[TC29] The Snow Horse

[1980SomethingSpaceGuy]

3 hours ago, Teo LEGO Technic said:

This MOC is amazing, it really went through a lot of iterations, but the functionality and looks of the final model are worth it  

If I'm understanding your steering setup correctly, the two L motors that drive the track also drive either side of a differential, so if one is spinning faster, this causes the diff to spin, and it is connected to the steering rack, and steers the skis, is that correct? Does the white clutch gear have enough resistance to steer the model, or is it too weak? I guess you are intending it to operate while it drives, and primarily on a more slippery surface like your hardwood floor, so it works great for that purpose?

Overall, I love it, can't wait to see the final version! (Although it already looks fairly finalized)

Thanks! You got it perfectly right; the differential is used in subtraction; it'll only move if both motors are not spinning at the same rate. And yes, the clutch has enough friction to steer the skis on most surfaces. I initially meant it to ride the big white fluffy carpet in my living room, but it ended not well; the model sinks into it and would only painstakingly crawl through. So now it's tuned to ride the hardwood floor and that works well. I would love to see it on the ice one day!

[Paul B Technic]

You have done an amazing job with this.

[MangaNOID]

Looks very accomplished!

Nice way to get around the servo issue 

[Teo LEGO Technic]

12 hours ago, 1980SomethingSpaceGuy said:

Thanks! You got it perfectly right; the differential is used in subtraction; it'll only move if both motors are not spinning at the same rate.

Very cool solution! I haven’t seen that idea before, it’s clever ;)

[1980SomethingSpaceGuy]

11 hours ago, Paul B Technic said:

You have done an amazing job with this.

Thanks a lot, Paul!
I spent a lot of time improving on the first body design; when I had to rebuild the whole frame, I wasn't sure the second would be as good. Especially since I had to cram the steering gearbox between the tracks and the skis, which is bound to taking more space than just the servo. But I managed to use minimal additional space (only one stud for a 20t gear, the rest fitting in the length of the L motor) and arrange the gears lower than where the servo used to be. This freed some space on the top where I could fit the battery box, which in turn allowed to improve the seat. I love how issues sometimes turn into opportunities when building LEGO.

11 hours ago, MangaNOID said:

Looks very accomplished!

Nice way to get around the servo issue 

 

1 hour ago, Teo LEGO Technic said:

Very cool solution! I haven’t seen that idea before, it’s clever ;)

Thanks a lot, guys! 
Along with almost everything we sometimes think we invent when fiddling with Technic, I'm sure this has been done before. I first thought of doing this when I got 42095 in 2019 (Remote-Controlled Stunt Racer with PF) but never did, then ended getting a PF servo so I the idea was simply forgotten. When this servo died (as I mentioned, it's not my first failing the exact same way; it seems a common issue with these parts) I seized the opportunity to actually implement the concept. It works surprisingly well! Grip on a hardwood floor is bad, so the tracks tend to slide a lot. 42095 is in fact built around this; friction with the ground is dynamic all the time, allowing you to drift and powerslide all about. This very context of dynamic friction also allows to control both tracks separately just to steer the skis without too much of an impact on the actual trajectory, the latter being really dictated by the skis themselves. In opposition to how a tank would behave, moving only one track, or even both in opposite directions, will in fact barely move the model at all; they are very close to each other and the skis firmly anchor the front. So difference in motor speeds will only change the steering angle; when it's ok, use both motors together and the model will follow the direction of the skis. Of course, those cause additional friction and the model itself is considerably heavier than 42095 so it's not as nimble, but the gear ratio is basically the same, so the top speed shouldn't be too much lower. And finally, it looks like an actual snowmobile when moving, where the RC stunt racer looked more fictional.

tldr; I was quite disappointed when the servo died, but it ended allowing me to try something new (at least to me) that works well!

[Jurss]

On 6/28/2025 at 7:06 PM, 1980SomethingSpaceGuy said:

As before, face, seat, side panels, foot rests and the back platform all are easy-to-take-apart sub-assemblies.

Like these options, as also all build. 

Only thing to improve, maybe it is possible to do, that steering stays in place, when panels are removed?

[1980SomethingSpaceGuy]

15 hours ago, Jurss said:

Like these options, as also all build. 

Only thing to improve, maybe it is possible to do, that steering stays in place, when panels are removed?

Thanks a lot; these positive comments from all you Lego fans and experts mean a lot to me.

