Category:Motors

Inside the Meccano No.1 reversing motor

The motor casing is a pair of sturdy metal plates with Meccano holes around the edges, held apart by four spacers. There's a square winding key post on one side, and the output shaft is a Meccano rod threaded though a Meccano pinion that can be removed or adjusted so that the rod (or another, longer rod) can protrude from the winding side, the opposite side, or from both.

Behind the winding post is a large coiled flat strip spring, and behind that is a large gearwheel fitted with a slip ratchet arrangement so that the winding shaft can only wind in one direction.

This large gear (#1) drives a much smaller gear (#2, which has to rotate much faster to keep up. On the same shaft as #2 is a mid-sized gear (3), which engages with either one or two smaller gears depending on the reverse switch position, after which there's a small pinion which can be removed or replaced, and which is mounted on the final (removable, replaceable) output drive shaft.

Because of the multiple gearing stages, the output shaft runs much more quickly than the large gear attached to the unwinding spring, but is also considerably weaker.

Regulator and brake

Gear #2 also engages with another small gear on a shaft with a larger gear which then drives another small gear, giving another two boosts in rotation speed on the final shaft, which rotates very fast. This other output shaft is purely for control, and has two functions:

1. Because of the extra gearings, the force available on this final high-speed shaft is extremely weak, and it can be stopped rotating with a tiny amount of friction. The brake lever applies the necessary friction, so that the motor can be stalled with a very light touch.
2. The shaft is also fitted with a centrifugal regulator - The shaft has a hole drilled through it that takes an arm, holding a small brass weight on one side and a retention spring on the other. As this arrangement spins at high speed, there will be a critical speed at which the brass weight is thrown outwards by centrifugal forces enough to compress the spring on the other side, so that the weight extends and grazes the sides of a circular metal wall that is welded to the back of the upper plate housing, encircling the regulator. At this speed, the tine amount of friction (given the gearing) is enough to brake the motor until the speed reduces to a value at which the weight is barely touching the circular wall.

If the motor is designed to run naturally at a speed that makes the regulator cut in, then it'll run at a fairly constant speed no matter how tightly its spring is wound.