670Views17Replies

Author Options:

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?

Tags:motor

17 Replies

user
steveastroukBest Answer (author)2009-12-27

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 ?

Select as Best AnswerUndo Best Answer

user
lu2a (author)steveastrouk2009-12-27

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

Select as Best AnswerUndo Best Answer

user
seandogue (author)2009-12-27

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.

Select as Best AnswerUndo Best Answer

user
lu2a (author)seandogue2009-12-28

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 .

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)lu2a2009-12-28

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.

Select as Best AnswerUndo Best Answer

user
lu2a (author)steveastrouk2009-12-30

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) .

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)lu2a2009-12-30

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

Select as Best AnswerUndo Best Answer

user
lu2a (author)steveastrouk2009-12-30

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

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)lu2a2009-12-30

Try it, and report back.

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)seandogue2009-12-28

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

Select as Best AnswerUndo Best Answer

user
seandogue (author)steveastrouk2009-12-28

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..

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)seandogue2009-12-28

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

Select as Best AnswerUndo Best Answer

user
seandogue (author)steveastrouk2009-12-28

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.)

Select as Best AnswerUndo Best Answer

user
seandogue (author)seandogue2009-12-28

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.

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)2009-12-27

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

Select as Best AnswerUndo Best Answer

user

...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.

Select as Best AnswerUndo Best Answer

user
nfarrow (author)2009-12-27

Try looking at a Tattoo gun. that is the kind of moment  you might need.

https://www.instructables.com/id/How-to-make-TATTOO-GUN/

Select as Best AnswerUndo Best Answer