Motors Stock mini titan motor heat issue.

Hi helicopterers, I don't have a heat meter to measure the temperature of the motor of my mini titan but the thing is that on the first battery all looks fine, after the second you can touch the motor with your finger easily, but after the third battery you can only touch it for 2 seconds. It burns a lot. I have to leave it for 15 minutes and then burn 3 more batteries. I am running a yge 40amps esc which remains very cool no matter how many batteries you use. Is this normal for a 450 motor? Or something else may goes wrong? The rotor head seems to rotate as it has to. I want to change the bearings of the main shaft though. Just to be sure. What do you thing about the finger rule as it is mentioned for a motor?
 

murankar

Staff member
First off is this an issue that has been going on or did it just start?


If it just started then I would consider doing some maintenance. I would tear down the motor and check the bearings and see if they are notchy and not spinning freely. If the bearing have any kind of drag then replace them.


As for motor heat your going to have some kind of heat. Especially after 3 packs back to back. If this motor is a scorpion re-brand then it's going to run hot. Most scorpion motors run hot.

Last thing to check is the timing and pwm in the esc. If you have not played with them then they should be good if you have not had this issues before.
 
Thanks for your consider, this heat of the motor has been going around since the beginning. Back then I replaced the stock esc. With the programming card III I set 18 degrees timing as this value considered to be for an out runner motor of 450 size. Now the PWM frequency is set at 9 kHz. I haven't tried the value of 10 or 12, though its an equation which gives your motor kHz: (KV * NOMINAL V OF THE BATTERY * No of poles of motor) / 20 = No of Hz /1000 = kHz . My motor is a stock thunder tiger OBL 29/35 10H but I am not sure what KV it has. If it has say for instance 2300 KV the equation with 12 poles that I am counting in the motor and 11.1 nominal volt of 3s lipo gives me at about 15 kHz. Which means I should set 14 kHz in the prog card. But I have it set at 9 kHz and I don't know how many KV is my motor. If that plays a role to the heat of the motor. What KV could have a thunder tiger OBL 29/35- 10H motor? It isn't written on the motor. I want to check the bearings of this motor though.
 
Many thanks, I just found out that the poles of obl 29/35-10H are 8 and not 12. 12 are the stators arms. So if the above equation is correct that gives me 15 kHz!
 
Guys though the above equation gives me to use 15 kHz pwm, I tried it and the motor is overheated from the first battery pack. At 9khz this temperature is achieved after the second pack. So 15 kHz heats the motor a lot. And something else. I took off the motor so I could hear it under no load. And I played with 10,12,14 kHz. At 14 kHz when you are say at 60% throttle and you go at 85%, the motor accelerates, do some interruptions and then goes at 85%. Dangerous stuff. So I let it at 9 kHz where I think its nice. Now for the timing, I don't know, the manual with the stock ace rc esc has only to choose low, medium and high timing. I ve got the yge 40A so I have it set at 18 degrees. And for this particular motor I cannot find a source with the appropriate settings of timing and pwm. However today I bought a infrared heat meter. Cool..
 

Smoggie

Well-Known Member
GRH,

Something is strange then because higher PWM frequency should make the motor run cooler, not hotter. The down side of the higher PWM is a hotter ESC. As a general rule the PWM should be as high as the ESC can support providing the ESC doesnt get too hot. The formula you quoted is actually for the minimum PWM, higher is better. On every electric power system i have (that's a LOT) i always set the PWM to the max that the ESC can support and so far I've had no problems.

Timing is a different issue. Too high timing will make the motor run hot. 18 Degrees is the normally recommended 'medium' value for the YGE, but you could try the 'Auto' timing setting I've had good luck with that in the past. Or just try a slightly lower fixed timing value.

There are a few other possibilities:
  • Have you maybe got the mesh too tight between pinion and main gear?.. there should be slight clearance between the gears at all points in rotation
  • Is the gearing standard? (running higher gearing will cook your motor)
  • Are the blades standard? Running longer blades (or multi blade heads) will put more load on the motor and cause it to cook.
  • Any stiff bearings or anything else that causes friction in the drive train?
  • Are you sure that the motor is too hot? They usually do get pretty toasty, the rough and ready method is can you hold your finger on the motor for a few seconds? If you have infrared thermometer aim for about 60C (140F) as a conservative safe max.
 
I am ok with all the above aspects. I want to change all the bearings of the main shaft though. At the moment I tried some WD40 on the bearings, though I don't think there is a particular problem. Once in a while I will use WD40,it's magic. I haven't tried the infrared thermometer yet.
 
An average of 70 celcious degrees maybe 75 gives me the thermometer for the motor after each flight. I burned 6 packs almost back to back. I pointed the thermometer on the top of the motor. If I point it on the side of the motor gives me minus 15 degrees. And the speed controller at about 40 to 45 degrees. All these with the same emissivity coefficient set up on the thermometer. Normally depending on the material you measure you have to change this coefficient at the thermometer. So these values are at about reliable.
 

Smoggie

Well-Known Member
That is a bit hot. If it were me I'd reduce the timing slightly and increase the PWM to it's maximum, then chaeck again.
 
Guys I did a test to the motor. As at 14 kHz pwm I had some kind of interruptions to the power of the motor as it was accelerating I decided to leave it finally at 9 kHz. Where I think it works fine. So I took off the blades and I tested it for 5 minutes at 90% throttle, each time, at a timing of 18/12 and 6 degrees. The results are: 18 degrees timing motor temperature 69 Celsius degrees. esc 36 Celsius. At a timing of 12 degrees: motor temperature 65 Celsius. esc:35 Celsius. And at a timing of 6 degrees: motor temperature 60 Celsius. esc 33 Celsius. So these are my final settings for the motor. Timing at 6 degrees and pwm at 9khz.
 

Smoggie

Well-Known Member
9 deg C reduction is a lot, hopefully that's the problem fixed. Just be careful when running low timing that the motor doesn't stutter or stall when rapidly advancing throttle, the motor usually makes a screeching noise if this happens so it's easily spotted.

I'm amazed the higher PWM caused problems. I've used that exact same ESC and many others and always used highest available PWM without issue, but what matters at the end of the day is that you have a setting that works, nice one!
 
A scorpion motor of 3900 kv, similar to mine, but with 6 poles instead of 8 that mine has, gives settings of 8khz pwm and 5 degrees timing. Actually almost all the series of scorpion helicopter motors gives this setting. So I don't know if the formula (kv*nominal voltage*No of poles)/20 = pwm frequency in kHz, is actually reliable. I cannot find either the appropriate criteria and the knowledge for choosing timing and pwm frequency for a particular motor.
 

Smoggie

Well-Known Member
The Scorpion advice is rather outdated, it's based on older ESCs that wouldn't support higher PWM switching frequency. I run a few Scorpion motors and use 32KHz PWM. In fact some high end ESC's like Kontronik and the newest Hobbywing V4 dont even allow you to adjust PWM, they have it fixed at around 32kHz because that's what works best.

The formula you quoted is sound, it's based on achieving a PWM switching frequency that is 3 times greater than the commutation frequency. But this is a minimum value, not an optimum value, higher is almost always better from a point of view of motor efficiency, lower is bad for efficiency.
 

murankar

Staff member
I run my V3 hobbywing at 24 I think. It's been a while since I set it up. I also run a scorpion motor. Like Steve said scorpion has not updated any of their info in a long time. In fact all this numbers are merely suggestions as to a starting point now a days.
 
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