Home > Ideas > 2-speed Heavy Duty Linear Gearbox

2-speed Heavy Duty Linear Gearbox

February 27th, 2011 Leave a comment Go to comments

Compact, simple gearbox designed for use in Truck Trial races and high-torque applications. Step-by-step instruction and a two drive motors variant included.

Last year, the continuous development of the Truck Trial vehicles in our country resulted in the common use of gearboxes. Since the power-to-weight ratio of each vehicle decides how much points it gets, it is favourable to reduce this power to minimum. This is where gearboxes come in handy – they allow to use less motors, or less powerful motors, increasing gear reduction when needed, and decreasing it when less torque is needed. Without the gearboxes, all vehicles would have to use a gear reduction high enough to climb obstacles, which results in reduced speed and in a waste of time when e.g. driving downhill.

The loads exerted on vehicles’ drivetrains in our races are so high that it’s very difficult to use a gearbox with driving rings. In most cases, it results either in the driving rings disengaging under load, or in mechanical damage to them. Therefore it’s a common practice to use simple linear gearboxes, with as few gears as possible, as most vehicles can do very well with just a 2-speed gearbox. The need for reducing amount of gears to minimum resulted in integrating the drive motors into the moving parts of the gearboxes, so that the motors slide as the gears are changed. The idea, introduced by Emilus in his Truck Trial models, eliminates the need for complex transmission mechanisms between sliding driveshaft and stationary motor, and has practically no disadvantages, except for slight shifts of the vehicles’ centre of gravity caused by motors’ weight.

The following gearbox has been developed from a version used in my Fiat SPA35 Dovunque model. The Fiat’s gearbox has failed during the race, but it has given me the opportunity to observe exactly what are the causes of its malfunction. Based on this experience, the new gearbox has been reinforced in all the crucial spots and is practically immune to mechanical damage, while still being relatively compact and simple.

I have provided schemes, views from various angles and a full instruction for the gearbox, as well as a scheme and views of a version using two drive motors instead one. 聽Note that the sliding mechanism has not been included, because my experiences with Fiat have shown that it’s best to make it part of the chassis close to the gearbox, that part of the gearbox itself. Still, building such a mechanism should be fairly simple, as all it has to do is to slide the central bracing a single stud back and forth, and keep it in place. The mini linear actuators are one of the many options that can be considered here.


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  1. Goshik
    June 1st, 2016 at 21:24 | #1


    The gearbox is great and im building something like a trial truck

  2. Goshik
    June 1st, 2016 at 20:52 | #2


  3. Sariel
    June 1st, 2016 at 13:01 | #3

    You slide the part with the motor forward and backward by 1 stud.

  4. Goshik
    May 31st, 2016 at 20:37 | #4


    And also im a big fan of your creations

  5. Goshik
    May 31st, 2016 at 20:15 | #5


    The gears sometimes grind and how do you make it change gears

  6. tony
    March 26th, 2014 at 14:10 | #6

    ok thanks for the advise

  7. Sariel
    March 26th, 2014 at 09:22 | #7

    Use the 2-speed gearbox, or no gearbox at all. 4×4 drivetrain is not a problem, the problem is the suspension system, because it sounds like you don’t have parts to make it and without suspension your truck won’t work well outdoors.

  8. tony
    March 26th, 2014 at 03:18 | #8

    hi sariel big fan of your lego ideas and cars that you make i wanted to make a truck to go outside and go through hills and stuff but i dont have alot of pieces i was thinking of making a 2008 chevy suburban i want it to work good so i have two questions

    the first question is that should i use a 3 speed gearbox or the 2 speed gearbox that u made

    the second question is that i dont have any shock absorbers or suspensions and was hoping you have another way of making heavy duty 4×4 drivetrain

    i would appreciate it if you can give me some advise rather than me making something from you since some of the ideas i have made i cant use on the truck so please reply to this thank you

    from tony

  9. Sariel
    January 8th, 2014 at 22:43 | #9

    You look at it wrong. Output doesn’t change its position – input does, together with the motor. The gray frame that braces the gearbox should be fixed and not moving – instead, the gearbox moves through it.

  10. Alberto
    January 8th, 2014 at 22:35 | #10

    Hi Sariel, I just wanted to ask you one thing about the gearbox. The gearbox is nice, but I saw that the output change the position when I change the gear ratio. How can I solve that problem?

