[WIP] Sherman M4A1 Tank (started from various tank steering prototypes)

[SaperPL]

This is something I've built today after realising this could be used in a half-track:

The braked differential steering is a steering system that was widely used in tanks. The idea is that we lock one output drive from differential and thus all power goes to the other side. 

In theory it is simple, but with no dedicated brakes in Lego Technic it gets complicated. It was often used with differential lock for driving straight though, which complicates such mechanism even more in Technic model.

The drive input is in a poor position for the tank - I'll probably have to figure out how to connect the drive from the other side if I want to use it in a tank build, but it's not an easy task. It might be just in the right spot for the halftrack model though.

Edited March 19 by SaperPL

[2GodBDGlory]

Nice! That seems like a much more interesting way of steering a tracked vehicle than the standard two-motor setup, though it may lack something in performance.

[SaperPL]

9 minutes ago, 2GodBDGlory said:

Nice! That seems like a much more interesting way of steering a tracked vehicle than the standard two-motor setup, though it may lack something in performance.

Actually the two motors directly connected to track have issues on going straight line for heavier builds and at lower than max speed. Two motors don't have identical characteristic across whole output range.

[2GodBDGlory]

7 minutes ago, SaperPL said:

Actually the two motors directly connected to track have issues on going straight line for heavier builds and at lower than max speed. Two motors don't have identical characteristic across whole output range.

Well, I guess it could be summarized this way:

Advantages of two-motor setup:

1. High efficiency

2. No need for an extra motor for steering, allowing more motors (potentially) to be thrown at drive

3. Possibility of reversing one side to turn on the spot

Advantages of differential-brake setup

1. Better straight-line steering performance, since both tracks are locked at the same speed.

2. Better straight-line off-road performance, because even if only one track has traction, it still has 100% of the available power

3. Cooler

 

So there would be performance advantages to both systems, just different ones.

[SaperPL]

11 hours ago, 2GodBDGlory said:

Advantages of differential-brake setup

1. Better straight-line steering performance, since both tracks are locked at the same speed.

2. Better straight-line off-road performance, because even if only one track has traction, it still has 100% of the available power

3. Cooler

Well, as a point #3, I'd say it's a more realistic representation of how this worked in real life vehicles.

Also there's another type of differential steering, the double differential steering or subtractor steering that I've had video on previously, which is theoretically the best solution out of all three.

[SaperPL]

An update for this mechanism - built a halftrack chassis with it:

 

[SaperPL]

Under one of my previous videos about braked differential steering, someone noted that I have oversimplified the mechanism, and that it wasn't how it worked in WWII tanks. Actually he was right as I misinterpreted the attachment point of brakes in Sherman Tank differential documentation. So I did a thing to show how a correct realistic WWII braked-differential steering would look with Lego Technic:

Sherman Tank differential documentation: http://www.theshermantank.com/about/the-sherman-tank-powertrain-page/the-sherman-differential-normally-just-lumped-in-with-the-final-drives-but-not-here/

Edited November 27, 2021 by SaperPL

[gyenesvi]

Wow, that's a pretty interesting mechanism! I think compared to its complexity, the build is actually quite compact (it's pretty dense). It could fit inside a big yellow bulldozer :)

What's the problem with the braking system? Is it not possible to control it gradually enough? 

[SaperPL]

3 minutes ago, gyenesvi said:

 What's the problem with the braking system? Is it not possible to control it gradually enough? 

The issue is  that I expected it to work in a way that if you just touch the teeth, it'll slow down the rotation a bit and if you clench it/sqeeze it, you'll stop, but I guess without a big chunk of load, the red gears on friction pins won't turn. To have something that'll slow or stop it, I'd probably have to actually build an rc model that would need to pull itself, but it's pretty hard to showcase this as good as in place.

