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T-34's Talented Cousin - the T-50!

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T-34's Talented Cousin - the T-50!

Old 05-15-2022, 10:28 AM
  #26  
lposter
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This is one of those unglamorous, non-visible, tedious tasks that are no fun at all and annoyingly difficult some times.

There is no room at the rear for standard gearbox setups and the hull is narrow (the common problem for all small tank models) and I have lost all confidence in the ability of normal size motors to power metal tanks of any weight.

So I am going all in and using a set of big motors and gear boxes (common enough on ebay) which will connect to the drive shafts by chain and sprockets. Because they are easier than faffing about with bevel gear setups.

This means I have to build some way of mounting the gearboxes and motors. The hull is narrow and in their standard configuration the gearboxes cannot be mounted back to back. So I had to remove the the shaft from one of them, remove and reposition the spur gear on it and drill out the casing so it was now the mirror image of the other and they could be mounted back to back and thus fit the hull.

Then, using brass and steel bar stock, I fashioned a bracket that would fit between the two gearboxes and screws from one gearbox would go through the bracket holes and into the other gearbox, thereby holding them together.



This was achieved using a hacksaw, files and silver solder.

Then a base plate was made out of steel, 4mm thick flat bar. Two brass bars were soldered down the sides. This will allow the bracket pictures above to slide back and forward.

Then lugs were soldered to the bracket from brass and drilled and trapped. These lugs allow a long M2 hex bolt to adjust the position of the bracket along the base plate.

The base plate will be attached to the floor of the hull. A simple t-nut was made and an M bolt goes through the base and tightening of the bolt pulls the bracket to the base plate and locks it in position. This M4 bolts will go through a hole in the hull floor and allow tightening of the locking t-nut from the bottom of the tank.

The pictures probably explain it better than the text.

The two M2 bolts will allow for tensioning of the drive chains....something which has eluded me on other builds to some extent.

Its all a bit janky and is hardly pretty but it should do the job.






It all seems a bit overboard and I am sure a builder of more more finesse would devise a more elegant solution but for something cobbled together from bar stock ...it will do.

I have full confidence in these motors and gears as they drive bigger and heavier tanks I have so I am not expecting them to have any problems with the T-50.

Famous last words probably....

P
Old 05-15-2022, 01:17 PM
  #27  
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Wow. I've said it before and I'll say it again, if I had half your talent I'd have achieved world domination by now. Ahhhh, how cool that would be. You'd all have to call me "Your Grace" Bwahahaha

Seriously, great photos. If you ever happen to have the cover off that gearbox I'd sure appreciate a peek at the insides.
Old 05-16-2022, 06:24 AM
  #28  
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Originally Posted by Crius
If you ever happen to have the cover off that gearbox I'd sure appreciate a peek at the insides.
I can do that. The inside is pretty empty.

The worm and pinion (?) are brass - sacrificial I guess in the event of a stall. The rest are steel. The drive shaft is 8mm with a flat on it and mounted in two sealed roller bearings. The housing is some kind of crappy metal. They came with no grease so thats worth watching for. They are 160 rpm at 12 v, a bit less but same torque at 7.2 V. I think they come in a variety of flavours with respect to speeds.






Today I managed to pretty much finish my suspension racks. Surprised they went together painlessly as having to solder axles into all the spring rotation things was toasting my flakes.

I couldnt get them to solder as the axles are a very snug fit in the brass things. So there was no room for the solder to flow. I had to file little grooves in the brass piece to give the solder somewhere to go.






I have two adjustment possibilities - one being the springs. I ordered two sets, one being much stiffer than these so they can be changed. A third set being softer would have been smart just in case.

The second is the diameter of the shaft that works as a bump stop for the arm that pulls the spring. I wanted all the flats on the axles to be perfectly horizontal to function as a datum for the swing arms. So they can all be at a precise angle when not under tension.

But some of the flats are a degree or two off. This may or may not make a difference later on.

If it does, and this is one of the only bits of preplanning I have ever done.....I can sleeve the horizontal shafts that retain the spring arm or replace them with slightly thinner ones in order to adjust exactly the angle of the swing arm axle flats.

Hopefully I wont need to do that.

I have to solder some lugs onto the base of the racks to anchor them to the hull floor.

I haven't tried them in the hull yet but hopefully every axles will line up precisely with the corresponding hole in the hull wall.

If not....its more than flakes that will be toasted.......

