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Al Schwartz
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Discussion Starter · #1 ·
"Once upon a time" (actually, not all that long ago) while wandering through the dark forests of eBay, I came upon an offering for "hypoid gears". Not having seen such wonders in the realm of model parts, I though to myself "Some fool has misspoken, he thinks that "hypoid" and "bevel" are the same". Still in all, the asking was a mere pittance and my stocks of bevels were meager. I offered and won and shortly thereafter, several bags of golden hued parts were in my hands. With wonderment, I realized on inspection that they were, indeed, hypoid gears and by careful restoration and translation of the ancient runes, I discerned an ordained offset of 0.125".

I don't know what the offset of the new Slot-It gears are but 0.125" is a signifficant lowering of the heavy bits and I was anxious to try them. Of course, first we do the numbers: A typical can motor is 0.6" high /2 = 0.30". We drop this 0.125" below the axle center and the bottom of the motor is 0.425" below the center. A typical ground clearance requirement will be between 0.0625" (1/16") and 0.0787" (2mm). Adding those numbers to the motor bottom number, we get 0.4875 - 0.5037 as the tire radius or 0.975 - 1.0074 as the required rear tire sizes. Pretty much pre-war and a few immediate post war GP cars -I hardly know anyone who likes to model those!

I have one or two Benz's and a pair of Alfas - but no Auto Unions. What I do have is a pair of kits - one Matchbox, one Revell D type AU - appear to be the same, I don't know which is the chicken and which the egg. So the design process here is a bit backwards. Instead of deciding a prototype and a motor and then finding gearing to suit, the gears dictated the era and a range of protoypes.

My initial thought was to use a Pittman motor- sort of "emotionally" suitable to the gears and the car but while pushing parts around on the bench, I realized that, if I shaved the rear axle assembly to minimum length, an FK series motor (eg TSRF, Fox etc) would fit completely in the rear compartment, allowing a full cockpit.

This choice raises an issue: the gears are clearly 60's 1/24 stuff - the axle gear has a 0.125" bore and the pinion is 3/32". Some time ago, I came across an outfit specializing in "repowering" parts for model trains:

A-Line

They make neat little brass bushes that are 3/32" OD, 2 mm ID.

The rear axle carrier had to be made - the gears are too wide to fit the pre-made ones (e.g. BWA) that I had in hand. After taking a chunk of brass and cutting away anything that was not shaped like an axle carrier, I mounted the motor and gears for run-in:



As it turned out, hours of run in! When I first mounted the gears, I was convinced that I had gotten the measurements wrong or mounted the gears backwards. Turning them was like rubbing rough stones together. They are not really an example of precision gear cutting. After several hours of low speed running with regular applications of tooth paste, things began to smooth out. The current draw seemed well enough under control to let them run overnight. by morning, I had a very smooth gearset.

I added a little "parcel shelf" to provide a rear body mount and to make sure that the bracket didn't flex:



Still needs to be cleaned up:



The rest of the chassis is straightforward: 0.047" music wire, bent into a "U" supports the forward section with the guide pivot and the front suspension is a short pivot swing arm soldered to this forward plate (0.0625" brass):



The motor/axle offset is obvious in this shot.

To be continued......

EM
 

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1,133 Posts
I'll be interested to see how this comes out Ecurie - I have an Auto Union waiting to be "slotted" sitting downstairs!
 

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4,593 Posts
Excellent, EM! I'll drink to this one!
As a hoary old slotter with a hazy memory of the golden days, I seem to remember using MRRC hypoids- could these be they? Very useful, but as you say, needing a LOT of running in. I'm sure the guys with the complete collections of 'Model Cars' could find the details. Probably 2/6d a set or something. 12 1/2p in new money.
Ahh... in those days a man could get absolutely blasted on a quid and still get donked with a rolling pin when he got home.
 

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Gary Skipp
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6,476 Posts
I was thinking only the other day about use of bevel gears for inline cars. May have the terminology wrong as you pointed out something to do with hypoid, but anyway. Same principle no?


