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James Pickard, of Birmingham, like Boulton, a buttonmaker, in 1780 patented a counterweighted crank device (fig. 6) that was expected to remove the objection to a crank, which operated with changing leverage and thus irregular power. In figure 6, the counterweighted wheel, revolving twice for each revolution of the crank (A), would allow the counterweight to descend while the crank passed the dead-center position and would be raised while the crank had maximum leverage. No mention of a flywheel was made in this patent.[10]

Figure 6.—One of the steam engine "Crank Patents" that hindered James Watt's progress. This patent, granted to James Pickard in 1780, claimed only the arrangement of counterweights, not the crank. The crank pin to which the connecting rod was attached is at Aa. From British Patent 1263, August 23, 1780.

Wasbrough, finding that his "rotchets and clicks" did not serve, actually used, in 1780, a crank with a flywheel. Watt was aware of this, but he remained unconvinced of the superiority of the crank over other devices and did not immediately appreciate the regulating ability of a flywheel.[11] In April 1781 Watt wrote to Boulton, who was then out of town: "I know from experiment that the other contrivance, which you saw me try, performs at least as well, and has in fact many advantages over the crank."[12] The "other contrivance" probably was his swash wheel which he built and which appeared on his next important patent specification (fig. 7a). Also in this patent were four other devices, one of which was easily recognizable as a crank, and two of which were eccentrics (fig. 7a, b). The fourth device was the well-known sun-and-planet gearing (fig. 7e).[13] In spite of the similarity of the simple crank to the several variations devised by Watt, this patent drew no fire from Wasbrough or Pickard, perhaps because no reasonable person would contend that the crank itself was a patentable feature, or perhaps because the similarity was not at that time so obvious. However, Watt steered clear of directly discernible application of cranks because he preferred to avoid a suit that might overthrow his or other patents. For example, if the Wasbrough and Pickard patents had been voided, they would have become public property; and Watt feared that they might "get into the hands of men more ingenious," who would give Boulton and Watt more competition than Wasbrough and Pickard.[14]

Figure 7.—James Watt's five alternative devices for the conversion of reciprocating motion to rotary motion in a steam engine. (British Patent 1306, October 25, 1781). From James P. Muirhead, The Origin and Progress of the Mechanical Inventions of James Watt (London, 1854, vol. 3, pls. 3-5, 7).

(a) "Inclined wheel." The vertical shaft at D is rotated by action of wheels H and J on cam, or swash plate, ABC. Boulton and Watt tried this device but discarded it.

(b) Counterweighted crank wheel.

(c) "Eccentric wheel" with external yoke hung from working beam. The wheel pivots at C.

(d) "Eccentric wheel" with internal driving wheel hung from working beam. Wheel B is pivoted at center of shaft A.

(e) Sun-and-planet gearing. This is the idea actually employed in Boulton and Watt engines. As the optional link JK held the gearwheel centers always equidistant, the annular guide G was not used.

The sun-and-planet arrangement, with gears of equal size, was adopted by Watt for nearly all the rotative engines that he built during the term of the "crank patents." This arrangement had the advantage of turning the flywheel through two revolutions during a single cycle of operation of the piston, thus requiring a flywheel only one-fourth the size of the flywheel needed if a simple crank were used. The optional link (JK of fig. 7e) was used in the engines as built.

From the first, the rotative engines were made double-acting—that is, work was done by steam alternately in each end of the cylinder. The double-acting engine, unlike the single-acting pumping engine, required a piston rod that would push as well as