P
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Old 05-16-2022, 07:09 AM
  #29  
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Thanks for the photos. You're right, those do look pretty simple but I think that's a good thing. Less things to break. I'll be very interested to hear how they hold up over time.
Old 05-20-2022, 10:51 AM
  #30  
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After some concentrated efforts, I finally have the bones of the drive system finished. That includes the suspension racks installed and fastened, the motors mounted, the chain tensioning system working, the rear drive axle mounts installed.

The suspension racks were no issue. Some tabs mounted on the bottoms and then screws from the underside engage them.

The motors mounted as planned...fiddly to engage the t-nut on the slide plate but I am getting used it. In the picture below you can see the access to the two screws that move the mount on the slide and tension the chains.


Its a bit out of focus but its not easy to get the camera to focus on such a small detail instead of the bigger end s of the motors.



I had to add a supplemental structural plate under the front sloped glacis as I had made some mistakes. There are two widgets on the front glacis in real life (like round things with a hex headed bolt) and I am utilising those two things as fixing ppoints. I therefore added a plate to allow those fixing points and this knocked a mm off my measurements. So I had to shorten the suspension racks but that was OK. It was only a mm filing.




The rear axles were a problem. Its tight back there. So needle bearings were installed in the external hubs and then a central piece in aluminium, with needle bearings, served to support the other ends of the axles. Lining all these up was a major issue but it got done in the end. I will use shaft collars to hold the axles where they should be. I have to install the sprockets on the shafts and I am hoping that chains do not interfere with the back ends of the suspension racks but I think I will be OK: the chain should slot down between the two walls of the suspension racks.



Everything is very tight.....the sprockets on the shafts are within a 1/10 of a mm or so of the side walls. And I have a mm to spare when the top hull is on. For once my measurements did not let me down and it seems to be just fitting as it should.

You can see how close I am cutting it in the next two shots:




I was hoping to use the access hatch on the rear sloped glacis to access a switch and charging ports. Whether or not there is room is a different matter.

Next job will be to try and finish off the drive system and turn my attention to bump stops on the sides, return rollers, idlers and the dreaded....drive sprocket.

P


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Old 05-21-2022, 09:04 AM
  #31  
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Today I made up my chains and axles and did my first assembly of the drive mechanism.
I had to adjust the suspensin racks as they were too long. I moved the rearmost spring mounts down a centimeter and then simply ground off excess metal to shorten them as much as i could.

Then I assembled the drive.

In this picture below you can see the slack in the chain when the t-nut on the motor slide mechanism is loosened and the motors are pushed as far towards the axles as they can go.






Then I simply screw in the two adjustment screws on the slide and this pushes against the fixed slide rails on the mounting plate and the motors are moved away from the axles and tightening the chains.

The pictures below are not great but it may be possible to see how the chains have now tightened up and the motor slide has moved back.


A few things were learned from this fitting.

1. Its a royal pain to install....... that's why Heng Long and Hooben employ industrial designers I guess.

2. The link connectors on the chain.....they are catching on the side walls of the hull. This is not good. Its putting a stress on the motor mounts.




3. The link connectors are very stiff. I dont know why. I dont know how to fix it either. But the links on either side of the connector do not have th eflexibility of other links.

The solution to #2 is to flip the sprockets around so the chain is running away from the walls. I will do that tomoorow I think.

I cannot face that stupid t-nut again today.

P
Old 05-21-2022, 10:16 AM
  #32  
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Are the chains fully broken in? I used a similar set-up in my Hetzer and the chain movement got much smoother after having been run for a awhile.

How bad is the chain catching on the sidewalls? I mean, how much would you have to move the chain over to make it stop? I wonder (I know it's a pain taking it all apart) if you were to take .010 to .015 off each side of the center plate the trannies mount to if that would give enough clearance?

Old 05-21-2022, 10:24 AM
  #33  
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The chains are new....and are nice and floppy, run fine.

But once the connecting link is added, they bind where the chain joins the connector. I might try filing down the side plate of the connector.

The fouling on the side wall of the hull doesnt bother me. Having the chain run against the hull wall was a matter of taste. Turning the sprockets around should be a solution.

The stiff connector is more annoying as chain drives need a nice smooth chain action.

P
Old 05-21-2022, 12:33 PM
  #34  
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This chain thing was eating at me so I disassembled the whole thing. I then ground down the connector link plates a bit and filed off a bit off the chain links. This made things a bit looser.

