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rosco01

Cooper T53 Mk 2 - Second Build

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Hi folk,

back again, with #1 now boxed up and ready for dispatch to the upcoming Tasman Series proxy - I can dust the cob-webs of the parallel build - #2.

The basic chassis was already completed in this build - the motor, gears and wheels/tyres and axle assemblies have already been finished.

 

I'd probably have changed a couple of things in these - now having realised what subtle little differences were required to make the body fit - PLUS fitting of the driver... #3 will get all these benefits.

 

No pix yet - but I suppose it best if we take a few and post here to set the foundation on this thread.

 

For this build, I am using Tassie resin bodies kit - with some different parts from another supplier that I have taken a fond liking to.

 

The same motor with Ranch Design wheels and gear-set is used as for #1.

 

So, again - I would ask members of this great forum to pull up a chair and kindly offer up suggestion as we go through another "War and Peace" version of a scratch build.

 

frats,

Rosco

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Maybe an audio version of this thread this time around Ross. That way we can still 'work' on our own projects at the same time.

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bram1_zpsfkhrhndv.jpg

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Now, there's innovation - Bram..... I don't think you'd get much done either way - with my typed post dribble - at least you can either look away or even turn the computer off..... an audio version would not afford any greater ability to concentrate on anything else.... not many here have ever "chanced" a one on one "Rosco" session.... those who have, don't post much any more for fear of a recurrence....

 

frats,

Rosco

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Ok folk,

got some of the domestic backlog cleared.... time to kick this build off again.

 

When I dragged the poor little thing down - I realised what I'd done..... I had used body #1 and chassis #2 for the first build... why?. well, I liked the look of the first body better and had issues with the first chassis... so, what we are about to create in build #2 is chassis #1 and body #2... but, we'll just call it all Cooper #2.... OK?

 

The body, well - yes, it's in two bits..... and will get the same intake manifold as #1... but, I'll put it back together a bit more precisely - now that I know the pitfalls and penalties for not lining things up correctly the first time - and having to pull it apart and redo it.....

 

Body.....

 

body%20001%20mail_zpshrniqpfr.jpg

 

Ok Chassis #1... and why I ditched it when the rush job eventuated.....

 

Those blasted brackets - both front and rear....

 

You might recall (you really don't want to go through all that other thread, do you? - no, well I'll fill you in and save you the toil) - I had both chassis' in rolling/running state.... minus the guide.... but, both had been bench running.

The chassis I chose for the first build simply ran better... and would stall at a much lower voltage.... around 0.3v, in fact.

Chassis 2 (this one) had issues.... I had to really work hard to get it to run.. and spent a lot of time getting the gears to mesh - thought there might have been a mis-match issue - never suspected the rear bracket (remember, later I re-visited that blasted bracket on #2 and fixed it by squaring it up - that's how I got down to a 0.3v stall point).

 

I started work today by spending a good bit of time looking at this one very closely... and yes - now with new tools and measuring equipment... it was all out of kilter - axle not square to the motor mount..... again.... both vertically through the motor shaft to centre of crown AND not motor shaft square to axle (both fore/aft and up/down)....

 

So, if there was one thing I would seriously suggest anyone with purchased brackets do - is measure the blasted things and square them up....

That took nearly two hours out of today....

 

Next - the front bracket.... and the second reason I ditched this chassis for the second.... rolling - across my 4' desk - it veered off to the left by 1/2" from one end to the other.. and no, not tyres... this was on the very well machined RD wheels.... the actual wheels are perfect.... I had issue with one hub.. but the wheels are simply superb.....

 

I found it.. but it took a while... yes, the front bracket... again - not square.... ok on each side up and down - although, you simply solder it to the rails to make this parallel with the rear axle... but not square as it sat in the axle housing holes.... by only 0.5 mm... but enough to throw it of centre line - and I now believe this has a lot to do with why some models run better than others.... I know chassis #2 ran true... right down the desk... both right way up and inverted..... it did this also after I trued the tyres front and rear.... I fully intend to have this one do equally the same....

 

But, I had to fix it... and that meant de-soldering the front bracket from the chassis.... I really didn't want to do this.. but.... well, you know - don't you..... it wasn't right - and things like this keep me awake at night if I know about them....

 

I now have the chassis ready for soldering up again... pix...

 

chassis%20002%20mail_zpssx3kevwp.jpg

 

chassis%20001%20mail_zpsq3wwqxp6.jpg

 

chassis%20005%20mail_zpsil2nm4ie.jpg

 

Ok - the rear bracket... what to check....

