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Gear ratio calculator 2 released

April 15th, 2010 Leave a comment Go to comments

The tool that has been available at my website for a long time – the gear ratio calculator – has been released in an entirely new version. It also includes an extra handy feature called the Gear Coupler.

Calculating ratio of two LEGO gears is fairly easy. It gets a tad more difficult when some less common types of gears are used and when there are multiple pairs of meshed gears. To provide an easy solution to this, I have created a simple on-line calculator designed specifically for LEGO gears some time ago. It was a very basic tool and now it’s finally replaced by a newer version.

The new gear ratio calculator provides a convenient graphic interface with pictures of gears (included are all currently used LEGO gears from 8-teeth gear to Hailfire Droid Wheel, along with all types of differentials, turntables and with a worm gear too), an ability to calculate the total ratio of up to 25 pairs of gears, and it works entirely in real-time, without reloading the page. It also comes equipped with a handy new feature called the Gear Coupler which shows gear combinations available at a given spacing between the input and output axle. It works in two modes, one for studless constructions (based on liftarms) and another for studfull ones (based on LEGO Technic bricks) – this is because in case of bricks the vertical spacing between the axle holes is different than the horizontal one. The list of gear combinations is provided along with pictures, gear ratios and explanations, and is ordered from the combinations providing the highest gear reduction to the ones providing the smallest one. Please note that this tool only works for parallel gears, hence no single bevel gears, no differentials, no turntables and no worm gears are taken into account. Still, it should be more convenient than having to manually check what gears fit into a given spacing.

Update: at readers’ suggestion, the calculator was given an ability to clear the selected driver or follower gear, as well as to remove an entire pair of gears. The total gear ratio of multiple pairs is automatically updated upon removal of any of these.

Update: the option to select the drive motor and see the theoretical output speed was restored. The calculator is also available via a new address, gears.sariel.pl.

The calculator requires a JavaScript-enabled browser and may not work properly under Internet Explorer in versions prior to 8.0. This is because of extensive use of the jQuery library.

The gear ratio calculator 2

Media reference:

Lego.Blog.hu (Hungarian only), Robรณtica recreativa y educativa (Spanish only), TechnicBRICKs, Tecnoloxia.org (Spanish only)

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  1. Simon Burfield
    September 7th, 2011 at 09:48 | #1

    Brilliant tool, could we show decimals on it. I was trying to get 1RPM which I setup but via a calculator its 1.44

  2. Sariel
    September 8th, 2010 at 13:06 | #2

    No, I haven’t. If I were to make it a mobile app, I’d rather go for Android first as I’m using Motorola Milestone.

  3. cbhs
    September 8th, 2010 at 13:02 | #3

    Hi, great tool, thanks! Have you considered making it into an iPhone/touch app?

  4. Eric
    July 10th, 2010 at 00:48 | #4

    The ratios are backward

  5. Sariel
    June 26th, 2010 at 20:57 | #5

    Yes, you’re right, but there’s no point to include it in the calculator.

  6. stefanmaster96
    June 26th, 2010 at 20:07 | #6

    sariel, wouldn’t the wheels vary the torque aswell, because the bigger the wheels are, the larger radius they have and the larger radius they have, the more leverage there is from the centre of the wheel meaning that models with big wheels reduce output torque. wouldn’t that be so?? please let me know ๐Ÿ™‚

  7. Sariel
  8. May 21st, 2010 at 16:54 | #8

    What’s the name of the very large hard plastic wheel on top of this page, so that I can find it on bricklink.com?

  9. Sariel
    May 20th, 2010 at 10:45 | #9

    The engineering report states what would happen – the strain would go to the control motor, which is why two motors of equal power would have to be used for both drive and control. This is one of the disadvantages of this design.

  10. samogitian
    May 20th, 2010 at 09:33 | #10

    Practical – shmactical ๐Ÿ˜€
    Please build it. At least as a proof of concept ๐Ÿ™‚ Plus it would be interesting to see what happens when torque is applied on the output shaft.
    I’d build it myself if I had the necessary parts…

  11. Sariel
    May 20th, 2010 at 09:15 | #11

    Well I think it could be theoretically built with Lego, but it will be of no practical use. If you take engineering reports into consideration: http://www.gizmag.com/d-drive-redux/15120/ you’ll see that it would not only be complex in Lego version, but it would also require a complex control system. Which means that the transmission itself would be larger than many Lego vehicles.

