According to the Mission Planner logs, the outputs of motors 3 and 4 are double that of motors 1 and 2. Consequently, motors 3 and 4 quickly overheat.
I'm trying to get my new multi dialed-in but after only 5 minutes of hover attempts [at about 45% throttle] both of my CW-rotating motors (3 & 4) get so hot you can't touch them, while the CCW motors remain cool. All calibrations have been re re re re re-run. ESCs, radio, accelerometers, compass, and everything appears to be balanced — fore-aft CG, props, etc. — yaw seems stable, I even disassembled the motors, balanced the bells, lubricated the shafts and bearings with EPIC oil for electrics (note that these motors are new and have less than 15 minutes run time on them).
To make matters worse, This is only the third real attempt to get a stable hover but I can't quite get there from here. I still require manual trim input on the Tx of about 5% right roll and 5% up pitch for it to behave as well as it does in the video. I'd love for it to be rock steady but I'm not sure know how to get there and with two overheating motors there's no way I'm going to attempt to fly outdoors.
I have an email in to HK tech support but no reply yet.
If anyone is interested the video is here and sample log files are here:
2014-03-08_2015-17-29_2062807.zip
For safety, the skids are covered in foam pipe insulation and a prop protector stick was added to each arm (the sticks are from 2 carbon fiber arrows -- $3.50 each at Walmart).
And yes, the props are right-side up =)
Specs
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Frame: Tarot Iron Man 650
Arducopter: 3.1.2
Props: APC 12x4.5
Motors: NTM Prop Drive 28-30S 800KV
ESCs: Turnigy Plush 40A
Battery: Turnigy 40C 5A 4S
Flight controller: APM 2.6 w/uBlox GPS
Receiver: FrSky D8R-II PLUS (modified antennas)
Transmitter: ER9X with FrSky ACCST 8CH module
Weight as shown: 2.4kg
Thanks!
My current PID settings:
Replies
Crady, I experienced the exact same phenomenon with a new fpv quad I have buil, new 3DR 880kv motors ( never used).
I think this is not a coincidence, it is weird.
I also can't explain why. I will now probably put each motor on a bench to test and eliminate all causes that would not be motor or ESC related.
By the way I am using a HK newly bought 30A 4-in-1 ESC which I suspect could be the cause.
I just did a test where I swapped positions between a cool motor and a hot one. Not the cool one is running hot and vice-versa which means the problem is very likely not the motors but somewhere else.
I almost went with a 4-in-1 ESC.
now swap ESC, maybe it's selected timing is very wrong.
I found the online manual for the Turnigy Plush 40A's and did an all-at-once reprogramming of the timing, setting all 4 ESCs to "high".
No change. The two CW motors are still overheating. You can actually smell them cooking after a 3 minute hover.
Tried re-programming again, but this time set all ESC timings to "low". Still having the same issue.
The log file shows the two CW motors need much more output from the APM.
Grrrrrrrrrrrrrrrrrrrrrrrrrrrrr
Whilst not likely on a new frame I had two motors getting hot like yours and it was a bent arm, so slight as to be almost imperceptible though but enough to cause my quad to use those two motors to fight the yaw.
Another reason could be different kv's of seemingly identical motors, a friend of mine who likes to rewind motors found 3 different numbers of turns on 3 of the same Turnigy brand of motors, their kv's differed by quite a bit too. You could swap them with the two that aren't getting hot to confirm. If they don't get hot in their new positions then it's alignment. Either bend the arms the other way or experiment with a washer under one side of the motors
The arms appear pretty locked-in and I used a spirit level to check for twist on each motor mount.
I like the idea of washers -- I'm half tempted to tilt each motor inward using washers under the mounts.
I'm beginning to suspect the winding as well. The HobbyKind motors seem to be very poorly built. Just spinning them by hand when I first got them revealed each was very different from the other. No consistency.
I would vote for motor inconsistency... I've got a remarkably similar setup to yours, 550mm, 28-30S-800kV motors, and 11x4.7 props, all up weight of 1600g. I'm flying a KK2.1 controller, but that is the only real difference.
The motors aren't super quality, for sure. I don't have anywhere near the issues you have, but after a few hard crashes I do have a slight yaw drift due to variable play in the motor shafts. The KK2.1 board doesn't have a compass and so doesn't try to hold heading - if it did, it would certainly send more power to those motors.
At least they are cheap and shipping from the USA warehouse right now - you may want to just get a few spare motors on order and see if that makes a difference.
I'm certainly leaning in that direction but that particular motor is backordered in the US (I just checked).
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