CS 8 Mk stack, and new Bl v 3.0. MT 2814-11 kw 710. Meijslik 13x4,2 Carbonprops. AUW with M5 and GH4, 7kg. Motors 2,4,6 (and 8) get much hotter than 1,3,5 and 7. Today 31c outside and only little wind. After 5 min easy flight, not hovering, hottest motor is 93c?!
Janne: Have you checked that all the motors are truly vertical -- you can see this kind of asymmetry if one motor is out of vertical and inducing a yawing motion -- the other motors are then driven to compensate. One of the easiest ways to see if the motors are all vertical is to take off, hover at eye level about two meters away from you, and look at the "disks" formed by the propellers -- you can pretty easily see if they are all flat or whether there is one that is canted over to one side. Andy.
Janne, the temps you're seeing are the BLs, not the motors, just to be clear. The reasons for this can vary, but if you have one of the even motors with a bad bearing that can happen. Another thing that can cause it is one of the odd motors being angled so that the even motors have to compensate to prevent yawing. This is of great concern because with my BL3.0 board I've never seen a BL temp higher than 45-48°C. And it actually looks like all your BLs are very hot. The variation in current draw of even vs. odd does show higher currents on the even motors, though. Your current draws don't look stupendously high, so I'd be concerned about what's going on. Do you have adequate airflow over the board? I don't know of anybody who's used 4S with the BL3.0 boards, so maybe there's something to be concerned about with 4S vs. 6S on that board. I'd try a short flight with a 6S LiPo just to see if there's any difference, as you're running 6S-compatible flight control. And one more thing: did you update the firmware on the BLs themselves? There have been a couple revs of the firmware for the brushless controllers. It's a pain in the ass to do the update, but I wonder if this could be one of the issues that was addressed? http://www.mikrokopter.de/ucwiki/en/BL_V3Update
Thanks Andy, after yet another cold shower I did just that ;-) Now testing the 3° tilt motor ¨trick¨ to get better yaw stability. Do you know how hot a motor can get before its damaged? Regards from hot ;-) Sweden.
Thanks Steve, the board is covered by the clear Freefly C8 cover, i´ll have to paint it white and make some vents in it. Also have to look into this Bl uppgrade! Regards. /Janne The M5 works fine with the blue dampers
Good question. There's the Curie Point at which neodymium magnets lose their magnetism. That can be from 310C to 800C. Hmm...I suspect the motor wiring and/or any soldered connections in the motor would fail before that....but I'm not sure what temperature at which that would happen. I managed to burn out a QC-3328 motor recently when I was testing it -- I'll see if I can find the data acquisition file and look to see what the motor's outer casing was when it melted. I was testing it under extreme conditions (e.g. it was pulling 600 watts -- but it's only rated for 450 watts!) Andy.
Janne, were the motors hot, too? Do you have an infrared thermometer that you can use to measure them? I'm curious about these motors, as they appear to be quite small, and with smallish props, there could be some kind of mismatch causing the BLs to work harder than they should. We are learning that the high-performance electronics in these modern machines can be very twitchy. I've had the opportunity to share quite a few emails with Holger from MK, and even he is learning a lot about some of these motors. For example, the high pole count motors vs. lower pole count motors can introduce a lot of complexity to the brushless controller in terms of managing things like commutation errors.
A good guideline for Motor Case temps is from ecalc. I think most motor companies use similar guidelines. the prediction of the motor case temperature is critical (>80°C/175°F). Risk of overheat, please check! That being the case if your motor cases were really 93C then yes you have an issue. If it is the BL's then you have some room left. Really needs an IR thermometer to be sure.