Something new for builders: The Universal Motor

[MileHigh]

I figure a lot of you must be getting really bored with making pulse motors.  Here is a different kind of motor that looks like it would be a real challenge to build, and challenge equals fun:

http://en.wikipedia.org/wiki/Universal_motor

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The universal motor is a type of electric motor that can operate on both AC and DC power. They are commutated series-wound motors where the stator's field coils are connected in series with the rotor windings through a commutator. This type of electric motor can operate well on AC because the current in both the field coils and the armature (and the resultant magnetic fields) will alternate (reverse polarity) in synchronism with the supply. Hence the resulting mechanical force will occur in a consistent direction of rotation, independent of the direction of applied voltage, but determined by the commutator and polarity of the field coils.

Universal motors have high starting torque, run at high speed and are lightweight and are commonly used in portable and domestic equipment.[1] They're also relatively easy to electronically control. However, the commutator has brushes that wear, so they are much less often used for equipment that is in continuous use. In addition, partly because of the commutator universal motors are typically very noisy.

When used with AC power these types of motors are able to run at a rotation frequency well above that of the mains supply, and because most electric motor properties improve with speed, this means they can be lightweight and powerful.

One useful property of having the field windings in series with the rotor windings is that as the speed increases the back EMF naturally reduces the voltage across, and current through the field windings, giving field weakening at high speeds. This means that the motor does not inherently have a maximum speed for any particular applied voltage. Universal motors can be and are generally run at high speeds. By way of contrast, induction motors cannot turn a shaft faster than allowed by the power line frequency.

Motor damage may occur from over-speeding (running at a rotational speed in excess of design limits) if the unit is operated with no significant mechanical load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In some smaller applications, a fan blade attached to the shaft often acts as an artificial load to limit the motor speed to a safe level, as well as a means to circulate cooling airflow over the armature and field windings.

An advantage of the universal motor is that AC supplies may be used on motors which have some characteristics more common in DC motors, specifically high starting torque and very compact design if high running speeds are used.
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Variety is the spice of life....

[Magluvin]

What would be the approximate efficiency of the motor in the pic of the wiki article? The one I am getting for the electric Fiero conversion is a constant torque type such as this also. Warp9. It can be run way beyond its data sheet ratings. The sheet says 72v. Some guys are running them on 300v with 1000A controllers. Im going to be using the automatic  3 speed trans. It is recommended to use a manual transmission and just leave it in 3rd or 4th gear as these motors have tremendous torque in the bottom end that taking off in 4th is like a high speed golf cart. But that seems to be an awful waste of power to try and accelerate in such a gear. So im going to take advantage of the leverage that the auto affords me.

So I have the 9in motor, keeping the tranny, with the CV axles, all together to motor the car.  From the motor to the wheels is not a great efficiency transfer, even with the 2.8 V6.

What I would like to see is the motors built into the wheels. Some companies have already used them and are beginning to use them in cars and bikes. A friend of mine at work used to work in the mines in Peru. The giant dump truck, im sure some here have seen them or pics of, and this was back in the 70s he says, the drive motors were electric built into the wheels. He helped repair them.

There must be a good reason for doing so.  And it would be difficult to do so with the "universal motor" without gearing, of which we lose eff.

Here is some of the insides of my Tidalforce M750 bike. It is regulated to 20mph and 749w(just under 1hp) to be street legal in all 50 states federally. Some states allow more, but could be illegal if confronted by a fed.  The m750x is 1kw and 30mph  They both run off of 30 nimh D cells in the front wheel hub capable of 36v and 50a cont. 100 amps peak. The pack is fused at 80 amps.

This motor is optically triggered, asymmetrical 16 magnets and 14 coils operated in 7 pairs. The difference between the m750 and the m750x is all in programming. No other differences.

My trek bike has a front hub kit. Its smaller in diameter than the M750 motor and has 52 coils and 52 magnets, symmetrical. Tiny mags 1x 1/2x 1/8  triggered by hall sensor.

For me, the universal motor is not the most efficient way to go. In many useful cases they need some gearing which creates losses. Unless its a fan.  Some of those use belt drives, larger ones.

There is a reason that more and more motors are using permanent mags instead of coils. And its not because the mags are cheaper than the copper needed. And brushes are really becoming old school, wouldnt ya say?

Mags

[ramset]

MH
Thanks for the offer,however some folks are addicted to pulse motors...
Pulseaholics anonymous is sponsering an event At TinMans Place
A pulse motor build Off, No holds Barred Or restrictions [as apposed to previous years "themes"]

I understand its even "sanctioned" and sponsered by some very heavy hitters in the field....the who's who Of Pulseaholics will be there
[date to be forthcoming]

@Mags
Shhe is one  sweet Motor yah got there... I like the "hub" concept
for a nice light chassis !!

Thx
Chet

[tinman]

@MileHigh
The universal motor is a pulsed motor-infact every DC motor runs on electromagnetic pulses,as dose AC brushed motor's.A universal motor can be rewired to be more efficient than any other electric motor out there.
Pulse motors ruel.
http://www.youtube.com/watch?v=szpJ97M58G4

[gotoluc]

Hi tinman,

great motor, test idea and video!   thanks for sharing it.

Your modified motor seems to be over 60% more efficient at turning the fan then the universal motor designed for it.

Should a universal motor not be in the 70 to 80% efficiency range already?... if so, how can such a large difference be?

Can someone please explain what I'm missing here

Thanks

Luc