[MOC] [WIP] The Command of the AT-AT

[Tommy Styrvoky]

Here's a thought for the affixing of the turntables in place, there could be a similar setup with planetary drives in the center of the turn table, then you could attach that planetary drive in the 24z opening of the turntable and adjust it inside the model with a couple worm gears that could surround a gear, if they were driven opposite directions you could control the motion of the gears from a single shaft. If the axle was solidly connected with a 24z gear in the center, I think it would put too much stress on the axle and easily twist it, also If you wanted to adjust the leg you would have to split the turntable every time it was changed. here's a image of a vehicle with planetary drives in the drive axles.

if you need more teeth for purchase there can be an extra 2 gears added to the sides of the main 8z gear.

Edited January 12, 2016 by Tommy Styrvoky

[Kristof]

^And then it's just a little step to walking RC AT-AT :D :D

This is great solution but I think it's overly complicated for the purpose here and mounting all these 8 tooth grars would be very intricate here (if not impossible). 24 tooth gear would do the same job here, whereas the job is not to drive the joint but to provide an axle connecrtion between the leg and some angle-locking 'gearbox' in the body part of the joint.

[Tommy Styrvoky]

^And then it's just a little step to walking RC AT-AT :D :D

This is great solution but I think it's overly complicated for the purpose here and mounting all these 8 tooth grars would be very intricate here (if not impossible). 24 tooth gear would do the same job here, whereas the job is not to drive the joint but to provide an axle connecrtion between the leg and some angle-locking 'gearbox' in the body part of the joint.

Well I have plans to make an AT-TE motorized, later this year, the only issue is figuring out operation of the middle joint with the middle 2 largest legs, so they can povot and turn.

[LiLmeFromDaFuture]

I am assuming that because of the multiple 8 tooth gears there would be a significant amount of friction experienced in the revolution of the turntable, correct?

[Tommy Styrvoky]

I am assuming that because of the multiple 8 tooth gears there would be a significant amount of friction experienced in the revolution of the turntable, correct?

Not as much as you would think, as all of the gears are rotating in the same direction( except for the centermost one). The planetary drive gives the gears more contact than a standard 3:1 reduction with a 8z and 24z gears. This allows one to apply lots of force into it. It's used for heavier motorized models, and you can mount custom tires onto the turntables. Edited January 12, 2016 by Tommy Styrvoky

[anothergol]

ive never sceen this. but there is always replacement parts

Well it's ALL the 1x2 brackets that are wrong. I assume LiLmeFromDaFuture knows, he used the large brackets for what's on my pic that simply doesn't work (-at all-) with the 1x2 ones.

But playing too much with brackets generally produces gaps, although things will hold fine.

[LiLmeFromDaFuture]

Well it's ALL the 1x2 brackets that are wrong. I assume LiLmeFromDaFuture knows, he used the large brackets for what's on my pic that simply doesn't work (-at all-) with the 1x2 ones.

But playing too much with brackets generally produces gaps, although things will hold fine.

Yes, I don't have any fashioned in that manner, but with the few I do use they are overlaid and secured with plates across them.

[Tommy Styrvoky]

What about using the 24z gear in the turntable and connecting a axle from it into a wedge belt wheel anchored into the "hip" of the leg. That would give a few different angles of motion.

[LiLmeFromDaFuture]

Would that require repeated detaching of the leg in order to change the angle?

[Tommy Styrvoky]

Would that require repeated detaching of the leg in order to change the angle?

yeah, you would only have to move the wedge belt wheel around.

[LiLmeFromDaFuture]

yeah, you would only have to move the wedge belt wheel around.

Hmm… Well, I am still having a difficult time visualizing the setup you are describing , but how about this; the 8 tooth gears are connected with axel/pins with friction:

[Tommy Styrvoky]

Hmm… Well, I am still having a difficult time visualizing the setup you are describing , but how about this; the 8 tooth gears are connected with axel/pins with friction:

That's a good thougt, i can mock something up tomorrow in ldraw to illustrate it better.

Edited January 13, 2016 by Tommy Styrvoky

[Kristof]

Hmm… Well, I am still having a difficult time visualizing the setup you are describing

Yea, this is hard to follow and I have to admit I get lost in that last description either. Anyway, let me celar out some facts:

• Planetary drive is basically a gearbox. It's main real-engineering use is to change the velocity/torque ratio on motor outputs or some drive shafts in general, where it has some very convenient advantages.
  
• There are even special modifications of this mechanism that are supposed not to be back-driven easily - that would be good for you but unfortunately, that's not what you can make with lego (and this particular setup with turntable and 8-tooth gears) - it involves spiral worm ggears and some other rather special stuff.
  
