A vibratory drive system comprising: a first rotatable drive shaft having a rotational axis; an out-of-balance wheel located coaxially with said first rotatable drive shaft and being rotatable relative to said first drive shaft about said rotational axis; a rotary transmission system coupling the first drive shaft to the wheel in order to transmit rotational movement of the first drive shaft to the wheel, wherein said rotary transmission system comprises: a shaft rotary transmission component fixed with respect to said first drive shaft; a wheel rotary transmission component fixed with respect to said wheel; at least one intermediate rotary transmission component (48A-48F) coupling the shaft rotary transmission component to the wheel rotary transmission component for transmitting rotation of the shaft rotary transmission component to the wheel rotary transmission component, wherein said at least one intermediate rotary transmission component is carried by a carrier that is rotatable relative to said first drive shaft about said rotational axis, and wherein said at least one intermediate rotary transmission component is rotatable with respect to the carrier, and wherein the drive system further includes an operating mechanism for rotating the carrier relative to the first drive shaft. a first rotatable drive shaft having a rotational axis; an out-of-balance wheel located coaxially with said first rotatable drive shaft and being rotatable relative to said first drive shaft about said rotational axis; a rotary transmission system coupling the first drive shaft to the wheel in order to transmit rotational movement of the first drive shaft to the wheel, wherein said rotary transmission system comprises: a shaft rotary transmission component fixed with respect to said first drive shaft; a wheel rotary transmission component fixed with respect to said wheel; at least one intermediate rotary transmission component (48A-48F) coupling the shaft rotary transmission component to the wheel rotary transmission component for transmitting rotation of the shaft rotary transmission component to the wheel rotary transmission component, wherein said at least one intermediate rotary transmission component is carried by a carrier that is rotatable relative to said first drive shaft about said rotational axis, and wherein said at least one intermediate rotary transmission component is rotatable with respect to the carrier, and wherein the drive system further includes an operating mechanism for rotating the carrier relative to the first drive shaft. a shaft rotary transmission component fixed with respect to said first drive shaft; a wheel rotary transmission component fixed with respect to said wheel; at least one intermediate rotary transmission component (48A-48F) coupling the shaft rotary transmission component to the wheel rotary transmission component for transmitting rotation of the shaft rotary transmission component to the wheel rotary transmission component, wherein said at least one intermediate rotary transmission component is carried by a carrier that is rotatable relative to said first drive shaft about said rotational axis, and wherein said at least one intermediate rotary transmission component is rotatable with respect to the carrier, and wherein the drive system further includes an operating mechanism for rotating the carrier relative to the first drive shaft.