Cartwright’s Straight Line Mechanism

This model comes courtesy of Dick Watson of the North West Meccano Guild, and has been rebuilt by myself with modifications, as I do not have some of the parts he used in stock.

The model is of Cartwright’s Straight Line Mechanism for converting the reciprocating motion of a piston rod into rotary motion to drive a machine. The Meccano Magazine in January 1931 ran an article about this mechanism and used illustrations of the original (see the third photo). The Science Museum website has further information and a model using this mechanism.

The construction of my model uses some Meccano-compatible parts, notably the gears, which are Stokys 2:1 pairs parts 201 and 202, and a pair of Marklin Balanced Cranks.

The model is driven by a Mike Rhoades medium-duty motor running on 12V DC driving a 6” pulley. This drives a pinion, a Stokys 201, which drives two Stokys 202 and they each drive a crank. Attached to each is a linkage to the piston rod, by way of a 13 hole multi-hole strip. The piston rod is journalled in the centre of the multi-hole strip by way of a octagonal coupling holding the piston rod. The piston rod slides in an open piston, as I do not having a long 3½” cylinder in stock. The two cranks have to be in phase, or no motion is transmitted to the piston rod.

It is not known how many of these machines were built or whether it was successful in practice as the manufacture of the gears would have been difficult at the time, in the early 1800’s.

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