Snowmobile (failed) project

[miguev]

Hi all,

I'm about to disappear for several months, but before I go I'd like to leave something here for your amusement... and hopefully get some advice

It all started with

, best one I've seen so far. I wanted to do something similar, preferrably with a softer rear suspension that would behave realistically on a bumpy ride (piterx setup seems stiff). Trouble was, I had no clue how these work. I had to

like a gazillion times, to finally make sense out of photos and other models. In the end, I think I got a reasonable setup, using custom shocks also inspired by piterx Ford Fiesta.

Now, for the fun part: I'm new to snow. I grew up in Tenerife, where you'd only ever see snow when it was old, unless snow caught you by surprise above 2,000 m. and then you'd be stuck there for days. No kidding, my dad used to work in the telescopes up there, when it snows there, you better not be there. And I never travelled much. So I'm utterly clueless about the different states / kinds of snow, let alone which ones are good or bad for what. I just took my protoype for a quick ride in the only moment I had a chance. The result is rather embarrasing, but I hope you find it amusing:

I guess snow was too soft.. how should it be to ride a Lego snowmobile this size? And what weight would be reasonable for the model?

Should I first build a snowgroomer and use it to prepare snow for the snowmobile?

Some improvements I've been thinking of (but not sure they're good ideas):

• Longer, wider (4L) skies, specially at the front.
  
• Longer suspension arms (6-7L), to separate skies for better sidewise stability.
  
• Move weight to the rear, for better traction on the tracks.
  
• Center weight sidewise, this prototype was always leaning towards the right.
  
• Reduce weight, this prototype was already ~700 g. without any bodywork!
  
• Use outer output from Buggy motors, which is stronger.
  

If you're curious about the targeted aesthetics, it'd be something like this:

And if anyone knows the physics behind

, I have an itching curiosity: how light should a snowmobile should be to be able to ride on water with the inner (fast) output of 2 buggy motors? (my guess is: lighter than the motors plus a PP3 9V battery)

[D3K]

Haha, love the part at 0:47!

Too bad you won't be able to finish it Hope you'll be able to finish it, it seemed to be working reasonably well in my opinion.

I made one last year using the radio control parts (with two buggy motors) that seemed to be reasonably fast, but I never got around to trying it on actual snow Hope to rebuild it later this winter, or more likely next year

Edited February 24, 2015 by D3K

[nerdsforprez]

I also think that it worked reasonably well. Just FYI, if you think to scale, the soft snow you tried your vehicle in is like trying a real snowmobile in two or three feet of soft snow, which, trust me, I know - a real snowmobile would not operate in that either. I grew up in the wasatch mountains (North America) and rode snowmobiles all my life. They are notorious for getting stuck just like your model in the deep snow. Not too far from real life

[Liege]

This may be completely irrelevant to your problem but if that was a 4wd on sand I would have said you're using too much go pedal. Maybe you could put a 2 speed gearbox with a low torque starting gear and then a cruising gear. Don't ask me I'm only just getting into custom technics and have done any gears yet.

my other suggestion would be wider rear track, increase the footprint for more traction and spread the weight around more so it floats on top of the snow.

[DrJB]

Looks like a Black Lamborghini Aventador ... the one in London, that got wrecked by a WV.

[miguev]

Thank you guys. I'm really not finishing it this winder, already took it apart, but I hope to get back to it some winter in the future. Hopefully SBrick Android app will be usable by then, I'm hoping that would help with the problem of "too much go pedal" which I agree plays a big role here.

nerdsforprez, how hard should snow be for this scale snowmobile? Or, how much soft snow can a real one handle?

[MajklSpajkl]

About wider tracks, here is my try from a couple of winters back:

It was way too chunky for two buggy motors so I switched to double XL - hence snailmobile instead snowmobile. Also the skis are quite wide, but I can't say that was good idea either. I guess trial and error approach will bring you best results ;-)

[miguev]

I started like that, with 2 tracks, to work on a bigger scale to understand the rear suspension, but once understood I scaled it down to avoid the weight problem. And I still think I have to scale it down even more in terms of weight, but I need to learn using more axles and less pins. To that end, I plan to spend the next months building from instructions and leave MOCs for now... will see if I can manage

[Kelkschiz]

Besides what is already mentioned it might also be that the applied force is simple too much for the underground, any wheel or track will do a burn-out given too much applied power. Perhaps an M-motor would do the trick...

[DrJB]

I've seen enough snow in my life to tell that some of it is suitable for sliding toys, other might not be. How well the vehicle handles/grabs the snow depends a lot on the size of snow flakes. This is especially true with the small lego liftarms. One rule that seems to work: The bigger the contact surface, the better the vehicle can 'float' on the snow. Back on topic: Very nice contraption that you have and will definitely following this thread.

[piterx]

well i wouldn't call it a total disaster :P

the main problem you have is that all the weight is before the track, when you really want it just on top of it like there's someone riding it :)

that is gonna give you a light front wich is not gonna sink

i would use the second output for the buggy motor... so it doesn't even need to be sealed :P