  12. samogitian
    May 20th, 2010 at 08:37 | #12

    Talking about gears -> http://www.youtube.com/watch?v=F6zE__J0YIU

    Perhaps you’ll consider building such a wonder ๐Ÿ™‚

  13. Beppe
    May 5th, 2010 at 09:56 | #13

    The gallery should be public now.

  14. Sariel
    May 4th, 2010 at 22:19 | #14

    I got torque right from there, from Philo’s site, and no, they’re not stalled ones.
    The link you posted leads to a non-public gallery, I’m afraid…

  15. Beppe
    May 4th, 2010 at 21:45 | #15

    Very nice indeed! From where have you gotten the torque numbers? They are not stalled numbers, are they? According to http://www.philohome.com/pf/pf.htm the PF XL motor has a stalled torque of 40 Ncm, but that is without the current limiting IR remote receiver as I understand.

    I had a bit of an accident with a somewhat odd wheel assembly (http://www.brickshelf.com/cgi-bin/gallery.cgi?f=430079). And as a consequence I got interested in the amount of torque a LEGO axle can handle. If you can find out that number maybe you could issue a warning in the calculator when that torque is reached!

  16. Sariel
    May 4th, 2010 at 07:01 | #16

    @C Shepherd
    I corrected that.

  17. May 4th, 2010 at 04:16 | #17

    It is great stuff, I just actually used it.

    I noticed that you may have the wrong number of teeth for the big turntable.

  18. April 28th, 2010 at 21:14 | #18

    Thanks, this is really usefull! The turntables have 56 teeth.

  19. Sariel
    April 27th, 2010 at 19:44 | #19

    Perhaps your liftarms were bending. I’ve checked it many times and it works.

  20. SPIGHT
    April 27th, 2010 at 17:12 | #20

    No, I used the liftarms and it didn’t work.

  21. Sariel
    April 25th, 2010 at 19:35 | #21

    You can use t36 to t20 with liftarms and t36 to t24 with bricks. Check which units you were on.

  22. SPIGHT
    April 25th, 2010 at 17:28 | #22

    In the Gear ratio calculator when put 3 to the right and 2 to the bottom, it wrote i can use the 36 tooth to the 20 tooth gear, but it didn’t work. I had to use 36 to 24 tooth gear. Do you maybe have a mistake?

  23. April 18th, 2010 at 11:28 | #23


    Hi you can go here to have the wheel speed, depending of motor and battery :


    The gear coupler is awesome sariel, very usefull !

  24. Alex
    April 17th, 2010 at 21:39 | #24

    Please add the motors as in the older Gear Ratio Calculator !
    It is useful to see what’s final wheels speed. Thanks

  25. Nils
    April 17th, 2010 at 08:35 | #25

    Very nice, thanks!
    Small suggestion: for the gear coupler you have red-crossed the no-go options far from the starting gear position, however some closer oprions are also no-go. Maybe you could red-cross these also.
    Good luck with your great work!

  26. legomaniacman
    April 17th, 2010 at 00:06 | #26

    I like, bookmarked for future use ๐Ÿ™‚

  27. Jail
    April 16th, 2010 at 21:05 | #27

    Great! (but i like jetros, philos and chilis suggestions)

  28. Craig
    April 16th, 2010 at 14:12 | #28

    Great tool. Thanks!

  29. Yoraish
    April 16th, 2010 at 13:00 | #29

    Thats great!
    Thanks a lot!

  30. Sariel
    April 15th, 2010 at 21:13 | #30

    All your comments contribute some valuable ideas ๐Ÿ™‚ I need to check if there’s an LDraw model of the PM wheel… you did one Philo, didn’t you?

  31. Jetro
    April 15th, 2010 at 21:05 | #31

    Thanks for a great update. The only thing I miss is an ‘undo’ or ‘remove gear pair’ option.

  32. April 15th, 2010 at 21:04 | #32

    Excellent (especially the Gear Coupler!)
    One very minor gripe: the ratio calculator doesn’t offer the choice to drive the inner gear of turntables…
    Farfetched possible improvement: add inner gears of Power Miners wheel and drill ;o)

  33. Chili
    April 15th, 2010 at 20:56 | #33

    Chili likey new configuration!
    Except the motors could be added there, if it isn’t too much to do

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