Hi Chris

I would connect the drive to the 28T gear, the 12T gear on the same shaft would then drive the 37T gear on the wheel axle.

The simple way to work out gear reduction is to divide the number of teeth on one gear by the number of teeth on the second gear then multiply the gear ratios together. Obviously the drive gear needs to be smaller than the driven gear to increase the ratio. In this instance it would be...

28/1 (worm and first gear) = 28:1 (assuming the worm is a single start)

37/12 (second gear and wheel axle gear) = 3.03 (lets say 3:1)

Therefore the overall reduction would be 28x3=84:1 (84 revolutions of the motor shaft to 1 revolution of the wheel)

Which is a quite impressive ratio! You have to bear in mind the centres of the gears though, the radius of the gears cannot be greater than the distance between the gears including the ###### (if you are using one).

I hope that makes sense and more importantly helps and I am sure if I am wrong someone will say something!

Missy

Ah, the ##### word is the black plastic tube that holds the wheels together that the 2mm SA use!!!

Agreed with the general layout suggested by Julia.

I'm slightly sceptical of the 37:12 reduction on the second stage, on several grounds, so I would suggest you double check the following:

1) 2mm Association Yearbook gives 9.91 mm as the outside diameter of the 37 tooth gear if it is 100dp. Will that clear the rails at a crossover? (What diameter wheels are you using?)

2) No entry in the Yearbook for a corresponding 12 tooth gear - there's a 13 tooth on 64 dp, otherwise the smallest is 14 tooth on 100 dp, and both the metric ranges.

3) More generally, your 12 tooth gear will have a diameter of about 1/3 of the 37 tooth gear. I'm not convinced you can simultaneously fit the larger one inside the diameter of the driving wheel and the smaller one over the usual 3mm "sleeve" (to avoid the censor's wrath). Perhaps you are using another source for the gears, but the same general dimensional restrictions apply.

I would have expected 34 and 14 teeth to be the best you could manage, which still gives a pretty impressive overall reduction of 28:1 first stage and about 2.5:1 second stage, so about 70:1 overall.

David

Ah, the ##### word is the black plastic tube that holds the wheels together that the 2mm SA use!!!

Do you mean the drive gear ###### (3-100 Black acetal axle ###### for Drivers (3.2mm dia)) ?

Chris, looking at the gears you have listed, I'm a bit concerned - are these from the Association shop? My concern is the the 28T (3-354?) spur gear you're referring to is not intended to be used with a worm, something to do with the cutting of the teeth on an angle; the gears for using with worms are 3-364, -365, & -366 (or the dedicated gear-sets).

I'm no expert on this (and may be barking up the wrong tree!) but I've just been going through a similar exercise a 57XX pannier and like you found the 'gearing' to be very confusing. If you have more details - ie planned layout, motor type and speed, desired top speed of the model, there are some quite useful articles on the VAG on calculating the necessary gear ratios and the spacing between centres.

Chris,

The gear that will mesh with your worm needs to have skew cut teeth, ie. the teeth aren't at right angles to the edge of the gear, but at a slight angle. That will limit the choice of this gear to one of the 3 worm wheels shown in the 2mm shop listings (3-364 to 3-366). The other gears can be any of the range of spur gears.

Could you post a sketch of what you've got with a few more details?

Andy

Are you sure the 38:1 and 14/28 tooth gears would work Don? Drawing it up in CAD I think that 38 tooth helical gear would foul the m*ff carrying the 14 tooth gear.

Pix

Thats how it gave its name to our thingy.

I never saw a furry one of our thingies though

To add something to the discussion:

I would use the 64dp (or M0.3) gears for a first attempt. They are more forgiving. a 30:1 worm and something like 14T/18T is what I have in at least one of my pannier tanks. Don't, whatever you do, use two of the same gears together. It is impossible to work out whether a tight spot is in the gearing or the wheels/coupling rods if you do. I started a 2-6-2T with an 18T/18T gear pair and cannot find the fault. This is possibly a more valid reason not to use gears that are multiples i.e. (14T/28T) but I can't think why right now. I guess my brain is having the day off.

The alternative layout where the spur gears are first has the problem of how to mount the layshaft which would then run parallel to the frames. Although it has been used in tender drives where it can have the added benefit of lowering the cardan shaft.

There is, somewhere on the archive cd (sorry dvd, mine's an old school 1st edition), an article by the late Pete Wright about making what he described as a cannon gearbox, where the spur gears come first. Iirc it was in the magazine around the time I joined, so look around 2003.

perhaps thats why the gear mesh calculator suggested the 14t was 15t.

The 14T gear might be pitch adjusted so that the diameter is large enough for it to have a hole large enough to fit over the not furry item with the same name as a lady hand warmer without the material getting thin. If so it has to be considered as a 15T gear for centre distance calculations because it has an enlarged diameter (equivalent to a 15T gear).