Stir motor type: stepper or brushed?

[chuck-h]

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 .

• cheaper motor
• simpler drive (one transistor & diode)
• fewer microprocessor pins

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]

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 <[email protected]>

To: hivebio/ministat-1 [email protected]
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 .

• cheaper motor
• simpler drive (one transistor & diode)
• fewer microprocessor pins
  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?—
  Reply to this email directly or view it on GitHub.

[ptschnack]

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

[chuck-h]

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

[zanghell]

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 [email protected] 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]

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 [email protected]
To: hivebio/ministat-1 [email protected]
Cc: ptschnack [email protected]
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 [email protected] 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]

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.