Answers.Body: <p>Here's an idea for converting the movement of a moving train to rotational motion track side. This is <a href="https://www.youtube.com/watch?v=JEnRYtAE2dA" rel="nofollow noreferrer">shown</a> in set 6991:</p>
  <p><a href="https://i.sstatic.net/7m3B1.gif" rel="nofollow noreferrer"><img src="https://i.sstatic.net/7m3B1.gif" alt="6991 action shot" /></a></p>
  <p>The mechanism in this case is a tire hanging from a universal joint so that it engages the train without interfering too much:</p>
  <p><a href="https://i.sstatic.net/U6VGx.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/U6VGx.jpg" alt="build step 1" /></a></p>
  <p><a href="https://i.sstatic.net/Xtoic.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Xtoic.jpg" alt="build step 2" /></a></p>
  <p>This core idea could be mechanically adapted for other purposes, such as the 180 degree rotation that you are looking for.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-05-22T01:03:23.560Z
Answers.LastActivityDate: 2021-05-25T02:02:59.570Z
Answers.LastEditDate: 2021-05-25T02:02:59.570Z
Answers.UserDisplayName: jncraton
Answers.Body: <p>If I understand the problem correctly, you have a track, on which something is moving in a straight line. Then you want to have another, stationary object to rotate when the moving something has passed a certain point on the track, right? Like a semaphore transitioning to another state after a train has passed a switchpoint?</p>
  <p>If so, then the simplest solution would be to attach a piece of straight gear rack to the moving object and set up a gear by the tracks in a way so that the gear rack meshes with it as the object moves past. If the rack has exactly half the number of teeth as the gear, the gear will be rotated 180° upon their passing.</p>
  <p>Possible combinations: <a href="https://brickset.com/parts/4566045/rack-w-ball" rel="nofollow noreferrer">4566045: RACK W. BALL</a> with 6 teeth: <a href="https://i.sstatic.net/qVL62.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/qVL62.png" alt="enter image description here" /></a></p>
  <p>and <a href="https://brickset.com/parts/4141454/double-conical-wheel-z12-1m" rel="nofollow noreferrer">4141454: DOUBLE CONICAL WHEEL Z12 1M</a> with 12 teeth: <a href="https://i.sstatic.net/8Dznf.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8Dznf.png" alt="enter image description here" /></a></p>
  <p>or: <a href="https://brickset.com/parts/374302/toothed-bar-m-1-z-10" rel="nofollow noreferrer">374302: TOOTHED BAR M=1, Z=10</a> with 10 teeth: <a href="https://i.sstatic.net/dAM7E.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dAM7E.png" alt="enter image description here" /></a></p>
  <p>and <a href="https://brickset.com/parts/4141455/double-conical-wheel-z20-1m" rel="nofollow noreferrer">4141455: DOUBLE CONICAL WHEEL Z20 1M</a> with 20 teeth: <a href="https://i.sstatic.net/qeSFB.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/qeSFB.png" alt="enter image description here" /></a></p>
  <p>Due to the tight tolerances offered by these kind of teeth the alignment must be precisely calibrated and the passing speed should not be too high (especially if the rotational resistance or inertia is high) - in such cases <a href="https://brickset.com/parts/4174349/technic-angular-wheel" rel="nofollow noreferrer">knob</a> or <a href="https://brickset.com/parts/6306064/gear-wheel-2x2-z6" rel="nofollow noreferrer">splat</a> gears could provide better characteristics.</p>
  <p>Or for very high speed applications the gear rack could be replaced with a <a href="https://brickset.com/parts/4162781/left-shell-3x12-w-bow-angle" rel="nofollow noreferrer">long slope</a>, which engages a single protruding piece and rotates it a bit by a horizontal axle while passing by. The resulting motion can then be amplified through adequate gearing to give 180° at the desired point and incorporate a ratchet to prevent returning after the slope has passed.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-05-21T08:31:29.693Z
Answers.LastActivityDate: 2021-05-21T08:31:29.693Z
Answers.UserDisplayName: zovits
Body: <p>How do I rotate a block 180 degrees after an item (like a car or train) passes a certain point in a track?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2021-05-21T09:16:37.397Z
Comments.Text: Do you have any prototype that you could share?
Comments.UserDisplayName: Alex
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2021-05-21T10:59:28.250Z
Comments.Text: Can you clarify if the block you would like to rotate is on the train or on the track? As many details as possible about your design would help too!
Comments.UserDisplayName: Ambo100
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2021-05-21T17:13:30.827Z
Comments.Text: I do not have a prototype. I was thinking a small switch to activate a rotation off the track after the vehicle passes the point. I noticed the power function set could be close to what I am looking for. I dont know of that helps.................................. Track-vehicle-switch activation-vehicle ........... .........................block turns
  .
Comments.UserDisplayName: Scooter
Tags: <building><gears><automation>
Title: Automating rotation of a block on a track
UserDisplayName: Steven
ThreadText: # Automating rotation of a block on a track
  
  (Asked by: username_0 on 2021-05-21)
  
  How do I rotate a block 180 degrees after an item (like a car or train) passes a certain point in a track?
  
