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electromagnetic lineair actuator

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  • fnmul
    Hello everyone, mostly walkers have rotating motors, but their movements are linear (they don t have wheels). Let s forget for a moment (to keep it simple)
    Message 1 of 1 , Sep 8, 2002
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      Hello everyone,

      mostly walkers have rotating motors, but their movements are linear
      (they don't have wheels). Let's forget for a moment (to keep it
      simple) that legs of walkers have rotating joints.

      When linear movements are used for robotics, it mostly isn't for
      legs. When a linear movement is necessary mostly mechanisms like
      Timing belt/pulley, spindle/nut or a gear along a guide are used.

      Thinking about factors like speed ratios, mechanical friction and
      backlash we don't need to have much imagination to understand that
      mechanisms like these are not very power-efficient. Moreover, when
      the mechanism is more complex (more gear steps etc.) the mechanical
      rigidty is smaller (as much as important as power efficiency).

      Until so far nothing new, you will think. In some scientific areas
      experiments are done with direct linear movement. For instance the
      CWRU made a hexapod Robot III (check it out:

      This Robot III is an impressive cockroach-like hexapod. Every leg of
      this hexapod has 4 segments that gives all the necessary degrees of
      freedom. Really im-pres-si-ve (the opinion of someone with a
      mechanical background)!! The thing can correct its attitude when
      absorbing shocks and accelerations (some sort of force-feedback
      mechanism). The linear movements are realised with pneumatic

      Ah, there we are, you think. And, yes, as far as I can judge it,
      Robot III is not stand-alone. It needs a "lifeline" with compressed
      air. So it doesn't tow around it's own little compressor cart.
      (wouldn't make a realistic cockroach anyway)

      Another approach is that of air muscles. Air muscles are a kind of
      strengtened rubber tubes that will get shorter when inflated with low
      pressure air (see for instance
      8.html and http://www.imagesco.com/catalog/airmuscle/AirMuscle.html).
      But again a compressor is needed.

      But now the electronics domain. I must say, with intervals I follow
      the discussion about robots on the internet and haven't seen many
      instances of the use of electromagnetic linear actuators. Is this
      strange, or is there a logical explanation for this? I assume the EMC
      shielding of these devices will ask a lot of attention. Further, to
      analyse a leg with a few segments, springs and
      electromagnetic "cilinders" will ask a lot of control engineering.

      But still, my doorbell has coil magnet lineair actuator and I removed
      a few of these things from an old cassettedeck. Although those ones
      need a high voltage (24V), can't they be made for the low voltage
      domain of solar bots?

      I would appreciate if someone could give me some answers. What are
      the bears on the path I don't see? If there are possibilities, can
      someone point out what issues can be encountered when developing
      these things?

      Thanks for the attention,

      Ferdinand Mul
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