Hi, just been testing my Y6 with it's new 6000mah 4S pack and noticed the motors are getting hot. This is affecting the bottom motors more where if you touch them on the base, non rotating part, they are too hot to touch for more than a few seconds. The rest of the motor is hot but can be held without issue.
To check I did another flight with a 3S 4400mah setup and the motors were again getting hot, not as hot but the flight time was 5 mins vs 13 mins.
It's also worth noting with the 4S setup the ESCs were also getting hot, again after a 13 min test flight.
The flight itself basically consisted of a 13 minute hover in loiter mode, I was testing battery times, and consumed 5000mah. The weather for the UK was hot, 25 deg C. The Y6 is a new 2014 B version weighing 1900 grams or so, std config plus 600 gram pack, with std 10 inch props and 850 blue motors.
And finally to the question, is this normal of does something sound wrong?
The only thing I can think I haven't done is balance the props, guide for this would be handy, but I have no vibration issues looking at the data log.
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I honestly haven't given that much thought of cooling in the way of vents or vanes. I'm more concerned with rigidity of discs and conductive heat transfer. The motors facing down have no clear way of get air blown into windings and I feel that cutting holes to allow air in though the bottom is not worth loosing strength in the mounting process that I use based on 3DR designs. I'll entertain ideas though, but for me a simple disc is all I seek.
I was thinking conduction rather than convection as well. A metal plate with just a touch of heat sink compound would probably pull a lot of heat into the metal arms.
The frame of this thing is like a giant heat sink separated from an overheating part by a thin insulating plate. Free the heat!
Convection still trumps conduction when it comes to electric motor cooling. A computer cpu is a completely different animal and the surface area of the coolers are immense for a 200w cpu (which still require a fan to move the heat). Even then the heat must be removed from the case, and that is done with fans as well.
I've been looking at the various multirotor motor mfr's designs. Most are designed to accommodate a "+" style motor mount to expose the bottom cooling holes and have as little metal surface area contacting the motor bottom as possible.
I'm not saying aluminum plates won't help, but airflow is the notable way to cool an electric motor. Perhaps adding holes to them to expose the holes is a good idea and worth trying, but I don't think 3DR did their thermodynamics homework when deciding to use flat plates. Then again, maybe I'm wrong. What I do know is whenever there is a heat problem on the 200-800hp motors we use to build the machines at work, it's nearly always caused by blocked or limited convective heat flow.
I'm collecting temperature readings on the 850kv motors mounted on CF plates. I will swap them out for the plus mounts and conduct additional temp readings. When I get the aluminum discs I will again post my temp readings for all.
I also plan to assess the heat dissipation readings on all three configurations after each flight and use indoor temperature to measure the drop in temp over time to ambient temps.
This should provide all a relative idea of the inflight temp readings just after landing and the time it takes for these mounts to pull heat away from the motors.
Keep in mind this is only for the lower motors as the upper ones have no real heating issues that anyone has posted.
I would think blocking the bottom holes is restricting convective heat transfer, so while my Y6 has been down for a week and stewing about what to do about the broken motor plate from the last crash (something is really jacked.....3DR is now thinking the Pixhawk may be the culprit) I remembered the steel motor plates that came in the box. So, I'm going to try one. Hopefully the motors marked "bad" are good enough to at least get the thing up in the air. They aren't bent, I just didn't like the feel of them; seemed like the bearings were bad. We shall see.
Convection is the most efficient form of heat transfer. The hole and gap between the arm and motor is quite a large area for heat to get out.
Brushless motor temps should run between 71-93.3C* /160-200F* safely ..the reason its hot at the base is because its not spinning and cooling like the rest of the outrunner it's also absorbing the heat thats travelling into the motor mount and arm that acts as a heat sink to help keep the motor cool...also you'll see a difference in temp. if you run a smaller and lighter mah battery pack...it will make it run cooler and less stress on your motors...balancing props would also help it run smoother with less vibration.
Makes sense. The base of the top motors is probably cooler because it's in the prop downwash, but the motor plate between the arm and the bottom motor may be preventing the wind from reaching the base of the bottom motors.
What materials have a higher heat conductivity than the motor plate and still have the structural properties to do this job? Extra points if I can cut it at home with a hacksaw. ;)
Aluminum would probably do the best and would conduct the heat to the arms, and you could cut the plate with a hack saw. If we could get a group to commit I would be willing to make a bunch of sets on the water jet that would look great
Measured my Y6 mounting discs and they are 45mm diameter.
I'm willing to order 6 plates, but I need to measure the Y6A carbon fiber discs to provide the correct diameter needed.
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