It "looked" fine - but the gears didn't mesh well.... they did when I bedded them in... but, could not get the stall speed down to a low voltage.. it wasn't the motor - I tested that on its own... so, it had to be something to do with the gears... I thought..... wrong!.... bracket.

 

Today, I pulled the rear axle assembly apart - all shims and spacers - again, with zip gap on both sides of the crown.. tears came to my eyes when I did this... it took so blasted well long to get this so right.. and I'm about to ruin it ... I knew it would be bracket... just knew it...

 

When I put it back on the tile - and started measuring with a very small engineer's square.. it was out all over the place...

 

I spent a good hour filing/straightening/sanding and measuring that face until I got the motor shaft to point exactly at the centre of the axle horizontally and also at the centre of the crown vertically whilst square to the axle.... so, we really need to get these square in not only the 2 dimension - but all 3....

 

When I put the assembly back together - it just "looked" better... don't know why.. but it did... then I measured things again... all square now... the motor actually sits perfectly against the bracket with no gaps.... the screws nip up the motor very well with only the last 1/4 turn needed from a slack drive to a nip.... I'm pretty happy now....

 

So, I then add all the shims and spacers... but need less on one side and more on the other...

My mesh is out... binding on two places as the crown rotates in mesh with the pinion.. and - it's the same places on the crown.. so - the crown now has issues......

 

It's not much - but enough to make it bind... not lock.. just bind... you can "feel" it as it gets tight then free's up... two places - guessed it yet.....?

 

Yes - the exact places it would if the blasted bracket face was not square in two dimensions - but ok in the third.....

 

I decide, now that I have a perfectly square mounting face for the motor to the axle... I'm going to bed the correct mesh in... so I set about running, cleaning, running repeatedly until the aluminium crown beds to the brass pinion..... which it does eventually... not a lot of metal came out.. but it got better and better as I went through it.

I stopped a few times to gently scrape and clean the pinion... which also was picking up aluminium...

 

After some time... I connected up the motor and it ran much, much better.... I used some cutting compound to bed the mesh in under power and within seconds - the "din" the mesh was making began to disappear... and the speed of the assembly increased....

 

I stopped quite a few times to clean and re-apply compound and I now firmly believe I have a better mesh than model #1... there is not back-lash at all between the gears.. no clearance between the axle bushes... and the crown runs in a perfectly straight and square line to the motor shaft....

 

Stall speed - 0.4v..... this will come down with running.... it took considerable time on the bench to get #1 down to 0.3v.... this one has done almost nothing and it's at 0.4v already....

 

Ok - folk.... last pix..... look very, very closely at the work on the face of the rear bracket... there's a good two hours in this....I

It is much, much easier to get that face square BEFORE you decide to solder the chassis up.......

 

pix..

 

chassis%20003%20mail_zpshxnj0zfe.jpg

 

chassis%20004%20mail_zpsdmmxbhje.jpg

 

So, folk - we're off and running on the next build..... again....

 

Same deal - if it gets too much, I won't be offended if you jump ship... but, if you do follow this one..... please - constructive comments please... I'm up for any suggestions/recommendations which will make this build easier, better and hopefully get the jump on build #1.....

 

frats,

Rosco

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That is very interesting having the motor shaft perfectly perpendicular to the rear axle. Love your work and learnt so much with todays post.

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Fiery, the pinion and crowns I am using do not have any offset - as such, it is essential that the motor shaft points directly at the centre of the axle AND is square on to it....

 

It doesn't matter one jot that the arrangement can result in the motor pointing up down or even vertically - as the mesh won't be compromised.. but - the motor shaft and axle need to be aligned properly...... shaft pointing directly at the centre of the axle - and square to it.

 

Where the 3D come into it - is the relationship with the axle bushes/axle... to the chassis..... you must have the bracket (with its correctly aligned motor/crown/axle) square on to the chassis.... or, the axle simply will not be square on to the centre-line of the chassis and the drive of the rear tyres will try to throw it left or right - which ever way it is out of square ... it will drive towards the shorter distance from the bracket.

 

Similarly, the front axle - must be exactly parallel to the rear axle... and also square to the chassis.... the two axles must be in the same plane - and equal distance from each other at both ends....

 

You can have one axle higher/lower in the chassis - but they must be in the same plane... either pointing up or down - along the chassis side centre-line.

I wouldn't suggest doing this... as the chassis rails would point uphill or down hill.... but, I suppose you could if need be to fit a driver etc.

 

I do know of builders .. perhaps they may even be the majority.... that deliberately make a bend in the chassis rails so that the motor points down... and this allows them to fit a driver body over the motor with less of the meat cut away (bad expression) from the body.

