MOCpages : Share your LEGO® creations
LEGO models my own creation MOCpages toys shop Centrifugal tachometerTechnic
Welcome to the world's greatest LEGO fan community!
Explore cool creations, share your own, and have lots of fun together.  ~  It's all free!
Centrifugal tachometer
Rate it  12345       Add a comment Add a comment   Zoom in  Zoom in
Not exactly a practical tach, but kinda fun to watch all the same.
About this creation
Please feel free to look over the images and skip the verbiage.

This centrifugal tachometer works on the same principle as a Watt steam governor. Consider it more a demonstration of principle than a practical tool.



On this page:Warning! Always wear eye protection when working or playing with high-speed LEGOŽ rotating machinery and keep valuables and bystanders (including pets) a safe distance away -- especially when testing new designs.




How it works

An L motor powered by an old 9V LEGOŽ train transformer turns the flyball mechanism via a 1:2.78 overdrive transmission.





As the spinning black flyballs move outward under centrifugal force, a pendulum linkage akin to that used by Watt on his own steam governors pulls the central DBG "sleeve" upward against the dark bronze "return spring".



A square LBG "follower" confined to a groove on the rotating sleeve then translates sleeve height into red needle angle via a simple 4-bar linkage and 3:1 reduction gear.







Compressing the entire range of flyball speeds (0-995 RPM) into the desired 120° of needle deflection took quite a bit of fiddling -- especially with spring and flyball selection and the needle linkage and gearing. None of the LEGOŽ springs I tried were soft enough.

To keep vibrations in check, I had to find just the right rubber feet and fine-tune the mass, stiffness, and geometry of the frame supporting the upper end of the governor shaft.





The consistent jumps in needle angle in the first video aren't due to a flaw in the tachometer. Rather, they reflect jumps in transformer output as the dial is turned.



As seen in this 2nd video, the jumps vanish when a continuously variable power supply is used.

<< Back to top




First-order dynamics (optional)

To first order, the outward centrifugal force on each flyball is proportional to the flyball's mass and the square of its angular speed. The pendulum linkage converts the centrifugal forces on the flyballs into an upward force on the sleeve. The downward force on the sleeve is the sum of (i) sleeve weight, (ii) follower weight, and (iii) the restoring force exerted on the sleeve by the compressed return spring. The last is proportional to the rate constant and shortening of the spring.

Hence, sleeve height varies roughly with the square of flyball angular speed. Needle angle then varies roughly linearly with sleeve height via the needle linkage.

Ideally, equilibrium between the upward and downward forces acting on the sleeve would enforce a smooth one-to-one relationship between flyball angular speed and sleeve height. The model, however, exhibits a mild hysteresis, in that the sleeve height obtained when a given speed is approached from above differs slightly from the height obtained when the same speed is approached from below. Friction is the most likely culprit.

Among other things, the return spring increases the flyball mechanism's maximum operating speed and dynamic range. The latter refers to the difference between the operating speed that first pegs the needle and the speed that first gets it moving.

<< Back to top




Specifications

Overall dimensions:172x110x224 mm (LxWxH) excluding power supply
Mass:365 g excluding power supply
Maximum speed:995 RPM
Motors:One L
Electrical power supply:9V train transformer
Modified LEGOŽ parts:None
Non-LEGOŽ parts:Return spring and washer
Credits:Original MOC
See also:Hartnell steam governor, SBrick-based continuously variable 9V power supply, and Power dog

<< Back to top




Recommended reading

Denny, Mark, 2007, Ingenium: Five machines that changed the world, The Johns Hopkins University Press, Baltimore (highly recommended)

Denny, Mark, 2002, Watt steam governor stability, European Journal of Physics, v.23, p.339-351.

Fasol, K.H., 2002, A short history of hydropower control, IEEE Control Systems Magazine, August, p.68-76.

