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motors , and AC supply ! Answered

 hi  , my question is

what  would happen if i connected a simple motor ( 3v ) to an AC power supply of the same volt ?
will the motor keep turning in both directions right and left .. and so on ? if yes , how can i convert a 3v DC to AC ? and how to control the speed ?
coz i need an idea to make a power circuit that can make a simple motor do so (turn right and left and right and left and so on ..... in a controllable speed ) , can you help me?



A standard DC motor will buzz and burn out on AC. You can't readily convert a Permanent magnet DC motor into an AC one.

What you want to do is not achieved by applying "AC" to a motor. If I were you, I'd look at using a model servo and a drive circuit.

How fast do you want  to move the motor, in degrees/sec ?

thank youfor reply

i'd like it to move in about 60 degree angle ( right and left and so on ) like 3 cycles/sec
is there any easier way than servo to make such a move ?

my intention is to attach a laser pin to this motor , okay , and by turning on the motor , the laser pin point will move (from right to left) so it will form a horizontal line. just like the oscilloscope monitor .

any idea will help , and thx again

This is usually done using a galvanometer, a special form of motor designed for rapid oscillating motion from an AC source, and as Steve said, it's used to accomplish the task by attaching a small mirror to the end of the galvanometer axle. (Note, most galvanometers I've worked with over the years had return springs embedded to return the axle to the home position , ie, 0 degrees)

The laser and galvanometer are collocated (mounted together) after optically aligning the laser and galvanometer mirror.

Galvanometers are often driven using a push-pull or bridge amplifier, similar in many ways to an audio amp, into which a signal is fed from a waveform generator.

For experimentation purposes, a hobby servo might be more suited for this task than a simple dc motor. remember to keep the mirror as small as possible.

thank you , and thank you Steve

well, i don't have a galvanometer , but i have an old hard drive
can the actuator  inside this hard drive do the job ?

if yes , how much power do i need ? and how to convert DC from battery to AC to try this ? with controllable speed and controllable power limit if this possible .

My way, the motor is just run on DC, the mirror wobbles around like the picture shows, riding on the cam, which is turning three times a second.

good idea , i'll try this .

except i still need to know if the AC method will work with the hard drive actuator or not ?
i think it will work , but i need an easy circuit to convert a battery DC to AC with controllable power  (milli volts) .

It won't work. The motors in a hard disk are brushless DC ones, and need fancy controllers.

i didn't mean the spinle which is stepper motor
i mean the actuator , the arm and the sliding head parts

Yebut, yebut...a galvo is overkill for 3 cycles/sec isn't it ? 

All depends on what you're doing. I mean, you could run a cam off a motor for all it matters to avoid the issue of attempting to run a dc motor off ac in the first place, use a hobby servo, or skip the mechanism altogether for an optical solution. There's a million ways to skin a chicken. But for oscillating turning mirrors, my mind goes directly to galvanometers and steppers, regardless of whether the scan frequency is 3 Hz or 10kHz..

How much are they ? Its 15 years since I last dabbled with them,

idk...it's been a while since I purchased one as well. That's why I keep saying "hobby servo". galvanometers are not cheap. hobby servos are similar in operation, and although they don't have the same torque profile, they'd be fine for this app as a direct mechanism for oscillating the mirror if it were stood on end off the servo's star armature. (even hot glue would suffice for mounting.)

But for a simpler method to make a cheap line generator, a cylindrical lens will do the trick quite nicely for hobby purpose. you can pick up a line generator for a song on ebay.

For that, I'd just use a mirror and a crank off a slow motor.

...or make a polygon mirror....for these sort of speeds, you could make a simple hexagonal mirror with a block of wood, and glue mirrors on the facets.