Bowman Magnet Motor Open Sourcing Project

Status: Project commenced Dec. 2003 with claim to a working device, which later, after three months, ended up running down due to demagnetization.  No replications were accomplished though several were attempted.

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PES Network Inc > Open Sourcing Projects > Magnetic Motors > Bowman > Instructions > Specs

Bowman Magnetic Motor Specs

Design Specifications

Mann said he used the dimensions of the Bowman motor given at (complete URL is in link, not spelled out here because of its length [printout copies, try]).


Mann said these drawings are to scale, and that they are accurate with exception of the actuator.  He changed some of the materials too.  He took the below image, printed it, and enlarged it to 2x scale and used it as a blueprint.  The image comes from

click for enlarged gif

Here are some additional drawings:

Note that as rotors turn, the meeting magnets will be aligning most closely on the horizontal plane exactly.  This relationship is maintained between every magnet in turn.  Without the actuator, a baseline target is a perfectly balanced "zero resistance" state, freely turning.  See "tuning" instructions below.

Dimensions and Materials

According to the page Mann referenced, along with notes he conveyed by phone, here is a materials list.  All materials, besides magnets, need to be non magnetic conducting.  (See note: Use non-magnetic materials for rotors and body.)

NOTE: Where Mann used Delron, he would like to use Lexan, which is see-through, making for a better demo unit.

  • Scale: Do conversions based on main rotor diameter = 8 inches.
  • Rotor Magnets:
    • "NEO 32" [Neodymium 32; Gauss = ?]
    • Shape: cylindrical
    • Magnetism - polarity at ends.
    • Size: 3/8 inch diameter by 1.75 inch long. Mann said he went with this size because it is an "off-the-shelf" standard size.  [Remember:  Exact size is not as crucial as the 1 : 4.5 ratio of width to length.]
    • Quantity: Buy extra so you can select those of the closest actual Gauss.
    • Orientation: The magnets are situated lengthwise in the rotors, parallel with the shafts that hold the rotors.
    • Ends of magnets "were accordingly ground so as to pass close to opposing wheels with only a minute gap."  Mann did not grind his Neodymiums, but selected the most uniform and used them as is.
    • Plating: Mann's magnets were Ni-plated (protects from corrosion of the Neodymium).
  • Actuator Magnet:
    • "NEO 32" [Neodymium 32; Gauss = ?]
    • Shape: rectangular box
    • Magnetism - on the flat side, with the 1/2" dimension holding the polarity.
    • Size: 1/2" x 3/8" x 1 3/8 " 
      Note:  The ratio of dimensions is 3 x 4 x 11. 
      Note:  The ratio of the length of the actuator magnet to the length of the rotor magnets is about 80%
    • Quantity: Buy extra in case the one is damaged.
    • Orientation: The south pole is closest to the rotor.  The length of the magnet is parallel to the shaft of the rotor.
    • Plating: Ni-plated
  • Rotors:
    • The large rotor diameter is 8 inches, using Delron, milling the magnet holes so they nearly breach tangent, allowing close proximity to the actuator magnet.
    • The two small rotors diameters are 4 inches (to perimeter of magnet; extra material beyond is okay here), using Delron.
    • Thickness: not crucial, but should be adequate to (1) hold magnet securely, (2) allow for some adjustment of the 1.75" magnets parallel to shaft.  Recommended: 1 inch.
    • Magnet holes are milled for tight fit of magnets so they can be adjusted with ~15 lbs pressure, but stay fast against the ~5 lb pressure when passing other magnets when installed and in motion. [Paper can be used as a temporary wedge.  Glue could be used (but not until optimal position is determined by the timing procedure given below); or plastic synch screws could be fashioned].
    • Hole positions for magnets:
      • On small rotors: Exactly 0, 90, 180, 270; situated  with outside edge of magnet as specified in the drawing.  Material may extend beyond for strength in holding the magnet.
      • On large, main rotor: Exactly 0, 45, 90, 135, 180, 225 270, 315; situated  with outside edge of magnet as specified in the drawing.  Material should just end where the magnets end, so the actuator magnet can get close.  A small amount of coverage (full enclosure) beyond the magnet would be okay for strength, but not more than 1.5 mm.
        Note: If the actuator gets too close to the main rotor magnets, a "locking effect" comes into play, so some clearance is not only okay, but actually necessary.
      • Mann recommends that when machining the holes for the magnets that the bits turn at low speed.  The higher speed tends to melt the plastic and leave a larger hole, through which the magnet does not fit snugly.  In this case, you can use paper wedges to restore a snug fit.
  • Bearings
  • Frame:
    • Device is mounted on a ~-inch (thickness not crucial) Delron base.
    • Two upright sheets that hold the shafts are also made of Delron ~-inch (thickness not crucial)
    • stainless steel bolts used to fasten the vertical support to the horizontal support.
  • Shafts: three parallel shafts
    • made of "3-16 stainless steel" [not sure of nomenclature representation in writing]
    • -inch diameter. 
    • center shaft needs extra length to attach to load (e.g. torque wrench)
    • position of small rotors on shaft needs to be adjustable to within 1/1000ths of an inch, and +/-  inch in relation to main rotor as shown in diagram.
  • Gears:
    • 2:1 ratio spin rate of small rotors in relation to main rotor.
    • the center, large rotor spins in opposite direction to the two smaller rotors on either side.
    • Material: Mann had his gears made of steel.  "They are far enough away from the magnets," he said.
    • Tolerance: very tight.
    • Configuration: standard "3rd gear / spur gears" so there is no clicking as the gear tines come together. using -inch belt.
    • Alternative: Not recommended until Mann's device has been replicated successfully as is.
  • Actuator Holder:
    • Needs to have a plastic thumb screw to hold magnet as close as possible to main rotor, and be able to move +/- inch in any direction relative to that position.
  • Misc tools needed
    • Torque wrench: typical, inexpensive, measures foot-lbs.  Mann uses a 240 in-lb range wrench 1/4 drive. He said the force range that most will be working in is about 15 inch-lb max to zero.


