Monday, 28 April 2014

Rack and pinions...

The current 7-model Multiset
A week or so ago, our friend and fellow Meccano nut, Subrata, from Sikkim, India, posted a picture of a working spring balance on the Spanner II list. It was built from parts taken from the current 7 - model, Multimodel set. Subrata was following on from my post of the 16th April regarding making small models from larger sets. The original post is HERE.

Subrata's spring balance
The weight of an object placed on the tray will compress the spring and cause the rack to be pushed downwards. This will rotate the pinion mounted on the rod (journaled in the grey bracket) that carries the indicator mini strip at one end. Subrata has used the rack and pinion, from the 7-model set, to covert linier motion into rotary motion, the reverse of how it is normally used in Meccano sets.

The plastic rack (P/N A343) was introduced to the system in 1998.  Since then it has been used in various sets and it is normally employed as the 'rack'  in a rack and pinion steering system.  Using the part described as 'Steering Wheel Mounting Bracket' (P/N A425) as a bearing it can be paired up with a 12t pinion to make a self contained rack and pinion mechanism most commonly used in Meccano to facilitate steering. Subrata has used these parts as the basis of his spring balance model.

Using the steering wheel bracket to support the 12t pinion and rack
The rack has 18 teeth and when meshed with a 12t pinion, one revolution of the pinion will transverse the majority of the rack leaving a few teeth spare either end. this rate of gearing works fine with most models where the idea to replicate some sort of rack and pinion steering. To generate a greater movement of the rack, meshing it with a 24t pinion would then mean the rack can be transverse to the same extent as when using a 12t pinion, with only half a revolution of the rod supporting the 24t pinion.

The new bracket allows the 24t pinion to be used with the rack
To achieve  this another bracket is required, and along it came in the Evolution ATV set. This new bracket (P/N C920) has longer lugs with extra hole holes spaced in order to facilitate the 24t pinion at the correct spacing for meshing with the rack.  Using this set up in the ATV gives a much better steering response to the handlebars than if the lower-geard 12t set up had been used.

More and more parts are emerging from these new sets and combining these with the existing range of parts available opens up a wealth of new possibilities.


1 comment:

  1. Very informative article, Ralph. Thanks for including my spring-balance's photo.

    With Best Regards,

    Subrata, Sikkim, India