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DC Motors and speed control

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Jon Cavendish

May 2, 2016
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Hello EP!
New to the forum, not so much to electronics (though I am no expert).

A quick run down:
I'm building a rotary speaker cabinet (Leslie-style). This is a standard speaker with a baffle that rotates in front of it to throw the sound around the room, giving excellent Doppler/chorusing effects.
The originals were built with 2 speeds (fast/slow) using an AC motor stack that had a large motor for fast and a small one for slow. This setup works just fine, but it is mechanically noisy and has too many moving parts for my liking (after all, it's 70 year old tech).

I want to build a DC motor circuit that can turn the baffle at 2 speeds, and have those speeds be switched by a foot pedal. I have built a switching rig using relays and 12vDC to switch AC mains. I am good with an iron and can read a schematic.

My question is this:
What is the best motor to use, and what is the simplest way to build the speed controller? I have read a bit on using PWM to slow the dc motor, and also that you can use a varied voltage to change the speed. I'm really just at the starting point, so any info you can offer will be much appreciated!

Feel free to send links to other threads/forums if this has already been answered somewhere before.

Thanks!
-Jon
 

Minder

Apr 24, 2015
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A small DC motor is a good choice, the size will depend on the torque required for the application.
You can use a simple 555 PWM such as http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
The motor power can be whatever the motor is rated for with a suitable sized mosfet, I would use 15v on this circuit for the 555 power.
M.
 

Alec_t

Jul 7, 2015
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To keep noise down I'd go for a brushless motor rather than a brushed one, and use belt drive rather than gear drive.
 

Arouse1973

Adam
Dec 18, 2013
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I was thinking a large RC Servo, modified for continuous rotation if needed or of it's just back and forth then just PWM it.
Adam
 

duke37

Jan 9, 2011
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A resistor in series with a DC motor will reduce its speed, chose resistors to get the two speeds you want.
You could look at a modified windscreen wiper motor which would give masses of torque at about the correct speed. A trip to the scrap yard is called for.

I spent a lot of time repairing a Hammond organ, I later learned that it had been scrapped and the Leslie speaker used by a band. Sacrilage!:(
 

Minder

Apr 24, 2015
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If mechanically noisy using a BLDC motor is not going to change a thing, I have used ex T.M. at 5Khz-10Khz PWM with no electrical noise evident.
M.
 

jackstone

Sep 12, 2023
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I get to learn about different types of tools and how they work. One of my favorite topics is the difference between brushed and brushless motors. Brushless motors are more efficient, faster and durable than brushed motors, but they also cost more and require more sophisticated electronics. Brush motors are simple, inexpensive, and easy to improve, but they also generate high heat, noise, and wear. I want to compare the pros and cons of both types of motors and see how they perform in different applications. I'm always interested in hearing from other people who share my passion for power tools and motors. If you want to know more about brushless vs brushed motor.
 

Minder

Apr 24, 2015
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Incidentally Brushless motors come in two flavours, BLDC and 3ph AC, both identical in construction, but the commutation and power applied is completely different.
 

jackstone

Sep 12, 2023
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Brushed and brushless motors are both types of DC electric motors that convert electricity into rotating mechanical force, but they differ in how they achieve this. Brushed motors use brushes and commutators to convert current into a coil, which creates an electromagnet that interacts with a permanent magnet outside the motor 1. Brushless motors use an electronic controller that senses the position of the rotor and controls the current accordingly, eliminating the need for brushes and commutators2.Brushed and brushless motors have their own advantages and disadvantages, depending on the application. Brushed motors are simple, inexpensive, and easy to control, but they also produce more friction, noise, heat, wear, and sparks because of the brushes. Brushless motors are more efficient, powerful and durable.But they also cost more and require more complex electronics. I want to know the pros and cons of both types of motors and how to choose the best one for a particular situation.I also like to compare them to other types of motors, such as AC motors, stepper motors, and servo motors. I am always interested in sharing my knowledge and experience with other people who are passionate about motors. If you want to know more about the difference between brush and brushless motors.
 

Delta Prime

Jul 29, 2020
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. I am always interested in sharing my knowledge and experience with other people who are passionate about motors
Me too. I don't regurgitate textbooks. You ever had an accident working on a brushless DC motor? Funny tail , close call, something unusual happened, tell me a little about that?
 

jackstone

Sep 12, 2023
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I've been working with brushless DC motors for quite some time, and while I haven't had any major accidents, there have been a few memorable moments. One that comes to mind was when I was testing a new motor controller for a quadcopter project. I had just finished assembling everything and was about to power it up for the first time.

As I connected the battery, I noticed a strange smell coming from the motor. I quickly unplugged the battery and inspected the motor, only to discover that a small piece of debris had somehow found its way into the motor housing. It was causing the motor to seize up, and that's what was causing the smell. It was a relief that I caught it in time because if I had powered it up, it could have caused some serious damage to the motor and possibly even started a fire.
 

davenn

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Sep 5, 2009
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guys, this was a VERY OLD thread, Please always look at the last posted day before resurrecting the dead

thread closed
 
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