Stronger Turntable Alternatives

[timslegos]

Hello,

Recently I faced the difficulties surrounding one of the weakest Lego parts, the turntable. In my latest MOC, a second try at a walking excavator, the turntable separates when playing around with it. Both the top and bottom half are solidly built. The only weakness lies in the connection of the two. In this project I am using the old style studded turntables.

Here is an early picture of the MOC (dont want to give it all away ).

Since this photo, I have completed almost the entire cab and super structure. While the turntable did not separate during the early phases, as the weight increased, so did the separation of the different sides of the turntable. I have searched around online, and I cant seem to find any solutions to the problem. One idea I had was to increase the surface area of the area around the turntable, like the picture below, although I have no idea whether it will help or not.

I would appreciate any suggestions, as I am really at a loss for ideas.

tim

[dhc6twinotter]

I may have a solution for you, but give me a coupe hours to post it.

I like your project.

[Lakop]

Hi,

Great looking model. You need to consider taking some of the weight off the turntable. increasing the surface area should help or could you possibly use two turntables side by side and pin them both down. You would need to experiment but be carefull not to break any turntables.

Look forward to the finished model.

H

Edited July 24, 2013 by Horace T

[jorgeopesi]

Interesting post, I like to see new ideas about stronger turntables, I like to build big machines and the turntable is always a problem. With my front shovel the solution was put tiles to prevent looseness.

[Erik Leppen]

If you add a counterweight, the superstructure (everything above the turntable) will be better balanced, meaning the center of gravity will be closer to the turntable center, and that will put a lot less strain on the turntable.

So, as soon as you'll drive the functions with motors, try putting as many motors as you can and the battery box in the back (like 8043 has done).

For example you could take the M motor used for extension, out of the arm and replace it by a drive train all the way to the back and put the motor there. The motor for the gripper will be a lot harder to move, this will only be possible wih the new red 8t gears found in 42009. You could replace it with a micromotor if you own the correct conversion cables (but I have no experience with this).

But to answer the original question, maybe this is an idea:

http://www.brickshelf.com/cgi-bin/gallery.cgi?i=3062478

Edit: also I have the feeling the newer studless turntables do not snap as easily. I never had any turntable snapped, but they feel as having less "play" between the two halves. Also, unlike studded turntables, they come assembled in sets, I assume that is done for a reason.

Edited July 24, 2013 by Erik Leppen

[Alasdair Ryan]

Tim the idea you have posted above should work,the main reason that cause turntables come apart is uneven weight.

So making a extended level platform to rest the top on should work well.

[EyesOnly]

That and roller-bearings. Removing friction might help. The trick is of course to find a roller bearing assambly that will fit the model. But that's mostly a problem for really big cranes so in this case it might be a good start to look at fixing the centre of gravity.

[1974]

As other have said, your problem is balance. When balanced and it's still wobbling, use bearings. However this means a lot of parts and thus a bulky build. In my experience those turntables hold up åretty well even with several kilos attached .. if balanced properly

[dhc6twinotter]

Tim, here is what I'm thinking:

It's basically two turntables sandwiching the vehicle chassis (red beams). The yellow beams are what your superstructure would be attached to. Using this setup, there is no way your superstructure can separate from the chassis. I would suggest using some counterweight too though, otherwise the yellow beams could break from stress. The only downside to this is that there isn't really any room for a drive shaft going up through the center, unless you got all fancy with the design. There is room for wires though.

The farther apart you place the turntables, the better it will be. It would also be better to have slew drive gears on both turntables.

I haven't built a real version of it, but I'm planing to use this idea on several future builds.

Edited July 24, 2013 by dhc6twinotter

[Bricktrain]

Tim, here is what I'm thinking;

great idea, it does take up a bit of room but should be unbreakable. It shouldnt be too hard to make room for one axle though.

[Erik Leppen]

If you need the central axle, you could do it like so:

Edited July 25, 2013 by Erik Leppen

[EyesOnly]

Thanks for the ideas on how to strengthen turntables. Might come in handy some day.

