80b shutting down ? - RC-Monster Forums

stampy · **80b shutting down ? -** 08.03.2006, 03:25 PM

Ive had my quark 80b for about a month now and resently (as soon as i put it in my ruslter i got) it has been shutting down at random for some reason i dont know if its thermling or what but it shuts down for a little bit and doesn't respond to throttle imputs the steering works but thats it. i give it about 5 sec or so and it starts working agian but as soon as i give it some throttle and take off it does it agian. as far as i can tell its not getting that hot, 140ish maby, i can hold my finger on the metal heat sink for almost 2 full seconds the motor on the other hand is hot enuff to sizzle water latterly could that be the problem way the controller is shutting off maby? :032:

squeeforever · 08.03.2006, 03:58 PM

Your gearing sounds to low.

stampy · 08.03.2006, 04:09 PM

took it out agian and when it shuts off the yellow led comes on what does that mean :002:

Mike.L · 08.03.2006, 04:32 PM

whats your gearing?

stampy · 08.03.2006, 04:36 PM

it was 84 18 but i stripped the spur on the first blip of the throttle so i put my 64t 32p spur in it with a 14t pinion basically the same ratio but i just put them in for the durability. i dont know what the tranny ratio is so i dont know if i need to go up or down :002:

08.03.2006, 04:43 PM

My 125 does this. I think it's losing the motor. I.E. Motor thermalling. Next time it does it, tap the brakes then go forward. Usually finds itself.

stampy · 08.03.2006, 04:46 PM

Quote:

Originally Posted by Darren

My 125 does this. I think it's losing the motor. I.E. Motor thermalling. Next time it does it, tap the brakes then go forward. Usually finds itself.

ya thats what i have to do but sometimes i have to let it sit for a bit before it goes again it gets bad though basicly it shuts off i wait 5 or 6 seconds then i can take off agian then it goes maby 40 feet and shuts off :035: .

smhertzog · 08.03.2006, 05:07 PM

It sounds like its a thermal issue, I have a 125 and when the case gets about 140 it thermals. I think it is set to thermal at 170f but that is internal temp not case temp. If you search the subject there are a few threads on it but I think they are about the 125 not the 80 but they should apply to both.

jhautz · 08.03.2006, 05:16 PM

Get a heatsink and fan on that thing. The motor too. If you can sizle water, you r gonna fry the motor sooner rather than later.

08.03.2006, 05:22 PM

Yeah. The motor must be at 100*C or 212*C to sizzle water.

My quark sits at about 95*F so it's definetly undergeared.

glassdoctor · 08.03.2006, 05:31 PM

How does the controller know what the motor temp is?

smhertzog · 08.03.2006, 05:42 PM

Quote:

Originally Posted by glassdoctor

How does the controller know what the motor temp is?

It doesnt, it is a measurement of the internal case temp. of the controller it has no idea what the motors temp is. When the motor is 200f the the controller isnt far behind. The motor heats up the three leads going into the controller which transfers the heat into it. Add this to the heat the controller itself is producing and you have got one hot controller. If you would measure the heat of the case and compare it to the heat of the three solder connections (were the three motor leads are attached to the exposed board sticking out of the controller case) you would see a 20-30f difference.

jhautz · 05:51 PM

As I understand it... The motor heats up if you spinn it to fast. When it heats up it loses effiency. When it loses efficency, it draws more amps. when it draws more amps the ESC heats up from the higher load. When the ESC heats up too much.... it thermals.

squeeforever · 08.03.2006, 06:16 PM

Well how it works is a BL motor has a "sweetspot" as for gearing. If you undergear it the motor will run hot from no load and from a lower amp draw, if you over gear it the motor will run cool but the ESC will run hot because of the added amp draw from the excessive load of being overgeared.

BrianG · 08.03.2006, 09:57 PM

From an amp-draw perspective, what Squee said may not make much sense, but you have to remember that these BL motors are AC motors. As such, there are other factors like inductive reactance, power factor, etc that come into play that can make a large difference in current draw and temperature.

When motor current draw is high, but there is little motor heat, this means the motor is presenting a highly inductive load, which tends to be hard on the driving circuitry (ESC) and heats it up.

When the motor is hot, the motor is presenting more of a resistive load to the controller due to the frequency of the AC signal and loading of the motor. Resistive loads are the easiest to drive and therefore the ESC is cooler (still depends on the current draw though somewhat).

If the motor and ESC are about equal in temperature, then there is a good balance of resistance and inductive reactance, and power factor is closest to the ideal value of "1".

It's the resistive component of the motors windings that create the heat (and any other mechanical/electrical losses). On an ESC, the majority of the heat is generated by the rise time of the square wave pulses across the FETS devices. During this time, the voltage is neither on or off so there is a voltage drop AND current draw - hence the heat. When FETs are off, there is a voltage drop but no current draw so no heat. When the FETs are fully on, there is is current, but no voltage drop, so no heat there either.

This is oversimplification because there is a LOT of thought that goes into the design of an ESC and its feedback/speed sensing circuitry.

BTW: Ask any master electrician and they can tell you all about BL motors but they know them as "squirrel cage" motors and have been around for a LONG time. AC drive circuits are not new either, but their use in R/C is relatively new in comparison because we take DC and create PWM AC to drive the motor. ANY 3-phase AC motor is really a brushless motor.