 

Personally, and I don't know why - it just makes sense to me to keep everything straight and flat on the building board, until I learn more about the engineering of these great little cars..... and can be enlightened as to the benefits in performance....

 

frats,

Rosco

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As I understand it, the main advantage of having a bend in the chassis rails is to lower the centre of gravity by having the front of the motor as low to the ground as it allowed.

This is also the theory behind using offset gears.

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I have and still do sometimes use Standard crown gears and offset them up to 1mm below the axle line, once run in there is no problem.

I have also offset the crown gears from the centerline and angled the motor about 15 degrees, still using standard gears. A couple of manufactures do this with their RTR cars.

Rusty is right about the bend in the chassis, to lower CoG.

It is surprising what can be done and works very well.


Phil

 

Hobart Miniature Car Club

 

Tassie Resins

 

Email

 

 

 

 

 

 

Logos%2016_17.small_zpswkcwjf0q.jpg

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Thanks SR and Phil.... I'm completely new to this new world.... my first little build seems to run ok... I plan on making this second one exactly the same.

#3 might have some of these more advantageous alterations.... long way to go yet before I understand enough about this to design something of my own....

 

Ok - we're moving along with #2.... spent a good hour getting that front bracket set and soldered in.

I fitted the axles and wheels and did the "desk" test... it tracks straight now..... amazing what such a little bit out has made such a difference...

It just "feels" like it wants to run freely along on its own... only 0.5 mm out of parallel laterally - but putting it right has made a enormous amount of difference.

 

I spent tonight making up the brake backing plates.... drilled out all holes - but this time, my wishbones will only be from 0.8 mm rod - not the 1 mm I used on #1... also - the steering lingages will only be from 0.5 mm rod... not the 0.8 mm of #1...

 

pix..

 

front%20bracket%20001%20mail_zps9mhisbgl.jpg

 

front%20bracket%20002%20mail_zpsr1hib7tt.jpg

 

Tyres have now been glued to wheels and set aside to dry (water based contact cement - coated tyre and wheel - then set to dry for 1 hr... then re-applied to wheel and tyre fitted. Then straightened on wheel to run true.. and finally "rolled" along a flat surface to extrude all excess adhesive).

 

Hope to start truing and sanding down the front tyres tomorrow night... then I can measure up and fit the guide post brass tube...

 

Amazing, when one is done - how quickly the second one seems to go together.... guess most of my time is spend contemplating and designing/planning.... now that I know what my plan is... the build is certainly running a lot faster than #1...

 

frats,

Rosco

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They say experience is recognising a mistake the second time you make it.


John Warren

Slotcars are my preferred reality

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Hi Rosco.

 

Better I think to recognise mistake after event first time and try to not make second time. Alternatvely as Munter says if you find it happening again being able to correct before set In concrete.

 

Good to see you looking at rod sizes. Partly due to criticism during past event I checked mine while building BT4. Tried to estimate actual size as I could not find actual dimensions and scaled down. Assumed max. 25mm so used 1/32nd rod. Do not recall whether I used same size for steering arms.

 

Regards Chas Le Breton

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Thanks Rosco

I have heard of offset with gears etc but did not realise what it was. I always thought it must have been to do with the shape of he crown gear Than you again as I have learnt some more.

fred

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Offset gears have the teeth on the crown wheel cut differently. The pinions are the same (thankfully).

 

A really good example of how the teeth are cut is on the Revel / MRRC sebring chassis.

The FF-050 motor is about 3mm offset, and the crown still meshes nicely due to the VERY offset cut on the teeth.

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I have a Slot-it 1mm offset crown running in my fairly standard ex-IPS Ferrari 250 GTO and it meshes great.

 

Regards Chas Le Breton

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Aah this means the crown has to always be on the right hand side of the car when looking from the back also. What are the reasons for using offset gears? Do you guys have a preference?

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Wow - fella's - I'm chuffed..... all this great info - I still don't quite get why we seem to have the tooth side of the crown on the right... is there a reason?

 

I can appreciate offset now, thank-you.... to get that blasted great pair of magnets down lower...

 

Sadly, I don't think I can do this with the next three models.. my very small little RD crowns and pinions were cut with no offset....

I might ask Steve at RD if he is able to supply them with a 1mm offset.. but, being so blasted small - I doubt very much there would be enough diameter in the crown to achieve this... will contact him and report here....

 

Ok - continuing....

Another two full days.... and a lot of disassembling.... the chassis (again - third time).

 

As you read somewhere above - the spacing between axles was 0.5 mm out.. and the model tracked off centre over a 4 foot length...

