Understanding Geometric Motors
If you select points and planes to define the motor, you are creating a geometric motor.
PlanePlane translation motor—Moves a plane in one body with respect to a plane on another body, keeping one plane parallel to the other. The shortest distance between the two planes measures the position value of the motor. The zero position occurs when the driven and reference planes are coincident.
In addition to the prescribed motion, the driven plane is free to rotate or translate in the reference plane. Thus, a planeplane motor is less restrictive than a motor on a slider or a cylinder joint. If you want to explicitly tie down the remaining degrees of freedom, specify additional constraints such as a connection or another geometric motor.

One application of a planeplane translation motor would be to define a translation between the last link of an openloop mechanism and ground.

PlanePlane rotation motor—Moves a plane in one body at an angle to a plane in another body. During a motion run, the driven plane rotates about a reference direction, with the zero position defined when the driven and reference planes are coincident.
Because the axis of rotation on the driven body remains unspecified, a planeplane rotation motor is less restrictive than a motor on a pin joint or cylinder joint. Thus, the location of the axis of rotation in the driven body may change in an arbitrary way.

Planeplane rotation motors can be used to define rotations around a ball joint. Another application of a plane–plane rotation motor would be to define a rotation between the last body of an openloop mechanism and ground, such as a front loader.

PointPlane translation motor—Moves a point in one body along the normal of a plane in another body. The shortest distance from the point to the plane measures the position value of the motor.
You cannot define the orientation of one body with respect to the other using only a pointplane motor. Also note that the driven point is free to move parallel to the reference plane, and may thus move in a direction unspecified by the motor. Lock these degrees of freedom using another motor or connection. By defining X, Y, and Z components of motion on a point with respect to a plane, you can make a point follow a complex, 3D curve.
PlanePoint translation motor—A planepoint motor is the same as a pointplane motor, except that you define the direction in which a plane moves relative to a point. During a motion run, the driven plane moves in the specified motion direction while staying perpendicular to it. The shortest distance from the point to the plane measures the position value of the motor. At a zero position, the point lies on the plane.
You cannot define the orientation of one body with respect to the other using only a planepoint motor. Also, note that the driven plane is free to move perpendicularly to the specified direction. Lock these degrees of freedom using another motor or connection. By defining X, Y, and Z components of motion on a point with respect to a plane, you can make a point follow a complex, 3D curve.
PointPoint translation motor—Moves a point in one body in a direction specified in another body. The shortest distance measures the position of the driven point to a plane that contains the reference point and is perpendicular to the motion direction. The zero position of a pointpoint motor occurs when both the reference and driven point lie in a plane whose normal is the motion direction.

The pointpoint translation motor is a very loose constraint that must be used carefully to get a predictable motion. You cannot define the orientation of one body with respect to the other using only one pointpoint motor. In reality, you would need six pointpoint motors for this.

Also note that the driven point is free to move perpendicularly to the specified direction, and may do so if you do not specify otherwise. Lock these degrees of freedom using another motor or connection. By defining X, Y, and Z components of motion on a point with respect to a plane, you can make a point follow a complex, 3D curve.