Tri-copter power drop while flying

[gator44860]

Novice tri-copter builder/pilot

Here is my issue, as I am flying I get a power drop on the front right motor, which causes the tri-copter to fall from the sky, or drop for a second or two and continue flying. Here are my specs;

3X Emax 1470Kv motor's
3X ready to fly 30A ESC's
8X4.5 propellers
KK 2.1.5 with the latest Steve’s software
Emax 12g ES08MALL Metal Gear servo
Tri-copter weight 714g

My battery power is coming from (2) 3s C25 2200mAh batteries connected in parallel, and using a power analyzer (without Propellers) at ½ throttle my reading are;

3.4A
12.23V
41.5W
0.011Ah

At ¾ of a throttle my readings are;

3.9A
12.17V
47.4W
0.019Ah


My questions are to fold does anyone see something I may have miss trying to figure out why I have and intermediate drop in power on the front right motor while flying, and has anyone else experience this type of problem and how did you solve it.

Any help will be greatly appreciated,

Gator 44860

 

[joshuabardwell]

Just for perspective, power readings with props off don't mean very much. Maybe, in theory, you could diagnose a bad bearing by measuring a good motor's no-load current compared to a failing one. It doesn't tell you anything about what's happening in the air, though.

My gut says you're well under 30 amps with those motors and those props, so I wouldn't think that thermal cutoff/failure of your ESC would be an issue.

Consider swapping your two front motors and see if the problem stays on the same side or moves with the motor. If it moves with the motor, the motor is the issue. If it stays on the same side, it is either the ESC or the flight controller.

Does the issue happen with the props off, on the ground? Or only when you are actually flying?

 

[gator44860]

It didn't happen when I took the props off. We been having bad weather down south, so I have not been able to go flying. However, during my initial flying I notice the battery alarm on the KK 2 began to sound within one or two minutes of flight. I will not only do the swap test you recommended, but I will also do a thrust test on one of the motor to see what type of readings I get. That way I can hopefully pin point the problem.

Thanks for your help!

 

[joshuabardwell]

If the battery alarm is going off, that could certainly explain it. The ESCs may have a low voltage cutoff and/or they may be programmed to reduce power on low voltage. Normally, for a multirotor, you do NOT want this. With a fixed-wing, if the motor cuts off, you can still glide it in to a landing. With a multirotor, you would usually rather run the battery flat and destroy it than lose a motor and crash the copter.

What exact ESC do you have?

 

[gator44860]

I am using Ready to fly 30A ESC's flash with simmonk software from witespyguad.gostorego.com

I when ahead and did a bench test on on the motor with the drop in power, here are the result of the power analyzes using a 8x4.5 propeller.

25.0A
11.14V
278.5W
0.042Ah

At full throttle!

I will try swapping the motor and taking it for a flight as soon as the weather clears.


Thanks a million!!!

 

[joshuabardwell]

4400 mAh @ 25C = 110 amps.
25 amps @ WOT * 3 motors = 75 amps.

My experience has been that battery C ratings are often ambitious, so you are probably seeing some voltage drop at high throttle, but probably not an excessive amount. Maybe as much as 0.5 volt.

The battery alarm is certainly something to explore. Is the KK board monitoring the pack voltage via a separate sensor, or is it alarming when the voltage it's getting from the BEC goes low?

4.4 Ah / 75 Amps = 0.059 hours run time to full discharge = 3.52 minutes. That's at WOT, mind you. I'm a bit surprised the battery alarm went off after only a minute or two of flight, unless you were absolutely thrashing the thing.

 

[gator44860]

Joshua,

I have the KK2 board monitoring the pack via the connection on the board (KK2.1.5 battery connection). I did not time the alarm on the board, so it could have be longer then a couple of minutes with 2 3s2200mAh 25c pack in parallel. I have only flown the copter a twice. My first flight a single 3s 2200mAh 25C that flight took a couple of minutes before the alarm went off and I started loosing power, so I decided to add a second 3s 2200mAh 25C battery in parallel.
How much different would it make a running the packs is series?

 

[gator44860]

Joshua,

I have the KK2 board monitoring the packs via the connection on the board (KK2.1.5 battery connection). I did not time the alarm on the board, so it could have been longer then a couple of minutes with 2 3s2200mAh 25c pack in parallel. I have only flown the copter a twice. My first flight a single 3s 2200mAh 25C that flight took a couple of minutes before the alarm went off and I started loosing power, so I decided to add a second 3s 2200mAh 25C battery in parallel.
How much different would it make a running the packs is series?

 

[joshuabardwell]

Do you know what voltage your alarm threshold is set to?

Do not run the packs in series. This will double your voltage and possibly fry your ESC's, at the very least, if they are not rated for 6S. If your ESC's are rated for 6S, they won't fry, but then your motors will probably fry as they spin twice as fast as before and suck much more current than they are rated for. Remember: parallel packs increase capacity; serial packs increase voltage.

 

[gator44860]

I set the voltage alarm on the board to 10.5 volts.

Side note: Thank you, and the entire flitetest team for all your shows, podcast, articles, and specially the forum. I have learn so much from your guys!

 

[joshuabardwell]

If the ESC does have its low-voltage cutoff enabled, 10.5 may be low enough that it is cutting in. You may want to look up programming instructions for the ESCs and see about making sure LVC is disabled. You can usually do this by setting the ESC's battery type to NiCd.

 

[gator44860]

Joshua:

Here is everything I found regarding the ESC's from Ready to fly quads, where I got them from (http://www.readytoflyquads.com)

This all new ESC was designed ground up for multirotors and uses all new Fets for superior performance. The real benefit to this standout ESC is the high voltage design. With up to 6 cell lipos, you can have longer flight times without the high weight penalty of all other 6S ESC's on the market.

Features
All new Fets on a compact PCB
Smaller and lighter than standard 30A ESC's
30Amp constant with 35Amp burst
Dual Capacitors for reduced voltage spikes
OPTO, NO BEC ONBOARD

2S through 6S Capable!

Weight:
Standard with wires: 25 Grams

All N-channel FETs
External Oscillator:
Boot-loaded Enabled

Flashed with the famous SimonK OpenSource Firmware for super-fast throttle response, which makes your quad more responsive and "locked in". These ESCs do not overheat, burn or lock out - unline many other ESCs flashed with the SimonK firmware. The Gold standard ESC for multirotors. Free reflashing if new firmware comes out, flashed with the most currect firmware. ESCs now have the bootload firmware which can be upgraded by using TURNIGY USB Linker.

These ESCs are completely re-designed from the ground up. Flashed with the famous SimonK OpenSource Firmware for better throttle response . New firmware means direct, linear throttle response, making it suitable for multicopter use. Up to 600Hz input rate is supported, with immediate updates to motor pwm duty. Each ESC is tested with a motor before and after loading new firmware.

The the external 16MHz oscillator line up exactly with the numbers in microseconds, but the internal rc oscillator ones will drift quite a bit based on temperature.

The ESCs use only N-channel FETs have the advantage of lower resistance, less losses and hence more efficiency.

All N-Fet:"The ESCs which use only N-channel FETs have the advantage of lower resistance, less losses and hence more efficiency."*

External Oscillator:"An external oscillator may supply a more consistent timing signal and steadier motor speeds" "but the internal rc oscillator ones will drift quite a bit based on temperature.

These ESCs are a revision of the nearly-perfect F20A & F-30A ESCs with high quality board layout and components to make them perfect. Do not settle for anything less.

NOTE: This firmware does NOT check battery voltage or ESC temperature. Always use a LiPo alarm and monitor pack voltage while using.

NOTE: These are not I2C ESCs and as such are not directly compatible with Mikrokopter-style interface, however they can be used with I2CPWM converter

Joshua thanks for hanging in there with me!

 

[joshuabardwell]

NOTE: This firmware does NOT check battery voltage or ESC temperature. Always use a LiPo alarm and monitor pack voltage while using.

That's the info I was hoping to find. Thanks.

 

[gator44860]

Thank you, Joshua you have been a great help!