I also flipped the sprockets around. Needs some fine tuning but that will be done.



That cut out the fouling on the hull walls.

Then I decided to take Crius' advice and let it run in for awhile. And while it was doing that, I stuck a dial indicator on it to see what sort of run out I was getting. I wasn't optimistic given that it was cobbled together by hand.


But it turned out to be about 0.03 to 0.04 mm (1.5 to 2 thousands of an inch for those Stateside). Not so bad! The clacking as the stiff link goes over the sprocket is noticeable but Im guessing it will soften up with time.

P
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Old 05-22-2022, 04:41 AM
  #35  
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Default amazing stuff

This really is model engineering, wonderful stuff
Old 05-23-2022, 01:39 AM
  #36  
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Sorry, wrong thread.

Last edited by Crius; 05-23-2022 at 01:47 AM.
Old 07-07-2022, 09:20 AM
  #37  
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Time for an update on this tank.

Two of the tricky things on this tank were always going to be 1) the sprockets and 2) the turret.

The tank is using Pz III tracks but there is not room to use those sprockets. The real sprockets have a scale diameter of about 38mm across the teeth. The pitch of the scale tracks is 7.5 mm and a sprocket of 15 teeth has a pitch diameter of 36 mm.

I bought some 40 mm diameter steel bar and asked a local chap to make me some blanks....these being 18 mm thick disks with side wall thickness of 2 mm. And a 1 cm "stem" so I have something to hold them with. I got 6 of them made.

I started off marking off 24 degrees around the circumference and filing teeth. That was a disaster. Then I started drilling 4 mm holes around the pitch diameter with a view towards opening them up with a file. The chuck I use on the rotary table I have couldnt hold the blank and there was slippage which caused problems. So I bought an ER16 collet holder and that was better. Then I wasted about 10 plastic blanks perfecting my method.

here is some of the wastage. They are rusty because I spilt flux liquid on them.



After some more practice I perfected my technique which was as follows:
Th eblank was put on the rotary table under the little proxxon drill.
Then I drilled 15 holes at 24 degree increments around the 36mm diameter pitch circle. This only left very thin walls on the outside of the holes.
Then I swapped the bit for a 5 mm diameter diamond burr in the Proxxon and simply opened up the holes.

Oddly enough....this worked well!

The tracks engage well and all they need is to soften the teeth with a flap disk or something. Then drill them out, get rid of the stem and finish them off.

Here they are now:



And with tracks wrapped on them:



Very pleased with this as there are many tanks for which various tracks will work but for which there are no sprockets. Now I can with confidence make sprockets and expand my target tank list. Tanks that can use Pz II tracks being my main target.

The next problem was the turret. Because I had not noticed this:

"This" being the fact that it is not symmetrical around any axis! It is completely skewed in all directions. I really struggled with that but in the end I made a top plate and a bottom plate from the drawings and then used four steel threaded rods of correct height to attach top and bottom in the right orientation relative to each other.
Then I clad the outer two sides with thin steel and soldered that in place.





Then I clad the rest of it and manufactured a basic mantlet. The gun and all the other bits need making but it is the correct shape.




Another tricky bit were the screens covering the air intakes/exhausts. Pictures show everything from mesh to what look like lumps of bent rebar. So I tried to replicate the latter. This was a hassle but I made two frames and then just used brass rod to fashion the grills. Its diog rough but so were the real things and I'm willing to live with it.



Here they are with turret on the hull.



Aside from that... I spent a lot of time making hatches, bump stops and a whole dose of other things that will not be attached until th eend.



Still looks a bit janky but its getting there slowly.

​​​​​​​P
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Old 07-10-2022, 11:13 AM
  #38  
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Had to try and complete the sprockets so I went at that. The central hole is 8mm to fit a drive shaft of that size. But I need flats on the drive shaft and the sprocket to allow engagement. I had to make an insert for the sprockets to provide the flat. I did this by filing down an 8mm steel bar that was drilled to 3mm (to allow a screw to link with the end of the drive shaft). It was filed down to 2 mm height (ie. the flat will be 2 mm deep on the shaft) and the flat bit is 8mm long. The round bit is 32mm thick.

These were then pressed into the sprocket using a vice and silver soldered in there. Should be OK but I may pin it as well as a belt and braces approach.






I also soldered on all the bump stops to the side of the hull. Sorry about the dirt.



