Michael,
Yes, ac/dc universal motors can be reversed by swapping the internal lead of the brushes with respect to the armature.
However, for many of these motors - it is impossible to get to the connections because they are buried internally under other wrapped coils of armature wire.
In addition, for optimum operation of these universal motors the brushes are set at a precise lead angle with respect to the armature for running in one direction.
If one is successful in reversing the motor direction - many times the motor runs very poorly and with a huge amount of brush sparking if reverse motor operation is attempted.
But, as Mark pointed out; the typical smaller brush style dc motor may be easily reversed by simply swapping the motor leads with respect to the + and - connections on the power supply. This switch may be easily accomplished with a double pole double throw switch that has been cross wired.
By the way, here is a picture of a recent build to eliminate the AC universal motor on an Alps wrapper and replace it with a DC motor. The conversion works extremely well and makes it easy to control the speed of the chuck at speeds down to 2 rpm and have the ability to be reversed with the flip of a switch.
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www.rodbuilding.org]
Best wishes.