• In this lego form, this is just a bi-drirectional gearbox and one of the good ways how to drive a turntable. Notice that it's all about driving.
  
• What you need is is creating either friction or ratchet (easier to imagine) mechanism that allows you to position the leg but locks effectively it from further moving.
  
• I see no real advantage in using planetary gearbox mechanism for your purpose. The only fact that could be a bit advantageous is that the aspect ration of this planeraty drive reduces the torque by the factor of 3. Yet, there is no salvation in it. On contrary, I see several big cons:
  

• The more gears, the more room for twist and play. That's for certain.
  
• 8 tooth gear are much more flexy and bendy in general - also their axle hole is less rigid.
  
• The amount of torque you will be getting there (considering at-at standing with tilted legs and feet not fixed to the ground) could even damage the 8 tooth gears. This is because not all of their teeth are engaged in one moment (actually only few of them do and some just partially). And since your mechanism is supposed not to move very often, this will make for significant wear on some teeth while the others never get to work. Notice that with full 24 tooth gear in there it's whole different storry.
  

• Using planetary drive to introduce friction (your idea with friction pins) to the system is not really nonsense but again, considering your high torque application, you'd need dozens and dozend of friction pins to make for sufficient hold.
  

So, what I suggest is this:

1. First you need to reverse the turntable, so the half with inner gear ring is fixed to the leg (with your current setup, neither this nor planetary would work).
   
2. Then you put classic 24 tooth gear in there
   
3. build the shoulder hub (that drop-shaped thing), fix the other end of the turntable in it and leave the hole in the center for the axle that connects to 24 tooth gear
   
4. Now, in theory, you can execute some mechanism (worm gear gearbox/ratchet) in the shoulder hub that will allow you to position the leg without need to remove it.
   

However, step 4 may be impossible to do due to lack of space i the shoulder hub (I don't really know how big and thick this thing can be) or high requiremets for it to be a rock solid segment. So the alternative way would be:

1. ...
   
2. ...
   
3. Build the shoulder hub and fix the turntable so it's not very difficult to disconnect it. Build the fixed axle cross hole in the middle.
   
4. When assemblig, you would need first to choose which angle of the leg you want and place the 24 tooth gear accordingly, then connect the leg to hub via turntable and inserd the axle into the gear.
   

As I was writing this, I though about third option which may be the best actually - similar to second option but the 24 tooth gear is able to 'slide' in and out of the gearbox inner tooth ring, while this sliding could be operated from either leg side or shoulder hub side (or both if necessary), probably via pushing/pulling it's axle. So in theory, you would push the axle (or whatever) to slide the gear out, thus unlock the rotation in the joint and when choosing different angle, you'd push it back in.

I don't know how comprehensive did I manage to be. Unfortunately I have no time for sketching up my ideas in LDD now. But hopefully you got the idea.

I must admit, however, that the more I think about this problem, the less I believe it can work out. Especially because of @dmaclego thoughts and experiences. You may come up with a perfect shoulder joint but the legs (and especially the ankles) are still as they are, so in the end, you may need to fix the feet to the base anyway. And then, all this fanciness in the shoulders will become moreless useless.

[Tommy Styrvoky]

Ok here's my solution, the long technic friction pins can have the stop on the side with the turntable. The gray beam is what will attach to the hip/ upper body.( I think it's best to tie it into the body, so the legs are anchored and can't twist from side to side.) The wedge belt wheels can be removed, then the leg can be positioned and the wedge belt wheels can be replaced. This gives 3 possible positions for the (30°,90°,and 150°) I think the usage of a ratchet with a pawl would make the hip linkages too thick, because that would have to be supported on both sides of the ratchet, making it at least 3 studs wide. I also think that has a high chance of damaging pieces/ it could move on accident. A worm gear would be a better option , as it can't move if encased correctly.

AT-AT leg/hip joint by Tommy Styrvoky, on Flickr

AT-AT leg/hip joint by Tommy Styrvoky, on Flickr

Edited January 13, 2016 by Tommy Styrvoky

[Kristof]

^nice, that's a clever one. Just the minimum angle 60° makes it useless for given application. But it demonstrates the way of going pretty well.

[Tommy Styrvoky]

^nice, that's a clever one. Just the minimum angle 60° makes it useless for given application. But it demonstrates the way of going pretty well.

I wonder if there's any other part that could be substituted to give a angle of 45°or less.

