Decimal Counter

The example described here operates as does the odometer in a car. The right most dial indicates tenths of a rotation of the input shaft and turns continuously with the input. The remaining dials move in discrete steps whenever the dial to the right changes from 9 to 0 (or vice versa). The counter can fairly easily be preset to any value by manually turning the dials and it can count up or down. While this example has a total of five dials, and so can count to 9999.9 there is no reason in principle this range cannot be increased (though beyond some point there will be too much load presented to the input when all the dials have to change simultaneously), and of course it can easily be reduced.

The key observation, which makes this compact design possible, is that a 95t gear can be meshed directly with a 57t gear to provide a ratio of 5:3. This means that one tenth of a revolution of the 95t gear corresponds to one sixth of a revolution of the 57t gear, so that we can hold the 95t gear in on of ten discrete positions by instead holding the 57t gear in one of six discrete positions. This is easily accomplished using a six hole wheel disc with six double brackets bolted to it.  A diametrically opposite pair of these is then bolted to the 57t gear (boss in, with washers as spacers to prevent teeth fouling on the lugs of the double brackets). It is important the assembly runs freely on a rod. A roller consisting of a 1” pulley with rubber ring mounted on a pivot bolt in the end hole of a crank provides the detent, light pressure being applied by a tension spring (be sure to pick cranks with the tapped bore at right angles to the arm of the crank). Four of these assemblies are needed for a 5 digit counter.

PARTS REQUIRED: