Rotor Design for Newman Motor

[Guest]

I've obtained a few things already for this; the driveshaft
and PVC motor housing, bearings. Its a brass bar 1/4in diameter,
and the tube is 4 3/4 inside, 5in diameter outside and 1/4in thick.

The confusion I'm running into is in regards to the method by
which a set of magnets will be attached to the driveshaft.

The things I've been considering are as follows:

- Grind off a flat area from the center of the bar, and cast
an epoxy resin flywheel with the magnets permanently embedded
onto it.

- Have someone cut me a square aluminum (or brass) block, and
attach it at the center position on the driveshaft so I may
fashion a proper hardwood flywheel with cutouts for the magnets
to be glued in.

- Cut the brass shaft in two, then have plates attached to the
opposing ends to be used to bolt them onto a center flywheel.

The magnets would be 1in wide x 3/4in long cylinder blocks, and
I'm going to wrap the coils with 2lbs of 25g wire total for
approximately 13 one-inch layers per side.

[gmeast]

construction

I've obtained a few things already for this; the driveshaft
and PVC motor housing, bearings. Its a brass bar 1/4in diameter,
and the tube is 4 3/4 inside, 5in diameter outside and 1/4in thick.

The confusion I'm running into is in regards to the method by
which a set of magnets will be attached to the driveshaft.

The things I've been considering are as follows:

- Grind off a flat area from the center of the bar, and cast
an epoxy resin flywheel with the magnets permanently embedded
onto it.

- Have someone cut me a square aluminum (or brass) block, and
attach it at the center position on the driveshaft so I may
fashion a proper hardwood flywheel with cutouts for the magnets
to be glued in.

- Cut the brass shaft in two, then have plates attached to the
opposing ends to be used to bolt them onto a center flywheel.

The magnets would be 1in wide x 3/4in long cylinder blocks, and
I'm going to wrap the coils with 2lbs of 25g wire total for
approximately 13 one-inch layers per side.

Hi geotron,

I might suggest the simplest of construction. You have already procured the round shaped items such as the PVC and and brass rod. As for the rotor I suggest using wood. I'm sure you are not intent on building a high speed machine ... correct? You can shape the wood easily with hand tools. You can drill, gouge, chisel, rout (whatever) recess shapes or cavities for your magnets and epoxy them into/onto the wood. There is another reason to use a material like wood ... eddy current drag. Wherever there is a magnetic field, an internally shorted mass such as aluminum, brass, steel, etc. will produce a mechanical drag. (Eddy currents were used in early speedometers. A rotating magnetic rotor whirled around inside of a close-fitting pot metal or aluminum drum. The drum was spring-loaded against rotation by something like a clock spring. When the vehicle moved, a flexible drive from the transmission to your dashboard rotated the magnetic rotor and dragged the drum around against the spring in proportion to the speed of the vehicle, and thus, the magnetic rotor. The speedometer needle was attached to drum and it pointed to, and indicated, your approximate speed.) You don't want any drag on your rotor. Use wood, plexiglass, G-10, Phenolic ... anything but ANY metal in this type of open or air-core machine.

I have built many Newman motors ... large and small. Don't concern yourself with making a 'beautiful'-looking assembly. Yes ... it must hold together, be 'somewhat' balanced, etc, (use good bearings). Spend most of your time and effort on your wire coil and especially on the commutator. As crazy and zany as Newman sounds and acts, his emphasis on TIMING has resulted in unbelievable efficiencies of his prototypes. Again, spend your time on the coil and the commutator. Most Newman motor builders I've seen from these forums always throw some of their own design "inspiration' into their motors and all they do is spin ... and too many are too small to appreciate the real work you can get out of these motors for only a fraction of the electrical POWER. That's another thing ... make sure you know the difference between ENERGY and POWER ... Newman still gets confused with the formalities ... but that's just him. COIL, COMMUTATOR, COIL, COMMUTATOR, COIL, COMMUTATOR ... "TIMING IS EVERYTHING"

Greg

[Michelinho]

Wise words gmeast.

Hi geotron,

As gmeast did so eloquently emphasize the importance of the commutator on the Newman Motor, I will add that commutators with many contacts, 20 in the Newman's Motor, are more efficient than regular 2 contacts commutators. On my replication, the 20 contacts commutator needed ~370VDC and the 2 contacts commutator 570V ( at 30-33 ma avg ) to achieve the same RPM feed by the same power supply.

Also by making a ferromagnetic link between the 2 magnets, you get a stronger magnetic flux at both end of the magnets, a nicer magnetic circuit and a heavier rotor. Make your coil with lots of wire and larger wire than you think. The above mentioned motor, the 2 coils were made with 9 miles of AWG31, the next one will probably be made with AWG20 or 22 with 2 spools (11 lb each spool) of magnet wire.

You need to make big fat coil(s) and and a multi contact commutator to get above average results. Adjustable timing mechanism is of great help when tuning.

Take care,

Michel

[Guest]

Mechanical Options

The driveshaft material I have procured is extravegent then?

It may hold promise as an electrical conductor if nothing else
perhaps. I'm unaware of its specific alloy content.

I'll need a 1in flat steel bar instead, ground to fit into the
bearings. The magnets I'd like to use are .75in in length, and
the way I've marked their position on the rotor is with a .5in
span between the center driveshaft boundary and the inner surface
of the magnet. It may be that additional 1/4in thick 1in sq bar
peices could be stacked, onto which the magnets could sit. With
the relatively low cost of magnets though, the stack could rather
be populated more solidly with them instead.

Rather than grinding down 1 x 1/4in flat bar to fit, it may be
that I need a round steel driveshaft with center bar supports
as shown - having the correct size 1in bearings would be nice.

[Michelinho]

Hi geotron,

Why not use a shaft the size of your bearings and use your 1" steel rod as a magnetic link between the two magnets. If the shaft is say 1/2", just cut a piece of your 1" rod (Rotor diameter minus the length of your 2 magnets) to place between the 2 magnets and drill a 1/2" hole in the center of that 1"rod and slip it on your rotating shaft. Drill a hole in the rod and shaft and use a ciment nail (made of hardened steel) to lock them together. Use Scotch 897 fiberglass reinforce tape to prevent your magnets from flying away.

Take care,

Michel