  **Tags:** building, gears, automation
  
  > **Comments:**
  > **username_1**: Do you have any prototype that you could share?  
  > **username_2**: Can you clarify if the block you would like to rotate is on the train or on the track? As many details as possible about your design would help too!  
  > **username_3**: I do not have a prototype. I was thinking a small switch to activate a rotation off the track after the vehicle passes the point. I noticed the power function set could be close to what I am looking for. I dont know of that helps.................................. Track-vehicle-switch activation-vehicle ........... .........................block turns .  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_4 on 2021-05-22. Score: 2
  
  Here's an idea for converting the movement of a moving train to rotational motion track side. This is [shown](https://www.youtube.com/watch?v=JEnRYtAE2dA) in set 6991:
  
  [![6991 action shot](https://i.sstatic.net/7m3B1.gif)](https://i.sstatic.net/7m3B1.gif)
  
  The mechanism in this case is a tire hanging from a universal joint so that it engages the train without interfering too much:
  
  [![build step 1](https://i.sstatic.net/U6VGx.jpg)](https://i.sstatic.net/U6VGx.jpg)
  
  [![build step 2](https://i.sstatic.net/Xtoic.jpg)](https://i.sstatic.net/Xtoic.jpg)
  
  This core idea could be mechanically adapted for other purposes, such as the 180 degree rotation that you are looking for.
  
  
  ---
  
  ### Answer by username_5 on 2021-05-21. Score: 1
  
  If I understand the problem correctly, you have a track, on which something is moving in a straight line. Then you want to have another, stationary object to rotate when the moving something has passed a certain point on the track, right? Like a semaphore transitioning to another state after a train has passed a switchpoint?
  
  If so, then the simplest solution would be to attach a piece of straight gear rack to the moving object and set up a gear by the tracks in a way so that the gear rack meshes with it as the object moves past. If the rack has exactly half the number of teeth as the gear, the gear will be rotated 180° upon their passing.
  
  Possible combinations: [4566045: RACK W. BALL](https://brickset.com/parts/4566045/rack-w-ball) with 6 teeth: [![enter image description here](https://i.sstatic.net/qVL62.png)](https://i.sstatic.net/qVL62.png)
  
  and [4141454: DOUBLE CONICAL WHEEL Z12 1M](https://brickset.com/parts/4141454/double-conical-wheel-z12-1m) with 12 teeth: [![enter image description here](https://i.sstatic.net/8Dznf.png)](https://i.sstatic.net/8Dznf.png)
  
  or: [374302: TOOTHED BAR M=1, Z=10](https://brickset.com/parts/374302/toothed-bar-m-1-z-10) with 10 teeth: [![enter image description here](https://i.sstatic.net/dAM7E.png)](https://i.sstatic.net/dAM7E.png)
  
  and [4141455: DOUBLE CONICAL WHEEL Z20 1M](https://brickset.com/parts/4141455/double-conical-wheel-z20-1m) with 20 teeth: [![enter image description here](https://i.sstatic.net/qeSFB.png)](https://i.sstatic.net/qeSFB.png)
  
  Due to the tight tolerances offered by these kind of teeth the alignment must be precisely calibrated and the passing speed should not be too high (especially if the rotational resistance or inertia is high) - in such cases [knob](https://brickset.com/parts/4174349/technic-angular-wheel) or [splat](https://brickset.com/parts/6306064/gear-wheel-2x2-z6) gears could provide better characteristics.
  
  Or for very high speed applications the gear rack could be replaced with a [long slope](https://brickset.com/parts/4162781/left-shell-3x12-w-bow-angle), which engages a single protruding piece and rotates it a bit by a horizontal axle while passing by. The resulting motion can then be amplified through adequate gearing to give 180° at the desired point and incorporate a ratchet to prevent returning after the slope has passed.
  
  
  ---
  
  