2 Speed Leslie Controller

[rossp6304]

I don't know where to turn for help on this problem, so I will start here at diystompboxes. 

I have a Leslie cabinet that was ripped from an organ and I retro fit into an old television cabinet.  The rotating baffle is spun by either the fast motor or the slow motor.  In its current state I can activate either of the motors using the switches on the back of the cabinet.

Here's my question/challenge/dilemma.  I want to be able to control the speed of the baffle with an expression pedal.  Can anyone help me?

[R.G.]

Somewhere between maybe and probably not. If I remember correctly, those motors are AC motors. Controlling speed on an AC motor is easier these days than it used to be, but it's not a simple thing to hook up an expression pedal because you have to control the AC supply's frequency, not just its voltage. It can be done, but it involves using a microcontroller to synthesize a variable-frequency AC power source.

Maybe you could rebuild it with a DC motor. That's a different set of problems, but it does make it smoothly variable with a DC voltage.

[rossp6304]

Thanks R.G. I was kinda thinking that I would need to do something along those lines, which of course means that this is beyond me.  What I will probably end up doing is making the switch box seperate from the unit so it can sit on top of the keys or close to the guitarist.  Again, thanks for your help and promt reply.

RP

[R.G.]

One possibility - if you're the kind of guy who's tough enough to mount a Leslie in a different cabinet    - is to go to Surplus Center and get a DC motor to replace the AC motor, and construct a (big) DC supply to drive the motor. Then you have full control of speed and timing by the DC into the motor.

But it's a bigger job.

[wavley]

I currently have mine hooked to a variac to control motor speed steadily.  If you can/want to keep a constant pressure on a pedal then you can use a sewing machine pedal which is just a big spring loaded rheostat, I found it to be too much of a pain to control not to mention that if you take your foot off the pedal then the leslie will stop.

[Arn C.]

Why wouldn't it be possible to use a fan speed control in the pedal.   I use them all the time at work for fans,  that has an ac motor.

example:    http://www.aerocooler.com/shop.cart?action=ITEM&prod_id=CBLOK51

and it has a pot .  Usually the go from off to full on and as you go clockwise it gets slower, so if you wanted it slow to fast maybe can rewire pot and just set it
so you don't turn it off.

Just a thought!

Peace!
Arn C.

[Derringer]

they sound righteous when you can just toggle the switches


funny thing, when I saw this thread title this morning it made me recall a forgotten dream from last night.
in the dream, I was eye-ing up how to install a rotating leslie wedge somewhere behind the dual 2 1/2" mufflers on a big block chevy I used to have. I remember thinking that I'd need to find a way to monitor proper backpressure.

Now awake, I think it would make for an awesome sound if done properly 

[wavley]

Why wouldn't it be possible to use a fan speed control in the pedal.   I use them all the time at work for fans,  that has an ac motor.

example:    http://www.aerocooler.com/shop.cart?action=ITEM&prod_id=CBLOK51

and it has a pot .  Usually the go from off to full on and as you go clockwise it gets slower, so if you wanted it slow to fast maybe can rewire pot and just set it
so you don't turn it off.

Just a thought!

Peace!
Arn C.

Those things use SCRs to do their job I'm sure it would work, but it's electrically noisy.  I have to turn off all the dimmers and fan controls in my house when I record because the noise creeps in my amps.  If you improved the filtering somehow it might work.

[iccaros]

if you were to use a DC motor, AS RG suggested, I from my AUV building experience, would recommend a nice Strong Stepper motor, USE a H-bridge controller and PWM from a Micro controller.

http://www.bobblick.com/techref/projects/hbridge/hbridge.html

that would be my route.. 

[rossp6304]

Wavley – I think that is too much work for me, and like you said the motor will stop when you release the pedal.

Arn C. – I like this idea and since I have virtually given up on the expression pedal, I will probably go along this route.

Derringer – Your controller is very similar to what I think I will try, but with some dimmer switches like these.
http://www.amazon.com/LEVITON-A00-06683-0IW-ROTARY-DIMMER-SWITCH/dp/B004LWEV12
Also that is a weird dream.

Wavley – I hope that the switches I use will not be as noisy as yours, but I seem to remember hearing a distinct buzz from the ones in my house as a kid.

Iccaros – I will probably not be replacing the existing motors unless absolutely necessary.  I also hope to avoid a microcontroller because I am an accountant, not a electronics technician.

[pinkjimiphoton]

well...there's other things too, like using the speed control pedal from an old sewing machine. not reccomended tho, and if you wire it wrong (which of course i did) you will try to "brown out " your house wiring. not a good thing. i did get it to work, poorly.

usually in most of the ones i've messed with there's three terminals, fast, slow and common. some seemed to work best with all connected, some with just one or the other to change speed.

if you add a momentary switch to it, you can "ride" it, too...turn it off and on. i used to build mini vibratone cabs out of these things, take off the small speaker and put a 12" driver in 'em to drive the drum with, then build a cabinet around it with open sides...killer little boxes. i didn't know anything about anything electrical, or perhaps should say i know less than the not enough i knew then.. but if memory serves, my bud who ran a local electronics repair/FOH/pa rental place told me to use dpdt switches and big honkin' caps to nuke the clicking from switching transients.

forgive me if this is retarded....i'm sure what i did probably was potentially 90% lethal.

[Seljer]

The problem with AC motors (induction motors) is that they're locked onto the frequency of their power source (so if you have a 2 pole motor, with no load on it it spins at 3600rpm on 60Hz AC and at 3000rpm on 50Hz AC).

If you apply a load they slow down to somewhere around 20% or 30% of that speed before the torque of the load is too large and so it stops the motor: (100%-20%) * 3000rpm = 2400rpm. This value depends more or less on motor construction.
If you lower the AC voltage only the size of this breakdown torque changes, however it occurs at the same rpm.
You can use this method with fans (eg: with a TRIAC like that fan controller that was linked) because the load curve of the fan is proportional to the square of the rpm and is steeper than the motor's characteristic, allowing it to spin steadily in the area of operation that is generally unstable.

I assume the main load on the motor in the rotary speaker is just friction (which is roughly constant at all speeds) so I don't think it would work.