Those tyres are nice, are they readily available or storred from days gone?
 

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Premium Member
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2,143 Posts
While at the London Model Engineers Exhibition last weekend i came across a trade stand which sold mainly model steam components, among his many parts on display were 3:1 and 4:1 brass bevel gear sets which looked remarkably like MRRC gears!
The guy at the stand told me that he had these made recently and after having a close look i discovered that the 10 tooth pinion had a 2mm bore rather than the usual 3/32" bore, apart from this the gears seemed identical.
The gear sets are not cheap at £9.95 [original MRRC sets are still quite easy to find at a reasonable price] but i bought a 4:1 set to try as having a 2mm bore allows them to be used with can motors. This dealer also has worm drive sets with 3/32" gear bore and 2mm worm gear but the smallest i found was 20:1! might still be useful when building a rail car replica though.
These gears are available from "Tony Green Steam Models" Tel 01522 681989
[oneofwos]
 

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Al Schwartz
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3,390 Posts
Discussion Starter · #6 ·
QUOTE (JOHN SECCHI @ 27 Jan 2006, 23:41)While at the London Model Engineers Exhibition last weekend i came across a trade stand which sold mainly model steam components, among his many parts on display were 3:1 and 4:1 brass bevel gear sets which looked remarkably like MRRC gears!

<{POST_SNAPBACK}>

Funny coincidence - Last Sunday I spent a few hours at the "Cabin Fever" show in York, PA. This show was devoted to model engineering with a great assortment of machine tools, model engines - both steam and IC, radio controlled steam boats (on an indoor pond) live steam locomotives etc. While not nearly so grand as what I imagine the London show to be, it was facinating nontheless. I came away with a few photos - thought this one might be of passing interest here:



It is a 270 cu. in. Offenhauser. the model is about 12" long and is complete with a working magneto, 4 fuel injectors and two oil pumps, pressure and scavenge for the dry sump system. The owner and builder starts it in true prototype fashion with an electric drill chucking a long rod with a coupling on the front of the crankshaft.

Well, back to the project;

The front suspension presented an interesting problem. The kit includes a full chassis, suspension and engine. I built this in parallel with the model thinking that it would be a useful reference for postioning the suspension bits. When the chassis was offered up to the body it was clear that the center of the front wheels was actually forward of the opening in the bodywork (the suspension is via trailing arms which emerge from small openings further forward. the large open section accomodates the shock absorber arms and steering linkage (and, I am guessing, ouflow from the radiator) I didn't want to enlarge the opening, thinking of someday modelling the trailing arms emerging from the body and was also faced with restricted space for the guide post. the lower part of the body narrows abruptly just behind the opening precluding the use of a long quasi isofulcrum pivot like the one I used on the Talbot Lago so I decided to use a narrow based, short pivot assembly. I ended up making something like this:



(apologies for the poor focus - I don't know what the camera thought it was focusing on and I find the LCD on my digicam useless for close focusing - one of these days a DSLR) A piece of 1/16" music wire was bent up (with the two short pieces of 3/32" tubing already on it and a length of 3/32" music wire brazed across the ends - real silver solder done with a butane torch - and then the center bit cut out at the "X" on one side and the corresponding location on the other. (This is not a photo of the part finally used - it is first of 4 tries to get the shape and length right!)

The guide is a TSRF guide modified per Al Penrose by cutting off the post and repositoning it at the front with a piece of 0.049" wire down the center.

