This idea is for a toy which is deliberately designed to look like the motor should just spin without moving the car forward... but in fact, the toy moves quite well, even on carpet.

The toy has eight wheels, four top and four bottom, and can work either side up. None of the wheels is directly motor-driven, instead each wheel merely has a ratchet and pawl (or perhaps a sprag clutch), so it can spin forwards but not backwards.

There are four parallelogram shaped linkages, two top and two bottom, each linkage having two long segments, going across the toy, and two short segments, parallel to the sides of the toy.

Each short segment holds one wheel. Each long segment's midpoint is attached to the chassis with a pivot. A spring or rubber band pulls each linkage towards it's "neutral" position, so that the wheels are less likely to hit the sides of the chassis.

The two front linkages and the two rear linkages are mirror images of one another, so I'll only describe the front.

The front top and front bottom linkages are attached to one another via a differential gear and a reversing gear. When the middle of the differential is turned, the two linkages move from being parallel to one another, to forming an "X" shape.

(The reversing gear could be omitted, which would make the toy simpler, but it would vibrate more, since turning the differential would arrange the two linkages into a "/" or "\" instead of an "X".)

The differential is not turned by a gear or a pulley, but rather by a crank or lever.

Each of the toy's two levers are pushed and pulled by connecting rods. The two connecting rods are attached to the cranks of a single crankshaft. One end of the crankshaft goes to the motor, the other protrudes from the toy, and has a manually turn-able crank for playing with.

The two cranks that hold the connecting rods should be at an angle to each other, so that when one lever is at the forward-most or rear-most position, the other will be at it's midpoint. Similarly, when the two front linkages form an "X", the two rear linkages will be parallel to each other, and vice versa.

When the toy is placed on a surface, and the hand-crank is slowly turned, the bottom linkages won't move, but the top ones will.

Children's logic might suggest that turning on the battery powered motor will accomplish nothing but make the top bits move faster...

In fact, as the top parts speed up, the bottom parts come to life too!

The faster the top parts go, the more strongly the bottom linkages twist.

And since the bottom linkages have ratcheting wheels on them, the whole toy will move forwards.

Why does it work? It's a mystery!

I know why it works, and you, reading this, also might, but what age child could identify the forces of physics responsible?

If advertising jingle is needed, "The Marvelous Toy" comes to mind.
-- goldbb, Apr 23 2015

A diagram would be awesome.
-- RayfordSteele, Apr 24 2015


sounds more like a desk top toy than something a child would like.
-- dentworth, Apr 24 2015


I too would relish a diagram. Because it sounds like this might be makeable with Lego Mindstorm or a similar build kit.
-- bungston, Apr 24 2015


must... have... visual...
...hgn
-- 2 fries shy of a happy meal, Apr 24 2015


It's definitely LEGO-able, though the only fancy bits are a motor and two differentials, so one or two Lego Technic kits would suffice. Since no computer is necessary, a Lego Mindstorms kit is seriously overkill (though they do come with powerful motors).

If you don't mind *building* the differentials, you could probably do it with *one* Lego Technic kit, so long as it's got a motor and enough gears. Since the differentials are merely oscillated by a lever, and NOT rotated continuously, you'll merely need three gears for each one, and a "box" built of beams.

As for a diagram... my drawing-fu is too weak.
-- goldbb, Apr 24 2015


Then build it, and post video! Best of all!
-- bungston, Apr 24 2015


So a centrifugal governor from the twistability of the bottom linkages? The twist would indicate the use of the 'goldbb' Lego part. Lego is all slide, and rotate, no twist.
-- wjt, Apr 25 2015


wjt, by "twist," I meant "rotate in an oscillating manner." Actual twisting of individual Lego pieces is usually a bad idea.

bungston, A decade and some odd years ago, when I moved out of my parents home, I felt I should give away my childish things, including my Legos. Now I'm a man, and am not afraid of childishness, but it wouldn't be right to go and ask for my Legos back!

I *am* looking on ebay, though, to see if I can find a set with enough pieces to build this, that won't blow my budget.

Also, I'm in a *tiny* apartment, so I don't want to buy huge quantities of legos... storage is an issue.

If I do build it, don't expect video though, since my venerable cell phone only takes still photos.
-- goldbb, Apr 27 2015


I've been thinking about how to build it while buying just a single (reasonably priced) set, and while I haven't managed that I've thought of a slightly simpler linkage than a crankshaft and conventional differential.

Instead of a crankshaft, we have what's known as rhombic drive. Two gears are one above another, intermeshed. The motor will drive one of those gears. Onto those two gears, we attach two opposite pivots of a four arm linkage, with equal length arms.

Instead of a rotating differential, we can have a linear one.

On each of the front and rear pivots of the rhombus, we attach a free-spinning gear. Above each of these gears, place a toothed rack, teeth downward. Below each of these gears, place a toothed rack, teeth upwards.

As either gear moves forwards, it applies equal linear forwards force to the two racks it's sandwiched between... but, since the gear can turn, the racks don't have to move at the same speed as one another.

Attach each rack to one of the assemblies holding the wheels.
-- goldbb, May 02 2015



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