DC Motors and speed control

[Jon Cavendish]

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]

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]

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]

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]

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]

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.