Jim

[HELP] Generic Building Help Topic

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I have 42098, and I'm looking to do some modifications as a learning experience. One of the ideas I have in mind is a crane truck (like 8258). What is puzzling me to no end, is how do I make the gearbox work through the turntable? I believe that the room I have to work with will be smaller in the 42098 set, but I still have no idea how to tackle this problem.

At least one axle has to go through the turntable but is not enough. From the looks of it, the gearbox selector is on the side of the truck, so it has to be possible. Any hints you may have? Thanks!

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8258 has 2 functions going trough turntable. Just check building instructions.

I remember here was some topic, where there was solutions for more functions

here it is

 

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12 hours ago, Jurss said:

8258 has 2 functions going trough turntable. Just check building instructions.

I remember here was some topic, where there was solutions for more functions

here it is

 

This is brilliant! Thanks a lot!

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Can anyone tell me if the 3x13 panel is available on Pick-a-Brick? And if yes: what is the reference? How can I find it?

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@chlego Why would you use Pick a Brick? There is much more available at LEGO Bricks&Pices if you want to buy from LEGO directly...

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2 hours ago, Gray Gear said:

@chlego Why would you use Pick a Brick? There is much more available at LEGO Bricks&Pices if you want to buy from LEGO directly...

Yeah, it is a little confusing. Pick a Brick has almost no selection, but is significantly easier to find than Bricks&Pieces, which is accessed through the "replacement parts" button in the customer service section, I believe.

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23 hours ago, Gray Gear said:

@chlego Why would you use Pick a Brick? There is much more available at LEGO Bricks&Pices if you want to buy from LEGO directly...

 

21 hours ago, 2GodBDGlory said:

Yeah, it is a little confusing. Pick a Brick has almost no selection, but is significantly easier to find than Bricks&Pieces, which is accessed through the "replacement parts" button in the customer service section, I believe.

Ok thanks for your help.

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Posted (edited)

Hey everyone,  this is a driven front axle design that I came up with. I want to use it in an upcoming moc of mine, an rc front-wheel-drive hatchback in lego technic form. 

50993568661_f5a10f375a_c.jpg

I want to make the model as close to real fwd hatchbacks as possible. As you can see, it features a Mcpherson suspension design and a transverse 3-cylinder-engine. 

The issue that I ran into was the steering. I tried to implement several different steering setups into this axle, (I used different steering links and racks) but I ended up with a lot of unwanted bumpsteer and a significant toe out. 

50993561891_8dcf0bba70_c.jpg

Here you can see the geometry issue of this setup. The toe out only increases when the springs are compressed.

50992865003_c0aa9582e5_c.jpg

I'm grateful for every idea that you leave below because unfortunately I'm not able to continue this MOC if the front axle doesn't work well.

Edited by nano21

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Posted (edited)

So the problem with your setup is that there is no rotating point behind the springs: you are trying to make the whole axle rotate, and you don't want that. Also, the cv-joint is not at the same position as the point where you want to make the attachment rotate. This can cause issues on bigger scales, not sure if it is that important on your scale. 

Edited by chlego
added info

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3 hours ago, nano21 said:

Hey everyone,  this is a driven front axle design that I came up with. I want to use it in an upcoming moc of mine, an rc front-wheel-drive hatchback in lego technic form. 

 

I want to make the model as close to real fwd hatchbacks as possible. As you can see, it features a Mcpherson suspension design and a transverse 3-cylinder-engine. 

The issue that I ran into was the steering. I tried to implement several different steering setups into this axle, (I used different steering links and racks) but I ended up with a lot of unwanted bumpsteer and a significant toe out. 

 

Here you can see the geometry issue of this setup. The toe out only increases when the springs are compressed.

 

I'm grateful for every idea that you leave below because unfortunately I'm not able to continue this MOC if the front axle doesn't work well.

First and most obvious problem is that your linkages do not align properly. Their lengths and angles must be exactly equal, or there will be bump steering and toe outing.

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Posted (edited)
11 hours ago, chlego said:

Also, the cv-joint is not at the same position as the point where you want to make the attachment rotate. This can cause issues on bigger scales, not sure if it is that important on your scale. 

