Cycloidal planetary gear speed reducer

A cycloidal planetary gear speed reducer having a central shaft, comprising:

• at least one ring gear disposed so as to be rigidly mounted in a housing,
• a set of planet gears in mesh with the at least one ring gear,
• a rotatably supported planet gear carrier, on which the planet gears are mounted, and
• a plurality of drive plates arranged axially, one behind the other, in order to drive the planet gears, wherein the drive plates are mounted eccentrically on the central shaft in order to execute a circular translation movement, wherein at any given time during execution of a circular translation movement, the drive plates are in engagement with at least two planet gears, wherein in order to engage with three planet gears, the drive plates form in each case three concave circular arc-shaped tooth segments, which correspond with said three planet gears and which have internal gear teeth on the outer periphery, with said internal gear teeth having an opening angle that is greater than 180 degrees;
• or in order to engage with four planet gears, the drive plates form in each case four concave circular arc-shaped tooth segments, which correspond with these four planet gears and which have internal gear teeth on the outer periphery, with said internal gear teeth having an opening angle that is greater than 150 degrees.