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How much of this motor rotor can I remove?

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  • How much of this motor rotor can I remove?

    Here's a rotor from a small electric motor.



    I'm planning on using the stator coil and rotor as an electrodynamic brake for a winch drum. The shaft and inner part of the rotor will be removed, and the remaining part of the rotor will be attached to the end plate of the drum.

    I want the rotor to be as light as possible, but still provide sufficient braking force to stop the drum quickly from high speeds.

    Applying 12V DC to the stator coil induces a current in the aluminum segments in the rotor. Since that current is shorted out by the aluminum rings, the rotor resists rotation. It seems to be very effective as a brake.

    My questions:

    How much of the aluminum rings can I remove without a significant loss in the braking force?

    Will drillng several small holes (parallel to the shaft and through the aluminum rings) for the attaching hardware have much effect on the braking force?

    Roger

    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    The thickness of the aluminum ends is needed because there is basically one turn of conductor through each of the slots in the laminations, and very high currents need to flow. If you introduce more resistance by removing material, it will reduce the braking effect fairly quickly. If you were to remove much of the inner metal part, leaving say an eighth inch or so of laminations before the aluminum ends are touched, that will have minimal impact on it's effectiveness. In other words, you can remove much of the central core from the shaft outwards, before you affect it's torque capabilities much. If possible, keep your mounting holes just inside of the aluminum ends, in the lamination metal.
    Also, if you drill holes through the rings, you will be removing some lamination material as well. This will accellerate the loss in effectiveness as both the current conductor, the aluminum, and the magnetic field conductor, the laminations, are needed to make it work. You probably know this, but your braking force will be highest when the rotor is turning the fastest, and will drop to zero as the rotor speed drops to near zero.
    It seems to me that you might have better results from a centrifugally actuated drum brake setup.

    [This message has been edited by darryl (edited 05-12-2004).]
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #3
      That sounds resonable. I think I'll take a light clean-up cut and turn a shoulder on one of the rings. Then I can shrink- fit the rotor onto a matching shoulder on the drum to keep things concentric and reduce the need for large fasteners.

      Roger
      Any products mentioned in my posts have been endorsed by their manufacturer.

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