DC motor run characteristics differ in reverse then forward???
deno
Posts: 242
Well, the subject line just about says it all.· Using PWM to ramp up (slow start) a DC motor, (regular brush type) I noticed that in one direction, the motor starts or comes up to speed very fast, but in the other direction (reverse or forward, depending on how you look at it), you can see and hear the "ramp up" as programmed by the PWM.· I should also mention that an H bridge is driving the motor, and the motor does the same thing, with 2 different H bridges.
Could it be the direction of the windings on the stator or the armiture???
Deno
Could it be the direction of the windings on the stator or the armiture???
Deno
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Searider
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Most DC motors are configured so that there forward torque is equal to their reverse torque.· This is usually a mechanical configuration or adjustment, but can also be adjusted if there are multiple coil options to drive the motor from.· Typically the "energized" armature coil is perpendicular or 90 degrees·to the field magnets resulting in an equal forward/reverse torque.· If you allow the field magnets to rotate so that they have a relation other than 90 degrees, you can slightly increase or decrease the available torque in a particular·direction.· The sacrifice is that if you increase·torque in one direction, you loose it in the·other direction·and vise-versa.
Also... if you have a motor·that has spun a majority of its life in only one direction·and the brush contacts are slightly loose or out of alignment, this can cause them to·wear·unevenly.· As a result,·a noticeable·speed difference when comparing one direction over the other is likely.· …. Solution: try changing the brushes if it is applicable to the motor.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 6/15/2008 6:14:54 PM GMT