So just "how hot" is "too hot"

[clittle]

I've been running brushed motors previously and have just upgraded myself to a Sidewinder 5700. I was running it today for a while, not really going flat out because the track was way too tight, and when I'd stopped I noticed that it was really hot. A lot hotter than the brushed would get.

Is this ok? I almost burnt my finger after a second.

Should I be gearing down (or up) to make life easier on the motor?

Do the brushless motors run hotter?

[Mr. Constructor]

Only a few ones will run hotter (like the feigao 540 series) normally a BL Motor should run within a 20-80 Degrees Celcius range.
esp. when going over 80 Degrees Celsius it becomes critical, as the rotor inside the Motor already has around 100 degrees wich is very close to a temperature where the magnets loose their strenght (wich will start at roughly 115 degrees celsius).

Your Motor shall only run below 70 degrees and a short "let-it-cool-down" phase between the runs isn´t that bad either.

[clittle]

Only a few ones will run hotter (like the feigao 540 series) normally a BL Motor should run within a 20-80 Degrees Celcius range.
esp. when going over 80 Degrees Celsius it becomes critical, as the rotor inside the Motor already has around 100 degrees wich is very close to a temperature where the magnets loose their strenght (wich will start at roughly 115 degrees celsius).

Your Motor shall only run below 70 degrees and a short "let-it-cool-down" phase between the runs isn´t that bad either.

Thank you very much for your reply. This was the first run for this motor and car. Come to think of it, I probably ran for longer than I should have in one stint.

I'll keep an eye on it.. thanks

[vashon10]

You should have temperature gun and then you can check it exactly.
Mamba motors have a temp limit of 200 degrees F measured on the can.

[rccardude04]

Vehicle, battery, and gearing please. :)
Brushless systems don't really like being over/under geared very much, and the Castle CM36 motors run kind of hot anyway... So you have to watch them a bit.
-Eric

[GSMnow]

Most likelyyou are over geared a bit, and running it at part throttle to go slower will make it much hotter than proper gearing and full throttle to go close to the same speed. Under gearing may not be ideal, but it certainly won't hurt the motor at all. As long as the battery voltage multiplied by the KV comes out to an RPM that is below the max safe rpm for the motor, you could rev it with zero load and not hurt it. In fact I rev my Mamba Max 5700 setup flat out with no pinion to check the KV from time to time to make sure the motor is still in spec. Measuring the actual DC voltage into the ESC and the true RPM of the motor shaft, you can do a quick divide and get true no shaft load KV. This is typically just a hair lower than true zero load KV. If you measure a value much higher than rated, you rotor magnet is getting weak. Mine measures 5800 now. My motor has been over 205F a few times now, so I am sure it is getting weaker.

As rccardude04 asked, "Vehicle, battery, gearing please." from there we can give you a very good idea of what is going on. A 5700 on 6 cell NiMh or 2S lipo should be geared for 30 - 40 mph in a 4 pound 1/10 scale car or truck. You may get away a little higher if you run in a big open lot. If you run more than 6 cell NiXx, then you need to go smaller on the pinion or the current draw goes way up. Start with the Castle Link timing set to normal, or even a bit lower. More tiking will give a tick more power, but with quite a bit more heat.

[chilledoutuk]

gsm do you use a strobe to measure the rpm?

[GSMnow]

At full throttle, the waveform on the 3 phase windings is actually very clean, so I just use a frrequency counter across two of the leads to the motor. It does not work at part throttle due to the PWM pulsing making a much higher frequency. I used to use a big 32 tooth pinion painted half white and half black and a photo tach. That worked on any motor, even brushed. I checked it a few times with a scope to make sure, but my trusty Fluke 76 freq count mode is rock solid as long as I am at 100% throttle. Of course the number is revolutions per second, don't forget to multiply by 60.

[clittle]

Vehicle, battery, and gearing please. :)
Brushless systems don't really like being over/under geared very much, and the Castle CM36 motors run kind of hot anyway... So you have to watch them a bit.
-Eric


Thanks a lot for the replies.

I'm running a Tamiya TA05R.
Battery is an Eagle Racing 3000mah Nimh 6 cell.
Spur is 105
Pinion is 40

and I was not running at full throttle. There's now way I could. I'll be going to get a smaller pinion very soon. :o

I also should mention that the setup of the Sidewinder ECU is the factory default.

[GSMnow]

Do you know the ratio from your spur to the wheels? I haven't found it on the web yet. Also, what size tires are you running? 40 to 105 is only a 2.625 primary ratio. The trans is probably between 2.0 and 3.0 so that is very tall. The XXX-4 has a 2.1 trans ratio and I will be starting with just a 16 to 92 pinion and spur.

[clittle]

Do you know the ratio from your spur to the wheels? I haven't found it on the web yet. Also, what size tires are you running? 40 to 105 is only a 2.625 primary ratio. The trans is probably between 2.0 and 3.0 so that is very tall. The XXX-4 has a 2.1 trans ratio and I will be starting with just a 16 to 92 pinion and spur.

According to the manual, the car has an inner ratio of 2.25.
That gives me a ratio of 5.91.

I'm running standard touring car rubber. Team Sorex 36R.

[aqwut]

MRC is right... I try to keep everything under 70 Degrees Celcius...

[GSMnow]

WOW!! I think you are seriously over geared.
6 cell NiMh should hold 6.6 to 7 volts under load. Might even go higher when it winds out. That is over 37,000 rpm at the motor. With a total ratio of just 5.91, that is a wheel rpm of over 6300. OUCH!
I have not been able to find the O.D. of the Sorex tires, but a normal touring car tire is about 60 mm + or - a bit. (The HPI's I found are 65 mm so it would go a bit faster still) So even with these smallish tires at .618 foot per rev you are looking at a theoretical speed of about at least 45 mph. If the drag is low, the motor could top 40,000 rpm and the tires could grow a bit. Change that 40 tooth pinion for a 33 or so and see how it goes then.

[clittle]

Thanks. I'd never actually put the numbers together. I chose the pinion because it was right in the centre of the chart in the manual.. I'll more closer to the top of the chart I think.

The track where I run doesn't need a high speed gearing, it's tight and technical.

Thanks again for your advice. I really appreciate it.

[clittle]

I just thought I'd give you an update. I've dropped it down to 33 teeth in the pinion and ran it tonight at the track.

I ran the motor for about the same length as before and the heat was a lot less. So much less. The car was also a lot more drivable around the tight course that we have.

Thanks a lot for all your help.:teacher:



WOW!! I think you are seriously over geared.
6 cell NiMh should hold 6.6 to 7 volts under load. Might even go higher when it winds out. That is over 37,000 rpm at the motor. With a total ratio of just 5.91, that is a wheel rpm of over 6300. OUCH!
I have not been able to find the O.D. of the Sorex tires, but a normal touring car tire is about 60 mm + or - a bit. (The HPI's I found are 65 mm so it would go a bit faster still) So even with these smallish tires at .618 foot per rev you are looking at a theoretical speed of about at least 45 mph. If the drag is low, the motor could top 40,000 rpm and the tires could grow a bit. Change that 40 tooth pinion for a 33 or so and see how it goes then.

[GSMnow]

I'm glad it worked out for you. Have fun.