electrical motor question
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electrical motor question
For one of my project, there is a part that need to rotate slowly, just like a cassette player when you press play. But all the electric motors out there seem to spin too fast. I even dissected a cassette player motor and tried to use it but even that spins too fast when connected to a battery. How do they do it in a cassette player so that the motor spins slowly when you play the tape?
I don't want to use any gearbox. I think they use electronic speed control, is that right?
Or are there any small DC motors out there that naturally spins slow?
What's the easiest way for me to get a power source that will spin the part slowly? (speed similar to that of a cassette player when playing an audio cassette)
THanks
I don't want to use any gearbox. I think they use electronic speed control, is that right?
Or are there any small DC motors out there that naturally spins slow?
What's the easiest way for me to get a power source that will spin the part slowly? (speed similar to that of a cassette player when playing an audio cassette)
THanks
Posting Guru
Joined: Jun 2005
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From: Location, Location.
Any tape player I've ever taken apart was always belt driven, with a small drive pulley on the motor and a large driven pulley, producing an effective gear ratio.
Posting Guru
Joined: Oct 2004
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problem is most small motors wont turn that slow no matter what you do to it. not and be a steady movment anyways, they get real jerky. i had the same problem when i was trying to build a small ceiling fan for a doll house.
Hotshot
Joined: Oct 2002
Posts: 18,488
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From: The Big, Oregon
You can custom build your own motor for smooth operation at low speeds. The more poles, the smoother it will be, but it'll be a pain to make.
I used to replace five pole armatures in model locomotive motors with a custom built 9 or 11 pole to get phenomenally smooth low speed operation, but it wasn't cheap.
A pulse width modulator speed control will work much better than a rheostat, but it will whine a little bit.
You may also want to look into a clock motor or miniature synchronous drive. These have a little gearbox built into the motor housing, nothing external needed.
I used to replace five pole armatures in model locomotive motors with a custom built 9 or 11 pole to get phenomenally smooth low speed operation, but it wasn't cheap.
A pulse width modulator speed control will work much better than a rheostat, but it will whine a little bit.
You may also want to look into a clock motor or miniature synchronous drive. These have a little gearbox built into the motor housing, nothing external needed.
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
Postmaster
Joined: Oct 2005
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From: Clarksburg WV
What about a worm gear?
We had a pump at work that had an adjustable speed control (1-10 or something like that), but if you turned it down below 4 it wouldn't turn at a constant speed, like these guys said...it was real jerky.
We had a pump at work that had an adjustable speed control (1-10 or something like that), but if you turned it down below 4 it wouldn't turn at a constant speed, like these guys said...it was real jerky.
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Postmaster
Joined: Mar 2001
Posts: 4,968
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From: So Cal
Depends what you are doing, but RC models use a lot of DC motors which can be controlled to run slowly. I think the sizes are about the size of the last knuckle of your thumb up to maybe as big as a lemon. There are other DC motors of tiny or really big size, but these are what I have seen in RCs.
They also sell the speed control, but they are not cheap. Probably for a stationary application you could just make up a potentiometer setup or build a simple variable DC supply.
My RC car can go at a crawl but there is some gear reduction.
With an AC motor you can only vary it a bit unless you want to build an expensive controller from what I recall. There are Pusle WiIdth Modulation controllers that can control an AC motor down to a crawl but I am not sure if they require reduction too. I just played with one yesterday, a 2hp 230v AC motor running off a TB Woods controller, which could run fairly slow but it did have a belt reduction.
Good Luck,
Jim Henderson
They also sell the speed control, but they are not cheap. Probably for a stationary application you could just make up a potentiometer setup or build a simple variable DC supply.
My RC car can go at a crawl but there is some gear reduction.
With an AC motor you can only vary it a bit unless you want to build an expensive controller from what I recall. There are Pusle WiIdth Modulation controllers that can control an AC motor down to a crawl but I am not sure if they require reduction too. I just played with one yesterday, a 2hp 230v AC motor running off a TB Woods controller, which could run fairly slow but it did have a belt reduction.
Good Luck,
Jim Henderson
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MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Three ways:
1. Potentiometer (rheostat)
2. Mechanical gear reduction.
3. Pulse width modulation. Easiest way for that would be to buy a motor controller.
I think everyone has pretty much mentioned those already.
1. Potentiometer (rheostat)
2. Mechanical gear reduction.
3. Pulse width modulation. Easiest way for that would be to buy a motor controller.
I think everyone has pretty much mentioned those already.
Super Moderator
Joined: Apr 2004
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Combine reduction via belt or gear with the rheostat. That way, your motor will slow down, but remain in an rpm range sufficient to prevent overheating or jerkiness, but your final drive will be s l o w.
Cargo Master
Joined: Aug 2002
Posts: 2,117
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From: Over Yonder, MN
It really depends on what your doing, a rheostats been mentioned, but if your looking to just plug in a motor and go or have some resistance to overcome then you need to find an AC synchronous motor commonly found in industrial timers and are relatively compact, these are usually coupled to a gear head and run about 3 RPM’s at 120v AC. Another option is a parallel shaft gear motor, which can be had in a huge range of rpm’s, some as low is .5 RPM’s, and in a large variety of voltages. These motors usually run in the $40 - $60 range new.
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