Which resistors, capacitors, etc. to choose for H-Bridge DC Motor Controller?

[bonbonbaron]

Hi, I'm building a legged robot whose wheels at the base I want to control with an MSP430. I need to build an H-Bridge for each wheel's motor. The motor's stall current is 2A. I can use 4 AA batteries in series, but don't necessarily have to.

I know how most circuit components work and what they do, and I know how to do the math. So my question is, with so many components required for a circuit, where does one even begin to know what values to use for resistors, capacitors, transistors, and such?

Thanks a bunch in advance!
Michael

 

[Martaine2005]

Hi bonbonbaron.
I ask myself the same question.
I am sure I will get shot down here by the experts but, for me it depends on the individual circuit.
I am having a major problem with a 9v circuit at the moment.

Also I would add to break down the circuits to individual voltages. That's where the datasheets come in handy.
IC's might have a wide range of power input, say 3v to 18v but their output is only 1 or 2 v.
So if you need to power several circuits with different voltages, say 3.3v, 5v and 12v then the mains transformer has to be at least 12v. Or a transformer with different secondary voltages.
Then there are the power requirements. Could be micro amps to several amps. That's where your math comes in. V=I*R , I=V/R, R=V/R.
So either work from the inside out or work from a higher input voltage and regulate each voltage rail to the needed requirements. From there you should be in the 'safe' zone for breadboarding your project.
Hope this gives you an idea of how 'YOU' could do it, but by all means 'NOT' how it should be done.

Perhaps a designer could share some light on this subject as I have never really thought about it. Obviously.

Martin

 

[donkey]

my theory behind this is start with the motor, max current is 2Amp.(stall, never a good idea to stall it).
this gives me an upper limit for current then I would choose transistors to match. when I got the transistors I want I will find the current needed to switch it on then choose the resistor.... I think. don't quote me on this I just made a PSU go black...... dumb cup of water

 

[Old Steve]

Hi, I'm building a legged robot whose wheels at the base I want to control with an MSP430. I need to build an H-Bridge for each wheel's motor. The motor's stall current is 2A. I can use 4 AA batteries in series, but don't necessarily have to.

I know how most circuit components work and what they do, and I know how to do the math. So my question is, with so many components required for a circuit, where does one even begin to know what values to use for resistors, capacitors, transistors, and such?

Thanks a bunch in advance!
Michael

Michael ,the first thing to do is to post the schematic diagram of the H-bridge circuit that you intend to use including, if possible, the control system connections. You could leave out the actual component values for now.
You'll find plenty of schematics online for H-bridge circuits and their control connections. You'll want something that takes PWM input for speed, and high/low levels for direction.
Dedicated H-bridge chips are available for this, too. Off the top of my head, I can only think of the L298N, but that'll get you started. I think it has a 2A max output capability per side. (Not continuous, they get too hot.)

Edit: Actually, I just had a look and there are plenty of ready-made modules based on the L298N available. Might be the way to go.
Here's the L298 datasheet:-
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000240.pdf