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TOPIC: 2x Thunder Dragons - the good & the ugly

Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14120

Thanks for the damage pics. I never knew the T-Shot series had so many weak spots.

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14122

Didn't get much done again tonight, got distracted...
Cleaned the chassis bits the other night, but can't remember if I posted a pic or not, so here it is (Possibly again)



clean gearbox & transmission parts.
Note the semi-shredded counter gear - probably the result of incorrect motor pinion spacing. Not surprised really, if you haven't got the special spacing tool, there's no other easy way to get this right, as there are no inspection ports etc on the gearbox to see what's going on inside



clean diff bits...



Knowing that the intended new owner has a fascination with dirty puddles, plan is to replace all of the bearings that are in contact with the outside world with rubber sealed ones. I've ordered them, but until they turn up, most of the assembly work will be on hold.
The internal bearings will be replaced with normal ballraces, seeing as I've got loads kicking about at the mo!

So, I'll just put some of the gear clusters together for now, just to reduce the number of small parts rolling about on the bench!



The spur gear has since been cleaned up with a scalpel blade, & it looks like it'll be usable.
Whilst building the diff assemblies, I thought of a couple of simple tricks which I just take for granted, but others out there might find useful to know (If they don't already)

- Only apply grease/lube that won't harm the materials it's likely to come in contact with.
Most petroleum based greases will do something nasty to most plastics, even if it's not immediately obvious, so best not use it for toy car bits. I personally use food-grade silicone grease, which is cheaper bought as such, rather than "specialist toy car grease".

- Only use enough grease to lubricate the parts. Over greasing can cause more problems than it prevents.

- Self-tapping screws in plastic: When replacing screws in previously used holes, insert the screw straight, then with only light pressure slowly rotate the screw backwards until it "clicks" into the existing thread. Then, again slowly with only light pressure, turn the screw forward until you're sure it has picked up the existing thread, before screwing it in fully. By using this method (ie re-using the existing thread) the holes remain usable for more insertion/extraction operations, remain stronger for longer, have less chance of "stripping" & in the case of "pillars" (ie the round upstands in some mouldings) there's less chance of splitting.

Whilst fitting the bearings, I was alarmed to find something I'd not noticed before with Tamiya stuff - the fitting tolerances shaft-to-bearing are wrong. I don't know if it's just this particular model, or if they're all like it & I've never noticed before BUT...
Standard accepted engineering - unless specified otherwise, a shaft will be the correct "size" (ie 5.00mm in this case). I/D of the bearing will be slightly oversized to allow fitting. Usually, at this size, this fit would be 0.02mm clearance (ie an 1150 bearing should be 5.02mm I/D to fit a 5.00mm shaft). The O/D of a bearing will be "size" (ie 11.00mm for an 1150) & the pocket it sits in would be oversized to allow fitting (ie 11.02mm in this case).

Having a measure to find out why the bearings are such a sloppy rattle-fit on the shaft...


I/D of bearing's right, so why's it such a poor fit on a 5.00mm shaft?


Ahh, that'll be why then...
I immediately had a measure of all the other "5mm" shafts, & they're all like it.
Pants I said. Poor, very poor.
I know it's only a toy car, but if you're gonna do it, at least get it right!

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14123

Paused for thought - the "slop" is about the right amount allowed for clearance on meshing gears of this pitch... I wonder if the gearcase designer didn't allow for gear clearance/tolerance when specifying the shaft centre distances, & modifying shaft material was the quickest/easiest "get-around"? (Rather than remaking 20+K worth of injection moulding tooling for the 'cases)
I mean, for the shafts to be the wrong size, they would've had to have been purposely ground that size (If you buy shaft material off the shelf, it comes in "Sizes", not over/under/odd sized).
Good theory, but doesn't explain why the stub-axles are also like it...

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14148

A little more progress tonight - thought I'd have a proper look at reinforcing the dreaded A-parts.
Before I started doing that, I thought I'd have a quick look at my "Heat the screws to relieve the stressy plastic" theory - plop the screws through their holes & screw them in just enough to locate the other ends in their holes. Then, use a soldering iron to heat the screws to a point where the plastic is JUST starting to melt. Whilst it's all still hot, screw the screw in as far as it will easily go (You'll find it'll suddenly get stiffer as it cools below the plastic's melting point). Keep heating the screw & screwing it in some more, until it's seated. Let it properly cool (Or cool it in cold water) then unscrew the screw again, just to feel the difference - you should find the screw isn't stiff in its threads, but will still pull down tight.
What we have done here is used heat to form a proper thread in the plastic & thus removed the stress factor from the brittle plastic. This SHOULD at the very least prolong the life of your A-parts, if not completely cure the cracking problem.

