Answers.Body: <p>This required a clever design and one novel element.</p>
  <p>The power for the light comes from the very bottom of the model where a battery box is stowed inside the mountain:</p>
  <p><a href="https://i.sstatic.net/Sf81g.png" rel="noreferrer"><img src="https://i.sstatic.net/Sf81g.png" alt="Step 60 (Book 1, page 64)" /></a></p>
  <p>The wire leaves the mountain via the top and heads upward.</p>
  <p><a href="https://i.sstatic.net/4O5Ed.png" rel="noreferrer"><img src="https://i.sstatic.net/4O5Ed.png" alt="Step 210 (Book 1, page 192)" /></a></p>
  <p>It then snakes its way around and up into the tower. Interestingly, the Powered Up lights include dual LEDs, as they are often used for headlights. Only one is needed for main light, so the other is used to add a glow to the woodstove in the cabin.</p>
  <p><a href="https://i.sstatic.net/UO11z.jpg" rel="noreferrer"><img src="https://i.sstatic.net/UO11z.jpg" alt="Step 309 (Book 2, page 38)" /></a></p>
  <p>Up at the top, the light is attached facing upward underneath a construction that will be powered by the motor in the bottom of the lighthouse via a long vertical axle.</p>
  <p><a href="https://i.sstatic.net/vGWbF.png" rel="noreferrer"><img src="https://i.sstatic.net/vGWbF.png" alt="Step 488 (Book 2, page 141" /></a></p>
  <p>We need the light traveling horizontally, so we add a stickered mirror at roughly 45 degrees to vertical:</p>
  <p><a href="https://i.sstatic.net/iSplB.png" rel="noreferrer"><img src="https://i.sstatic.net/iSplB.png" alt="Step 494 (Book 2, page 144)" /></a></p>
  <p>This would sort of work, but the light from the Powered Up LEDs disperses significantly and is not able to travel very far. In real lighthouses, a <a href="https://en.wikipedia.org/wiki/Fresnel_lens" rel="noreferrer">Fresnel lens</a> if often used to appropriately direct the beam from a diffuse light source. The basic operation can be seen here:</p>
  <p><a href="https://i.sstatic.net/bVLgh.png" rel="noreferrer"><img src="https://i.sstatic.net/bVLgh.png" alt="Fresnel lens diagram" /></a></p>
  <p>TLG saw fit to create a Fresnel lens element to enhance the performance of this set. Here are some of the prototypes that folks iterated through:</p>
  <p><a href="https://i.sstatic.net/D0z0E.png" rel="noreferrer"><img src="https://i.sstatic.net/D0z0E.png" alt="Prototype lenses from set instructions" /></a></p>
  <p>The final version is a unique element with the footprint of a 2x4 plate. It attaches to our mirror assembly providing light that is now traveling in the correct direction and is more focused than it would have otherwise been.</p>
  <p><a href="https://i.sstatic.net/3em6Q.png" rel="noreferrer"><img src="https://i.sstatic.net/3em6Q.png" alt="Step 496 (Book 2, page 144" /></a></p>
  <p>This assembly is then attached to the top of the lighthouse and driven by gear so that it is able to rotate:</p>
  <p><a href="https://i.sstatic.net/7VYO0.png" rel="noreferrer"><img src="https://i.sstatic.net/7VYO0.png" alt="Step 497 (Book 2, page 145" /></a></p>
  <p>In this way, the mirror and lens assembly is able to rotate without the wired lights rotating and creating twists and tangles.</p>
  <p><a href="https://i.sstatic.net/aYbpF.gif" rel="noreferrer"><img src="https://i.sstatic.net/aYbpF.gif" alt="Lightroom animation" /></a></p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-12-13T15:45:23.033Z
Answers.Text: Possibly of note, they theoretically could have created a new [slip ring](https://en.wikipedia.org/wiki/Slip_ring) part to allow the LED itself to be rotated, but such a part would have been far more expensive to produce, as well as being far less reliable than the approach used, and even then they would probably still need the Fresnel lens piece to make it project the light well.
Answers.UserDisplayName: Austin Hemmelgarn
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-12-14T10:59:13.257Z
Answers.Text: +1 Only tangentially related but a nice image: [What is a 3rd-order Fresnel lens?](https://physics.stackexchange.com/q/472415/83380)
Answers.UserDisplayName: uhoh
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-12-12T17:56:44.553Z
Answers.LastActivityDate: 2022-12-12T22:40:39.690Z
Answers.LastEditDate: 2022-12-12T22:40:39.690Z
Answers.UserDisplayName: jncraton
Body: <p>I'm curious about the <a href="https://brickset.com/sets/21335-1" rel="noreferrer">Motorized Lighthouse (21335)</a>:</p>
  <p><a href="https://i.sstatic.net/EGsOF.png" rel="noreferrer"><img src="https://i.sstatic.net/EGsOF.png" alt="Set photo" /></a></p>
  <p>As the title suggests, this set is motorized to allow the light on top to rotate continuously:</p>
  <p><a href="https://i.sstatic.net/osGMr.gif" rel="noreferrer"><img src="https://i.sstatic.net/osGMr.gif" alt="Continuous rotation animation" /></a></p>
  <p>From the looking at the inventory, it is clear that it uses the Powered Up lights:</p>
  <p><a href="https://i.sstatic.net/TN0o4.png" rel="noreferrer"><img src="https://i.sstatic.net/TN0o4.png" alt="Power Up Lights" /></a></p>
  <p>How does the wire not get tangled/twisted while the top of the lighthouse rotates?</p>
  
Tags: <motor><powered-up><ideas><lighting>
Title: How does the motorized lighthouse rotate continuously without tangling the wire powering the light?
UserDisplayName: jncraton
ThreadText: # How does the motorized lighthouse rotate continuously without tangling the wire powering the light?
  
