP 844 MOC. The 4xAA holders fit snugly into a space that is 8-studs wide.

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When I first started to play around with this, I somehow misinterpreted the information and ended up wiring the batteries up like this:

do NOT do this
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DO NOT DO THIS! This will make smoke come out of the PF IR receiver box.

My PF receiver is now a pristine example of what a PF receiver should look like from the outside. Inside, it’s toast.

The Crane Project Page

Thursday, March 18th, 2010

I’ve blogged about this project already, and I’ve finally gotten around to making a proper webpage for it on my site. Although at this point, the webpage isn’t finished yet :-)

At any rate, I just wanted to announce it and get it out there:

click to view page

Projects & Stuff – Feb. 2010

Thursday, February 11th, 2010

TexLUG’s display at the Healthy Baby and Child Expo in Houston was a good success (see more info and pics here). Our modular tables (based on the MichLUG design) made their debut and worked quite well.

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It was very nice to have a flat, level surface (roughly matching LEGO dimensions) to set our stuff on.

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Finally… I have taken photos of my train work :-) I’ve been messing around with two things. The first is an 8-wide bogie for freight cars.

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I did a lot of test runs at the HBCE show, and the fatal flaw in the design is that the outsides of the bogie fall off. Their attachment to the inner frame is a little weak, and that’s something I’ll revise.

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My other train work has been on a compact, powered bogie. This design will be useful to make a powered (using LEGO’s Power Functions parts) boxcar or perhaps a tender for a steam engine.

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It’s problem is that the whole assembly torques to one side when running. This presents a problem when running through switches. I’ll work on debugging this design.

I’m making the switch to using PF trains and getting away from the old 9V system. One of my old 9V motors died recently, and it’s just the push I needed to move to PF. Aside from that, I’m really attracted to making PF trains because I get to design and build the drive systems. That’s Technic-related stuff and that’s what I enjoy.

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And finally we have Project X.

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More about that later :-)

August Update

Friday, August 28th, 2009

Ugh… sorry that it’s been over a month since my last post here. I have not touched my bricks lately because of a hectic, super-busy schedule (work, life, etc.). That’s just how it goes…

Plus I’ve got a load of stuff to break down and sort. I’m not looking forward to that so much :-)

But hey, I built some trees for the train show last month. That’s something new here on the blog.

The big tree makes use of a bunch of different brown Technic connectors. These brown parts came mostly from all the old Starwars Technic sets I got years ago, and until now, I haven’t found a good use for them.

I also have a small back-log of ideas that I need to photograph and post here. Yep, I have plenty of house-keeping work to do!

On the side of serious building… I’m stuck in a rut. I cannot decide what to do. I’ve been wanting to build a new, very large crawler crane. I’ve built crawler cranes in the past, but I want to build the ultimate crawler crane MOC now that I have a lot of lessons learned and experience. The trouble is that everyone and their dog has built crawler cranes.

Sometimes I can’t get motiviated to build a MOC if there are too many similar ones out there by other builders! :-)

10-foot Bridge Success

Wednesday, July 15th, 2009

The bridge made it through our train show (see photo gallery)! It held up great. I was quite surprised to find that no member or cross bracking loosened noticeably. Usually, on trusses like this, a piece of cross bracing will come loose at some point due to vibrations from the trains.

packed up and ready for the show (click for larger)

I packed up the model by breaking it into four sections, and then piggybacked two section pairs together.

at the show (click for larger)

TexLUG’s layout consisted of three 8-foot long tables on either end of the bridge. One of our members (Matt S.) brought two 2.5-foot small truss bridges, and we used those on one side of the layout.

inside view (click for larger)

Super Chief crossing (click for larger)

The bridge did endure some heavy loads. At one point, we had two very long trains on the main loop, and they managed to end up on the bridge at the same time. Both trains were longer than the bridge :-)

Tony’s Allegheny (click for larger)

Their were a few accidental human contacts, but it survived. The worse was when my 4-year old son was underneath and suddenly popped up. He buckled a section of deck with his head. I managed to press it all back together quickly before the train came back around :-)

10-foot Bridge

Wednesday, July 8th, 2009

Over the past two weeks, I’ve been working on a new bridge. This will be for TexLUG’s display in an upcoming model train show.

The design length of the bridge, measured from center-to-center of the end supports, is 10.46 ft (3.19 m). The actual clear span will be just 1/2 inch, or so, less than this distance. The actual length, in reality, will be just slightly less or more, depending on how the structure settles.

click larger view

click larger view

I designed the bridge by determining the sizes of all the main members and also the deck and hanger pieces. I modifed my old truss spreadsheet for this design:

member sizes (click for larger)

deck members (click for larger)

I changed a few things about the construction of this bridge as compared to how I normally build trusses. I’ll describe all the fine details later on when I make a formal webpage for this bridge.

I had to correct a few things after I had mostly built the whole bridge. I wished I had realized some of these things from the start:

1. It wasn’t wide enough. The original design would have accomodated 8-wide trains just barely. However, I realized later that we’ll have 12-wide trains (i.e. “natural” 10-wides with extras hanging off the sides; e.g. Tony Sava’s monster Allegheny). I spent a lot of extra time making the portal frames wider.

2. Height. The end portals of the bridge were lower in height in the original design. I had to change up the design (by lengthening some members) to create extra height so that trains passing through would have adequte clearance.

3. Strength. After I had the original structure built, I noticed that the main chords deflected a lot when I loaded the bridge. I experienced the same trouble with the 17-foot bridge I built 4 years ago. So, I doubled-up most of the main truss chords on this new bridge. When Tony’s Allegheny rolls accross it, I want the bridge to stay intact! :-)

Anyway, the bridge is nearly complete, and I hope it will hold up this weekend at the show.

Small Turntable 2

Thursday, June 25th, 2009

Here’s a small turntable design using a thrust roller bearing. It’s still a work in progress, but I think I’ve sorted out the main geometry.

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Not shown is the matching ring. When assembled, it kinda creaks a little bit. I’ll have to fine-tune things to make it roll smoother. But I think this one will turn out well. I’d like to make a different design for the rollers – I’d like more of them and with smaller diameter wheels.

This design uses the “solid core” concept that I’ve used on some of my other turntable designs. This concept proved to be too flexible for a large turntable, but I’m hoping that it works for a smaller one like this.

I’ll post a part 2 later on when I finalize this design.

I’ve just finished a new medium-sized turntable design that looks like it will work well. This turntable will be used in my new tower crane (see the triangular cross-section truss entry below – these developments are all for the tower crane). I need to take some photos of this new turntable, but I’ll post it here in the coming weeks.

Crane Boom – Triangular Cross Section

Thursday, June 11th, 2009

One of my next projects is to build a simple tower crane. I’ve developed a new turntable (more on that later :-) ), and I’m working on a boom with a triangular cross section.

It’s not too hard to make a triangular cross section, but it’s an added challenge to create a design that will transition between sections of different heights.

This design (below) makes use of a truss chord on the top that is oriented normally. This allows the height of the truss section to change along its length fairly easily (it’s the link between sections that becomes very difficult unless the top chord is oriented normally).

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click for larger

My goal is to build the boom of the tower crane as a cantilever type and not use guy wires as typically seen on many tower cranes. The tower base of the crane will make use of the boom sections I built for the crane project.