I corrected this by removing the front bracket and re-soldering it.... I had managed to get it both square and parallel again .. and the little chassis rolled true... in both the right way up and also inverted (just in case there was any "bias")..

 

To my horror today - I went to fit the body for dimensions... and it's out... way, way out... a good 1.2 mm too long between axles...

I checked the specs for the body - and found them to be fine..... soooooo - the chassis..... duh! wrong holes in the ceramic tile.... grrrrrr.. stupido! - I really don't believe I did this... but, folk - I did.....

 

I nearly had tears of blood emerging as I de-soldered it again..... both sides - it was absolutely schmick.... exact...

 

I set it up on the next pair of holes back, got all the alignment sorted on those holes - heights and parallel in vertical plane... but - couldn't get them in the lateral (horizontal)......and folk - this is where I found my original 0.5 mm error to be... I simply has "assumed" that the holes in the ceramic tile were congruent right along the tile.... and to anyone who has one of these - I must tell you - they are most certainly NOT!

 

I spent some time up and down the tile searching for a 72.5'ish set of holes.... nope - none on my tile.....

 

I then pondered on how I had achieved the correct alignment with build #1.. and, as you might recall - it was originally done on the tile - but "twigged" later when I had issue with that blasted rear bracket..... I had used a square and ruler to put that one back together.. not the sets of holes in the tile... hence why that chassis tracked true.....

 

So - dilemma.... tile, or no tile.... it's only the front bracket I needed to re-solder....

 

I spend a good two hours making a jig of my own..... exactly at the 72.27 mm axle spacing... exactly square to the chassis centre line and exactly square to the motor bracket mount face.....

 

I made it out of 42 mm x 19 mm pine.. (yes, I know - you can't solder on pine).. and drilled 1.6 mm holes at 8 locations to "trap" and secure the made up axle extensions (3/32" brass tube with 1/16" stainless TIG rod within)....

 

What I did, which worked - was to "spot" solder the chassis rails and bracket in place... enough so that it would not let go when I placed the chassis loosely on the tile....

 

I was very careful to then flood solder the bracket to the rails... in half runs.... top and bottom.

 

When I put it back into the jig (after grinding away the high solder high spots) - it again sat beautifully in the jig....

 

So - end of today.... I am back to where I was Friday... but, this time - I've got a true chassis - with axle spacing of exactly 72.27... which is the scale dimension for the proto-type...

 

Yesterday - it was body day... I set out with a body weight of 7.58 grams.... which I believed was reasonable for the body when I first trimmed it...

By last night - I had reduced this down to 5.24 grams....... some of it is pretty thin.... but I did not break through anywhere.

Holding it up to the light allowed me to decide whether to go deeper or move onto the next area... I was careful to leave places which would be prone to stress a little thicker - and will apply a short strip of fibre-glass tape and cyano acrylate to the known breakage point between the windscreen and nose....

 

This body is ever so much lighter than that of Cooper #1... the first one ended up with a gross running weight of some 60.8 grams - if I can't bring this one in a lot lighter than that, I'm simply wasting my time....

 

So, we have the chassis in running state - we now have the body re-assembled and reduced in weight.

 

The brake backing plates have been made - next, I expect - will be building up the suspension again.

This time, I will angle the upper wishbones correctly - in the pix I have of Coopers - the top wishbones seem to rise from the chassis out to the wheels... the lower ones appear hoizontal.

 

By having the top of the upper wishbones lower, and using thinner rod - will allow me more room to fit the springs/dampers...

 

Ok - nothing done tomorrow - firing at Puffing Billy.... Looking forward to Tuesday - more drilling of brass and soldering up another 4 sets of wishbones...hope to have the four sets with backing plates all on Tuesday night.

 

frats,

Rosco

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" I still don't quite get why we seem to have the tooth side of the crown on the right... is there a reason?"

 

Something to do with the way the motor spins and the way we wire the cars - positive on the right rail etc put the crown on the left and the car goes backwards :)

Edited by dangermouse

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And yet the Scaley Toranana has the crown on the left. Why would they do that?


bram1_zpsfkhrhndv.jpg

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Normal crown gears ( no offset) can go either side of the pinion. The motors are "supposed " to be neutral timed so rev the same in both directions.

Offset gears are made to only go on one side of the pinion as the teeth are off set below the centre line of the gear. If you run it on the other side the motor shaft would need to be above the centerline.


Phil

 

Hobart Miniature Car Club

 

Tassie Resins

 

Email

 

 

 

 

 

 

Logos%2016_17.small_zpswkcwjf0q.jpg

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I still don't quite get why we seem to have the tooth side of the crown on the right... is there a reason?

