How do I calculate how long my robot's battery will last?

[victorjiem]

I am building a robot with multiple types of sensors, 2 motors for locomotion, 2 motors to control a robotic arm. I want to know how do i factor in all these components to determine a length of how long my battery will last. Lets say I was using a 7.2 V/1600 mAh, now how could I determine its length of life using the voltage and current of each component. I am using a variety of color,IR, tilt sensors and such. So could someone give me a good solution.

[pwagen]

As not all components are used all of the time, if you want to calculate it, you'll need to know (on average, I guess) how much each component is used. Then use that value with how much power each component uses. Then add all the values from all the components together, and that could be quite tedious. However, it's very much simplified if you've got the specs for each individual part (like the motors, or the sensors). You'll drastically reduce the number of components you need to include in the calculations.

 

Another way is to attach an ampere-meter to the robot and check how much it uses up when idle, and when using all the functions, then use some median value. This would be pretty inaccurate.

 

But the simplest way is probably trial and error. Use the robot with a fully loaded battery, again and again, with different load and idle time, to get an average time the battery will last. If the robot is to do a specific, automated task, fire it up to do that, and just see how long it lasts.

 

Edit: For the calculations, add them up as thus (arbitrary values):

motor A x 2: 30 mA

motor B x 2: 40 mA

sensor: 5 mA

 

Total: 75 mA

 

1600 mAh / 75 = 21.3 hours worth of battery life (neglecting other variables which might be important to include, but you get the idea)

Edited May 31, 2013 by pwagen

[ewmon]

But the simplest way is probably trial and error.

...yes, especially with Peukert's Law complicating theoretical estimates. You may want to monitor the battery's voltage to ensure that it stays within the manufacturer's specs so as to avoid ruining it. You might be able to use Peukert's Law to compute the battery's average current drain, and then, using that value, to use it again to compute how long other batteries would last.