Thoughts on Half-Tracks?

[OrangeKNight]

Basically, I'm coming out of my dark ages and want to mess around moer and more with Technic, especially after seeing lots of Mahjqa's fantastic creations(and others as well of course) and Got me thinking, I always liek Tracked vehicles, and as a kid I always tried to incorperate tracks into my creations, but this is back when the best way to do that was with the 1 size rubber tracks as found in the Mindstorms set OR by using a lot of those really small chainlinks(which I actually did once, ran half decently xD)

But now thanks to my use of Brick link and such I'm finally able to really get back into this, and I wanted to start with something simple, so I built one of Mahjqa's simple Car Rigs and while right now I'm missing the XL motor and all the remote control stuff, I built it anyways and make do with one M motor and a Batt Box, just to see it work and all that, which it does(or half at a time at least xD) and I kinda messed around with it a bit to see if I can do a half track with it, it was somewhat sucessful, maybe it would have been more if I had found out about how you can easiy adjust the gear from Hi to Low, but I figure before I go back and try again I should ask to see if anyone has any tips regarding this kind of thing.

Basically right now I'm just using the track parts from 8263 Snow Groomer but with Bricklink now mostly figured out I can easily grab some other parts too. But if anyone has some good tips to share regarding wither half tracks specifically or even just tracks in general I'm all ears!

*Looks up*

Dammit, guess I kinda rambled on a bit didn't I....sorry about that!

Mike

[Aqualize]

I haven't built any half-track vehicle myself but I have the 8043 excavator (same type of tracks as the snow groomer). If you want your half track to be able to traverse ruff terrain I think they are not so good. Problem is that they are not made out of rubber. I write that I think it is so because the 8043 when running around indoors had problems with slopes.

Check out this video (Stilzkin Igniz offroad vehicle - Стилзкин Игниз):

It uses this part for the track links: http://www.bricklink.com/catalogItem.asp?P=45590 Problem is that it is not so common. There are only a few shops at bricklink that have big quantities of the piece, if you vacuum out all those from a few shops you will have enough.

[Tobbe Arnesson]

Welcome back into the light!

8043 Motorized Excavator is a great parts pack, especially if you're into tracked vehicles and remote control.

mahjqa's Stilzkin Igniz offroad vehicle has some very potent tracks, I've posted a few ways to gather enough of the rubber (and other) parts in the link.

[DLuders]

Be sure to check out Sariel's "Crusader" halftrack: http://sariel.pl/2009/04/crusader/ :

Egwin14 posted this short (37 seconds)

of his Lego Technic Halftrack with Power Functions:

Lego7777777 posted this

of his Halftrack that uses the small Technic Link chains:

If you don't have a lot of parts, jojoguy10's Halftrack would work:

.

[OrangeKNight]

Well as I said, Mahjqa's stuff is a big part of why I want in to all this kind of stuff, so I've seen his stuff. I'm also not worried about making stuff as effective as mahjqa's, Basically I just want to chase my cats around.

My biggest concerns with using Mahjqa's Car frame are turning, and driving the tracks, they are kinda connected problems really, I'm worried that the front wheels might have trouble turning the car with the long-ish tracks, and I'm worried that the stock design's Differential might make it less effective at actiually moving the car forwards, but also if I were to remove the Diff it would compounf the steering problem.

Mike

[mahjqa]

Hi! Thanks for your praise; it's great I've got someone interested in technic.

I hope that I can answer some of your questions.

For starters, the tracks of the snow groomer should work very well. Because it's plastic it's a bit slippery, but in this case it should work to your advantage. The reason Lego uses plastic tracks is so vehicles like bulldozers can not only move forward, but turn as well. to do that, you need a tiny bit of slipperyness.

Also, because there's a bit of slip, you can lose the differential and just use a regular gear instead.

Hope this helps a bit :D

(And because I can, I'm dropping this differential video here. If you haven't seen it yet, do so. It only takes a few minutes, but it's the best explanation I've foudn so far)

Edited January 25, 2011 by mahjqa

[OrangeKNight]

Thanks for the reply Mahjqa, it's cool to know you're willing to dip down to this mortal plane to bless us with your help! xD

But a question regarding getting power to the tracks;

Where is the best place to do that? Up at the front, in the back, in contact withe the groin or above it(for tracks with an upper and lower leveling track bogies)?