  11. josh
    July 9th, 2013 at 18:35 | #11

    hey i just want to say this is an awesome creation, i love the 2 motor version

  12. Sariel
    September 7th, 2012 at 18:55 | #12

    It’s all explained in the text.

  13. MrBronzegoat
    September 7th, 2012 at 17:53 | #13

    hey man please tell me how to switch the gears/accelerate

  14. jimmy3
    August 20th, 2012 at 17:04 | #14

    I put this in one of my cars and it was SO strong unlike my gear boxes that fall apart as soon as it goes.

  15. June 13th, 2012 at 22:40 | #15

    tanks anyways @Sariel

  16. Sariel
    June 10th, 2012 at 00:56 | #16

    @jordan thomas
    You can connect it any way you like.

  17. June 9th, 2012 at 23:24 | #17

    i think he means like can it be directly driven to an axle with out raising it up and using a gear system if you still don’t understand look at the under body picture of your South Africa MRAP and your gear box it raised up and uses two gears to connect to the drive system he means directly to the main drive shaft to the @Sariel

  18. June 8th, 2012 at 19:31 | #18

    thanks this gearbox won me a truck trial

  19. Sariel
    February 2nd, 2012 at 09:51 | #19

    No, it doesn’t change itself. I have no idea what is this “ground level” question about.

  20. johnboy104
    February 2nd, 2012 at 02:18 | #20

    How does the gearbox change by itself? Do you have to shift it to high and low ranges? Does it work on ground level?

  21. Sariel
    November 16th, 2011 at 07:54 | #21

    Yes, of course. You don’t need to ask 馃檪

  22. Grant
    November 16th, 2011 at 03:39 | #22

    Great Instructions! May I translate this article also?
    ( In fact one LEGO fans on our forum had already finished the translation, and we will add the author and url to this site. )

  23. qwertyuiop
    October 6th, 2011 at 07:51 | #23

    when i first tried to make a 2-speed gearbox on my own, not knowing how they worked, i ended up with a 1:1 ratio for the low gear and a 1:5 overdrive for the high gear. it didnt work very well

  24. Sariel
    October 3rd, 2011 at 18:26 | #24

    @Erik Bussink
    Yes, it does. The gearbox is too simple for the extra torque to get wasted.

  25. October 3rd, 2011 at 18:07 | #25

    How does the heavy-duty work with two engines vs one. Does it truly add nearly twice the torque ?

  26. Sariel
    June 4th, 2011 at 09:12 | #26

    @zeke labelle
    Linear actuators? Motorized lever? Rack and pinion? Scissor mechanism? There are dozens of possibilities.

  27. zeke labelle
    June 4th, 2011 at 08:42 | #27

    it works good so far but how can i get it so i don’t have to change the gears by hand and i don’t have any pneumatic’s plz help

  28. zeke labelle
    June 3rd, 2011 at 00:13 | #28
  29. Sariel
    June 2nd, 2011 at 20:34 | #29

    @zeke labelle
    You can do anything you want with it.

  30. June 2nd, 2011 at 20:30 | #30

    is it ok if i use it on my wheeled tank

  31. panos
    June 1st, 2011 at 14:42 | #31

    Its the best gearbox for vehicles i have ever seen on most LEGO forums including YouTube etc Robust,convienient changes and relatively small.Great work!!!

  32. Sariel
    May 23rd, 2011 at 07:57 | #32

    @Tanner T.
    Not at all. That’s why I published these things in the first place – to be used by others.

  33. Tanner T.
    May 23rd, 2011 at 02:06 | #33

    Would you mind if I used this gear box and your 4 speed manual in a vehicle I am working on?

  34. Aram
    May 20th, 2011 at 03:40 | #34

    nice gearbox it works well compared to a gearbox i tried to make

  35. Sariel
    May 8th, 2011 at 20:46 | #35

    Well, you can always use gear acceleration between the LA and the motor. I used miniLAs in the Humvee and it was slow, but I didn’t need it any faster there.

  36. Mehley
    May 8th, 2011 at 18:22 | #36

    Hello Sariel! Eariler you mentioned, that a small actuator would be slow for changing gears.. however, in your Hummer you used this mechanism 馃檪 As I saw, it worked great, and wasn’t slow at all. Do you think it can work with a big size LA fas enough?

  37. Sariel
    May 2nd, 2011 at 22:02 | #37

    They are NOT mounted together. Look closely at picture 6, they have two separated axles.

  38. NikJan
    May 2nd, 2011 at 21:46 | #38

    Is it possible that the motors get damaged when they’re mounted together like in picture 5?

