SaperPL

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

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Functions look superb!

13 hours ago, SaperPL said:

 I had to increase the size of the whole thing

Looking at the real model, I'd suggest to use the bigger sprockets front and rear, but this would mean a new design for the idler tension mechanism...?

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Just now, Jundis said:

Looking at the real model, I'd suggest to use the bigger sprockets front and rear, but this would mean a new design for the idler tension mechanism...?

Sprockets at the front are the correct size, but there needs to be an additional sprocket on the side of the one that is actually holding the track for it to look like in the Sherman.

The idler wheel at the back is the problem because it's slightly smaller in the original than the front one, but not as small as the small sprocket is in comparison to this medium sized sprocket that I use at the front. And like you said, the problem is that if I were to make the idle wheel with some wheels on the sides of the tracks and not sprockets, then I would have to change the tension mechanism and it would get ugly.

I suppose I'll either use this small sprocket for the sake of it being built with original pieces or I'll try to design and print a sprocket sized that is in between these two, but it's not optimal. I'm not sure if the size of the idler is that critical though, but I know that this small size difference of it makes that sloped track at the back detail in the looks of the original.

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Holy wow. The recoil really makes for a special touch, I don't believe I have seen any others with that built in. 

Will be very interesting to see what new building techniques you come up with for the shell. 

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5 minutes ago, 2ndgen said:

Holy wow. The recoil really makes for a special touch, I don't believe I have seen any others with that built in. 

Will be very interesting to see what new building techniques you come up with for the shell. 

Thanks! I actually want it to be made in supercar model approach where the interior is fully furnished with details and mechanics are somewhat representative of the actual historical tank, but there's some limitation coming from the fact that the hull will have double floor fitting mechanisation, so it's going to be vertically inaccurate in the driver and hull gunner compartment most likely.

I don't think that there's going to be a lot of unique building techniques, maybe apart from how the rear is slanted as there's a lot of complex things going on there both in terms of fitting the RC hub/battery and making the engine compartment historically accurate.

I'm strongly considering making some custom parts though as there is a list of details that are making it hard for the looks. Starting with the hull gun ball mount as the only thing that would be functional will look like this:

n4oNVb4.png

I'll probably prototype pieces for this based on the big ball mounts (the ones used in suspension pieces that fit universal joint inside and/or the ones in helicopter swash plate).

Apart from that I'll definitely use a custom sized 8T sprocket:

Qtk2yq1.png

as the idler wheel at the back. Already have it printed, I'm just short on the track links and not yet 100% ready to pull the trigger on pick a brick order for this project.

Apart from this there's:

  • a commander's cupola which I think is impossible to do with what we have in Lego, at this scale,
  • gun mantlet cover in the front which is a specifically shaped piece that would be hard to make and attach,
  • again at this scale, sprocket/idler fronts matching the looks of the original (but that's just finishing detail to be honest)
  • 4L liftarm thick with all pin holes as suspension arm
  • Browning .30 cal box/internal part for coaxial and hull gunner

But I'm not really sure if I should go with customising it this much with custom printed parts.

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Quite cool! I like that supercar-esque approach, and the functionality looks pretty unique!
Are those black wheel arch pieces 3D-printed?

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4 minutes ago, 2GodBDGlory said:

Are those black wheel arch pieces 3D-printed?

Yes they are - those are actually ripped from studio, but I have a better model since then, but just didn't have enough time to print it. The reason is that the arch is not available in DBG.

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2 hours ago, SaperPL said:

Yes they are - those are actually ripped from studio, but I have a better model since then, but just didn't have enough time to print it. The reason is that the arch is not available in DBG.

Yeah, I ripped Sian wheel arches from Studio too for 3D printing, back when I was trying to piece together a multicolored Sian from my collection!

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6 minutes ago, 2GodBDGlory said:

Yeah, I ripped Sian wheel arches from Studio too for 3D printing, back when I was trying to piece together a multicolored Sian from my collection!

There's this guy on the grabcad which has good quality parts made in solids so you can also edit them in CAD: https://grabcad.com/dk 

For most of the parts I can manage myself, but the panels have complex curves and I just gave up. I would probably have already printed those versions if not of the another part request from eric trax which occupied my printer for some time :P

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54 minutes ago, SaperPL said:

There's this guy on the grabcad which has good quality parts made in solids so you can also edit them in CAD: https://grabcad.com/dk 

For most of the parts I can manage myself, but the panels have complex curves and I just gave up. I would probably have already printed those versions if not of the another part request from eric trax which occupied my printer for some time :P

Wow, that's really impressive stuff!
Thanks for the link!

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9 hours ago, SaperPL said:

Thanks! I actually want it to be made in supercar model approach where the interior is fully furnished with details and mechanics are somewhat representative of the actual historical tan

But I'm not really sure if I should go with customising it this much with custom printed parts.

Ya that's a call only you can make.

However it is Lego, nothing is going to be perfectly accurate, but that's sort of the point of it, get as close as you can using creative piece placement, I always find it amazing when something is close that was just not expected to be done with with the parts there are to work with. 

 

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I know you already built the whole mechanical system and everything, but have you thought about a functional cannon?

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11 minutes ago, Sentinel said:

I know you already built the whole mechanical system and everything, but have you thought about a functional cannon?

