Hi, I was hoping you experts could help me troubleshoot a problem with my quad I've just encountered.
I'm testing out the lab's quadrotor with the 880 motors and 20A 3D Robotics ESCs. I've managed to tune most of the settings to my satisfaction, it is responsive in flight without being wobbly and can alt hold to about a meter without sonar.
My problem is that after about 5 minutes or more of flying, the rear arm will dip and the quad will basically fall out of the sky tilting backwards. I've crashed a few times like this. It is always the rear arm. I am not using bullet connections, my connections are soldered. My suspicion is that either the rear motor or ESC is going bad. I'm going to replace them, but can anyone shed more light on this problem?
Hi Stephen, have you checked the temperature of motor and ESC after that happens, or leave it running with motors at about 70/ 80% but tight to a base to see if the motor stops and check the temperature to see if that ESC / motor is getting hotter than the others. You may have a bearing damaged causing the motor to drain more amps and getting the ESC to reach a shutdown temperature. Also, check if the battery safety shutdown threshold from the ESC is at the same level than the other ESCs. If you have the other ESCs with 2.9 shutdown voltage and that with 3.3 (for example), that ESC will slowdown or shutdown much earlier than the others. This is what I can remember.
The simplest way of testing if it is the cutoff voltage is to set the battery type to NiMh rather than LiPo which will basically disable the LiPo protection in the ESC. Time your flights so as not to kill your battery though.
What voltage was your battery at when it crashed?
How well is the battery handling the loads?
I don't think it was the cutoff voltage. The battery was not near empty when I was flying, I even changed batteries because I was afraid low battery might be causing my problems.
If cutoff voltage is the only other idea, I think I'll just replace the motor and ESC and see what that gets me.
Thanks for your insightful answers, I'll report back when I've test flown.
I'm not saying it was a cutoff voltage, however, even with a fully charged battery, if it has a low discharge rate, it can have a very high voltage dropout causing a cutoff if you have a let's say 3.3v threshold protection. The best thing is to put the ESCs in NiMh mode and use a low voltage alarm connected to the lipo balance connector.
From which ESC your APM is getting it's power?
If your APM is powered my the BEC of your rear ESC, you might have the same problem I had.
I had a similar problem where after a 10-15min of flight the ESC that was powering my APM, receiver and telemetry started to overheat and my quad crashed.
I solved the problem by using a stand alone BEC to power my APM, receiver and tememetry module. None of my ESCs BEC are used now so they no longer overheat.
The power to my APM is indeed coming from the rear ESC! I'm not quite sure what a BEC is, let alone how to install a stand alone one for my APM. Can I connect a fifth ESC but only use it to power the APM, not any motor?
The BEC is the Battery Eliminator Circuit that generate the +5V that is on the middle pin of the 3 pin servo connector of the ESC.
Now 99% of all ESCs have an integrated BEC so that people do not need a separate battery pack to power the APM, radio receiver and telemetry module.
The problem with this is that most cheap ESCs use a linear BEC that generate a lot of heat especially with 4S LIPO (the higher the battery voltage, the more heat the linear BEC will generate.)
Most stand alone BEC use a switching regulator so they generate a lot less heat even if the battery voltage is high.
To know how to connect a stand alone BEC look at this diagram: http://www.castlecreations.com/products/ccbec_diagrams/ccbec_wiring...
Remember that the red wire of the servo connector of ALL ESCs must be disconnected when you use a standalone BEC.