[MOC]/[POC] RC Snowmobile

[2GodBDGlory]

So, this model was thrown together in about two days after inspiration struck! I had been driving my non-Lego RC excavator (A ~$100 USD Top Race one I snagged at a thrift store for $7! All I had to do was throw in my old lithium camera battery to replace the old Ni-Cd one.) out in the snow, and having an awful lot of fun. Anyways, its having tracks and being fun in the snow inspired me to try to build something out of Lego that would be just as fun, and I set on a snowmobile. I don't think these are particularly common to build with Technic, and they're even less common to make RC. I made one a few years back, but it was rather small and weak, and thus no good in the snow. Anyways, I decided to go big and powerful for this one, and am quite pleased with the result!

Now, it is a rather quick, crude mock-up, which is why I have the Proof-Of-Concept tag in the title. I really only wanted to build something for fun, which precluded building a body, so normally I wouldn't be posting this, except that it seems to be a rather unique concept. To make it large, I doubled up large tracks and added 9L beams onto them for traction, setting the scale more or less.

I drove it using two Buggy motors, directly driving planetary hubs using old female CV joints, which directly drove large sprockets. I originally used medium sprockets, but the large ones got me better speed, as well as more contact with the track.

Steering was done with two hard-coupled PF servo motors, since I expected to need a fair bit of torque to steer the skis.

The front suspension was a simple double-wishbone setup using two 9.5L hard shocks, but the rear was more complicated, and I had to do some research on the real systems to figure out how it works. Basically, the track support is only attached to the frame by two longitudinal links (11L DBG beams here), a shock absorber, and the track itself. There is a second beam connected to this support, which uses three long shock absorbers to tension the track. It's kind of hard to describe the system, but it basically has normal up/down suspension, plus allows for tilting of the track forwards and backwards as it travels over obstacles. My system could probably have used some work, because the track would often skip over the drive sprockets when the going got tough, but overall it didn't perform too badly!

All the electronics were controlled by my new custom 3D-printed 3S lithium battery box. It uses three 18650 lithium cells wired in series and charged while outside of the battery box, to deliver the same theoretical voltage as a Buwizz 3.0, but for way, way, less money. Because of this, I have jokingly inscribed it with the letters PMBW, for Poor Man's BuWizz. Of course, the poor often need to make sacrifices, and in this situation, that mostly means that I have to use external receivers without proportional control. I used two 2.4 GHz Chinese receivers, which ensured a good connection and plenty of current for each buggy motor.

Overall, I really enjoyed the project! It was fast and interesting to drive, and also quite interesting to engineer. I'd love to see some other folks take this basic idea further, with higher power, perhaps, a bodywork, and a better tuned suspension! Maybe this is something the Buwizz team would be interested in trying?

More images at: https://bricksafe.com/pages/2GodBDGlory/big-snowmobile

[Jurss]

Good concept.

It seems, that You need to improve somehow steering stiffnes, as each ski goes its way. Yea, I know, it is mainly lego parts defined issue. But maybe somehow those ball connections are possible to replace with more pin based linkage.

Also, for better steering, maybe some ridge/groove can be made on skis, so that it steers better on snow.

And some weels inside, to steer on asphalt :)

[Jundis]

Love the idea! :-)

I think the front is a little bit too heavy because of the servos. How much weights you custom battery box and the whole vehicle?

[gyenesvi]

Nice one, I have actually been thinking of the same idea (just came back from skiing holiday, and saw a couple of them and got inspired). Just like you, I thought of doubling the tracks, and you driving them with buggy motors is a really good one, the shape of those motors seems like a nice fit for this, and I also like the use of the planetary hubs.

I was wondering if it needs more wight on the back so that the tracks get more traction maybe? And also something is weird with the steering, because the play seems more than lego parts would allow for in a typical setup. Maybe too much play in the way the servos are coupled?

[2GodBDGlory]

7 hours ago, Jurss said:

Good concept.

It seems, that You need to improve somehow steering stiffnes, as each ski goes its way. Yea, I know, it is mainly lego parts defined issue. But maybe somehow those ball connections are possible to replace with more pin based linkage.

Also, for better steering, maybe some ridge/groove can be made on skis, so that it steers better on snow.

And some weels inside, to steer on asphalt :)

Yeah, the steering was definitely flawed. Because of the way the motors were attached, I ended up going with a suboptimal attachment of the steering links, allowing for major bump steer. The way the suspension worked in practice, this resulted in some pretty major toe in. It shouldn't be too hard to come up with a better design, though.

The ridge could be an interesting idea, and I actually did have a wheel in each ski; I just didn't mention it in the post!

3 hours ago, Jundis said:

Love the idea! :-)

I think the front is a little bit too heavy because of the servos. How much weights you custom battery box and the whole vehicle?

Yeah, it probably was front-heavy. It seems like the way the weight is distributed is important for tuning the way the front and rear suspension, and because I didn't build a seat over the rear track, it did end up being heavier up there. I think my custom battery is likely a similar weight to an AA battery box, but I've already taken apart the model, so I can't get you a weight for it.

1 hour ago, gyenesvi said:

Nice one, I have actually been thinking of the same idea (just came back from skiing holiday, and saw a couple of them and got inspired). Just like you, I thought of doubling the tracks, and you driving them with buggy motors is a really good one, the shape of those motors seems like a nice fit for this, and I also like the use of the planetary hubs.

I was wondering if it needs more wight on the back so that the tracks get more traction maybe? And also something is weird with the steering, because the play seems more than lego parts would allow for in a typical setup. Maybe too much play in the way the servos are coupled?

Thanks, I'll look forward to seeing what you come up with! Both of those ideas would be a good thing to try to change to improve performance, as pointed out above.

[FriedlS]

Very cool! What is the weight of this vehicle?

[2GodBDGlory]

33 minutes ago, FriedlS said:

Very cool! What is the weight of this vehicle?

Thanks!

I'm not sure what the weight is, though, and I already took it apart, so I can't measure.

[Samolot]

Nice try. I used to build something similar. Maybe it will be helpful.

[MOC] Desert Skidoo - LEGO Technic, Model Team and Scale Modeling - Eurobricks Forums

 

[2GodBDGlory]

2 minutes ago, Samolot said:

Nice try. I used to build something similar. Maybe it will be helpful.

[MOC] Desert Skidoo - LEGO Technic, Model Team and Scale Modeling - Eurobricks Forums

 

That is cool! It's got quite a similar track/drivetrain design, but is much more polished overall.

[ninoguba]

On 2/10/2022 at 4:16 AM, gyenesvi said:

I thought of doubling the tracks, and you driving them with buggy motors is a really good one […]

I was wondering if it needs more wight on the back so that the tracks get more traction maybe? 

Like this? 😉

 

[2GodBDGlory]

That looks like fun! Will you be testing it in snow soon?

[ninoguba]

50 minutes ago, 2GodBDGlory said:

That looks like fun! Will you be testing it in snow soon?

Yes, someone’s gonna test it for me. 😁 Right now where I am its a heat wave so snow no go.

I have another video on my channel where I tested the “slower” version of my snow buggy on real snow. You can check that out for the meantime.

[2GodBDGlory]

1 hour ago, ninoguba said:

Yes, someone’s gonna test it for me. 😁 Right now where I am its a heat wave so snow no go.

I have another video on my channel where I tested the “slower” version of my snow buggy on real snow. You can check that out for the meantime.

Ok, sounds good!