[Headline: Diagnostics ain’t rocket science]
We all run into problems now and then. It doesn’t matter if you’re new to electrics or have been doing it for years. The key is knowing how and where to look for the things that might be contributing to the problem. You don’t need to be an engineer, but it helps to have a plan and be organized.
Tools of the Trade
It doesn’t take much, but there are certain things all electric fliers should have: a watt meter of some sort, a battery meter (to check individual cells in a pack), temperature gun, voltmeter, balancing charger, and a program such as ElectriCalc or MotoCalc.
None of these are expensive and there are calculator programs online at some of the vendors’ websites, but I suggest buying one of your own to help you evaluate projects. They are approximately $40. If you have a good battery checker, you might even get away without a digital voltmeter, but they’re so cheap now that I’d suggest owning one anyway.
Finally, I love ESCs that have some sort of data-logging capability. If you don’t have one, you can buy a small data logger from places like Eagle Tree Systems that will give you critical data. Some radio systems are also incorporating telemetry that can record motor data. This type of information is invaluable. Without data, there is no diagnosing a problem.
I frequently receive questions about why a system is giving someone only 5 minutes of flight time when it “should be giving a lot more.” The first thing to do is determine if your expectations are realistic. If it’s a 5S system drawing 80 amps from a 5,000 mAh LiPo pack, it’s only going to run 3.75 minutes. How do I know? Easy …
A 5,000 mAh (5 amp-hour) pack has 300 amp minutes. To determine that, multiply the 5 amp-hour rating by 60 to get the amp minutes (5 amp hours x 60 minutes = 300 amp minutes) That’s the usable time for the pack and if you divide that by the 80 amps you’re pulling, you get 3.75 minutes of flight time (300 amp minutes ÷ 80 amps current = 3.75)
Know how to interpret data logs. I recently had a request for some help and he provided the logs from three flights. This was great! The problem was that he told me the average current was 35 amps when it was actually closer to 60.
What he didn’t realize was that the data log included the time the battery was plugged in to arm the system—then it sat for a couple minutes while he got ready to fly. That time was spent at zero or near zero current draw and figured into the total time when it averaged the flight. It saw the flight as the time between arming and disarming.
Within the program to evaluate the logged data there is a way to pull the parameters in to only see the actual flight time. That is the time we’re interested in and the real data. It’s an easy mistake to make and easy to fix. When we got the actual average current figures, the total flight time was within reason.
No Shotgun Approach!
Please, please, please … if you take nothing else way from this column, take this: do not make multiple changes at once! I get questions from people who wonder about a duration or heat problem and they’ve made several changes at the same time. Do one thing and see what it did for your issue.
If you make several, you don’t really know which helped or hindered your progress. Remember your high school science class and use a scientific method such as follows:
• Ask a question.
• Do background research.
• Construct a hypothesis.
• Test your hypothesis by doing an experiment.
• Analyze your data and draw a conclusion.
Think about your problem, determine some possible causes, and take an action to correct it. Only one action! Reevaluate and go to the next solution.
Did you make some progress with the first? Is there another option using the first attempt (different propeller if you’re trying propellers, etc.)? This is common-sense stuff, but we all get in a rush to get flying and will often throw the kitchen sink at a problem.
Think About Common Things
I could have stated, “Use the KISS principle,” but you get the idea. We sometimes overlook the obvious and go far deeper into something than necessary.
Did you use the suggested propeller? Did you grab the right battery pack? Is the pack fully charged? Are all the cells good? Is your wiring done well? Are the connectors of good quality? Is your solder work done well? Are your ESC settings correct? Is your transmitter set properly?
In other words, don’t start calculating commutation frequency and exact pulse-width modulation (PWM) settings before eliminating the obvious. I always assume I did something wrong before blaming the equipment. After I rule out my own error, then I can move on.
Wrapping It Up
I’m going to expand on some of this next time, but I hope this brings some common sense thoughts back to the forefront of your diagnostic method. Hopefully you don’t even need to diagnose a problem ... but sooner or later, you will.[dingbat]
Eagle Tree Systems, LLC