Junior Gears

We temporarily missed the target audience when designing Gear with Me - in the creative frenzy we slightly forgot that The Toddler is (at the time of writing) only two years old. Sure, that won't last, but for now it is probably not quite suitable - The Mother might have reservations about small pieces, sharp edges, and overall complexity, and she may have a point.

A gentler introduction seemed to be needed - this led to Junior Gears, presented here for your enjoyment, and for the benefit of all toddlers in your immediate vicinity. With chunky rounded gear teeth instead of involutes, and using the side of the bath (or any other smooth surface) as a freeform playing field, these gears can serve as an introduction to mechanics, unsubtly indoctrinating the pliable young mind by making learning fun.

The Toddler enthusiastically volunteered, nay, insisted to act as our beta-tester, with valuable feedback obtained from observational studies conducted mainly during bath-time.

For now we limited the gears to only five sizes, with tooth-counts from 6 up to 10. Each gear is fixed to and with a rubber suction cup sporting an M6 bolt, bought at your favourite Eastern bazaar. 

The design is specifically dimensioned for these suckers - if you search for something like ‘M6 Screw Rubber Suction Cups 3.5cm’ you will probably find it. Or you could use Visual Search using the above images. Get ten or more of these, as well as at least 5 stainless steel M6 x 20mm bolts.

Unlike snakes, gears in a single plane soon pall, so we also have vertical versions; each size of gear can be mounted on its corresponding post (itself on a suction cup), to rise out of the plane of play. These vertical gears can be positioned to mesh with the plane gears, and also with themselves, not only at right angles, but at many weird and wonderful inclinations, thanks to the rounded teeth which permit a multitude of misalignments.

The standard gears are mounted on the M6 bolt in the suction cup, between two washers, and finally topped off with a blind nut. This nut should be hard to turn - you can even use a pair of pliers, if needed. If it turns too easily, it will work itself loose sooner or later, so either apply a drop of glue, or reprint it a smidgen smaller and try again. Tighten it until the gear still has a small amount of play left on the axle - it should spin freely when flicked with a finger (the gear, that is). I printed the washers simply because I did not have a stock of stainless steel M6 x 16 washers at hand, and stainless steel only tends to come in one boring colour. Even if you cannot see the top washer, below the nut, I still know it is there, and brightly coloured to boot.

The vertical (post-mounted) gears are slightly trickier. For this you need an M6 x 20mm stainless steel bolt - preferably with an Allen head (i.e. round on the outside, not hexagonal). Any of the types shown below should work. Get as many as you want vertical gears, i.e. probably at least 5, there being five sizes of gear.

Screw the bolt through the transverse hole in the post. It too should be tight, but if the going is really too tough you can run a suitable drill bit (say 5.7mm in diameter) through the hole before installing the bolt. There is no thread - you cut it yourself while screwing in the bolt. Then the gear, which should match the number on top of the post, is mounted on this bolt in the same way as the flat gears: washer, gear, washer, nut. And again the nut is tightened until the gear is only just free to spin. Because the gears have different diameters, they each need their own post length, to ensure that the gear ends up at the correct height to facilitate meshing with flat gears.

The hard part is mounting the post on its suction cup. It should be screwed down tightly, but it is hard to get a grip on the bolt in the suction cup. Use pliers, use glue, use violence, use ingenuity, do what you have to do to ensure that it cannot easily turn when the post is grabbed and manhandled while the suction cup is stuck to the side of the bath, or perhaps a window.

For playing with water we also have a reservoir, which can be filled up with a suitable beaker or jug, preferably made of plastic if it is going to be used in the bath by tiny tots. This reservoir generates a stream of water which can be used to spin gears - any of the vertical gears should work as a turbine, but you will also find two gears (a #8 and a #10) with extra vanes to help, if desired. These work well when mounted flat, with the water stream directed at the vanes. If you want to use a water-driven gear to drive another gear, or perhaps more than one, the latter should be positioned carefully to ensure minimal mechanical losses. The turbine is not especially powerful, although you can of course increase the torque by letting the water fall from a greater height, thereby sneakily introducing the concept of potential energy, and its conversion to kinetic energy. The reservoir is mounted on two suction cups - I cleaned out the holes in its side with a 5.7mm drill bit before screwing in the bolts, for they, too, should be firmly fixed. Or use a drop of superglue to simplify your life.

The teetertotter has its own nut, with two arms that act as stoppers. Assemble like the gears, by sandwiching it between two washers on the bolt, and then screwing in the TTnut instead of a normal nut, again stopping while the mechanism still has some play allowing it to move freely. The Toddler still needs assistance with this one: it has to be positioned with the nut pointing upwards as in the picture (with its two arms stretching down at equal angles). When tilting from side to side the top edge of the moving part should end up horizontally each time. And the entire mechanism should be centered directly in the water stream, i.e. with the jet aimed at the axle. This may take some experimentation and frustration to get right, so perhaps you should leave this part out at the beginning, until you and your victims are more comfortable with the others.

Printing

Printed in PLA at 15% infill, with variable layer height - but 0.2mm should do too, if you prefer to keep it simple. PETG should also be perfectly fine.

The only places where supports are needed are on the inside of the teetertotter, and in the transverse holes of the posts. For your convenience everything is set up and prepared as described, in the file named JuniorGears.3mf. 

The intent is not to print all of it in one go as presented (for then you will probably have everything in just one boring colour). Instead enable the components selectively - as it is you will probably want to print at least two sets of Gears #6 through #10 (for flat and post mounting), perhaps even more, and you will need as many nuts as gears, and twice as many washers.