Yes you are right, the cv-joints swing just a bit when the hub rotates. However I decided to ignore this for my purposes because it was just a very small effect. 

 

11 hours ago, chlego said:

you are trying to make the whole axle rotate

What do you mean by "making the whole axle rotate"?

Thanks for your answers so far :grin:

9 hours ago, howitzer said:

Their lengths and angles must be exactly equal, or there will be bump steering and toe outing.

Yup, figured that out. Do you have any part suggestions to fix this issue? 

Edited by nano21

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Something else too, the upper steering pivot is stationary while the lower pivot point moves as the suspension works, which will cause issues as well.

 

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11 hours ago, nano21 said:

What do you mean by "making the whole axle rotate"?

By seeing this I understand that there is no pivot behind the suspensions/springs. However, there needs to be one that is centered on the axle (and on the center of the wheel), and on the same level as where the steering linkage arrives at the wheel hub.

Hope you got it, I'm pretty bad at explaining stuff...

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15 hours ago, Johnny1360 said:

Something else too, the upper steering pivot is stationary while the lower pivot point moves as the suspension works, which will cause issues as well.

Yea thats one of the major issues of this design. 

 

12 hours ago, chlego said:

By seeing this I understand that there is no pivot behind the suspensions/springs.

Yes, the pivot points are off... guess I will dump this whole setup and think of a different approach to a front axle. Thanks for your answers. :wink:

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On 3/3/2021 at 7:35 AM, Jurss said:

I remember there was some MOC with mcpherson type front suspension using shorter shock absorber. Maybe that setup is somewhere in axle collection thread. Take a look there.

Maybe just try search forum for mcpherson, there is something

https://www.eurobricks.com/forum/index.php?/search/&q=mcpherson

Thanks a lot for your suggestions, however I've decided to use Nicjasno's Mcpherson front-suspension. It is compact, works well and it doesn't have any geometry issues.

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Hi folks. It's been a while since I built anything with Technic. To put a little perspective on it, my last set was 8850, and before that, 8660 .. so I am really unfamiliar with a lot of the new parts. I am hoping you might be able to advise on how to achieve this motion in a more compact solution. Or even just highlight some sets that have had something similar that I can go and examine. I don't have a lot of parts to test build with, but am willing to go out and purchase once I know I'm not wasting money on dead-end ideas.

Essentially I am building a system/model submarine that looks mimics a fish. I have most movements sorted, but along the roof will be a series of six spikes of some type, that will resemble a dorsal fin. I am trying to achieve a side-to-side waving motion with these, with bonus points if they move in sync like a wave - (as opposed to all left/all right).

See this style of motion:

 

The outer shell will look something like this, with maybe six poles. My solution at the moment links each two as a pair, so three sets of two.

ZPmWWtP.png

 

My WIP so far looks something like the following

PLwQoC1.png

A "spine" axle runs the length of the fish, and provides the initial drive at (1). This drives an engine crankshaft at (2) (the smallest crank possible?). This means the liftarm at (3) is not free enough to fully rotate, and instead only operates with a slight up/down oval motion. Transferred through to (4), we see the fin spoke moving in a very limited back-and-forth manner.

I achieved this so far through a lot of trial and error. And a whole bundle of parts that are not this clean - just the same measurements and connects.

Can anyone suggest a better way to achieve the desired effect? or even to suggest a more compact version with some parts I'm not aware of perhaps? Ideally, I'd like to fit the entire mechanism into a section of the ship that can run the full length, but to be limited to 4 bricks wide and four tall.

 

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Instead of going for a 1/2 lift arm (I have no idea how that crankshaft part is called), you can go for a 2 stud or even 3 stud long one, I guess. Right?

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2 hours ago, chlego said:

Instead of going for a 1/2 lift arm (I have no idea how that crankshaft part is called), you can go for a 2 stud or even 3 stud long one, I guess. Right?

From experiments, I think the radius on the lower cog needs to be smaller than the radius of the upper cog, in order to maintain the back-and-forth and not let it jump to doing full loops. And smaller by at least a stud (more if bigger cogs). So I was just going to the 1.5 where I could to try keep the whole thing compact.

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My question has to do with the comment in the post below:

Since asking there is off-topic, I am wondering if here is a better place.