I guess it's not really a simple kind of answer, but any kind of insight would be good to know.

Mike

[vmln8r]

in contact withe the groin

Wwwha?

Anyway, I'd use as few gears as possible for reliability. Check out the instructions for 8275 which I believe uses three 16zs from each XL motor to the tracks. Build a test chassis with weights (to simulate the completed model) and experiment with the infinite power/drivetrain/chassis combinations.

[OrangeKNight]

Wwwha?

Ugh, my iPhone must have auto corrected it to groin from However I misspelt "ground" xD

Mike

[mahjqa]

Wherever the track makes a 180 degree* bend is best. At those points, a driven sprocket has most contact with the track, and is least likely to slip off when powered. So here:

 _________________
/O               O\                 
\_________________/                             

Tanks and other tracked vehicles usually drive the rear sprocket, because this gives the most direct power to the tracks in contact with the ground. Note that Lego vehicles can get away with driving either the rear or the front one, like in the Motorised bulldozer. Here, one motor drives the front sprocket, the other the back. Since you're making a halftrack, you can simply power both tracks with the same motor. Using the back sprocket is propably easiest to build.

On tanks, the sprocket driving the tracks is not in contact with the ground. This is because then it can easily stay in one place, while the lower wheels can easily be outfitted with springs to get better contact with the ground.

*or slightly less

Edited January 26, 2011 by mahjqa

[Aqualize]

Thanks for the reply Mahjqa, it's cool to know you're willing to dip down to this mortal plane to bless us with your help! xD

But a question regarding getting power to the tracks;

Where is the best place to do that? Up at the front, in the back, in contact withe the groin or above it(for tracks with an upper and lower leveling track bogies)?

I guess it's not really a simple kind of answer, but any kind of insight would be good to know.

Mike

While I haven't experimented with this my intuition is that one should drive the rear wheel inside the track. If we let the track be a little bit longer than it needs to be (it will be slack). Then if you power the rear wheel the strain will be on the links that currently is in contact with the ground. If you drive the front wheel instead it will strain the links above the the air and then those down on the ground.

If the track is without slack this reasoning perhaps is invalid or the difference is not measurable.

I don't own the 8275 (and haven't read the building instructions) so I don't know which wheels it powers. And it would be interesting to know how it is done in reality.

Edit: Hadn't seen mahjqa's response (hadn't refreshed the page) when I wrote. Seems I was on the right track (pun intended!) with my reasoning.

Edited January 26, 2011 by Aqualize

[Crtlego]

I haven't really used my tracks as much as I could have.. I used to have those two rubber tracks that came with the Mindstorms and I got a long one of the old chain tracks from a Starwars set.. but they have been pretty useless. Now that I have gotten the 8043, I have a bunch of the new tracks and I already built a really fast tank that I will probably put in a post later on..

I also tried building a small half-track, before I built the fast tank, with the two wheels from the telehander.. But I never finished it.. It went pretty fast but I think my problem was that it was working on the wrong scale.. But I drove it using the front wheels of the tracks.. not the back ones.. Too bad I didn't take any pictures..

About a week ago.. I built a really awesome rally car. The idea was that I woke up one day that I was supposed to go to school but it was canceled due to snow and ice.. So I decided to play with LEGOS!!! What I had in mind was something that was small, had all wheel drive and some sort of suspension, but would drift.. I ended up using the two drift wheels I bought off ebay from the supersonic RC set... And not only did it drift outside but it also drifted inside as well.. I'll eventually post some pictures and a video or two since today was canceled as well!

Now that I read this about building a half-track.. I'm thinking I could remove the two rear wheels and put on some tracks... But it is four wheel drive.. with differentials in the front where the steering is.. Do you think that would work? I'm going to try building it anyways and I'll post back when I'm done..

Seems I was on the right track (pun intended!) with my reasoning.

Hahaha!! That's actually pretty funny!

[DLuders]

Here's a nice Lego Technic Halftrack by marthart. He posted 15 pictures on his Brickshelf gallery, and wrote that the "Tracks driven by XL-motor and differential, front wheels steering with linear actuator and with suspension. Opening doors and hood, working headlights and winch in the front bumper". Here it is without its body:

Edited January 30, 2011 by DLuders