[SaperPL]

I managed to make a compact version of this kind of steering that does not completely break one side of the track but sets a fixed ratio between the two tracks:

Here's a video that shows a bit how it drives, but I'll make a full showcase once I complete the model:

 

[vascolp]

I have seen all your videos carefully and I have learned a lot!

Very nice work!

[Fluwoeb]

@SaperPL, I watched all of your videos. You did a great job constructing that design and simulating the original drivetrain system. I panicked watching the first video at 3:47 when you put that 3L axle with stop into the O-frame. Lol. I have had situations like that where I got the axles with stops stuck in an O-frame or something only I would have put a bushing on the 3L axle. Anyways, I really enjoyed this topic because I am interested in Sherman tanks as well.

Evan

[SaperPL]

I changed my approach to this steering to reduce the footprint of it. Steering with one side being slower can be achieved without clutch/gearbox switching:

 

[Jundis]

This is waaaay better than the typical 1 drive / 1 steering motor approach!

Great way to use the 2 motors power at the same time for propulsion.

[SaperPL]

I'm close to finishing the design for this tank chassis. I managed to squeeze in the mechanization for turret rotation and gun elevation:

The tricky part that is left is how to connect the fake piston engine to the drive shafts while keeping it shifted up so the frame can be closed/ribbed at the back.

Edited January 28 by SaperPL

[SaperPL]

Another update:

 

[2GodBDGlory]

Nice job!
Seeing those upside-down engine blocks has me intrigued with where else that could be useful! I've tried making some W-16 and VR6 engines in the past, and that could be a useful technique for that!

[SaperPL]

20 minutes ago, 2GodBDGlory said:

Nice job!

Thanks, I'll have another video coming with the build of the engine tomorrow, so stay tuned.

21 minutes ago, 2GodBDGlory said:

 Seeing those upside-down engine blocks has me intrigued with where else that could be useful! I've tried making some W-16 and VR6 engines in the past, and that could be a useful technique for that!

I'm kind of wondering why is Lego still using the same old engine block design for Technic after shifting to liftarms instead of studded beams. At some point when I was thinking about this radial engine and trying to figure out how would this be possible to assemble, I was thinking about 3d printing custom engine blocks like this:

  

Or even cutting off that bottom portion of the sides completely. 

[Lego Tom]

Amazing build! Would it be better the make the frame a bit wider so the engine will sit down in between the rails rather than at an angle? That could help your turret problem as well.

[SaperPL]

3 minutes ago, Lego Tom said:

Amazing build! Would it be better the make the frame a bit wider so the engine will sit down in between the rails rather than at an angle? That could help your turret problem as well.

The thing about the Sherman with radial R-975 is that this engine was at an angle:

I ended up with a bit steeper angle, but I'll tweak that and maybe I'll shave off some space there. The problem is that I want the engine to be roughly in the correct place as historically and there simply is not enough space in front of it for the motors and the gun elevation mechanism.

At the same time, I feel like using micro motors may not be optimal if I'm going to move them away, and still I have to figure out what to do with the cables.

The biggest disappointment for me so far is that I couldn't figure out a way to have small enough double two-way-to-one-way rotation mechanism that would connect the engine to the drives - this way the engine would rotate even with neutral drives and also there would be same rotation speed in all scenarios. I had an idea to do it with four T8 gears swinging on a 3L liftarm and switching onto two T20 gears, but it was a bit too big and had really low RPMs anyway.

Also the problem with fitting this radial engine inside the frame is that while the engine's frame is 8 stud wide, the pistons are sticking out for slightly more than half stud so it won't fit within 9 studs of space within the frame.

[SaperPL]

 

[Lego Tom]

On 2/5/2023 at 4:17 PM, SaperPL said:

The thing about the Sherman with radial R-975 is that this engine was at an angle:

I ended up with a bit steeper angle, but I'll tweak that and maybe I'll shave off some space there. The problem is that I want the engine to be roughly in the correct place as historically and there simply is not enough space in front of it for the motors and the gun elevation mechanism.

