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# Further cogging torque problems

- To: "Femm@Yahoogroups. Com" <femm@yahoogroups.com>
- Subject: Further cogging torque problems
- From: "Robin Cornelius" <robin.cornelius@hirst-magnetics.com>
- Date: Tue, 27 Nov 2001 15:18:08 -0000
- Importance: Normal
- Reply-to: <robin.cornelius@hirst-magnetics.com>

    Dear Group.

    I have now got my model behaving reasonable well and get results that tie up
    with the actual rotor.

    I am trying to reduce the cogging torque and have looked at a halbach
    magnetisation process. My current rotor is 6 pole (radial), femm predicts
    that a 6 pole halbach has minimal savings, over the redial. A 4 pole halbach
    can produce aprox. 1/4 of the normal torque (leaving the stator as 6 pole)
    but a 4 pole (6 stator poles) radial magnetisation will be comparable to to
    hallbach cogging torque. I don't (yet?) have a halbach fixture but I do have
    a four pole fixture that fits the same rotor and physical tests agree with
    in 10-20% of femm ie only 1/4 of the original cogging torque.

    I am stuck with the 6 pole stator but can easily adjust the magnet. Does
    this tie up with other peoples results of this type of work ( I though
    hallbach produced very low cogging torques) (maybe I am doing it wrong!).
    Any other suggestions would be most welcome

    Best Regards

    Robin Cornelius
    robin.cornelius@hirst-magnetics.com

    Hirst Magnetic Instruments Ltd
    Tesla House
    Tregoniggie Industrial Estate
    Falmouth
    Cornwall
    TR11 4SN
    UK

    Tel: +44 (0)1326 372734
    Fax: +44 (0)1326 378069
    Web: www.hirst-magnetics.com

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