 

Just to add a bit to Phil's post, for gears that are manufactured to the true 'offset' (Hypoid) tooth shape, the tooth shape is different to 'normal' gears.

 

In 'normal' gears the centreline (CL) of the pinion is on the same plane as the CL as the axle, which makes the teeth radial from the gear's centre.

 

On hypoid gears, the CL of the pinion is on a different plane to the CL of the axle.

 

If the motor is set parallel to the track and is 1.0mm lower than the axle, then the pinion CL is under the axle CL. And to achieve a perfect tooth mesh, the teeth on the crown will need to be slightly angled down, and the teeth on the pinion would need to be cut on a slight spiral to match the crown.

 

So, if you flip the crown over to the other side of the pinion, the crown would now be expecting the pinion to be above the axle CL to achieve the perfect mesh.

If the pinion CL remains at the lower level, the teeth will not mesh properly.

 

For the crown to be flipped to the other side, the whole chassis would need to be flipped to retain the pinion/axle relationship.

 

Now, in our slot cars, the teeth on a normal crown are radial, and on plastic teeth, the bit of mismatch by having the pinion offset a small amount is not a problem.

 

If you wanted to have a hypoid set-up using plastic crown gears, a better mesh can be achieved by adjusting the crown/pinion so they are a little bit tight. Not too tight that prevents the motor from running. Then run the set-up on low volts (3~6v) while holding the crown about 100mm above a lighted candle. The plastic will soften, and deform to the shape of the pinion. When this happens, the gear mesh gets quieter, take it away from the candle with the motor still running, so the plastic can re-harden. Adjust the crown to the normal backlash clearance, add a drop of your favorite lubricant, and you're good to go.

 

Sorry for the long winded post and hi-jack.

:huh:


Steve K.

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Not at all, Slotbaker - you post whatever you like in my threads which pertains to subject..

 

Yes, I can very much appreciate that with an offset pair - they must be fitted as designed... and that, of course - is most likely/is with the crown on the rhs.

 

But - is it just co-incidence or "that's always the way we've done it" that this is done with most models I have - including those from the 70's...

all of mine - the crown is in the rhs.... and none of them have offset...

 

Thanks for the heads up on pairing pinions and crowns not designed to be offset - I could try this using nylon/plastic crowns.

With my little Coopers - I have fitted the alloy RD crown - no chance of running that over a candle.. so, for the next few builds using these - I will set the bushes up in line with that of the motor shaft... i.e. - everything pointing directly at the centre of everything.. they run very smoothly after a few goes at getting the mesh to bed in.. a couple of my pinions developed burrs... which bit into the soft alloy crown teeth... but a few more shims on the crown side/bush and a bit of progressive bedding in with Brasso and toothpaste soon had them nicely settled again...

 

Keep posting please, Slotbaker.... I'm new to almost all of this scratch-building stuff.. but, am picking things up as I go into each build.

 

frats,

Rosco

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OK, cool.

But - is it just co-incidence or "that's always the way we've done it" that this is done with most models I have - including those from the 70's...

all of mine - the crown is in the rhs.... and none of them have offset...

Not sure about how they ended up on rh side. Maybe the ready to run cars (Scaley etc) were supplied that way??

The thinking back in the good old days was to run the gears as designed to get the best possible mesh, also cost of std gears were cheaper than hypoid ones which were available as after market bits. A company named 'Tradeship' were one that sold brass hypoid bevel gears, which performed beautifully when set up right.

In the late 60's/early70's, the angle winder revolutionised the pro slot car scene, and effectively through the old thinking of perfect alignment out the door.

 

... bedding in with Brasso and toothpaste soon had them nicely settled again...

You could also try graphite powder (from locksmiths) on metal gears, once the clearance/backlash is adjusted correctly.

Edited by slotbaker

Steve K.

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Hmmmm. This is a personal preference type of thing.

My rule of thumb is to adjust the clearance between the pinion and crown (or spur) gear so that you can feel the clearance but can't readily see it.

 

That is, make the clearance so small that you can still feel a bit of clearance between the teeth when you rock the axle back and forth, but it is difficult to see the movement.

 

This method is reasonable easy to do with gears that are held in place with grub screws, and very difficult to do with pressed on gears.

 

Pretty hard to describe and understand, but if you have a go at adjusting the gears, it should be more easily understood. I think!! :huh:

 

As the pinion and gear wears, the clearance should be checked each time you use the car and adjusted as required, and a drop of oil doesn't go astray either.


Steve K.

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