[LiLmeFromDaFuture]

Ok here's my solution, the long technic friction pins can have the stop on the side with the turntable. The gray beam is what will attach to the hip/ upper body.( I think it's best to tie it into the body, so the legs are anchored and can't twist from side to side.) The wedge belt wheels can be removed, then the leg can be positioned and the wedge belt wheels can be replaced. This gives 3 possible positions for the (30°,90°,and 150°) I think the usage of a ratchet with a pawl would make the hip linkages too thick, because that would have to be supported on both sides of the ratchet, making it at least 3 studs wide. I also think that has a high chance of damaging pieces/ it could move on accident. A worm gear would be a better option , as it can't move if encased correctly.

I don't know it will work with the limited positions… Here it is at a 30º angle:

• How would you implement a worm gear when it is bigger than a technic hole, wouldn't that be an issue?
  

• Is there a way to make a locking system with gears?
  

[LiLmeFromDaFuture]

There is no ratchet in the turntables by default. But you can lock them by coupling with gear that has some hard lock on it's shaft.

Once you can, could you expound upon this on how it could be done or provide a photo to portray what you are describing?

• The more gears, the more room for twist and play. That's for certain.
  
• 8 tooth gear are much more flexy and bendy in general - also their axle hole is less rigid.
  
• The amount of torque you will be getting there (considering at-at standing with tilted legs and feet not fixed to the ground) could even damage the 8 tooth gears. This is because not all of their teeth are engaged in one moment (actually only few of them do and some just partially). And since your mechanism is supposed not to move very often, this will make for significant wear on some teeth while the others never get to work.
  

Is this the same for both types of the 8 tooth gear or just the old one?

As I was writing this, I though about third option which may be the best actually - similar to second option but the 24 tooth gear is able to 'slide' in and out of the gearbox inner tooth ring, while this sliding could be operated from either leg side or shoulder hub side (or both if necessary), probably via pushing/pulling it's axle. So in theory, you would push the axle (or whatever) to slide the gear out, thus unlock the rotation in the joint and when choosing different angle, you'd push it back in.

That is a good idea, however, as I see with the technic turntable type 2 in LDD, you would have to pry it apart just enough to insert a 24 tooth gear.

[Tommy Styrvoky]

Once you can, could you expound upon this on how it could be done or provide a photo to portray what you are describing?

Is this the same for both types of the 8 tooth gear or just the old one?

That is a good idea, however, as I see with the technic turntable type 2 in LDD, you would have to pry it apart just enough to insert a 24 tooth gear.

it's impossible to slide the 24z out of the center of the turntable without splitting it, as i have done this in real life.

[LiLmeFromDaFuture]

it's impossible to slide the 24z out of the center of the turntable without splitting it, as i have done this in real life.

Yeah that was the unfortunate part.

Both of you suggested a ratcheted system with gears, but how would that would be achieved?

Or with worm gears, with the difficulties its size would cause?

[Tommy Styrvoky]

Yeah that was the unfortunate part.

Both of you suggested a ratcheted system with gears, but how would that would be achieved?

Or with worm gears, with the difficulties its size would cause?

the simplest solution for a worm gear would be to mount it on the outside of the turntable, I think a newer 28z smaller turntable would work for that, as it's less bulky. Though to split a turntable it's a rather easy process, it can be done by inserting pins into the ends with beams to use a leverage and pry the two apart, or use a dull butter knife and slip it between the two parts of the turntable and pry around it gently or I think you can buy them as seperate parts on bricklink. I can take a look at a worm gear system later tonight. The problem with the ratchet is that it turns only one way, unless you have 2 pawls locking motion of the gear.

[LiLmeFromDaFuture]

@Tommy Styrvoky & krisandkris12

Here is what I thought I could simply do with the worm gear but it bulges out too much…

[Tommy Styrvoky]

@Tommy Styrvoky & krisandkris12

Here is what I thought I could simply do with the worm gear but it bulges out too much…

here's a thought have another 8z gear come from the inside of the turntable connect to a axle and have another 8z gear mesh with a wormgear. I can mock it up later.

[anothergol]

Rotated legs is important, but don't you think that eventually you will go for a fixed pose and never change it? You may simply pin beams at specific angles, no?

[LiLmeFromDaFuture]

here's a thought have another 8z gear come from the inside of the turntable connect to a axle and have another 8z gear mesh with a wormgear. I can mock it up later.

I would appreciate that.

Rotated legs is important, but don't you think that eventually you will go for a fixed pose and never change it? You may simply pin beams at specific angles, no?

Yeah, that's what I have been pondering ever since krisandkris12, Tommy Styrvoky, etc., suggested using a 24 tooth gear fixed at the desired position. That would be an ultimate option if all else would not work in the given space. After all, the walker won't be so much a playable model because of how heavy it will be.

I don't know if beams could be pinned in a normal way without forcibly abusing the elements—if that is what you mean?