Wikipedia, 2016, Centrifugal governor

<< Back to top




Comments

 I made it 
  February 6, 2016
Quoting droid hunter I do love me some Tacho's
Thanks, DH! I'm afraid this one isn't very tasty, but I might be able to fix that with some guacamole and green chili sauce.
 I like it 
  February 5, 2016
I do love me some Tacho's
 I made it 
  January 29, 2016
Quoting jds 7777 The Lego gallery was how I started out. But left because of poor number of views and comments (and because Lego took it down for several months). Then I discovered Mocpages, but get likes and comments here is even harder! However most of the people on the Lego Gallery were and still are) between ages 6-12. So, pretty easy to impress I guess. The Lego mindstorms blog used to be awesome as there were a lot of teenagers on there building awesome stuff with their NXTs. But then they all grew up and got busy with school, or started youtube accounts, or other stuff. Much of what I know about mechanics I learned from I mindstormer who went by Builderdude35. Now he's an avid YouTuber, but does occasionally post on the Mindstorms blog. (Which is now overrun with a bunch of younger kids who don't put as much thought into their creations as the others used to.) I hope you don't mind my rambling ;)
Not at all! Interesting history of a sector of the LEGO experience off the radar screen of many GFOLs (geezer fans of LEGO) like me.
 I like it 
  January 29, 2016
The Lego gallery was how I started out. But left because of poor number of views and comments (and because Lego took it down for several months). Then I discovered Mocpages, but get likes and comments here is even harder! However most of the people on the Lego Gallery were and still are) between ages 6-12. So, pretty easy to impress I guess. The Lego mindstorms blog used to be awesome as there were a lot of teenagers on there building awesome stuff with their NXTs. But then they all grew up and got busy with school, or started youtube accounts, or other stuff. Much of what I know about mechanics I learned from I mindstormer who went by Builderdude35. Now he's an avid YouTuber, but does occasionally post on the Mindstorms blog. (Which is now overrun with a bunch of younger kids who don't put as much thought into their creations as the others used to.) I hope you don't mind my rambling ;)
 I made it 
  January 26, 2016
Quoting Oliver Becker Sorry for my late reply, Jeremy! You're right, Flickr is "IN" and has much more pic- quality! But it's connected with a Yahoo- account and I'm no big fan of inquisitive "social"- media... I participated in the demise of LDD- Gallery for several times, now LEGO is stopping support for the software! Maybe no money to make with the MOCs of the kids there... Also ungrateful, they don't remember their bad times...! MOCpages was an institution, I hope it will be still on: Most young MOCcers come from the LEGO-Galleries now to start here! So I like to stay (as I remarked it on my main-page here) 'cause these "youngers" are LEGO future and it will be interesting here because of that. Sounds a little pathetic, but never mind... ;)
I hope MOCpages survives, too, Oliver. I've met a lot of good e-friends here, including you. Too bad some of them don't seem to be around anymore. Too bad also about LDD support. Not familiar with the Gallery you mentioned, but it sounds like TLG would have smarter to keep it going.
 I made it 
  January 26, 2016
Quoting Didier B Well, seems that "Mocpages" faces big troubles those days... I made a comment on this moc a few days ago but it seems that it was not recorded. I don't remember the wording but it said that I like what you do Jeremy. Keep bricking ! Didier
Many thanks for those kind words, Didier, and for commenting twice as well. Means a lot.
 I like it 
  January 26, 2016
Well, seems that "Mocpages" faces big troubles those days... I made a comment on this moc a few days ago but it seems that it was not recorded. I don't remember the wording but it said that I like what you do Jeremy. Keep bricking ! Didier
  January 25, 2016
I hope to stay around. I couldn't care less about popularity, but it is nice to have a decent audience to not only share stuff with, but also discuss ideas, etc. Personally, I don't see me going to Flickr, as there is not much chance for discussion there. However, Mocpages does seem to be dying. I think it says something that on the Technic forum of eurobricks there are few builders that are part of Mocpages. BTW.... are you a member of eurobricks? Their forum for Technic builders, IMO, is the best forum to post and discuss MOCs. You mocs would fit right in.
 I made it 
  January 24, 2016
Quoting Nerds forprez I agree with Oliver. Us Technical geeks need to band together! I wish there was more of a voice here on Mocpages for Lego Technic models.
