need help slowing down a DC motor

[john9898]

i need help slowing down this motor for a school project! im hoping for 5 RPM. i know about electronics i just suck at the math. here are the specs. of the motor: 1.5-3VDC voltage range
8700+/-12% RPM at no load, 5800+/-12% RPM at max efficiency speed
im powering it with a 1.5V battery.
I tried to put a resistor on it but like i said i suck at the math and the resistors i buy stop the motor completely. with out the resistor it's like superman.
i read about using gears or something to slow it down but im only limited to a 4 1/2X 4 1/2 inch base. please help!!!!!

 

[cowana]

5rpm isn't going to be possible with an ungeared DC motor.

Your best option would be to use a stepper motor (especially if an exact rotation speed is desired) - or add a high gear reduction (eg 1200:1 through a series of multiple worm gears) to the existing motor.

Andy

 

[john9898]

i dont know what a steeper motor is. im 14 i dont know much :l

 

[ronv]

Something like this might work. I'm not sure it will run on 1.5 volts, but if you keep looking at dc gearmotors you might find a 3 volt one.

**broken link removed**

 

[john9898]

if i put enough LEDs in the circuit will that slow down the motor to 5 RPM?

 

[picbits]

A couple of questions, what is the motor connected to i.e. how much torque do you need ?

If it's not connected to anything, why do you need 5rpm ? How accurate do you need it to 5 rpm ?

Stepper motors as suggested above are pretty easy to control, if you have a unipolar motor you only need to pulse the phases in sequence to make the motor move around a preset amount each pulse. Easily done with a counter type circuit.

You *may* be able to get your motor down to a much slower speed using PWM to control it but 5rpm may well be pushing your luck.

 

[picbits]

if i put enough LEDs in the circuit will that slow down the motor to 5 RPM?

Your problem is going to be overcoming the internal friction of your motor, you need enough current to get it to start but then once you've overcome the friction, it's going to speed up a lot.

I.e. the motor may need 200ma to get it moving but will happily run on 100ma at say 50% speed.

There is *no* easy way other than gearing to get your motor running at 5rpm I'm afraid - look at other options and save your time.

 

[john9898]

english? and the motor is hooked up to a 1.5v battery AA. and its for a rotating picture

 

[picbits]

english?

Ummm you're on an electronics forum - we tend to speak electronics on here

Seriously though, you'll struggle with anything other than gearing by the sound of things, especially running on 1xAA battery.

Maybe put a small pully on the motor, a large pulley on the picture and a rubber band connecting the two - grab an old VCR as there is normally lots of gears and pulleys in there to strip.

 

[ClydeCrashKop]

You might find enough gear reduction in an old clock or timer to get close to 5 RPM.