At the same time, I feel like using micro motors may not be optimal if I'm going to move them away, and still I have to figure out what to do with the cables.

The biggest disappointment for me so far is that I couldn't figure out a way to have small enough double two-way-to-one-way rotation mechanism that would connect the engine to the drives - this way the engine would rotate even with neutral drives and also there would be same rotation speed in all scenarios. I had an idea to do it with four T8 gears swinging on a 3L liftarm and switching onto two T20 gears, but it was a bit too big and had really low RPMs anyway.

Also the problem with fitting this radial engine inside the frame is that while the engine's frame is 8 stud wide, the pistons are sticking out for slightly more than half stud so it won't fit within 9 studs of space within the frame.

The early M4A1 did have a steep angle, but the radial engine - as your cutaway picture shows - was much smaller in proportion to the rest of the tank. Later versions, including the picture below of an M4A4 straightened out the drive line and mounted engines (there were many different engines used in the Sherman) much straighter. Using your slightly out of scale radial to represent an earlier build with the angled engine/drivetrain will as you stated, require raining the deck height, which will also effect the overall accuracy to scale of the model.

A cutaway of a M4A4 with the multibank Chrysler engine for comparison:

EDIT: The severe limitation on picture size here forces me to use a link instead of posting the picture directly - sorry!

Sherman M4A4

[SaperPL]

4 minutes ago, Lego Tom said:

The early M4A1 did have a steep angle, but the radial engine - as your cutaway picture shows - was much smaller in proportion to the rest of the tank. Later versions, including the picture below of an M4A4 straightened out the drive line and mounted engines (there were many different engines used in the Sherman) much straighter. Using your slightly out of scale radial to represent an earlier build with the angled engine/drivetrain will as you stated, require raining the deck height, which will also effect the overall accuracy to scale of the model.

 A cutaway of a M4A4 with the multibank Chrysler engine for comparison:

EDIT: The severe limitation on picture size here forces me to use a link instead of posting the picture directly - sorry!

Sherman M4A4

I already know that there were multiple engines for Shermans and also Lee's & Grants and Rams. The thing is the radial engine was used by both types of the hull, while the cast rounded hull variant, which I expect to be actually easier to be done thanks to the curved panels that Technic has, was only with the radial engines.

I know about the Chrysler A57 and while I'd love to make one, it doesn't make sense in this scale - I won't have a way for return of the pistons if I make them small with pins or axles - I would need to use rubber bands which would quickly get janky and add resistance to the engine, while building it with full size pistons would make this huge.

As for the radial six I'm fitting in my build - it's not really a problem as it's barely sticking above the line of side skirts:

I think I will have the proportions slightly distorted because of how tall the bogies are and I would have to stretch the whole thing by four or six studs, but then the bogies would look weird and I'd have to scale them up somehow horizontally. So the whole thing might end up slightly stretched vertically in comparison to real thing.

The engine itself is not that much oversized in comparison to the real thing, but the angled mount is taking sone space. But note that the placement is as correct as I could make it - the piston line pivot is over the rearmost drive wheel and the pivot of the frame of the engine, which kind of represents visually the big fan that this radial had in front of it, is over the centre of the bogie. In this context I feel like I should be okay with it.

[SaperPL]

Another update on the chassis:

After some designs in studio I had to increase the size of the whole thing because otherwise I wouldn't match the size of the bogies with the size of the hull and turret, so here we are - me, making usually small things now building this behemoth...

[Lego Tom]

48 minutes ago, SaperPL said:

Another update on the chassis:

After some designs in studio I had to increase the size of the whole thing because otherwise I wouldn't match the size of the bogies with the size of the hull and turret, so here we are - me, making usually small things now building this behemoth...

Yeah, that looks much better!  Great job! The Sherman isn't an easy object to duplicate however they made so many versions. including those the Israelis used well into the 70's that you have more than just one 'acceptable' version to go after. Please keep posting!