Thanks, NFP! Me, too. Hmmm, if the apparent exodus to Flickr is real, this might be a good time to work toward pumping up the Technic audience here -- provided we get e-mail notifications back soon. (If not, I may not stick around, either.) Getting more Technic on the front page would be a start. That would mean actively seeking out new Technic offerings and leaving likes =and= comments for them within the first 24 hours (if deserved, of course). In my experience, an MOC needs to garner 3-4 likes =with= comments in 24 hours or so to make the front page. If it fails to reach the front page, it will become all but invisible very quickly. Bolstering the Technic presence would also mean adding more Technic builders as favorites so as to harness the power of e-mail notifications, which helps tremendously with the front page thing.
 I like it 
  January 24, 2016
Sorry for my late reply, Jeremy! You're right, Flickr is "IN" and has much more pic- quality! But it's connected with a Yahoo- account and I'm no big fan of inquisitive "social"- media... I participated in the demise of LDD- Gallery for several times, now LEGO is stopping support for the software! Maybe no money to make with the MOCs of the kids there... Also ungrateful, they don't remember their bad times...! MOCpages was an institution, I hope it will be still on: Most young MOCcers come from the LEGO-Galleries now to start here! So I like to stay (as I remarked it on my main-page here) 'cause these "youngers" are LEGO future and it will be interesting here because of that. Sounds a little pathetic, but never mind... ;)
 I like it 
  January 23, 2016
I agree with Oliver. Us Technical geeks need to band together! I wish there was more of a voice here on Mocpages for Lego Technic models.
 I made it 
  January 23, 2016
Quoting Henrik Jensen Always great to see your mechanical experiments. I have always been fascinated by the cetrifugal steam govenor, and it must have been a great break-through when it was introduced as a regulator for keeping constant speed on Machinery. Your model demonstrates perfectly how it Works. Regarding people going to Flickr: MOC-pages numerous break-downs is a constant source of annoyance, but also the limping activity board makes MOCpages look amateurish. But somehow I still like it here, and I will keep on posting here even though I also have a Flickr account.
Too kind, Henrik! Glad you're still around despite the hassles. You're spot-on about the historical significance of the centrifugal governor: The Industrial Revolution would have at best limped along without it. The governor also kick-started engineering control theory, upon which much technology depends nowadays. More on the history and impact in the footnotes to the Hartnell steam governor I'll be posting in the next day or so. Stay tuned!
 I like it 
  January 23, 2016
Always great to see your mechanical experiments. I have always been fascinated by the cetrifugal steam govenor, and it must have been a great break-through when it was introduced as a regulator for keeping constant speed on Machinery. Your model demonstrates perfectly how it Works. Regarding people going to Flickr: MOC-pages numerous break-downs is a constant source of annoyance, but also the limping activity board makes MOCpages look amateurish. But somehow I still like it here, and I will keep on posting here even though I also have a Flickr account.
 I made it 
  January 23, 2016
Quoting Oliver Becker Your job as an consulting engineer h.c. here on MOCpages is again well-pleasing done, Jeremy! I believe that your machines are a great knowledge transfer for most people here or could be for sure, my friend! Because the MOC-appeal is stronger in your videos than in the pics maybe some clicks are lost going to the popular themes and characters... unfortunately and really NOT deserved! May the general knowledge be with us and them... ;)
Thanks for the encouraging words, Oliver! Agree, the videos are essential, as my builds are generally more about what they do than how they look. Mechanical MOCs certainly aren't mainstream on MOCpages, and my pages ask a lot of visitors, so I can't expect a big audience. I stick it out because when it works, the blog-like format here is better suited to the way I like to present my MOCs than alternatives like Flickr. BTW, have you noticed that we haven't seen much of some previously very active folks recently? They seem to have gone to Flickr.
 I like it 
  January 23, 2016
Your job as an consulting engineer h.c. here on MOCpages is again well-pleasing done, Jeremy! I believe that your machines are a great knowledge transfer for most people here or could be for sure, my friend! Because the MOC-appeal is stronger in your videos than in the pics maybe some clicks are lost going to the popular themes and characters... unfortunately and really NOT deserved! May the general knowledge be with us and them... ;)
 
By Jeremy McCreary
Add to my favorite builders

8
people like this. See who.

2,596 visitors
15 comments
Added January 21, 2016
 


LEGO models my own creation MOCpages toys shop Centrifugal tachometerTechnic


You Your home page | LEGO creations | Favorite builders
Activity Activity | Comments | Creations
Explore Explore | Recent | Groups
MOCpages is an unofficial, fan-created website. LEGO® and the brick configuration are property of The LEGO Group, which does not sponsor, own, or endorse this site.
©2002-2019 Sean Kenney Design Inc | Privacy policy | Terms of use