  (Asked by: username_0 on 2022-12-12)
  
  I'm curious about the [Motorized Lighthouse (21335)](https://brickset.com/sets/21335-1):
  
  [![Set photo](https://i.sstatic.net/EGsOF.png)](https://i.sstatic.net/EGsOF.png)
  
  As the title suggests, this set is motorized to allow the light on top to rotate continuously:
  
  [![Continuous rotation animation](https://i.sstatic.net/osGMr.gif)](https://i.sstatic.net/osGMr.gif)
  
  From the looking at the inventory, it is clear that it uses the Powered Up lights:
  
  [![Power Up Lights](https://i.sstatic.net/TN0o4.png)](https://i.sstatic.net/TN0o4.png)
  
  How does the wire not get tangled/twisted while the top of the lighthouse rotates?
  
  **Tags:** motor, powered-up, ideas, lighting
  
  ---
  
  ## 1 answers
  
  ### Answer by username_0 on 2022-12-12. Score: 35 | Accepted answer
  
  This required a clever design and one novel element.
  
  The power for the light comes from the very bottom of the model where a battery box is stowed inside the mountain:
  
  [![Step 60 (Book 1, page 64)](https://i.sstatic.net/Sf81g.png)](https://i.sstatic.net/Sf81g.png)
  
  The wire leaves the mountain via the top and heads upward.
  
  [![Step 210 (Book 1, page 192)](https://i.sstatic.net/4O5Ed.png)](https://i.sstatic.net/4O5Ed.png)
  
  It then snakes its way around and up into the tower. Interestingly, the Powered Up lights include dual LEDs, as they are often used for headlights. Only one is needed for main light, so the other is used to add a glow to the woodstove in the cabin.
  
  [![Step 309 (Book 2, page 38)](https://i.sstatic.net/UO11z.jpg)](https://i.sstatic.net/UO11z.jpg)
  
  Up at the top, the light is attached facing upward underneath a construction that will be powered by the motor in the bottom of the lighthouse via a long vertical axle.
  
  [![Step 488 (Book 2, page 141](https://i.sstatic.net/vGWbF.png)](https://i.sstatic.net/vGWbF.png)
  
  We need the light traveling horizontally, so we add a stickered mirror at roughly 45 degrees to vertical:
  
  [![Step 494 (Book 2, page 144)](https://i.sstatic.net/iSplB.png)](https://i.sstatic.net/iSplB.png)
  
  This would sort of work, but the light from the Powered Up LEDs disperses significantly and is not able to travel very far. In real lighthouses, a [Fresnel lens](https://en.wikipedia.org/wiki/Fresnel_lens) if often used to appropriately direct the beam from a diffuse light source. The basic operation can be seen here:
  
  [![Fresnel lens diagram](https://i.sstatic.net/bVLgh.png)](https://i.sstatic.net/bVLgh.png)
  
  TLG saw fit to create a Fresnel lens element to enhance the performance of this set. Here are some of the prototypes that folks iterated through:
  
  [![Prototype lenses from set instructions](https://i.sstatic.net/D0z0E.png)](https://i.sstatic.net/D0z0E.png)
  
  The final version is a unique element with the footprint of a 2x4 plate. It attaches to our mirror assembly providing light that is now traveling in the correct direction and is more focused than it would have otherwise been.
  
  [![Step 496 (Book 2, page 144](https://i.sstatic.net/3em6Q.png)](https://i.sstatic.net/3em6Q.png)
  
  This assembly is then attached to the top of the lighthouse and driven by gear so that it is able to rotate:
  
  [![Step 497 (Book 2, page 145](https://i.sstatic.net/7VYO0.png)](https://i.sstatic.net/7VYO0.png)
  
  In this way, the mirror and lens assembly is able to rotate without the wired lights rotating and creating twists and tangles.
  
  [![Lightroom animation](https://i.sstatic.net/aYbpF.gif)](https://i.sstatic.net/aYbpF.gif)
  
  > **Comments:**
  > **username_1**: Possibly of note, they theoretically could have created a new [slip ring](https://en.wikipedia.org/wiki/Slip_ring) part to allow the LED itself to be rotated, but such a part would have been far more expensive to produce, as well as being far less reliable than the approach used, and even then they would probably still need the Fresnel lens piece to make it project the light well.  
  > **username_2**: +1 Only tangentially related but a nice image: [What is a 3rd-order Fresnel lens?](https://physics.stackexchange.com/q/472415/83380)  
  
  ---
  
  