Cromwell Mk.VI 1/6

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vanhasen
Posts: 12
Joined: Thu Jun 29, 2023 4:23 pm

Cromwell Mk.VI 1/6

Post by vanhasen »

Hi,
I purchased your project a few days ago, printers are red-hot doing their job - soon I shall be able to show some progress :)

Meanwhile I have a request - could you add alternative parts 04-03A and 04-05A - add option to print a casted port frame separately on SLA?

Konrad / vanHasen

vanhasen
Posts: 12
Joined: Thu Jun 29, 2023 4:23 pm

Re: Cromwell Mk.VI 1/6

Post by vanhasen »


50koruny
Site Admin
Posts: 18
Joined: Fri Aug 12, 2022 12:55 am

Re: Cromwell Mk.VI 1/6

Post by 50koruny »

Great as always.
I see you use resin wherever you can.
I can do those new alternatives to the parts, but I can see you've already got it done.

What material do you use for sprockets?
ABS is the best for me.
ASA is too flexible for this parts.
And this is especially true for parts 01-22 and 01-23, not only for sprockets.
I highly, highly recommend ABS for those.
There's a huge difference between 22 and 23 printed with ABS and ASA.

Regarding the non-functional [img] - I'll take a look at it and test it out.
Maybe some security restrictions.

Anyway, section created and thread moved, as you can see.

I'll add some recommendations about wheel drive axles to the support forum section shortly.

vanhasen
Posts: 12
Joined: Thu Jun 29, 2023 4:23 pm

Re: Cromwell Mk.VI 1/6

Post by vanhasen »

I am using PETG for all non-resin parts, I assume that if anything breaks - I'll fix it :)
Model is assembled and primed. I guess tomorrow I will start painting it.

Voila, two photos before priming:

Image
http://rctank.pl/forum/download/file.ph ... 184410.jpg

Image
http://rctank.pl/forum/download/file.ph ... 210330.jpg

50koruny
Site Admin
Posts: 18
Joined: Fri Aug 12, 2022 12:55 am

Re: Cromwell Mk.VI 1/6

Post by 50koruny »

This is a very fast and high quality build.
I also looked at the Polish forum.
Great job.

Regarding sprockets - I see you have modified it, but I must add that the original system works and is significantly different from the system on Hetzer.
There are supposed to be two nuts on each side of the wheel.
They are tightened against each other and held tight.
I still secure the inner nut on the outside of the wheel with epoxy.
That nut is the most important and transfers the force to the wheel.
I have been riding with this for months and have never had a problem with it.

But of course, that metal insert looks very good.
When you have the capability to make things like this out of metal, that's obviously the best way to go.

When your bevel gears come in, mill at least one flat in the wheel axle to secure the bolt of those bevel gears.
I don't know if I can describe it well in words.
I'll have to post some pics or drawings on this.
But I think with your metal parts making capabilities, you'll use a better wheel axle than a threaded rod, and you'll mill the flat surfaces for the bevel gears.

For the bevel gears bolts, I recommend using a bolt fixer (that blue or red thread glue).

You don't have to worry about the parts holding the motors.
Worst case scenario, the bevel gears will loosen before anything should happen to these mounts.

Regarding the 2mm suspension springs - I've tried them and haven't had a good experience with them.
The model acted very natural and real when moving, but didn't ride well off-road.
I eventually swapped them out for 2.5mm and it rides much better.

Here are some approx. calculations for the springs:
1,8mm dia - Spring rate = 0.7121 N/mm
2,0mm dia - Spring rate = 1.2352 N/mm
2,5mm dia - Spring rate = 4.0108 N/mm

So there is a huge difference between these diameters.
But you will see.

Regarding the use of ABS - not because PET(G) is not strong enough.
The problem is that it is too flexible and the wheel arms can bend.
Then the wheels would not be perpendicular to the tracks.
But I see from the pics that you probably don't have that problem.

vanhasen
Posts: 12
Joined: Thu Jun 29, 2023 4:23 pm

Re: Cromwell Mk.VI 1/6

Post by vanhasen »

Thanks :)
Swing arms do bend a bit, so I will probably print these parts once again, with ABS.
The same for the springs - I just had 2mm wire "on stock". Now I have 2,5mm too, so I can make one more batch of springs and mabe mix them. I want to try putting harder springs as first and last one.

Regarding sprockets - I used a sqare insert because I had an issue with wheel mounting concentricity. Probably my prints were not good enough and bend afrter tightening the screws. With lathe and a manual mill I can just baypass that problem.

Are you planning to extend your collection of 1:6 models? I am courious what you might choose as your next project.


vanhasen
Posts: 12
Joined: Thu Jun 29, 2023 4:23 pm

Re: Cromwell Mk.VI 1/6

Post by vanhasen »

After an incident with blown-up ESC capacitor (it was not correctly assembled) I managed to do first run of the model:

https://www.youtube.com/watch?v=rzEg7KTTgmY

Meanwhile I am working on the interior - battery, electronic box, loudspeakers. I also ordered a set of 2,5mm springs. I can make these myself, but size is not 100% consistent.

50koruny
Site Admin
Posts: 18
Joined: Fri Aug 12, 2022 12:55 am

Re: Cromwell Mk.VI 1/6

Post by 50koruny »

That looks really great.
Actually, it looks better than my own Cromwell, i think.
Congratulations.

vanhasen
Posts: 12
Joined: Thu Jun 29, 2023 4:23 pm

Re: Cromwell Mk.VI 1/6

Post by vanhasen »


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