The handlebars are merely cosmetic at this point: it's not even possible to steer the skis using them; the belt drive (black rubber bands) they're attached to has less friction than the clutch between the steering rack and the differential (it was even more true with the servo). So to me, they belong to the things I want to remove as sub assemblies when working on the insides. Moreover, they are a bit too flimsy to safely hold the weight of model when flipped upside down (which is handy to do when building). Why would you want to keep them in place?

[1980SomethingSpaceGuy]

I tweaked the track suspension to soften it a bit, adjusted the tail, moved the battery box one stud to the back and a few more details not even worth mentioning. As I caught myself smoothing edges with system parts, I thought it was time to record a small video.

Close up of the steering system:

 

[NV Lego technic]

Looks decently fast for what it is, excellent work and details!

[Jundis]

This turned out to my favorite model so far in the contest, what a brilliant job!

Just to get this right: You ditched the servo and just use 2 motors (one for each track) and when one motor drives slower it engages the steering via the diff and clutch gear, right?

[howitzer]

It looks really great in every respect!

I attempted to make a snowmobile for another contest, and learned the hard way that suspension is indeed anything but simple and in the end I couldn't make it work but apparently you have, which is great! And it's a good looking model too!

Makes me wonder why TLG has never attempted to create a proper snowmobile set...

[1980SomethingSpaceGuy]

5 hours ago, NV Lego technic said:

Looks decently fast for what it is, excellent work and details!

Thanks a lot! I spent an awful lot of time on small details, sometimes wondering if it was really worth it. I'm glad some of that effort shows 

4 hours ago, Jundis said:

This turned out to my favorite model so far in the contest, what a brilliant job!

Just to get this right: You ditched the servo and just use 2 motors (one for each track) and when one motor drives slower it engages the steering via the diff and clutch gear, right?

Thank you so much; means a lot to me 

Yes exactly. I made a quick render of the steering gearbox (viewed from below):

• Red is the left motor
• Blue is the right motor
• LBG is the steering

3 hours ago, howitzer said:

It looks really great in every respect!

I attempted to make a snowmobile for another contest, and learned the hard way that suspension is indeed anything but simple and in the end I couldn't make it work but apparently you have, which is great! And it's a good looking model too!

Makes me wonder why TLG has never attempted to create a proper snowmobile set...

Thank you very much for the kind comment!

The suspension system I implemented is of course a simplified version of the actual thing. It should rely on a compact torsion spring which is unavailable to us, so instead, I'm using the back suspension spring to tension the tracks. The geometry and thus the ideal length of the tracks change with suspension action, so this back tension spring has an active part in the suspension stiffness. It wasn't easy to balance this while still looking like an actual snowmobile suspension setup but the result is fair enough for a Lego model I guess.

Yes indeed; only simple, small models of snowmobiles so far from TLG. But having built one now, I may have a few hints as to why. We mentioned the track suspension system; implementing a realistic solution most likely would require new parts. The front suspension too is hard to build the way Ski-Doo work; Technic ball joints have sensible slack; I tried to work around this by putting each pair as far as I could vertically, but those are much lower on the real thing. Also, in order to carry motors, a battery box and receiver, the model has to be quite big but with very few features; I'm not sure how they would integrate this to their lineup. Anyway, this is the model I took inspiration from:

[howitzer]

10 hours ago, 1980SomethingSpaceGuy said:

Thank you very much for the kind comment!

The suspension system I implemented is of course a simplified version of the actual thing. It should rely on a compact torsion spring which is unavailable to us, so instead, I'm using the back suspension spring to tension the tracks. The geometry and thus the ideal length of the tracks change with suspension action, so this back tension spring has an active part in the suspension stiffness. It wasn't easy to balance this while still looking like an actual snowmobile suspension setup but the result is fair enough for a Lego model I guess.

 

Yes indeed; only simple, small models of snowmobiles so far from TLG. But having built one now, I may have a few hints as to why. We mentioned the track suspension system; implementing a realistic solution most likely would require new parts. The front suspension too is hard to build the way Ski-Doo work; Technic ball joints have sensible slack; I tried to work around this by putting each pair as far as I could vertically, but those are much lower on the real thing. Also, in order to carry motors, a battery box and receiver, the model has to be quite big but with very few features; I'm not sure how they would integrate this to their lineup. Anyway, this is the model I took inspiration from:

 

Any chance you could produce a computer image of the suspension system so we could see how it works? I'd be curious to have a good look on your implementation and the compromises you made (I tried some, but they wouldn't help enough to make it viable).

I guess that's true from TLG's part, while the suspension of the real thing is quite complex, perhaps that's not enough as a selling point for a set, and beside that and steering there's not much a snowmobile does...

