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Forum - Table-spanning module

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I'm currently in the planning phase of the largest module I've ever considered (if it comes off, it'll probably be the largest thing I've ever built, out of any material!). But before I get too far into it, I want to share what I'm thinking, so that those with more experience than I can warn me of pitfalls, or even tell me that I'm dreaming.

The aim is to have a module that can span a ~1m gap between two tables, and be high enough that people can walk underneath. I've designed a modular truss that I can use for the structure, but the particular portion I wanted to ask your opinion on was the conveyor belt.

In all I've seen of this kind of module, the conveyor belt goes up one side, and the balls roll along the not-quite-horizontal section, and then down the other side. But this requires 1) a jam-free way to pick the balls off the conveyor and 2) some way to dissipate the kinetic energy of the balls as they fall back down to table level. I'm planning to deal with both of those by having the conveyor belt itself go all the way across and down (and then back again). It'll look something like this: roughplan.png

What are your thoughts? Is this something that's actually doable? Or is the reason I haven't seen anything like this before that it's a terrible idea. I realise that it's probably going to be hundreds of dollars for the track alone, but I think it's worth it to not have to worry about crawling under tables.


Edit: I'm going to forge ahead anyway, at least while I can do it on my computer and I don't have to buy any parts. I'll post screenshots below, but keep the .ldr file (for anyone who wants more detail than you get from an image) up to date at this link.

Posted by Captainowie on 26 September 2015 at 13:41.
Edited by Captainowie on 2 October 2015 at 10:05.

The reason you haven't seen it before is probably that not many have the financial means to build on this scale. Haven't built anything like it myself, but my main worry would be friction. I don't know how much force the links can stand or how it will affect the wear on the sprockets. Bending them backwards on the underside of the bridge needs extra attention to minimize friction.

Other than that, just keep the frame light and the base wide.

Posted by Torso on 28 September 2015 at 15:12.

I think it's do-able. Thomas Mueller (a.k.a. tmspecial) has built conveyors at that scale. The price may not be as bad as you think. When I bought links for the 2014 Brickworld module, I found a very reasonable price at (~12 USD for 100 links plus sprockets). Your mileage may vary, of course.

I've never done a conveyor that long, nor an inverted one, so I can't help on that score.

Posted by ALittleSlow (administrator) on 29 September 2015 at 01:17.

Thanks for your input thus far. I'm building the whole thing in LDraw first (mainly so that I know how many parts to order). I did think of Thomas and his oversize modules - I've emailed him suggesting he take a look at this thread, but haven't heard back.

Would I be annoying people if I posted progress on various components, made comments on some design decisions, and sought feedback on how it's going?


Posted by Captainowie on 29 September 2015 at 09:23.

I think everyone likes seeing the progress. It can be hard to come up with responses to it, so don't see silence as a sign of lack of interest.

Posted by Torso on 29 September 2015 at 10:31.

Friction will be a killer, use sparingly :). Where are the balls coming off the conveyor? How are you getting the balls off the conveyor? Definitely good to see progress shots, learning for everyone.

Posted by Tom Atkinson on 30 September 2015 at 17:32.

Thanks for the encouragement. I'm in the middle of trying to buy a house on the other side of the country at the moment, but I hope to be able to put some pictures up in a couple of days or so.

Tom: I haven't yet got to anything specific regarding the pick-off point, but I'm planning it to be near the bottom of the leg, using essentially the reverse of how balls are typically loaded onto a conveyor - the ball will come down the belt resting on two pins, the pick-off will be a platform with gaps for the pins to pass through, and the ball will roll on down. (Does that make as much sense as it does in my imagination?)


Posted by Captainowie on 1 October 2015 at 13:07.

Ok, here are the first progress shots. I've started from the top - this is the front corner, where the conveyor comes up and goes across.

Spanner-top-front-corner1.png Spanner-top-front-corner2.png

Some design notes so far:

  • I'm planning to acquire most of the parts for this via LUGBULK, so I'm aiming to keep part variety down, rather than part count. Strictly speaking, I'm trying to cut down on the variety of parts that I need in large quantities - if I only need a couple of them, then that's fine.
  • Each truss segment has a 15L beam on each corner to provide a restraint for the track links.
  • I use a similar design for the horizontal truss as for the vertical. The vertical one uses 15L beams to join the truss segments, so is a little sparser than the horizontal truss, which uses 11L beams. This is to reduce the gap between the beams that the tread links sit on to one stud (rather than five). This is not such a problem in the vertical sections, because the beam form more of a guidepath for the track, than something for the track to rest on.
  • My quick not-scientific-at-all test indicates that tracks sliding along beams is quite smooth. I wonder how that'll scale though
  • I may have to put rollers at the spots where the track leaves the beams for the inverted curve. I won't be able to see if that's needed until I build the thing and see how it behaves

The thing I'm least happy with at the moment is the fact that the supports for the sprocket are so far apart. Even though the sprocket is only one stud thick at the axle, there's three studs between the supporting beams because of the thickness of the collar on the sprocket. Can I get a show of hands as to whether I should put a 3L beam in there on either side of the sprocket to give the axle just a bit more support?


Posted by Captainowie on 3 October 2015 at 12:38.

Spanning tables is definitely possible. Lots of people including myself have done it. As you mentioned a vertical conveyor lift with a slightly sloped bridge seems to be the most common approach. There have been lots of different approaches getting the balls down.

From my experience the best way to get the tread is LEGO Education. I am not sure if they have a division in Australia.

Posted by Tmspecial on 5 October 2015 at 02:05.

The problem with using LUGBULK to get the parts is the fact that you won't receive them until this time next year. Therefore you will not be able to complete the GBC until the 2017 season.

Posted by Tmspecial on 5 October 2015 at 02:10.

Posted by Tmspecial on 5 October 2015 at 02:10.

»The problem with using LUGBULK to get the parts is the fact that you won't receive them until this time next year. Therefore you will not be able to complete the GBC until the 2017 season.«
Oh yes, this is a long-term project!

Posted by Captainowie on 5 October 2015 at 08:34.
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