Estimated Tolerances for Possible Variations

Some aspects are crucial, others have leeway, as indicated here:

  • Material Composition
    • Needs to be non-magnetic conducting.
  • Magnets: flexible to approximate Mann's working device.
    • Type may vary, as long as the Gauss is +/- ~20% of the Alnico 8s.
    • Size may be +/- ~20%, but should maintain the 1 : 4.5 ratio of width to length
    • rectangular v. cylindrical: may be interchangeable (though not with identical output, as rectangular magnets are stronger).
      Mann calculated Bowman's rectangular magnets to be of dimension 5/8" x " x 2" (note: : 2 gives the 1 : 4.5 ratio; while 5/8 : 2 gives a ratio of 1 : 3.6.  Mann's tests show that the smaller face sets the ratio.)
      He had two sets of magnets: Alnico, and NEO. He first unsuccessfully tried the Alnico magnets, but was able to get the NEO magnets to work.
  • Rotors: size: flexible
    • increase or decrease of size should approximate increase or decrease in Gauss of magnets relative to Mann's Alnico 8s.
    • main rotor needs to be 2x size of smaller rotors, which need to be the same diameter.
    • rotor positions relative to one another needs to be adhered to closely, proportionately.
  • Gearing: 2:1 precisely, no variations.
  • Shafts: thickness, length, and material not crucial except that the material should not be magnetically conducting.

Note: For purposes of successful replication, you would be best advised to stay as close as possible to Mann's design.  At the same time, it would be good to implement means by which you can begin to introduce variations, once you achieve successful replication, in order to begin characterizing the device.  See Points of Design Variation for Characterization and Optimization below.

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Page composed by Sterling D. Allan, Dec. 14, 2003
Last updated November 06, 2004

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