low pass filter & buffer for motor

[greg2835]

Hi All,

I am using a low power geared (hobby) motor that has a time constant of about 0.002 sec. I would like to slow this down closer to 0.2 seconds. My first thought was to add a LP filter and a buffer (see attached) before the motor. The buffer has ±18V (2 9V batteries) at the rails. The source is an analog output of an NI module. My question, is the way I grounded the motor to the 9V pair the right way to do this? I have seen my EE colleagues add resistors and capacitors in places I would have never thought of, so I was wondering if I needed to employ something similar.

I should have said, I am an ME, so apologize if this is a bit simple Thanks in advance!

Greg2835
Mechanical Engineer

 

[3DDave]

The left hand side doesn't look correct. Isn't it floating with respect to the op-amp?

 

[greg2835]

Great question, and I don't know haha.

The thought was the left side source and op amp would be independent. The left side just gives a step input, and the motor gets power from the 9V batteries. I could connect the bottom of the capacitor to the ground between the batteries, but with my limited knowledge I wouldn't know if that is the correct way or not. I'm very open to hearing thoughts on this.

Greg2835
Mechanical Engineer

 

[greg2835]

Actually thinking about it you are probably right. The input of the op amp and its output need to be referenced to each other some how. So adding the ground there at the moment does make sense. Attached is an updated schematic.

Greg2835
Mechanical Engineer