Home > Construction Equipment > Caterpillar D9T

Caterpillar D9T

Model of a Caterpillar tracked dozer. Features remotely controlled drive, steering, blade and ripper.


Completion date: 09/05/2009
Power: electric (Power Functions)
Dimensions:  length 50 studs / width 26 studs / height 25 studs
Weight: 1.56 kg
Suspension:  none
Motors: 5 x PF Medium

I was interested in the unusual Caterpillar tracked dozers for some time, but I couldn’t build such a dozer earlier because the triangular shape of tracks required 6 sprocket wheels and I only had 4. Having finally acquired the missing 2 wheels, I proceeded with the construction right away.

Nowadays, when one builds a yellow tracked dozer it will be obviously compared to the famous Lego 8275 set.  Since it was clear from the beginning that my model would be significantly smaller, it was my goal to include in it more functions than the 8275 had, and thus surpass it in terms of functionality.

The basic difficulty is that the Caterpillar tracked dozers are unusually narrow – the width of the hull is only slightly greater that the width of a single track. When I calculated dimensions of model with the new tracks system which are 5 studs wide, it turned out that the hull will be just 6 studs wide.  It happened to be just the minimal possible size to house a battery box and several motors inside. Since with the coming of the new 8879 speed control enabled handset the subtractors have become obsolete, the model was supposed to be driven by two identical motors located side-to-side. With the hull just 6 studs wide the only possible choice were the PF Medium motors, and they turned out to be a fortunate one. However, to make them fit in the hull it was necessary to make openings in its sides, so that the motors actually traverse through it.

Another difficulty is the layout of the tracks: they have contact with the ground at a relatively long area, yet they are just 6 studs apart from each other. It makes the model’s weight distribution crucial for its handling. Hence the entire model is built in a perfectly symmetrical way, both externally and internally, with the only exception of bevel gears at the linear actuators and the on/off switch. Placement of the battery box low between the front part of the tracks was a second factor that contributed to the proper weight distribution.

With the drive motors successfully located in the hull it was relatively easy to make the rest of the motors fit in.  Several tricks were needed to handle the problem of model’s limited size; for instance the axle that controls elevation of the ripper is driven not by gears but by a system of very short levers. The gears would simply take too much space, and since the axle’s rotation is very limited, the levers can do the job. Moreover, the fifth motor that changes the ripper’s tilt is controlled by a switch inside the cabin, because a switch is much smaller than another IR receiver.

The ripper’s geometry makes it maintain its tilt as the elevation changes. The ripper is strong enough to lift the back of the dozer off the ground, but not strong enough to endure when the dozer drives in such position. The blade, on the other hand, is robust enough to lift the front of the dozer and endure any kind of manoeuvres. I tried to make the dozer lift itself entirely on the blade and the ripper, but in this case the ripper couldn’t take the load.

Other than that, the model’s performance was satisfactory and it was quite a pleasure to drive it, especially with the new handset (the difference in driving with the old and the new handset is presented in the video below). I was happy with its aesthetic side too, although I was aware of several compromises between model’s look and functionality. For instance the driver’s cabin was made longer by 1 stud to house the IR receivers, and it resulted in the changed shape of the dozer’s rear side. Additionally, the bonnet protrudes forward a little more than it should, because of the battery box located right behind it. On the other hand the model has no suspension whatsoever, since it was the only way to fit it with the proper number of properly sized bogies. And I have used metallic silver cheese slopes as the tips of ripper’s blades because it looked more realistic than any usual colour. A minimal amount of custom stickers was used to make the model appear more realistic. I chose not to use the lights, partially because of the limited internal space available and partially to avoid the wires hanging from the headlights, as was the case of my 854G wheeled dozer model.

The model was well welcomed as a good example of my building abilities. It was not better than was expected of me, but it did not disappoint anybody either. Personally, I have considered it to be a relaxing project noteworthy only for its compactness and the first example of the use of the 8879 handset.


1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg img_2056.jpg img_2061.jpg img_2065.jpg img_2066.jpg img_2068.jpg img_2074.jpg img_2080.jpg img_2087.jpg img_2092.jpg img_2093.jpg img_2099.jpg img_2101.jpg img_2108.jpg img_2118.jpg img_2120.jpg img_2121.png


  1. Sariel
    January 13th, 2013 at 17:32 | #1


  2. Mondo
    January 13th, 2013 at 15:01 | #2

    Hi Sariel, I have the originally 8275 tested in snow. The dozer turns very slowly on a position. When it pushes snow with the blade, i realise that the motors have not enough power.

