Buying close to the correct speed certainly helps, but you'll probably want to vary it a little to get the speed that looks right to you.
If we are talking about the micro motors for the radar ears, then the ones i got had a gear ratio of about 700:1 and a rated speed of 28rpm. They run a bit faster with no load, and the mass of the radar ears is almost no load, but can be slowed down by dropping the voltage. Running at 1.5v was no problem but with this method you do lose torque as well as speed.
The PWM controller Bob found looks like a good solution here, and is close to the same price as a simple voltage regulator.
mike
That looks a very similar pwm controller to the one I used to control the
crown and finger-light motor in my B9, it works perfectly and was very
cheap. I can slow the motor down to almost a stop with ease. I removed the
control pot from the board and mounted it to the torso knob so I can
adjust the speed with ease.
Adam S B9-0557
> I just bought one of these to test out. The price is right. I'll give an
> opinion when it arrives in a couple weeks and will maybe even make a
> video:
>
>
http://www.ebay.com/itm/DC-1-8V-to-12V-2A-PWM-Adjustable-Voltage-Regulator-Motor-Speed-Controller/391151074442?rt=nc&_soffid=5009616002&_soffType=OrderSubTotalOffer&_trksid=p5731.m3795
>
> On Mon, Sep 21, 2015 at 7:36 PM, Bob Darlington
> wrote:
>
>> Yes. You can run the motor at full or even higher voltage, but on a
>> lower
>> duty cycle with a PWM controller. Something like this, but probably not
>> this exact one:
>>
>>
http://www.amazon.com/50A-Digital-Motor-Speed-Controller/dp/B004M5NKH4
>>
>> -Bob
>>
>> On Mon, Sep 21, 2015 at 7:00 PM, Daniel Angel
danielscottangel@gmail.com
>> [B9Builders] wrote:
>>
>>>
>>>
>>> I suspect I know what the answer will be but what the heck

>>>
>>> I have a 6mm micromotor that I need to reduce the RPMs. I know the RPM
>>> range and have attempted to reduce that via a voltage controller but
>>> have
>>> had no luck. Are there any other options to bring this speed down?
>>>
>>> Thanks,
>>>
>>> Daniel
>>>
>>> --
>>> *Conquering the world one robot at a time....*
>>>
>>>
>>>
>>
>>
>