[1980SomethingSpaceGuy]

On 7/4/2025 at 8:45 AM, howitzer said:

Any chance you could produce a computer image of the suspension system so we could see how it works? I'd be curious to have a good look on your implementation and the compromises you made (I tried some, but they wouldn't help enough to make it viable).

I guess that's true from TLG's part, while the suspension of the real thing is quite complex, perhaps that's not enough as a selling point for a set, and beside that and steering there's not much a snowmobile does...

Here's a quick render of the geometry:

The upper (red) frame is attached to the chassis. The sled (blue) is on the ground. The tensionner (green) only supports the track.

This allows translation of the frame on the vertical axis, in which case the magenta spring barely works: red/dbg/blue/magenta form a parallelogram that squishes down. As this happens, the total perimeter of the structure gets longer, forcing the green spring down too and spreading the load with the yellow spring.

Front/back pitching happens around the pink axle (right in front of the pair of pulleys), in which case the front spring (yellow) barely works. Forward pitch (blue moving clockwise around pink) is limited by the length of the magenta spring, which is slightly compressed at rest. Backward pitch tends to shorten both the perimeter and the tensionner and both contribute to reduce track tension. This is not ideal but works for the angles allowed by the structure.

Altogether, this is far from an exact reproduction of the geometry of the actual suspension system referenced in my previous posts and does not address track tension flawlessly. But it allows the two degrees of liberty I needed (translation+pitch), work well enough for the requirement and look similar enough to the real thing.

[howitzer]

16 hours ago, 1980SomethingSpaceGuy said:

Here's a quick render of the geometry:

 

The upper (red) frame is attached to the chassis. The sled (blue) is on the ground. The tensionner (green) only supports the track.

This allows translation of the frame on the vertical axis, in which case the magenta spring barely works: red/dbg/blue/magenta form a parallelogram that squishes down. As this happens, the total perimeter of the structure gets longer, forcing the green spring down too and spreading the load with the yellow spring.

Front/back pitching happens around the pink axle (right in front of the pair of pulleys), in which case the front spring (yellow) barely works. Forward pitch (blue moving clockwise around pink) is limited by the length of the magenta spring, which is slightly compressed at rest. Backward pitch tends to shorten both the perimeter and the tensionner and both contribute to reduce track tension. This is not ideal but works for the angles allowed by the structure.

Altogether, this is far from an exact reproduction of the geometry of the actual suspension system referenced in my previous posts and does not address track tension flawlessly. But it allows the two degrees of liberty I needed (translation+pitch), work well enough for the requirement and look similar enough to the real thing.

 

For some reason your photos are not showing :( I even tried to follow the link to the original site and it's Onedrive showing the text "This item won't load right now" so maybe there's a problem with file permissions or something?

[JoKo]

47 minutes ago, howitzer said:

For some reason your photos are not showing :( I even tried to follow the link to the original site and it's Onedrive showing the text "This item won't load right now" so maybe there's a problem with file permissions or something?

Photos are showing OK for me. maybe it was a temporary issue with onedrive? That's what "won't load right now" sounds like to me

[1980SomethingSpaceGuy]

53 minutes ago, howitzer said:

For some reason your photos are not showing :( I even tried to follow the link to the original site and it's Onedrive showing the text "This item won't load right now" so maybe there's a problem with file permissions or something?

I have this issue with Onedrive sometimes where images won't show correctly. Clearing browser data fixes the problem.

[howitzer]

21 hours ago, 1980SomethingSpaceGuy said:

I have this issue with Onedrive sometimes where images won't show correctly. Clearing browser data fixes the problem.

Ok, I was able to view the photos now.

I tried to make much more faithful reproduction of the real suspension, but was unable to make it work as Lego axles are not nearly strong enough to withstand the bending pressures involved. I guess simplification like you did would've been in order, but after working on it for a good while and failing I lost motivation (and considering it was a contest there wouldn't have been enough time to finish the rest of the build anyway). Glad you were able to make a workable simpler version though!

[1980SomethingSpaceGuy]

Yep, I tried that too at first. It was bending where it shouldn't and not moving enough where I would have liked to. Moreover, I had no good solution for the torsion spring.

I picked this pragmatic solution with acceptable cinematic and external looks so that I could move on. But as we said, this is most likely one of the reasons why we haven't seen an official TLG model of snowmobile yet.

[Samolot]

Great model. Cool suspension. It's on such a scale that one of the Bionicle/Star Wars figures should fit it. I once built a similar model with such a figure.