reduce voltage

[8u8u8u]

hi everybody ! , i have a Micro Motor i wish to slow down, it is rated at 3v , and load current is 0.12 amps...the rpm is 13800 !!!...could i use resistors, of course just using one 1.5v battery would half the speed ?...but how to get even lower,its use will be for the tail-rotor on a model helicopter i am building ..its a small motor 10mm x 8mm x 6mm !!!....many thanks...peter

 

[alec_t]

Use pulse width modulation (PWM). Google for an explanation of PWM.

 

[audioguru]

Your little tail motor is HUGE compared to my tiny one. Mine does not spin too fast because its propellor slows its no-load speed.
Of course, my RC helicopter uses PWM for motor speed control.

 

[8u8u8u]

uncle

hi,thanks for that, my model is 1/24 Huey, so how would i go about PWM unit please, how small can these motors go !!!

 

[8u8u8u]

reducing voltage

hi again have looked at the 555 timer chip and circuit..looks fine,but operating values are 3-18 volts...the mini motor i am considering for tail-rotor of Huey is just 3 volts, and i need to reduce the voltage... how am i doing guys ?..any coments , thanks

 

[alec_t]

If the 555 works happily at 3V it should be an ok basis for driving the motor. Peak motor current may well stress the 555, so it would be advisable to use a transistor buffer between 555 and motor. Don't forget a back-emf protection diode across the motor.

 

[audioguru]

how small can these motors go !!!

The tail motor on my AirHogs Havoc heli is 1/2" long and less than 1/4" in diameter. Its tail rotor is less than 1.25" in diameter.
The tail motor on my Eflite Blade mSR heli is 5/8" long and 1/4" in diameter. Its tail rotor is a little less than 1.5" in diameter.

 

[8u8u8u]

hi, thanks for that Alec !...using 2 1N4148 diodes,, not sure about a transistor buffer,its not in the circuit i have, is it really needed ?

 

[8u8u8u]

wow !!! where did you get them from please ???

 

[audioguru]

hi again have looked at the 555 timer chip and circuit..looks fine, but operating values are 3-18 volts.

No.
The supply voltage for an ordinary 555 (NE555 or LM555) is 4.5V to 16V.
The supply voltage for a Cmos 555 (TLC555, LMC555 or ICM7555) Is 2V to 15V and its fairly low output current depends on the supply voltage.

 

[alec_t]

not sure about a transistor buffer,its not in the circuit i have, is it really needed ?

I don't know your motor or 555 characteristics so I can't say for sure. If the 555 is a CMOS one then it is needed. If you've actually tried the circuit and the 555 didn't get hot and the motor speed was reduced as required then the buffer clearly wasn't needed!

 

[8u8u8u]

thanks Uncle, looks like have my answer, am going ahead with it, can you please tell me where these small motors you mentioned that you have on your helicopters can be got please ? ..or even the brand...thanks help again..peter

 

[8u8u8u]

ah, motor is a MICRO-ELECTROMOTOR K10WA
out power...... 0.08
max torque.......0.006 Ncm
no-load speed...20500rpm
no-load current...0.05A
nominal voltage...3v
current at max operation.. 0.12v
load speed 13800rpm

have not started yet...

 

[colin55]

Here is a very clever circuit:
**broken link removed**
SIMPLE MOTOR SPEED CONTROL
This circuit is better than reducing the RPM of a motor via a resistor. Firstly it is more efficient. And secondly it gives the motor a set of pulses and this allows it to start at low RPM. It's a simple Pulse-Width circuit or Pulse-Circuit.

 

[audioguru]

thanks Uncle, looks like have my answer, am going ahead with it, can you please tell me where these small motors you mentioned that you have on your helicopters can be got please ? ..or even the brand...thanks help again..peter

AirHogs is the brand of cheap IR-controlled airplanes and helicopters available in North America. It is called Silverlit in Asia.
E-Flite and Parkzone make many ultra-micro electric airplanes and helicopters available world-wide but mainly in North America. They and their parts can be seen at wwww.horizonhobby.com . The motors do not have a manufaturer's name and do not have detailed spec's.
I think the tiny brushed motors are made to open and close the tray for a CD or DVD. The brushes wear out after running for some time. Slightly bigger airplanes have brushless motors that last for a long time.

 

[8u8u8u]

THANK YOU very much ! am off to check all this info out now, and copied circuit as well...

 

[8u8u8u]

thank you !!!