[MOC] Lego Technic A34 Comet Cruiser Tank

[Tarix819]

If some of the images aren't showing up, here they are linked on Imgur:

https://imgur.com/gallery/lLRkXIL

 

Greetings all!

Here is the post on my new Lego Technic model, which is of the British Second World War Cruiser Tank, A34 Comet:

 

 It entered production in late 1944 but didn't see proper service until early 1945. By Second World War standards it was an excellent vehicle, being fast, well armoured and equipped with a powerful QF 77mm HV gun capable of dealing with almost any enemy tank. It also saw action during the Korean War, however was shortly after superseded by the Centurion Main Battle Tank.

The Korean war saw the introduction of the Comet Model B, with the large engine vents sticking out like a spoiler, as shown in the image below. My vehicle is of the Model A which was used during the Second World War, which is noticeably different as it lacks this 'spoiler'.

Some information:

 

Weight: 5.9kg (Making it possibly one of the heaviest Lego RC tanks on YouTube).

Dimensions (mm): 290 width x 680 length (830 including the length of the main gun) x 300 height.

Motors: Nine Power Functions Motors in total (2 XL, 2 L and 5 M) Driving is done by the two XL Motors alone.

Fully functioning headlights and turret lamp.

Traversing bow machine gun.

360-degree traversing turret.

Elevating and depressing main gun.

Shooting mechanism which fires projectiles through the barrel.

Recoil mechanism for the main gun.

Spent shell casing ejection system - dispenses through the floor at the rear of the turret for collection (Not enough room for a proper collecting tray).

Powered by one PF 7.4v Li-Po Battery Pack in the turret, and one AAA Battery Box in the hull. The AAA Battery Box is equipped with three 3.7v 10440 Li-Ion Batteries and three AAA dummy batteries which when fully charged give the vehicle 11.1v of power, though they need to be recharged somewhat more often than a usual 6x 1.2/1.5v Battery Box would. This is how such a heavy vehicle can drive so quickly. 

Another benefit of this power set up is I could take the advantages of programming in the SBrick (Which is how the firing mechanism works), whilst achieving almost the same voltage as the BuWizz, without spending so much money.

The firing mechanism is quite powerful, and the footage doesn't really do it justice (probably in part due to the quiet sound), though its power is somewhat reduced by the length of the barrel and the small space inside the turret, still it is a good deal more powerful than most Lego Tank firing mechanisms on YouTube. It alone is controlled by three M motors. 

Speaking of the firing mechanism, this is the sole reason the model is so big. My firing mechanism as you have read is very functional, however it is also quite large and I needed more space inside the turret for it, as well as the Li-Po, SBrick and Elevation/Depression mechanism, and on top of that, room for it to recoil. The Comet already has quite a large turret in comparison to its hull, if I decide to build tanks with smaller turrets, they would be to an even larger scale.

The tank can only turn reliably on smooth surfaces due to its immense weight, however it is at least able to.

Powered by two SBricks, one for the turret and one for the hull.

 

A few last images: 

First photo of the in-development hull, I started work in early December 2019.

Photo of the in-development turret, showing the mechanism and SBrick.

Early photo of the turret married to the hull. Taken some time over Christmas.

The placeholder three-cylinder tractor engine I had in the tank before I built one which looked more like the Rolls-Royce Meteor. I like my 'Expert Builder 1977-1980' style of Technic engines.The SBrick and Li-Po (Which was originally in the hull) can be clearly seen.

Photo of myself next to the mid-development vehicle. The thing is huge and a pain to carry around.

The vehicle at about 90% completion.

The vehicle compared to the 8865 Test Car, showing the huge scale of the model.

The almost completed vehicle compared to the size of a mug. Prior to some last suspension changes, though the front fenders have been improved.

 

Thanks for reading.

 

 

Edited April 9, 2020 by Tarix819

[TimberBrick]

Very impressive.  I've often thought about how to make a track with the strength to support a heavy model.  Could you share how you did it?

Thinking about your Lion batteries, we build power hungry battle bots that we power with AA packs that have 5 Nimh and one LION.  We upgrade the bournes resettable fuse to 2.5 amps.  Recently we have gone to RC car 9.9v LiFe packs which is a revolution in power.

[MajklSpajkl]

That's a huuuuugeeeeee tank!!! :-)

Looks really good in dark tan. I love the recoil effect.