With this done, we were ready for a first trial fit of the body and initial testing:



As you can see, the motor fits neatly in the rear - that is one of the advantages of the FK form. a second advantage became apparent as the testing proceeded. I had simple grabbed whatever came first from the motor bin so we went to the track fitted with Patto's "Little Ripper" - well, it certainly was an Auto Union - smoking tires halfway down the straight and a real need for delicacy in the corners. Still in all, the lap times were respectable and the tail out cornering was predictable and very much in the spirit of the era. The second advantage of this form factor motoris that there is a range of motors, externally the same, with a broad range of power. I went through several, including the TSRF, one of the Ninco and finally ended up with this one:

Cheap Motor

Which has been extensively discussed on another thread on this forum. Not quite as quick as the Ripper but much more controllable. I think faced with a 20' to 30' straight, the Ripper would win but I don't run on many of those. (OF course, I still have those motors and it is a matter of two capscrews and about ten minutes to swap them out)

Part of the limitation here is, of course, the amount of rubber. The model is fitted with a mix of BWA and Patto's wheels. There are two alternate sets of rear wheels/tires. One set is made from cut-down BWA LMP (18" scale) wheels narrowed and a recess cut to mount EJ's # 15 tires and the alternative is Patto 1807/15 wheels with Ortmanns. All are fitted with BWA 1/24 resin WW inserts and Ninco knock-offs:



These are the BWA/EJ combination. I must confess that I am pleased with the over-all impression. This application illustrates for me the unresolved choice between resin inserts and photo etched wires. the latter are certainly closer to scale in spoke width and are clearly "metal" but they do not offer the three dimensional feel that the resin repros due with their ability to model the axial cross-over of the prototype.

Well, we're getting closer now - motor decision made and the "chariot racing" overlength axles cut to length and the wheels mounted:



In this shot, the chassis is wearing Patto/Ortmann wheels & tires at the rear and Patto/EJ at the front. The front wheels started as 5-40 threaded wheels, bore to 1/8" and sleeved with 3/32" ID aluminum which rides directly on the 3/32" axle stubs and are retained by soldered on washers behind the wheel inserts. (I fit my inserts with little dabs of silicon adhesive - seems to keep them in place but allow for prying out if needed)

Enough lecturing! What does it look like?









The body was primed with Tamiya rattle can primer (lacquer based from the odor) and given 3 coats of Alclad flat aluminum followed by the usual "Future" acrylic under and over the decals. The exhaust pipes are 1/16" styrene rod painted with Alclad Jet Exhaust. The wheels were painted with Alclad Steel and followed with a light overspray of Alclad semi-matte Aluminum. The driver figure is from Airfix military miniatures (better than I've done in the past but still a long way to go - I ascribe his position to the fact that the weather is threatening and he is trying to decide if a partiuclary nasty cloud calls for a pit stop for rain tires) I also should have used a bit of Milliput to convert his open shirt to a turtle-neck.

Well, there we are - suddenly it's MCMXXXVII :



Avanti!

EM
 

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Alan Tadd
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4,030 Posts
Fabulous Alan.....Magnificent car.

I'm just fnishing off my Talbot for the Early Birds event, so when it is finished I'll show you some alternative wheel/tyre combinations you might be interested in. Not easy is it?

Regards

Alan
 

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Graham Windle
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4,442 Posts
Great stuff Al that motor works so well in stuff like this ,But Im led to believe stocks are now depleted hopefully theyll get some more soon.
 

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Al Schwartz
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3,390 Posts
Discussion Starter · #12 ·
Gentlemen:

Thank you for your very kind comments - and I thank the forum as a whole for the inspiration to keep on trying!

Russell: - I think, in all honesty, that it is good but not fabulous - This is fabulous:



and was, of course, the inspiration for the second car in the last photo - still running very well on a genuine "Sheldon" chassis!

Alan: I shall be very interested in your results. I am, I guess a (well recognized) wheel "nut" - always pushing the envelope on this old stuff.

I'll be watching for the motors, Graham. In the meant time, I probably have a few more than I need so if anyone is in straits, let me know.

Yes, John, it's a wonder he could see where he was going!



I read somewhere that the straps on the engine cover were required by the British scrutineers at Donnington - something to add at some point. I'm going to guess that they were brown leather - I don't believe that any color photos exist.

The "Sratch Building" section is always my first stop on the forum - I learn something on almost every visit.

Well, one more down, only 2716 to go!

EM
 
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Really great looking Auto Union EM, I have always loved the look of these cars.

EM's Talbot will be going in the museum display on the 12/3.

Jeff.
 
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