DC electric motor rotation

Hai,

the output of your amplifier is push-pull type. if it is dc motor it will not be working properly. you can connect ac motor instead of dc motor of right voltage(say 5v because output of your amp. is 4.5v).

please tell me the motor specification which you have used in your show, such as wattage, ac or dc powered.

Excellent post, well writen...you are definitely on the right site.

A smaller lighter motor may help? (less inertial so it can respond quicker)..
Your capacitor filter is a good idea, filter out the higher frequencies...the motor will have more time to respond to lower frquencies.

There was a similar post some time back ... using stepper motors I think...try searching for light show, stepper motors etc on the 'Search this forum'

Welcome to CR4 (nice to se a youngster on board)

Del

Maybe a motor from an old optocal drive (CD rd/wr ) I just replaced the one on this PC and opened the old one up for a look...some fun stuff inside....

Vis, I thought I had already put a suggestion forward for this but it doesn't appear to have landed on the thread.

What I said was try putting a diode in line on the output of the amp. Use the capacitor if you want your motor to move in time to the baseline or an inductor for treble and to get the output up to 9v put a non-inverting opamp circuit from this National Semiconductors pdf

http://www.daxia.com/bibis/uploadasp/flies/%B3%A3%D3%C3%D4%CB%B7%C5%B5%E7%C2%B7%CD%BC.pdf

into the party with R1 and R2 being equal.10KOhm will probably be ok.

Al

@ peterjohn I did not use an AC motors because i have none and was not sure if they would work because the oscillations change in voltage and frequency, i believe.

i used multiple motors to see if there would be a difference. I did use an old motor
( pulled from record player. MAbuchi EG-500AD-9B 9VDC ccw )

that dose do full rotations but it is slow and since the mirror has to be at an angle i think it has loosened one of the magnets to were it hits the the shaft on every rotation. Which causes a lot of friction. I have also used another motor that i pulled from a VCR which is a Mitsumi

( There is tape on top of the information sticker so i can not make out the rest. i believe it is DC because it runs off of my AC to DC power adapter )

@ Del the cat i tried a couple of small, new, faster motors but they vibrated the most. I think that the slower the motor the better. So i went to radio shack a bought a small 5v DC hobby motor that was rated at 8500 rpm ( the slowest i could find ) but it did the same as the rest.

The capacitor must of had to much power running through it because after around six minutes i saw one edge of the lid up out of place, i think this means its blown. I don't know enough about capacitors to be sure though.

@ Bolton_Alan Sorry but this is a bit too advanced for me to understand clearly. What would the diode do? I also don't understand the what capacitor and inductor would do.
i understand what Non-Inverting Amplifier would be used for and how but i do not think this is the problem. But thank you. Wouldn't this make the motor unsynchronized to the music?

I am not clear exactly what you want to achieve, whether you want

1)the motor to rotate in one direction but with the speed controlled by the level of the music, or,

2) the motor to sweep back and forth in time with the music.

If you want 1) then feed the motor through a bridge rectifier and it will rotate in one direction only, but with the speed in controlled by the level of the music.

If you want 2) you have a problem. the lowest frequency component in music is normally 20Hz, often with little below 40Hz. If you feed 20Hz into a DC motor it will try try to reverse 40 times a second which it can't do because of its mechanical inertia so it just vibrates. In practice it is even worse as the frequency spectrum of the music is complex with a lot of higher frequency components.

Some disco laser scanners use micro-step motors, but these are specialist items that need special control circuits.

You could try a voice coil actuator. You could make a basic system by mounting small mirrors on a pair of old loudspeaker drive units (big heavy woofers will be best). If you mount them at 90 degrees to each other then you can create patterns with the beam. The effect will be better of one end of the mirror is pivoted and the other moved by the speaker coil.

If you are going to filter the signal it is much easier to do it on the input to the amplifier as you can use small and cheap components.

WARNING Laser light light is dangerous and can blind or cause permanent damage. Any setup must be rigged in such a way that it is impossible for the light to shine in any ones eyes. This includes reflections from any shiny objects in the room or worst case failure of the amplifier or the rig. If you are doing any shows you must have a risk assessment from a competent person.

thank you. this is what i was looking for. #1. I want the motor to turn in one direction but change speeds according to the music. What is a bridge rectifier??

The idea with mounting mirrors on a speaker it easy and i was looking for something a bit more complicated. I also wanted more control over the patterns which i do not know how to do with the speakers. By using motors i can change their directions and there speed.

A bridge rectifier is made from 4 diodes which may be separate or combined in one package. I suggest a little research on Google or Wikipedia for more information.

Be aware that a 30W amplifier can produce 15V ac into an 8 ohm load, when rectified with a bridge rectifier this becomes 20V ac. Larger amplifiers can produce rather higher voltages so be careful with the choice of motor voltage otherwise you may burn it out, I would avoid 5V motors unless you are using a very small amplifier.

when rectified with a bridge rectifier this becomes 20V ac.??

...(bit of a typo I suspect . It would be 20V rippley DC)

Thanks Del, I meant 20V dc. With a capacitor across the rectifier output, it will become a less ripply dc which would be a good idea anyway.