  39. claudio forlani
    April 22nd, 2011 at 11:22 | #39

    pity it would be nice!

  40. Sariel
    April 22nd, 2011 at 11:01 | #40

    @claudio forlani
    It’s large, it would be difficult to fit in the Jeep. You would have to modify the Jeep a little, perhaps make it longer. It will certainly affect aesthetics.

  41. claudio forlani
    April 22nd, 2011 at 10:36 | #41

    Basically I want to figure out whether you can insert this change in the jeep wrangler.(without affect the aesthetics and performance).
    It is understandable that you don’t understand, but I didn’t want to disrespect to an important person like you.

  42. Sariel
    April 22nd, 2011 at 09:45 | #42

    @claudio forlani
    Claudio, it’s hard to understand what you’re asking.

  43. claudio forlani
    April 22nd, 2011 at 09:34 | #43

    then okay for all models that you have built without moving anything?
    Perhaps it is a secret but I’ve told you how to change gears, I build a mechanism like you did with humvee?

  44. Sariel
    April 21st, 2011 at 19:03 | #44

    @claudio forlani
    Errr…. there’s no need to remove or raise anything.

  45. claudio forlani
    April 21st, 2011 at 17:57 | #45

    how do you do to change gear model?
    removing or raising the seats, it could be mounted on the jeep rubicon?

  46. Sariel
    April 21st, 2011 at 11:41 | #46

    Po co, skoro wi臋kszo艣膰 rzeczy opisuj臋 po polsku na LUGPolu?

  47. Szymon
    April 21st, 2011 at 10:24 | #47

    Sariel… a mo偶e zaczniesz prowadzi膰 bloga w dw贸ch j臋zykach ? ;]

  48. Sariel
  49. April 17th, 2011 at 13:42 | #49

    Sariel w jakim programie robisz lub polecasz robi膰 schematy, chodzi mi o projektowanie wirtualne takie jak np w powy偶szej instrukcji?

  50. Sariel
    March 14th, 2011 at 19:57 | #50

    Both will work.

  51. bob
    March 14th, 2011 at 19:12 | #51

    Is it ment to motorise with a linear actuator or with something pneumatic ?

  52. Sariel
    March 8th, 2011 at 18:56 | #52

    Not really, that would require a very different design.

  53. bob
    March 8th, 2011 at 18:47 | #53

    can you make this with 3 speeds?

  54. Sariel
    March 8th, 2011 at 14:33 | #54


  55. adithya
    March 8th, 2011 at 14:30 | #55

    anything even smaller than that?

  56. Trevor
    March 8th, 2011 at 09:52 | #56

    Correct, Thank you very much. I was having some trouble trying to explain exactly what the problem was. Thanks though, your always a big help whenever i have problems building.

  57. Sariel
    March 8th, 2011 at 07:46 | #57

    Perhaps you’re looking for this: http://sariel.pl/mocs/scania-dump-truck/10.jpg

  58. Trevor
    March 8th, 2011 at 01:16 | #58

    Yes I could, but it still wont switch gears is my problem. The initial problem is with my drive shaft because it wont allow me to push forward into the next gear. I need something that is like a +1/-1 stud set up to allow the gear box to shift fluidly with out the pulling out the axle of pushing the axle through my rear chassis and into the other knob gear.

  59. Sariel
    March 8th, 2011 at 00:35 | #59

    Can’t you just swap gears?

  60. Trevor
    March 7th, 2011 at 23:39 | #60


    I was wondering if you have a solution on how when the gear box switches into the higher gear it also moves one stud length further out. If i connect the gearbox to the frame of my truck it wont switch gears because it just pushes the frame and starts to grind gears. Is there any type of easy solution to this problem.

  61. Sariel
    March 5th, 2011 at 14:57 | #61
  62. adithya
    March 5th, 2011 at 11:56 | #62

    Hey, do you have a gearbox wich is a two speed one, but more compact?

  63. Mehley
    March 3rd, 2011 at 01:58 | #63


    Many thanks for the tip, I will try this method to change gears! 馃檪

  64. Sariel
    March 2nd, 2011 at 23:24 | #64

    Small actuator will be slow for this. In my Fiat truck, with similar gearbox, I was using a 4-studs long pushing lever driven by a Medium motor reduced 24:1 (with a worm gear driving a 24-tooth gear). It worked pretty fast.