    Have you tested your dozer alsoo in snow or outdoor?

  3. June 14th, 2012 at 20:33 | #3

    Thanks sariel

  4. Sariel
    June 13th, 2012 at 23:07 | #4

    @Jon Treasure
    Yes, I have used bevel gears.

  5. June 13th, 2012 at 22:48 | #5

    Hi there, I love all you models! I myself is building a D10T, slightly bigger and heavier than your d9, and having some trouble with the drive system. Its to narrow to have two motors side by side like i did with my last dozer (my d9). So i was wondering what gear setup you used to power your dozer? did you use bevel gears or what?

  6. MAN
    February 19th, 2012 at 19:31 | #6

    just asking

  7. Sariel
    February 19th, 2012 at 18:10 | #7

    Erm… no. Why should it?

  8. MAN
    February 19th, 2012 at 17:39 | #8

    does the engine loose its power when its running slowly????

  9. Sariel
    May 21st, 2011 at 19:37 | #9

    It didn’t.

  10. Jade2448
    May 21st, 2011 at 17:29 | #10

    did the back ripper come off when it was ripping dirt because it looks like it would.

  11. Kshomiv
    March 20th, 2011 at 00:35 | #11

    Nice dozer! My only critizism it that when the pieces that connect to the bottom of the blade are level, the blade should be touching the ground.

  12. Sariel
    May 19th, 2010 at 15:04 | #12

    Probably not, because it weights less and thus has worse traction.

  13. Tom
    May 19th, 2010 at 14:32 | #13

    great work dude.but can it push as much as the original lego bulldozer

  14. Boris
    August 22nd, 2009 at 11:53 | #14

    You are right, even when you put 2 PF M motors, they’re still 7 studs long, or in technic measurement, 6M’s. If you still have that bulldozer, you can try putting one on top of the other, and use some gearing to reach the Linear Actuator.

  15. Sariel
    August 18th, 2009 at 22:49 | #15

    Yes, I was thinking of that functionality, but the main problem was that there simply was no space for one more motor or even a small pneumatic circuit. It would probably take a larger model to include that functionality.

  16. Boris
    August 18th, 2009 at 21:58 | #16

    Also, just wanted to say this to everyone, some bulldozers can pitch their plow left-right, so as a solution to that, you can use some LEGO Bionicle parts, or some LEGO Bionicle Balls, so, when I earlier said: “…two motors are going to power the plow…” I meant on tilting it.
    So, you can just modify it a bit and put 2 pf motors, and some bionicle arms/legs with those ball things at the end, and when one linear actuator goes down and the other one goes up, it should tilt. =D

    I am a big fan of all of your creations. =D Keep up the good work!

  17. Sariel
    May 17th, 2009 at 10:25 | #17

    No, I have no idea.

  18. alex
    May 17th, 2009 at 10:13 | #18

    Hi Sariel

    Do you know if there is already in some Lego blogs a comparison of Pneumatic Air Compressors?

    It would make sense to know how much time it takes to fill an Air Tank with different combinations of Electric Motors/Number of Pumps.


  19. marycel
    May 14th, 2009 at 17:39 | #19


  20. Boris
    May 13th, 2009 at 17:41 | #20

    tl8, I also have a NXT set, and I am working on a bulldozer, but two motors will power the front plow. It will be finished once I get a second NXT set, LOL xD

  21. tacuisi
    May 13th, 2009 at 05:03 | #21

    very impressive job on fitting so many motors and functions into a chassis that small. well done, well done.

  22. tl8
    May 12th, 2009 at 02:18 | #22

    Very nice.

    It somewhat puts my bulldozer into the right perspective. I now see I did have ok proportions (and I thought it was massively too tall(only mildly to tall :P)) http://www.orbiter-forum.com/blog.php?b=47

    I did have the problem of not enough parts and very poor weight distribution as well as fitting the NXT motors in.

    Keep up the good work, I really get a kick out of looking at your creations and seeing how you tackled the various problems.

  23. May 10th, 2009 at 16:28 | #23


  24. teunj
    May 10th, 2009 at 13:48 | #24

    it is a beautiful structure but personally I had a slightly better finish but you expect technical things work fine for me

    PS I am waiting for your next model

    Greetings teunj:)

  1. No trackbacks yet.