After doing a little research I found out that I can change voltage by either using a voltage regulator chip or resistors. I have a couple different scenarios in which I'll have to drop the voltage for my motors and I was wondering which method to use for each application.
I'm using an H-Bridge to drive a bipolar stepper motor rated at 3.1V. I need the stepper motor's speed to change. Does the H-Bridge in this circuit drop the voltages as necessary to change the motors speed or is it simply able to rotate in either direction at a constant speed? http://arduino.cc/en/Reference/StepperBipolarCircuit
Driving a 7.2V DC motor with a PWM output ( http://www.vexrobotics.com/276-1668.html). I believe I'm supposed to wire up the power and ground of the PWM to the motor's 7.2V power supply and wire the signal wire to one of the Arduino's ports. This motor would also have to change speed.
Running a 12V air compressor.
Although I'd like to use resistors for all of my voltage drops/increases I believe I read somewhere that it cant be used if the appliance its connected to has to change voltages (ex. a motor that needs to change speeds.)
**All of these will be powered by one or more 9v batteries.
Thanks! So to summarize what I should do...
Stepper Motor - Wire the inputs to an H bridge with a 3v power supply. (2 AA cells in series) Although I'm planning on giving the stepper motor a seperate power supply to simply things, if I were to run it off the same power source (6 AA cells) as the Arduino, can I use a resistor to drop 9v to 7.2v and than supply that power to an H-bridge? Which would than be connected to the stepper motor.
7.2V DC Motor - Use an h-bridge to pulse 7.2V to the power and ground of the PWM and pulse the signal wire to control the motors speed? Or can I use resistors to drop 9v to 7.2v and than simply pulse the signal wire to control the speed? I'm not sure if the problem with the resistors dropping varying amounts of voltage depending on the motor's load would persist in this scenario. (Kind of similar to the stepper motor scenario except I'm pulsing the motor through a PWM motor controller instead of an H-bridge.)
12V Air Compressor - Wire several cells in series to hit 12V and than turn it on/off by using an H-bridge.
I actually have several 12v golf cart? batteries which can be found here http://www.andymark.com/product-p/am-0844.htm. If I were to use this, it would be with the 7.2V DC Motor and 12V Air Compressor. (The Stepper Motor is going on a moving vehicle which is way too weak to carry the battery.) I was thinking about using these batteries but I thought the amperes it gives out would far exceed what any of my appliances can handle. It'd be awesome if I can use this though! I'm constantly going through AA/9v batteries and its been getting quite expensive.
This is the diagram for the stepper motor circuit. It's set up pretty much the way I'm planning on running it.
This is the diagram for the 7.2V motors and 12V air compressor. The batteries shown there is actually a ~12V car battery. I'm still trying to figure out how I'm supposed to drop the voltage to 7.2. I looked at the LM317 adjustable voltage regulator but it can only handle current up to 1.5A and the motor I'm planning on using has a stall torque of 3.6A. The motor I'm using is NOT a servo but it's connected to a 3-wire motor controller (http://www.vexrobotics.com/276-2193.html) which uses a standard PWM signal to drive the motor. My plan is to connect the 7.2V power supply to the power and ground of the motor controller and to connect the motor controller's signal wire to one of the Arduino's ports.
The air compressor isn't shown but I'm assuming I can power it directly through the battery (with an H-bridge in between as a switch).