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Unfortunately, I have not enough of this parts, ref 45590, to make a a big tank. But, if you look at the Sariel test, here , you can see that it climb a slope with 2.4kg weight and a complex vehicule. If I will make a new big tank, which is already 2.5kg, this track it will add about 1kg. This is too much for the big Lego servos, but may be not for the track. But as you maybe know I am not an exclusive Lego maker. So if I am making my mind to do something, it will be most with a custom track that I am thinking about. I mean, a new track based on this Lego track principe. But anyway, I never found something better than my "D joint" for grip. About the sprocket, may be it will not grip the track with heavy weight because of the big elasticity of track, so it could slip ! My english is not good, hope you understand what I mean.

Thank you all ! Well, Sariel has already done some tests. I think this track is really good. But I say, it is 50% more heavy than my track. One day, may be, I'll make something like this in a DIY way.

After seeing the video of Sariel with his new track, https://www.eurobricks.com/forum/index.php?/forums/topic/150840-gaz-3351-articulated-tracked-vehicle/&tab=comments#comment , I thought to make a specific sprocket. Then the time passed and I did something else.But lately, a young boy with a lot of enthusiasm pushed me to bring out this project from the bottom of my drawers. I want to thank him here.Here is the result :

Thank you. Yes ! I though about it, but Lego servo are too big and not much powered. My goal, making that kind of tank, is to make something little. Maybe with non-Lego servos.

Here are some pictures of the new version. You can see how the actuator modify the length of the track. In this new version, I have used the @efferman Gear rack beam, https://www.shapeways.com/product/4QE5P2AC9/gear-rack-beam-4l?optionId=41744256&li=user-profile , thanks to him. Unfortunately, this new version does not work, it is much more rigid but much too heavy.

Thank you for your comments. - to drive 6 servos, I use this : http://www.mindsensors.com/ev3-and-nxt/21-multiplexer-for-nxtev3-motors - yes I use the EV3 remote control to drive the tank but the geometry modification is automatic, I use the EV3 Gyro sensor, testing angle of the tank. - the size of the track is not the same on the both perimeters. That why I realy modify the perimeter lenght with an actuator. You can't see this in the video. I will make pictures soon of that, but from a new version which is stronger and too heavy and unfortunately does not work.

In this video, I show that it is possible to make a reasonable sized tank for a private house which is able to climb stairs. To climb stairs, a tank sole must be about 62cm length. With such a sole, the tank reaches about 85cm total length. The variable geometry makes it possible to make a 55cm tank length, which by unfolding, reaches the 62cm necessary to the rise.

Hi Efferman. I received the new counterparts. They fit perfectly with the worm gear. Maybe a little tight, but with the use I think it will get better. Thank you very much.

Great! Did you be inspired by a real machine or is it a personal creation?

Excellent !

Very good ! A great entry into the world of Technic.

Great ! You can make animation as in nightclubs, write words on a wall or finely measure the thickness of an object by measuring the angle of reflection.

This looks very good. I am very impatient to receive them. Thank you.

That what I thought at first. Difficult to explain my english is not enough good. Please, look at this new pictures. As you can see the first shows a space and the other no space. The only thing I have changed is that I have intervert the face A and B of the right counterpart. It works better of course. In all, there are 4 mounting possibilities. In my opinion, this means that the gear is not symetrical to the pins axe. Of cours a track worm gear can't be symetrical, but you understand what I mean. Do you think is it possible to do some thing ? Thank you.

Hi. I am making an actuator by coupling two of your Worm Gear Counterpart. Unfortunately, there is a space between the two worms gear as you can see in the pictures. I wonder if it is possible to make a counterpart which is 2L or 3L long, with 2 or 3 pins on each side. Of course, I have made an actuator with only one of your Counterpart, but it is not enough rigid in my opinion. Thank you.

I have purchased for 8 "Wormgear Counterpart" , https://www.shapeways.com/product/WBXDZK8E7/wormgear-counterpart?optionId=43734647 This is a very good work. All fits very good. Thank you.

Here, you can see the video about my worm gear nut Tommy variant. Thanks to Tommy.

The goal here was to make an efficient worm gear nut. And I think, all together, we have succeeded. What we matter here is the nut and the guide of the nut. Of course, it is possible to make something with the 32L axle. Many of ours think about a 3D printer I presume. Why not ! But of course, this does not exempt to make a strong structure for your project. Please, make something and give us a feedback. Thank you all.

Here is a new variant inspired from the @Tommy Styrvoky variant... This one is 5 stud wide design, instead of 4. It is easier to make and much more adaptive. Furthermore, you can see that I have inserted 2 bushes in the back to block even more the third gear.

Yes, the little one can be useful. But because the worm gear is not blocked with the third gear it may slip when big torque. I believe that the 3 gears alternative path is the key of this worm gear nut. Thank you @LEGO Train 12 Volts

@Tommy Styrvoky. Here you can see your variants. The first is very good. It is very small, this can be useful. Yes unfortunately, the second can't fit with 4x8t gears, only 3. Nevers mind, the third gear, under, don't move either, it is blocked. This one is my preferred because you can easily make it stronger and associate beams and connectors.

Thank you @agrof and thank you all. Here, you can see somme photos about the @Didumos69 idea. The others will come soon.

It is me who thank you for all these magnificent variations. I will try to make all this right away and will show some photos.

The gears don't rotate, that's why it works. But your drawing seems good to me too.

This is very easy to try and you will see there is no problem. If too much torque, the full figure will explode before the tooth slip or broke.