Doesn't make sense to do this at this scale with what I want to make. I want to have the interiors like the supercar models have and there wouldn't be any space inside turret if I had to make a mechanism that shoots some axles or pins. Also the barrel would need to be large diameter or I would have to shoot beside it and still it wouldn't be a strong shooting mechanism at this scale, so that doesn't make sense to me.

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Non video update - not that much of new things to show yet. Also not that April Fools thing obviously. 
I've tested the round turret sides structure and it works perfectly:

lzV0aYVl.jpg WHoTj4Cl.jpg

And since this is taking shape, I can show off what's the actual plan here:

xGVQz1eh.png

I based the shape off the welded Sherman model that I could grab from the web, but I've adjusted proportions to match what I had, so it's still slightly stretched vertically.

lcBuI7Dh.png

Anyway compared to the IRL M4A1 it looks fairly OK:

3rXKh0Jh.png

kWbFOHnh.jpg

I've placed few orders for DBG coloured parts, but for those that don't exist in Lego colouring I may need to paint them as FDM 3d prints are not as rigid and don't looks so smooth as the original parts. Still a lot of things to figure out.

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Another update - got some more parts, the suspension is fully on the springs from yellow shock absorbers now. Body is more complete now, but still need to source DBG parts from 3rd party...

 

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DBG parts are slowly getting here. I sourced some 3rd party panels in DBG for now that these are not available from Lego in DBG at this point:

61msigKh.jpg

ywaOHuth.jpg

r6NwjQIh.jpg

Not really a fan of how those short curved panels are moulded differently, but I understand that is because of original shape being owned by Lego. Will have to wait and hope till there's a set with those in DBG.

I'm trying to figure out what to do with that angle at the back. I designed my own variant of angled panel and I'm trying to print it with resin printer, but I'd rather figure out how to make it with something available from Lego:

BG1mxHSh.png

Also I need to figure out what to do with this rear corner of the cast hull here:

gVv1dcAh.png

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Finally had time to assemble the parts that came to me from various sources. Not everything is original Lego, this model will probably need to wait with instructions till more parts are available in DBG...

 

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I got stuck on this for a bit longer than expected and I'm not sure which way to go with the steering mechanism.

The problem is, that the last iteration of the mechanism works great until I put a lot of weight on it, at which point the path of least resistant when trying to steer is to spin the motor that is not driven at the time instead of it working as a break and thus one side being slower.

There's various things I'd like to achieve here, but at this scale I can't achieve all of them:

  • make the steering with two sticks and not one stick is gas and one is servo
  • make the steering work on the same principle as the actual Sherman steering
  • make the steering behave similarly to actual Sherman steering

The potential solutions and their drawbacks:

  • single servo differential steering through connection at specified ratio outside of the differential - one stick for steering, not gradual steering angle, configuration is kind of weird when it comes to passing the drive input to the fake engine at the back.
  • dual servo with two gearboxes for steering of each side - should behave like its supposed to, but it's not a differential steering anymore, it's tricky to reinforce and is pretty long because of two servos placement.
  • the actual Sherman-like differential steering that had it's own separate video, but is really huge and it would mean either making the whole model bigger which I don't want to do, or designing quite a few 3d printed elements to shrink differential.

The twin gearbox approach would work really well with gradual steering on each stick, but it also means that drive motor(s) need to go somewhere and they would take input from the feature for turret, so I wouldn't have gun elevation anymore. Ideally I would have the motors driven off a battery box, but for that, I'd have to have gearbox disconnect drive output from the drive motors, and then it'd be weird that neutral is in the middle of the stick.

TT5IeICh.png

On top of that, it's kind of hard to figure out how to reinforce the orange shifters location so they won't slide while also they won't touch the reinforcing elements or the reinforcing elements wont collide with gears near them

2aeGnSZh.png

The single servo steering is the one from this video:

Which I think is the most reliable approach, but it's a bit annoying that it's controlled with a single stick. I dropped that approach earlier because it felt like it requires a lot of space, but I increased the size of the chassis significantly from that prototype already and also reworked the turret mechanism multiple times, so It might be the best bet.

Still, I'm not 100% sure if I should go this way, or is there a better approach, that's not just going yolo with two drive motors connected directly, which I don't really like, but at the same time it would allow for a cleaner, simpler build. But at the same time, with current weight of the model, the slight difference between motors or how to power is supplied from the hub will mean it won't drive perfectly straight.

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@SaperPL

Not sure if it'll help as i would go for the single servo steering but regarding fixing the orange shifters a bit better:
2023-11-04%2023_38_14-Studio.png

Not perfect where the big 28t gears are, but no obstuction and at least a bit more stable.
The lbg bushes fit with the 24t gear and i've used the 1 beam i think part since i noticed in a build that with 2 bushes there is enough play that a orange shifter can disengabe a gear.

Edited by Ryokeen

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@Ryokeen I was thinking about something like this, but I'm not so keen on having that thin liftarm close to the gears because there's a potential that the gear shifter will push it against the gear teeth if the driving ring is blocked against the gear. Should work most of the time, but it might be touching the gear.

I'm leaning towards a single servo mechanism as best compromise, just need to figure out the motor layouts to be solid and don't take up too much of space while having driving axle sent to the back of the whole chassis.

Edited by SaperPL

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