Mercedes W125. Or is it just a gearbox.....

[Peter Seager-Thomas]

For a couple of years now I have been thinking about some sort of double reduction gearbox. The reasons are two-fold.

Most cars I build are those with somewhat large wheels, and all ratios available I feel are unsuitable, with acceleration suffering, and braking even more so. The problem is compounded when the slimline motors are used.

I did wonder if Andi's Policar parts might do the job, but the availability of suitable gears for the axle (at a suitable price) knocked that idea on the the head. So, here's my own set up.



Bearing in mind that the total ratio of this particular drive is about 4.7:1, then the 30K motor used should do the job well.

The 9T primary pinion was found on the work-table, the 22T crown comes from All Slot.

The 14T secondary pinion and the 27T axle gear come from Mr Slot Car. The 14T pinion was a standard part to fit a 2mm shaft. It was drilled out to 5/32" and a stepped boss made and fitted to permit a more easily dis-assembled part.

A side benefit is that any offset likely to be needed is possible. The assembly shown is offset 2mm between motor shaft and axle.




Possible ratios very between 4.2:1 and 6.5:1. Improvements planned include mounting the shafts in ball bearings and perhaps a fully enclosed casing.

This prototype will almost certainly go into one of George's excellent Mercedes W125 cars; it is no coincidence that it will be a Swiss GP car, which ran with the larger rear wheels.

#2 gearbox is already started and will use a slimline motor. That, however, will be another thread.

Peter.

[Andrew Rowland]

Lovely Peter.
Andi

[Peter Seager-Thomas]

Well, it looks like it will be a W125, a GTM car I have not built before, and it will still be the 1937 Swiss GP winner driven by Rudi Caracciola.



The Bremgarten venue was one of the faster circuits, with larger rear wheels fitted by those teams which had them.

With the guinea pig car decided it was time to integrate the drive to the car, and this is pretty much it.



Quite a tight fit as made, the #2 drive will be made a little smaller.



The moderate weather in the near future should permit further progress. More in due course....

Peter.

[Mark Huber]

That looks brilliant.

[Peter Seager-Thomas]

In these days of 'home activities' I seem to be making more progress than usual.

The W125 chassis is almost done, but will possibly be re-made in the future. It all depends how it works. The front end springing may be a little hard.



The drive leaves a fair bit of cockpit space for most of a driver, though the use of a Flat 6 or a slimline powered drive would allow a lower gear train.....



The weather is not good enough for paint (though there is a little filling needed) and the club is closed so I can't test it! That's why another thread is being re-started....

Peter.

[richardh]

Peter
That is an awesome idea for a gearbox - those ratios are always an issue with the big tires.  Look forward to seeing more.

Richard

[dangermouse]

"the total ratio of this particular drive is about 4.7:1, then the 30K motor used should do the job well"

I don't run anything faster than a 16k motor in any of my Grand Prix cars - mostly I stick to NC-1 or an equivalent. In fact I don't run anything much over 25k in any of my cars. I am looking at that motor and it looks like an MRRC 30k motor - I had one in my MRRC Toyota Grp 5 and swapped it out for
a 20k motor because it was pretty much underivable with that motor.

I am curious and a little short on knowledge. How do you make a GP car with big wheels handle with a 30k motor?

Does the gearing help. My usual gearing is 3:1 sometimes a little higher and sometimes lower - eg a 24/9 or a 34/11 pinion may be used but when I am building cars I usually stick to a 3:1 - (whether that be 24/8 for 27/9) mainly because that is what most RTR cars have and the club I race with tends to prefer we stick to stock ratios. On some of my bigger 1/24 cars the gearing is lower - 41/11 and 50/10???

My understanding is if you gear a car say 27/11 it will be slower to accelerate but have a higher top end and if you go the other way say 33/9 it will accelerate quicker but be slower top end.

If there is an article or reference site I could read I would appreciate any information.

Don't mean to hijack your thread...

thanks
David

[Peter Seager-Thomas]

David.

Your comment 'My understanding is if you gear a car say 27/11 it will be slower to accelerate but have a higher top end and if you go the other way say 33/9 it will accelerate quicker but be slower top end. ' is of course spot on.

With the higher speed motor there will not be a slower top end. With the higher gearing ratio the theory is that I will benefit from good acceleration and a reasonable top speed, not to mention improved braking.

The latter to me is important as I have some narrow cars to build which will require slimline motors where from my point of view, braking is non existent.

Peter.

[dangermouse]

Thanks Peter

I will give it a try on a car

Agree with you on the brakes (or lack there off) when using FF050 motors.

Is your car twitchy in the corners with a 30k motor?

cheers
David

[Peter Seager-Thomas]

David, I cannot yet tell how the Mercedes behaves on the track as my 'test' track at home is about 7' in length.

The club at which I race has a Scalextric Sport track, mainly due to space issues regarding both track size and storage of track when dismantled. it is a mixture of a couple of long straights, a couple of fast sweeping curves, and a couple of hairpins. Thus the need for a car with all 3 attributes, (moderately) high speeds, good acceleration and good braking.

A regular 30K powered car is a handful, 25K is better, 20-22.5K is best. I do have 2 cars for which full throttle can be held on the longest straight. These cars have slow Mabuchi motors, do not accelerate and have zero brakes.

The aim is to try and make a car which has all 3 desirable attributes, plus of course ease of handling.

Doing such things is also good fun. The slimline double reduction sidewinder is getting closer!

Peter.