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soundbio / ministat-1

An open source turbidistat for cell culture
BSD 2-Clause "Simplified" License
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Stir motor type: stepper or brushed? #1

Open chuck-h opened 9 years ago

chuck-h commented 9 years ago

The UW turbidostat uses a stepper motor to turn the magnet hub for stirring. Apparently they recently switched motors and changed the circuit slightly because of supply problems with the first motor.

I suggest we use a small brushed motor like http://www.adafruit.com/products/711 .

Question: do we need speed control on the stirrer, or can we just give it a voltage and let it spin? This motor probably likes to run pretty fast, is that a problem?

ptschnack commented 9 years ago

I was thinking about this too. I Googled: 'adafruit speed control dc motor' and got this: https://learn.adafruit.com/adafruit-motor-selection-guide/dc-motor-control Upshot: we can use cheap dc motor and drive it with pwm. (Whew! Expensive steppers are overkill for this.)

  From: chuck-h <notifications@github.com>

To: hivebio/ministat-1 ministat-1@noreply.github.com Sent: Monday, January 26, 2015 8:35 AM Subject: [ministat-1] Stir motor type: stepper or brushed? (#1)

The UW turbidostat uses a stepper motor to turn the magnet hub for stirring. Apparently they recently switched motors and changed the circuit slightly because of supply problems with the first motor.I suggest we use a small brushed motor like http://www.adafruit.com/products/711 .

ptschnack commented 9 years ago

The uController has PWM outputs, right? Can these be used to drive a transistor or other power amp to run the motor?

chuck-h commented 9 years ago

PWM to a power transistor sounds like a great idea; I think we want about 1V at the motor.

zanghell commented 9 years ago

is that to replace a motor controller ? sorry if I missed something in the thread. Alex.

On Feb 3, 2015, at 12:44 AM, chuck-h notifications@github.com wrote:

PWM to a power transistor sounds like a great idea; I think we want about 1V at the motor.

— Reply to this email directly or view it on GitHub.

ptschnack commented 9 years ago

Yes. Small DC motor controllers are often just a pulse width modulator driving a power output stage. The uControllers we are using can be used as PWM drivers, so the uController itself can drive the motor. We just need to add a very simple power/buffer stage. Probably just a transistor with protective diode and caps for filtering. From: Alexandre Zanghellini notifications@github.com To: hivebio/ministat-1 ministat-1@noreply.github.com Cc: ptschnack ptschnack@yahoo.com Sent: Wednesday, February 4, 2015 10:05 AM Subject: Re: [ministat-1] Stir motor type: stepper or brushed? (#1)

is that to replace a motor controller ? sorry if I missed something in the thread. Alex.

On Feb 3, 2015, at 12:44 AM, chuck-h notifications@github.com wrote:

PWM to a power transistor sounds like a great idea; I think we want about 1V at the motor.

— Reply to this email directly or view it on GitHub.

— Reply to this email directly or view it on GitHub.

chuck-h commented 9 years ago

Last week I received the small stir bars and ran one in water with the DC stir motor. I used a PWM microcontroller output driving one channel of a ULN2003A darlington array. Motor speed and distance from magnets to testube have to be controlled in order to get stable motion, but I think it will work.