Having proved that works, I then moved on to making some reinforcing plates - quite a few of the screw-pin holes on this car are already cracked, so the method above won't fix that, something more drastic is needed!

Although I've seen the A5 part reinforced with an aluminium plate before, this isn't the best material to be using as it easily stretches & tears. So, stainless was the order of the day... I found an old bit of vacuum cleaner attachment kicking about in the shed, tube with 0.7mm wall, that'll do! Chopped it up & made it flat (Soo tedious being so skint you can't afford new metal!). Had a measure, mark out, cut, bend & drill & came up with some reinforcing brackets for A5 & B8. Looked at the gear cases & decided I'd do something similar with those too.
Lastly, I thought I'd make some brackets to sort out the front of the chassis. No easy/sensible way to do this as far as I could see, so I ended up just doing some tiny screw-on fish-plate type things

Below should be pics of the reinforcing plates, & their trial-fitting





Tiny screws for doing jobs like this can be had for very little money - look on Ebay in the laptop & mobile phone spares departments. I often keep an eye out at car boots for old electronic gadgetry, purely to pull to bits for the small screws, pins, springs etc etc, which always come in handy!

The broken front chassis lug will get fixed with either plasticard or polyester resin. It won't have to be that strong as the stainless plate will be doing the work. The "fix" will just be for looks & to give the gearbox pillar something flat to pull up to.

Still debating whether or not to do anything about the split holes in the rear of the chassis - I was going to make up a plate for either side, each drilled for the 3x holes each side, but when I looked closer, I realised that they're all set at different levels, so a flat plate won't work (Sasa fasan rasa....)
I might pop the holes out bigger & glue in some metal sleeves, that should at least take the load off the plastic when the screws are tightened. A tomorrow job methinks
Attachments:

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14151

Really nice work there Eddrick! Should solve or at the least take care of the problems for a looong time :laugh:
Always a pleasure reading your threads!

Cheers, Bram

Ps

I found an old bit of vacuum cleaner attachment kicking about in the shed,

Wait until your wife finds out you molested her vacuumcleaner....lol
Restoring Countach 58005
Restoring 58015 RR
Restoring 58098 F40
Restoring King Cab and Monsterracer
Restoring Audi Quattro rally
Restoring Mk.1 Sand Scorcher
Restoring Porsche 936

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Last edit: by BramMeijer.

Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14152

BramMeijer wrote: ...

I found an old bit of vacuum cleaner attachment kicking about in the shed,

Wait until your wife finds out you molested her vacuumcleaner....lol


It's not that unusual for people in Norfolk ;)

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14155

Sorry to hear about your undersized shaft, eddrick ... never mind, apparently it's personality that matters :lol: :laugh:



Moving on ...

eddrick wrote: ...

I've spent all evening on Ebay trying to find either a set of 4x wheels & tyres of similar size to the originals, OR just 4x tyres that would fit the rims I already have. Task was seriously hampered by lack of info on the sellers' part - I don't get it, how do people buy (Or expect to sell) wheels/tyres without either specifying what they're for, or worse still, what size they are?!
I think I'm gonna give up with the "convenience" of the 'net, grab a wheel & go tyre-hunting in proper shops instead.

Not too worried about drive-method at this point. Yep, 12mm hex converters is a simple & sensible way to go, but I'll wait until I know what cheap wheels I'll end up with before committing myself - eg if I end up with dish-wheels, they'll probably end up on the mill to be made more "posh-looking", so I could just make the wheels fit the original adaptors whilst I was at it.

...



I took a punt on a set of the tyres/wheels I linked to earlier for my Thundershit (which os still in bits, so I can't measure anything on that), they now have 5% (50p) off :whistle:


Tyres are preglued ...

Outside diameter of wheels is 62mm, Tyres to the outside are 83mm, or 88mm including the spikes.

Tyre width is 34.5mm, wheels themselves are less - 28.75mm.

Outside of tyre to start of boss = 19mm (or 16mm from the rim), hex is 4.5mm deep.

29.25mm fronts, 36.25mm rears,

Hotshot wheels/tyres are: 79.25mm diameter to outside of carcass, 85mm to outside of the blocks (though there were pretty knacked tyres I was measuring), and the wheels are 56.25mm diameter ... depth from inside of wheelrim to to the flat bit is 29.25mm on a rear wheel, 21.25mm on the fronts.


So ... they're narrower than Hotshot rears but wider than the fronts... Offset is potentially +2.25mm vs hotshot fronts, or -5.75mm vs rears ... but no doubt hotshot hubs are chunkier than 12mm hexes by 2 - 3mm ...