  65. Mehley
    March 2nd, 2011 at 23:18 | #65

    Thanks for sharing this efficient gearbox mechanism! I have just build it, it works great! However, changing the speed should be made fast, in order to prevent the gears from stucking. Did you realized this problem as well? Anyway, is there any chance to change speed remotely fast? Maybe a fast geared small actuator can do this?

  66. Mike
    March 1st, 2011 at 22:44 | #66

    I just realized you can’t put bushes there, yes.. sorry 馃檪 just looked at it now, and saw it.. but yesterday I’ve been looking at photos and didn’t see this. awww…
    Can’t wait to see how it’ll work ! 馃檪

  67. Sariel
    February 28th, 2011 at 18:19 | #67

    There can be no bushes Mark. If you put bushes there, the gearbox won’t have space to slide.
    As for the meshing gears, I don’t think it really affects the friction. But it’s still good to keep the gears meshed properly, or they may be more prone to mechanical damage.

  68. Mike
    February 28th, 2011 at 18:06 | #68

    Oh and one more thing. I know that these 20 and 12 toothe gears tend to cause friction when given a one-stud wide space like here. You know, the older e.g. 16t gears are narrower at the teeth, but these new ones aren’t. Once when I used them I had to put half stud bushes on each side of the gears to prevent this.
    Do you consider this friction minimal, or can it cause significant power consumption in a trial truck?
    The concept of this gearbox I think is great, I think this year you’ll have much better luck, this and other developments will bring better results! 馃榾

  69. Mike
    February 28th, 2011 at 17:58 | #69

    Do you use one stud long bushes between gears to prevent them from sliding on the axle?
    I’m curious because I rarely see them on your MLCad drawings, but I guess you always include every part you use in the real thing.

  70. February 28th, 2011 at 16:27 | #70

    Nie przejrza艂em wszystkich zdj臋膰 .
    Sory !

  71. Sariel
    February 28th, 2011 at 15:04 | #71
  72. February 28th, 2011 at 15:00 | #72

    Je偶eli masz zamiar zbudowa膰 trial贸wk臋 z mechanizmami zwalniaj膮cymi takimi jak w przednim mo艣cie od twojego Jeep’a to radze Ci je zmieni膰 na jakie艣 inne 偶eby ko艂a si臋 nie rozje偶d偶a艂y ka偶de w inn膮 stron臋 .
    Jeszcze jedno na zdj臋ciu http://www.brickshelf.com/gallery/Sariel/ideas/2speedHDgbox/5.png
    wida膰 偶e silniki s膮 z艂膮czone jednym Axle’m w ten spos贸b gdy w艂膮czysz dwa silniki w jedn膮 stron臋 bo inaczej przy rozwi膮zaniu jakie wida膰 na zdj臋ciu si臋 nie da knob kt贸ry b臋dzie odbiera艂 nap臋d nie b臋dzie spe艂nia艂 swojej roli poniewa偶 b臋dzie kierowany w du艂 albo do g贸ry .

  73. David Luders
    February 28th, 2011 at 14:58 | #73

    As always, your diagrams and explanation really help Technic fans with understanding complex mechanisms. Your work is really helping to advance the overall level of Technic models worldwide. Thanks for sharing!

  74. Sariel
    February 27th, 2011 at 20:44 | #74

    Dok艂adnie tak dzia艂a ta skrzynia. A prze艂o偶enie mi臋dzy ni膮 a ko艂ami mo偶na sobie dobra膰 pod mas臋 konkretnej trial贸wki.

  75. February 27th, 2011 at 20:26 | #75

    Wiem .
    Napisa艂em tak poniewa偶 moim zdaniem jedynka powinna by膰 wykorzystywana do podjazd贸w i pokonywania innych trudnych przeszk贸d , a dw贸jka do jazdy po r贸wniejszym terenie .

  76. Sariel
    February 27th, 2011 at 20:08 | #76

    Wystarczy 偶e dodasz redukcj臋 za skrzyni膮. Przecie偶 nikt nie powiedzia艂, 偶e wyj艣cie ze skrzyni musi i艣膰 od razu do k贸艂.

  77. February 27th, 2011 at 19:35 | #77

    Skoro ma to by膰 skrzynia bieg贸w do Truck Trial to moim zdaniem prze艂o偶enie jest niezbyt .
    Uwa偶am 偶e bieg 1 powinien mie膰 prze艂o偶enie 1:3 a pieg drugi 1:1 .
    Skoro napisa艂em co艣 藕le to przepraszam .

  1. November 5th, 2012 at 03:32 | #1