I also attached some hatches on teh hull and turret - these need final tweaking to remove screw holes and the like.



Hopefully I can push on with the lower hull over the next day or two to get that out of the way and see how th erunning gear fits.

P
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Old 07-13-2022, 10:28 AM
  #39  
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Small advances today but had to be done.

The rear hatch on the rear glacis ... this was not overly tricky but it has to open as it is the only realistic option for a switch and charging point. The whole engine deck needs a lot of work but it will get there in the end.




The rear hatch on the turret was done as well, bit rough in places but final fixings will sort out any issues.

The three lifting lugs on the turret roof were horrible to get together (very small) but they are on. The next thing on the turret is the ridiculous cupola but I have the main strokes sketched out.



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Old 07-17-2022, 03:19 AM
  #40  
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Might you want to consider the photo-etched parts used for the engine deck of the Tamiya KV-1/2 tanks?
Old 07-17-2022, 03:45 AM
  #41  
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I suppose I could. I am not a fan of photoetch however.

Fiddling about with microscopic bits turns something i like to do to pass a few hours into an exercise in frustration.

P
Old 07-18-2022, 10:39 AM
  #42  
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Slowly adding bits and pieces to try and move towards completion.

The turret is done except for a shot deflector behind the mantlet which should be easy. I also need to make the mount for the rotation mechanism. This has to be a press/friction fit on a 6mm d-shaped shaft as I have no other means of locking it to the shaft so I will see how that goes.

Most of the hull is done. Some gribblies to add on. I did the headlights which need a lens and gave up trying to make the actual mount type as it was just too small. So I just stuck them on. Im debating whether or not to make the stowage box on the fender as it has three different angles to account for and I am not sure I can be bothered.
I'm stil waiting for 3 mm needle bearings for the return rollers and as soon as they come, I can finish off the running gear once and for all and then I want to start priming the hull as this really needs a coat of something. There is no way it can ever be polished enough to let it sit in the bare metal.

P






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Old 07-18-2022, 02:12 PM
  #43  
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Your metal work is fantastic!!!
Old 07-25-2022, 09:04 AM
  #44  
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Today I was finished with the lower hull so I gave it a coat of etch primer and went about test fitting stuff.

With the motors in and the suspension and then a battery..... there is f&%k all space left for anything else. In addition there is a motor for the turret to go in.




There is a bit of head space as the upper hull arches upwards but as mentioned...there is a motor and gearbox for the turret to hang under the upper hull roof.

I have some small-ish ESCs from Hobbyking that would probably fit and a small receiver but I think that will be it. There is no room that I can see for a sound card of any size.

I may just scale down to 6V and buy a smaller battery. In addition the current draw on tanks of this weight necessitates fairly thick cables so I am going to have to be super tight on the lengths of wires used - there is no room for simply stuffing a rats nest of cables in there.

And I may have to lose the usual connectors I use as they are way to big. It may have to be Deans or something.

Now I need to attache axles to my swing arms of the correct length, attach those, another lick of primer and then move onto finishing the nightmare that is the ipper hull.

And the motor linkage for the turret.

P
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Old 07-25-2022, 09:10 AM
  #45  
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You might take a look at the xt30 connectors. They might even be smaller than Dean's and they're a very good connector. I haven't had anything small enough to have to buy those yet, but I do use the xt60s and the xt90s and I like them very much. I think they're way better than the Tamiya connectors.
Old 07-25-2022, 08:55 PM
  #46  
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Looks great, if I were you, I would have a look at li-ion batteries, that would save you about 2/3 of that battery.
Old 07-25-2022, 09:42 PM
  #47  
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I ordered some of the xt30 connectors today - they look very small indeed.

I have considered Li-ion batteries but freely admit to being petrified of them.......

p
Old 07-26-2022, 11:08 AM
  #48  
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Finally tested the road wheels. Always satisfying. They were the first things made and nearly the last to go on!

Some tweaks and fine tuning necessary here and there. Next will be the drive shafts and then finally get some tracks fitted!



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Old 07-28-2022, 02:03 AM
  #49  
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Quick test fit of the tracks......seem to be working fine. One of the teeth on a sprocket needs a filing but that should be OK.

Some final bits to attach to the hull, then a scrub with acetone and a coat of primer before final assembly I reckon.




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Old 08-02-2022, 01:51 PM
  #50  
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As always, this looks great. Your metal work always impresses me!!!

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