Battery voltage + motor selection

[Mossen]

Sorry for all the top posts today - lots of questions!

I was wondering if someone could explain how, at the design phase, you go about choosing what voltage motors you run in a robot? Do you typically find a motor first that meets your requirements, and then find a battery with that voltage? Or is there a common voltage that most hobby robotics motors run on that I should shoot for? I don't want to end up with a motor that requires a weird voltage. If you see one that has an "operating voltage range", of say, 4.8-8.4V, what is the benefit to running it at 8.4V when you could run it at 4.8v? Does it draw less amps if you give it a higher voltage?

mossen

[imarcianoloco]

There are a few typical ranges on DC motors such as 1.5 - 6v on small hobby motors. Some high-quality DC motors are designed for a specific voltage, such as 12 or 24V. The kinds of motors of most interest to robot builders are the low voltage variety, basically from 1.5 to 12 volts.
As for the current consumption of a DC motor respect to it's applied voltage, current draw always increases as you increase the voltage, but your motor will spin faster and stronger.

[WhomBom]

You should really plan thos things, i'm no expert on it   but as i build on my bots i tend to hit walls because i didn't think it all through.

I guess you should have a pretty detailed plan to what your bot should do and go from there. For instance I want to build al line following bot. You should think about how long you want to be able to keep following the line before recharging?
How fast do you want to follow the line? what sensors do you need to trace the line (at that speed) what voltage do they need? what voltage does your microcontroller need? what would be the total current consumption  etc etc  

when you have that picture you can choose motors to reach the speed you want. I'd choose the voltage rating (nominal which means as much as what it was designed for i guess) of the motors so that i could feed them directly off the same battery pack as my sensors and microcontroller (but use capacitors to prevent sudden voltage dips etc). You could also choose two separate packs, one for the motors and one for the electronics but it's more of a hassle charging the both.

Also look at the current consumption of your motors, it could be as much as 12A or more. make sure all your electronics regarding the motors can handle this. Lastly you would choose a battery pack with a mAh rating to fit your time demands. For instance a 7,2V 2000mAh pack would drive a 7,2V 2A motor for one hour. But keep in mind heavy on the mAh usually means heavy weight or heavy on the wallet.

Again i'm no expert but i'm sure someone will correct me when wrong 

[z.s.tar.gz]

Choose a motor that will give you plenty of torque and speed (at the very least 1.5x what you think you'll need. shoot for 2x) then get a battery based on that. There are lots of different motors out there but usually you're looking at around 6v for little ones and 12v for bigger ones. Based on your situation this may vary.

The motor produces more speed and torque at higher voltages but also uses more current (actually it's the current that causes the torque but you get the idea) if you want to get long battery life, use lower voltage. if you want maximum power, use the high voltage.

as with all electronics, just keep ohm's law in mind when working out what you need. given that the resistance stays the same, an increase in voltage leads to a direct increase in amperage.

edit: also keep in mind that it's far easier to get a good battery and good motors and just make a voltage converter than it is to find the specific parts.