Unfortunately I can't see the photos. From what I can see from the video - I don't like an L motor protruding from the bottom of the hull, given the size, I would think there is enough room to keep it inside.

Why did you only connect the tread links in one line of liftarms? There is enough room to interconnect them at least twice, the tread would be stronger that way.

In any case, congratulations are in irder - making such a big scale model move so smoothly is a great achievement.

Best regards,

Miha

 

 

[Tarix819]

4 hours ago, TimberBrick said:

Very impressive.  I've often thought about how to make a track with the strength to support a heavy model.  Could you share how you did it?

Thinking about your Lion batteries, we build power hungry battle bots that we power with AA packs that have 5 Nimh and one LION.  We upgrade the bournes resettable fuse to 2.5 amps.  Recently we have gone to RC car 9.9v LiFe packs which is a revolution in power.

The tracks are made using individual Technic track links - in total seven pieces each.

These tracks are a huge benefit to Tank-building as I can increase or decrease the width of the tracks from 3 to 12 studs as I please intead of being limited to the 4.5 stud width official Lego Technic Tracks. Another benefit they offer is that I have more choice in the size of sprocket wheel I use. Regular technic tracks are limited to size 3, 5 and 7 technic sprockets, however since these tracks use friction from Lego rubber tyres, my sprocket size is limited only by the sizes of Lego rubber tyres.

That said, the tracks are very time-consuming to build and are quite heavy, boosting the overall weight of the vehicle even more.

I did think about using an RC Battery pack, however I decided to be more 'purist' (Although i'm still using SBrick with this) and go for an unmodified Lego Battery Box. The only reason the vehicle has so much power is the type of Batteries used in the Battery Box.

Edited April 9, 2020 by Tarix819

[Tarix819]

53 minutes ago, MajklSpajkl said:

Unfortunately I can't see the photos. From what I can see from the video - I don't like an L motor protruding from the bottom of the hull, given the size, I would think there is enough room to keep it inside.

Why did you only connect the tread links in one line of liftarms? There is enough room to interconnect them at least twice, the tread would be stronger that way.

In any case, congratulations are in irder - making such a big scale model move so smoothly is a great achievement.

I hopefully fixed the photos issue, i've linked an Imgur gallery for those who can't see them.

Yeah unfortunately the way the turret ring is arranged meant an L-Motor sticks out a bit underneath, reducing ground clearance significantly. With a bit of intuition this could be fixed but I was rather lazy here admittedly, I never went back to fix it. Ground clearance is something I will take into account more so next time.

I don't think it makes much difference honestly, as they are the tracks are extremely sturdy, on previous vehicles I did interleave them, and for this one I was only testing having one link to connect them, though in future I will probably interleave them again as it gives a more tank-track-like effect.

Thanks very much!  :)

Edited April 9, 2020 by Tarix819

[Sariel]

Not a single photo is showing up, are you sure your photo album is public? The model is indeed impressive thanks to the size, the rare color and smooth ride. What struck me as a bit odd is that the model moves almost exclusively in straight lines in the video - is there a problem with turning?

Edited April 9, 2020 by Sariel

[Tarix819]

Just now, Sariel said:

Not a single photo is showing up, are you sure your photo album is public? The model is indeed impressive thanks to the size, the rare color and smooth ride. What struck me as a bit odd is that the model moves almost exclusively in straight lines in the video - is there a problem with turning?

I added the link to the Imgur album, so hopefully that's public?

Unfortunately the heavy weight of the vehicle means it only turns on smooth surfaces, which is why in the video I only demonstrate turning on smooth ground. If I try to turn the vehicle at any significant degree on rough ground the rear drive wheels lose grip. It's an issue I haven't solved yet, but hopefully will in future models.

[Sariel]

1 minute ago, Tarix819 said:

If I try to turn the vehicle at any significant degree on rough ground the rear drive wheels lose grip. It's an issue I haven't solved yet, but hopefully will in future models.

I've had this issue and solved it by driving both rear and front sprockets. But I guess in your model's case this would ruin the front sprocket's look.

[Tarix819]

Just now, Sariel said:

I've had this issue and solved it by driving both rear and front sprockets. But I guess in your model's case this would ruin the front sprocket's look.

Yes this is the problem I ran into. The front sprockets give off a very authentic look which I don't really want to sacrifice. In the case of your Lego Maus Tank the front sprockets are hidden so it works better. I'm sure i'll eventually find a way around it.