From what I understand, the gear worm has its length of almost 2 because the size between the gaps of the screw-thread need to be the same as the teeth of the gears, and otherwise you could not stack multiple gear worms on the same axle.

What I don't understand is why they couldn't make the screw-thread of the worm gear more diagonal so it would have had a size of exactly 2. @Zerobricks mentions pi, but just like @langko I do not see where the pi comes from.

Can someone point me to information about this? The topic linked in that page, Technic Worm Gear 3L with Bush Ends, does not have an answer as far as I can see.

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14 minutes ago, Lira_Bricks said:

My question has to do with the comment in the post below:

Since asking there is off-topic, I am wondering if here is a better place.

From what I understand, the gear worm has its length of almost 2 because the size between the gaps of the screw-thread need to be the same as the teeth of the gears, and otherwise you could not stack multiple gear worms on the same axle.

What I don't understand is why they couldn't make the screw-thread of the worm gear more diagonal so it would have had a size of exactly 2. @Zerobricks mentions pi, but just like @langko I do not see where the pi comes from.

Can someone point me to information about this? The topic linked in that page, Technic Worm Gear 3L with Bush Ends, does not have an answer as far as I can see.

I'm not sure if this is the real reason, but "stretching" the worm gear to match the 2L length would change the pitch of the screw, which might prevent it from working properly with spur gears. Or maybe it's because they wanted such a worm gear that cannot be backdriven, and changing the pitch might allow that to happen.

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59 minutes ago, Lira_Bricks said:

My question has to do with the comment in the post below:

Since asking there is off-topic, I am wondering if here is a better place.

From what I understand, the gear worm has its length of almost 2 because the size between the gaps of the screw-thread need to be the same as the teeth of the gears, and otherwise you could not stack multiple gear worms on the same axle.

What I don't understand is why they couldn't make the screw-thread of the worm gear more diagonal so it would have had a size of exactly 2. @Zerobricks mentions pi, but just like @langko I do not see where the pi comes from.

Can someone point me to information about this? The topic linked in that page, Technic Worm Gear 3L with Bush Ends, does not have an answer as far as I can see.

I understand you can’t make the threads more diagonal, they have to be at that pitch to mesh with the gears properly. What I didn’t understand is why you can’t just continue the thread to make the worm gear a mm or so longer. As well as you, I could not find any answers in that linked topic. My logic is that if you were to add a small shim on the axle to reduce the backlash (I used to build worm boxes for a living and we did this) the worm would still operate properly. Now what would be the difference between that and making the worm thread slightly longer? After that discussion in the AMA, I went and spoke to the head engineer/designer at my work, and he even told me that the length of the worm doesn’t matter (of course too long is pointless because you only need a certain amount of threads to engage the gear, and if it’s longer than needed the gears could skip under load). But given the intended application with LEGO I don’t see that being an issue.

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1 hour ago, langko said:

What I didn’t understand is why you can’t just continue the thread to make the worm gear a mm or so longer.

As mentioned above, I think it's so that you can stack multiple worm gears on the same axle and have the threads line up.  The tooth pitch is 2 * pi / 16 studs (a 16T gear has a radius of one stud, circumference is 2 * pi * r) which is 0.393 studs.  A 2L worm gear has 5 full turns and so has a length of 1.96 studs.  If you want to be able to stack gears you need the worm gear to be a multiple of quarter turns, so the next length you could use is 5.25 turns which is 2.06 studs.

 

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13 minutes ago, pdw said:

As mentioned above, I think it's so that you can stack multiple worm gears on the same axle and have the threads line up.  The tooth pitch is 2 * pi / 16 studs (a 16T gear has a radius of one stud, circumference is 2 * pi * r) which is 0.393 studs.  A 2L worm gear has 5 full turns and so has a length of 1.96 studs.  If you want to be able to stack gears you need the worm gear to be a multiple of quarter turns, so the next length you could use is 5.25 turns which is 2.06 studs.

 

I understand that also. (And thankyou for explaining the calculations in more detail). But my question in the AMA was if you were willing to sacrifice the stackability, wouldn’t a perfect 2l or even 3l worm gear be possible? (The answer was apparently no, but I don’t understand why that would be so)

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