Thirdly, also in 1830, Richard Roberts patented the first self-acting mule. Stalybridge mule spinners strike was in 1824; this stimulated research into the problem of applying power to the winding stroke of the mule. The draw while spinning had been assisted by power, but the push of the wind had been done manually by the spinner, the mule could be operated by semiskilled labor. Before 1830, the spinner would operate a partially powered mule with a maximum of 400 spindles; after, self-acting mules with up to 1300 spindles could be built.