[efferman]

dhc6twinotter it works good

Edited July 25, 2013 by efferman

[skriblez]

Cool picture Efferman. How strong is that crane?

[efferman]

if i reminds me correct the bug has a weight of 400gr. more i have not tested

[timslegos]

Thanks for all the advice and suggestions guys!

I have a few problems though, I do not believe it is a balance issue. The separation occurs when I am trying to scale some obstacle, and the the superstructure and base are at odd angles. For example, when the front of the machine is being supported by the bucket, and the back by the legs. Also, I only need a few wires to go through the center.

While there is not enough space for doubling up on the turntables, I may try some form of central axle, so that there is always pressure holding the two ends together. Is there any way of having a central axle without using two turntables? And one that would not be pulled apart easily?

@Efferman: In your crane you have pictured there is no bracing surrounding the turntable. Do you think the studless turntable is that much stronger? Should I try to switch the studded version for the studless?

thim

Edited July 25, 2013 by timslegos

[efferman]

i have used twin otters idea, nothing else.

[EyesOnly]

I recall seeing something a long time ago that might help. Unfortunately i don't remember where so i can't show you pictures. Basically it's like the double turntable version but instead of a second turntable there are axles on the beam going through the turntable that prevents it from being pulled apart. Make the axles slide on the same beams that hold the turntable in place and place some more beams between those or the axles would of course come of. The is much simpler in a studfull design than a studless unless you use a opencenter liftarm to hold the turntable. Does this make sense?

[Erik Leppen]

Should I try to switch the studded version for the studless?

It can never hurt to try and evaluate :)

[timslegos]

It can never hurt to try and evaluate :)

Except the time it takes to dissemble, rebuild and test over again.

In my testing, I discovered that the dual turntable technique required too much space, and I need a smaller solution. While messing around I came up with this idea to keep the turntable halves together.

I tested it myself, and the two halves stay together, obviously only when the two sides match up. I would have to keep the other two ends of it open so I could run the wires through the middle. What do you all think about this solution?

tim

[dhc6twinotter]

If you need the central axle, you could do it like so:

I wondered if that would work, although I wasn't sure if the half beams would be strong enough. It would be worth a try. Another option is to place the central axle next to the yellow beams, but that would make it one stud offset from center. Maybe there is a way to mount 4 half beams around an axle?

dhc6twinotter it works good

I didn't realize anybody has used this method already. Nice to see that it works well!

While there is not enough space for doubling up on the turntables, I may try some form of central axle, so that there is always pressure holding the two ends together. Is there any way of having a central axle without using two turntables? And one that would not be pulled apart easily?

Back before LEGO used the Technic turntables, LEGO used to use a threaded axle with nuts that was run through the center of a 4x4 turntable. The threaded axles came in 10L and 4L lengths. Nuts were used at both ends, with a technic plate above and below the turntable. Several sets used this method, although the Power Crane is the only one I can remember off the top of my head. The parts are available on bricklink, although you will probably have to order from Europe.

Instructions showing how the threaded axle was used on the Power Crane:

http://www.peeron.com/scans/8854-1/13/

http://www.peeron.com/scans/8854-1/17/

Edited July 25, 2013 by dhc6twinotter

[S.I]

The backhoe also used it. My axle broke many many years ago, and replacements were pretty expensive last time I checked.

[timslegos]

I too thought of using those threaded axles, but I would like to find a solution without ordering parts. What do you think of the one I just posted?

tim

[Alasdair Ryan]

I thought of something like this.....

Threaded axles would make this design even stronger along as using pulley wheels as washers.

[Blakbird]

The threaded axles are very weak. Although they are a theoretical solution to your problem, I think that structurally they are not adequate which is why they were produced for such a brief time. The cross section available to carry tension is only the core since the flanges are cut away by threads. If you try to use these for a heavy duty application you will only be depleting the already limited worldwide supply by destroying some of them.