Flight Time vs Amps

Use this simple calculator to estimate your flight time if you know how much current (measured in Amps) your drone uses when hovering. Remember, estimates from this calculator are based on all conditions being perfect. To learn more, please read the rest of this page.

What is "Reserve"?

Reserve is the amount of charge left in your battery after you have landed. If you run a battery to zero, you can damage it and it will no longer hold a full charge. If you're flying when the battery is near the end of its charge, the voltage will drop quickly and your drone could fall out of the sky.

Using a higher reserve can increase the lifetime of your battery. Many people prefer to use 20%. Different types of batteries require different amounts of reserve to get the maximum number of recharge cycles. Check with the manufacturer of each battery to get the recommended reserve.

Battery Size vs Weight

When using this calculator, remember that increasing the size of a battery also increases its weight. This will cause your drone to use more amps. You'll probably get more flight time with a larger battery but this calculator does not account for the added weight.

For example, the default example gives a 41 minute flight time with an 8000mAh battery and a drone that uses 10 amps to hover. If I switch to a 10000mAh battery, the calculator says 51 minutes. But, the 10000mAh battery is heavier and the drone will use more amps to hover. It might only fly for 48 minutes. Does that justify the increased cost and reduced camera payload?

If you have a number of different sized batteries, measure the amps your drone uses with each one. Then use this calculator to get the flight time for each combination of battery and amps. If you graph the results, you will learn which size battery is the most efficient overall.

How Can I Reduce the Amps?

The more important answers are at the top:

• Make your drone lighter. dCal was built to help you do that.
• Use lower KV motors with larger propellers. While this may not apply to racing drones, its an important factor if your're building a drone for photography or video.
• Find the best combination of propeller length and pitch to match your motors. This may require some experimentation.
• Tune the PID settings in your flight controller.
• Make sure your propellers are perfectly balanced.
• Keep track of how much current is used by all of the accessories- cameras, video transmitters, lights, etc.

Are those Default Numbers Realistic?

Yes. Those numbers are taken from a previous drone I built as a group project. It used 380kv motors with 15" props, and the current draw at hover was between 9.5 and 10.5 amps. I got fairly consistent 40 minute flight times with an 8000mAh 6S battery. It had a GoPro HERO4, separate FPV camera, remote switcher, and PIP board.

Reality vs Expectations

As my friend Forrest pointed out, conditions in real life don't always match calculated estimates. Here are some factors that could effect your flight times in the real world:

• Even though your battery says it has a certain number of mAh, it may or may not be true. That 8000mAh battery you bought on eBay, may only provide 7600mAh.
• Your battery wasn't fully charged. Sometimes, the settings in a Lipo charger have to be adjusted or the charger will shut off automatically before the battery is fully charged. Always read the documentation for your battery charger. Lipo batteries can be dangerous if you don't follow the directions!
• As batteries age, they may provide slightly less power. As I continued to test my last drone that began with 40 minute flight times, it was down to 38 minutes after 6 months of using the same batteries.
• Temperature will affect the output of a battery. Lipo batteries perform best when they are slightly warm. But if they get too warm, they can be damaged. Check with each manufacturer for the best operating temperature.
• Amps will slowly increase as the battery is discharged and the voltage drops. This varies depending on a number of conditions so it can be difficult to calculate. If you're using Ardupilot, you can get detailed logs from every flight. Using the log data, you can graph the voltage and current usage to check the performance of your battery in the real world.
  
  
  Here's a graph of the voltage during one of my 40 minute test flights. The graph was automatically generated by Mission Planner, a free software package available on the Ardupilot site.