I guess the main thing is if you can live with the more modern, low profile look ... but IIRC all the later plastic whizzy 'shot family had larger diameter rims anyway.

:)

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14165

Cheers for your enthusiasm Bram!
As for Wives & vacs, I have no wife, only a girlfriend. The main reason for no wife is that after lots of years looking for "The right one", I can safely say that none I've met have any idea what a vacuum cleaner is, let alone hold it more important than the sofa & Jerry Springer to use one. Me on the other hand, I've owned/fixed loads of vacs, hence the selection of spare parts kicking about, ready to be mutilated into toy car parts.

My shaft's fine Jonny, it's Mr Tamiya that has the size issue, but thanks for your concern!

Cheers also for the huge amount of info on Hotshot & Blacksmith's wheels/tyres.
I've spent another evening searching for something suitable.... It would appear that modern "1/10" aftermarket wheels/tyres are variants on the 1.9/2.2 size theme (90-115 O/D), & if you want something similar to Thundershot (etc), you need to be looking at Tamiya rears, or aftermarket 1/16 truck wheels/tyres. The wheels/tyres on the "good" Thunder Dragon are approx 75 (plain) - 80 (Over spikes) O/D x 37mm wide, ie they're a bit smaller than Hotshot, similar to Fighter Buggy rears size-wise I'd say.
Found some 1/16 truck wheels/tyres (Blacksmith again) but they're a bit more than I'd like to be paying for something that makes 5 quid or less when you re-sell!
Having a bit of a head-wobble over it, cos plan was to not spend anything, just use stuff I had kicking about, & I've already had to lash out on radio for it. Body's likely to be a pickup (Got one in the loft), the track of the 'Dragon is such that it would put the wheels inside the width of that body, so the "Monster Truck" look is out, it would be more like a short-courser. OR, I buy a "Buggy" body, & use whatever wheels fit.

At the end of the day, this one's not gonna be original or a shelfer, it's gonna be a runner/basher, & the only criteria is that it looks "right", functions, & survives for a sensible amount of time

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14168

eddrick, have you found any issues with the quality of the bevel gear molding in the gearboxes? I've had both Fire Dragon and Thundershot gears (Fire Dragon was a re-re but am unsure if the Thundershot replacement gears were vintage or not) that were distorted down in the roots of the teeth. They made a horrible clicking racket and sounded like a wind-up toy during running. Much careful trimming and filing remedied the situation.

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Re: 2x Thunder Dragons - the good & the ugly 7 years 1 month ago #14170

Nope, both the "good" car & this one (Which has been abused to death) have good bevel gears, & the Thundershot I had a while back didn't have any issues either.

It's funny you should mention it though, cos tonight I suddenly twigged that the make-up thickness of the metal washer & the plastic notched spacer (BW2+E1) might be similar to that of an 1150 ballrace, which they are, so I plopped a ballrace in each of the 3x places those parts occur.
The BW2+E1 combo is pretending to be a back-thrust bearing, & it's not immediately obvious that these could be replaced with a proper bearing. The thought that "I can see that causing heat build-up" was enough to make me strip the 'boxes & look again & replace the parts.

So, my question to you is, is your car ballraced in these locations? Could the deformation be heat/friction related?

Another possibility is ingress of grit etc which is getting packed down between the gear teeth, then the bevel is deforming as it is being forced to ride over it?
There are several places for this sort of contamination to find its way into your clean bits - again, the main culprit would be continued use of the plastic kit bearings. Ball races are better, but the metal sheilded ones aren't completely water/dust tight either, & it's quite possible for rubbish to find its way through them (Hence the use of rubber-sealed type on this project!). Main entry points for grit are the left/right diff output bearings, & the bevel/propshaft output bearing.
It will also get in quite badly if the card disc is missing from the front of the motor.

& finally... Were both front AND back bevels damaged, or was it just the back set? - the other possibility is the gears are running "off-centre" from eachother, causing heat & probably gear-whine &/or clicking. Again, is this portion ballraced in your car? - Remember me whining about the undersized shafts? Even with ballraces in there, the deflection at the bevel-end of the shaft (Before I replaced BW2+E1 with a proper bearing) was getting on for 1mm, which is quite a lot for a bevel setup to be skew-wiff, & I imagine the use of the plastic kit bearings on that shaft would make the situation much worse.

Actually, 1 more idea - what grease are you using? If it's normal automotive stuff, that can upset delrin/nylon gears - use proper grease for plastics. Watch out for automotive greases that say "silicone based" - they've got silicone in them, but also the bad oily stuff that upsets the plastic

Er... I think that's me done on ideas for that one!

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