What's new

  • Welcome to the new Flite Test Forum home! Please note that the migration is still undergoing and certain content, user privileges or features may be missing or limited until the transition is complete. Thank you!

Beef not performing as before

#1
hello everyone!! hope you all are doing great.
A friend of mine who flies with me gave me his beef to sort out the issue it's facing. strangely it's not providing enough thrust. it's clearly not the same as before. I've tried changing the ESC, lipo, rx-tx but to no avail. before you ask, yes, the prop was put on properly. his ESC works fine with my beef, but when I hook it up with his beef it doesn't provide the same thrust. it's close to having no power at all, the prop spins of course. it gives the same problem if I put my ESC on it. it has a 10*4.7 prop, 3s,2200 mAh lipo. any idea what could be wrong with it?
 
#2
You can test the stator resistance from leg 1-2, then 2-3, then 1-3 with an ohm meter. All of the readings should be the same from leg to leg and the same as the identical motor.
 

Hai-Lee

Old and Bold RC PILOT
#3
I recommend the multimeter checks but sometimes inter-winding leakage will not show up properly with such a low voltage test. One check I used to perform on permanent magnet motors was to drive the rotor with an electric drill and measure the voltage developed between windings and using a bank of light bulbs to check the power the motor could generate.

Doing the "Generator" test allowed the windings to handle the same sort of currents that the motor experienced in "Motor" operation and so any leakage or shorted windings were quickly apparent.

Just a blast from the past!

Have fun!
 
#4
thank you both of you!
unfortunately I don't have an ohm meter. would need to take it somewhere first. let's suppose it shows different resistance readings, what could be the problem then and what would I need to fix that?

hai-lee how would I go about the generator test? use any two of the three wires as negative and positive? in 1&2,2&3,1&3 formation? if it's a winding issue then I'd clearly need to rewind it right?
 
#6
thank you both of you!
unfortunately I don't have an ohm meter. would need to take it somewhere first. let's suppose it shows different resistance readings, what could be the problem then and what would I need to fix that?

hai-lee how would I go about the generator test? use any two of the three wires as negative and positive? in 1&2,2&3,1&3 formation? if it's a winding issue then I'd clearly need to rewind it right?
If the resistance is lower than normal, it would indicate a short in the windings. If higher than normal, it would be a broken/semi-broken winding. Unless it is an expensive motor, it may not be worth rewinding it.

If all three readings are balanced (the same) and the same as the other identical motor, then the motor windings are healthy and it could be a bearing issue. Or something else besides the motor.

I agree with Hei-Lee too. You can uncover obvious problems with a standard multi-meter but it really takes a high voltage device like a "mega-ohm reader" to uncover the actual issue sometimes. This device is usually called a "megger" but you are probably not going to run across one.

Did you happen to calibrate the ESC?

Good luck!
 

Craftydan

Hostage Taker of Quads
#7
So let's look at the symptoms once more . . .

If it's spinning at all, there are no broken connections in the Motor windings. One break and it'll stutter not spin.

It's possible one of the windings is slightly shorted (the short is jumping over a few of the loops on one of the phases) but this is generally a prelude to a "let the magic smoke out" failure. Sure, you loose thrust, but then sync drops out and shortly after that, lots of heat and more shorts and breaks occur with a puff of smoke.

I'm assuming the motor spins freely when you spin it by hand -- there's noting on/in/around the shaft that's binding and the rear end of the shaft isn't binding on the firewall.

Assuming it's not binding somewhere . . . did your friend say if they were running the motor a little hot? A lot hot? I have a feeling he pushed it too high and the magnets started to loose strength. Sad to say, once that's done, the motor is done. Not many replacement magnet sets running around on the open market :(
 
#8
thanks gazoo for the elaborative answer.yup, calibrated the ESC.
yeah, that's what I was wondering, that in case of a winding breakage the motor stutters (that's what I've read on different forms, pardon my limited knowledge if there's more to it), but this motor spins smoothly, the rpm seemed to have dropped significantly, hence the decrease in thrust. I checked, the shaft moves freely when it's powered on with a lipo or when I spin it with hand. It doesn't even get hot when it's powered on with a lipo. I was wondering, since it seems to be having a low rpm now, what would happen if I put on a much bigger prop, could be tried?
how can I make sure that it's the magnet failure which is causing this problem?
 
#9
Just for giggles.. remove the two screws holding the motor down that are on the side where the wires exit the motor. If they are barely touching the windings they could be leaching current thus keeping the motor from spinning up properly. The motor wont get hot but the frame would closer to the pdb somewhere.
 

Hai-Lee

Old and Bold RC PILOT
#10
hai-lee how would I go about the generator test? use any two of the three wires as negative and positive? in 1&2,2&3,1&3 formation? if it's a winding issue then I'd clearly need to rewind it right?
On a brushless motor there is no commutator and so not method of rectification. Therefore the output would be AC not DC and therefore there is no positive or negative rather an active and a return.

As for the output you are correct in that the voltage is measured between any 2 windings.

I normally used a bank of different 12V torch light bulbs to determine what power I could sustain. Differences would definitely mean a rewind would be required but these days a new motor might be cheaper in the long run!

Have fun!
 

Craftydan

Hostage Taker of Quads
#11
thanks gazoo for the elaborative answer.yup, calibrated the ESC.
yeah, that's what I was wondering, that in case of a winding breakage the motor stutters (that's what I've read on different forms, pardon my limited knowledge if there's more to it), but this motor spins smoothly, the rpm seemed to have dropped significantly, hence the decrease in thrust. I checked, the shaft moves freely when it's powered on with a lipo or when I spin it with hand. It doesn't even get hot when it's powered on with a lipo. I was wondering, since it seems to be having a low rpm now, what would happen if I put on a much bigger prop, could be tried?
how can I make sure that it's the magnet failure which is causing this problem?
So from the symptoms . . .

You're saying the heat is well managed, and the kv appears to have droped. That means the motor isn't overloaded with the current prop (which would be a good load for a stock beef on 3S). kV is inversly proportional to the number of windings, so shoring a coil would increase the motors kV -- either the motor would spin FASTER with a partially shorted coil, or would bog down under the new desire to spin the prop faster and overheat.

Your coils are fine. Smooth run with no stutter means no break. No overheat and slower spin at WOT ( on different escs) means no shorts.

You're left with

- magnets loosing pull
- lower voltage battery or excessive voltage sag at WOT
- the escs are both being told something less than WOT from the radio gear when the trottle stic is all the way up.

Without having something to compare it against (another beef motor) there aren't good measures of magnetic strength that would aid in troubleshooting. This is something you'd diagnose from the symptoms by eliminating everything else.
 

Hai-Lee

Old and Bold RC PILOT
#12
Just a note!

A shorted turn in any electrical motor will not cause an increase in speed but rather a loss of efficiency and extra heat generated.

In a sensorless brushless system the effect of a short is to produce eddy currents in the shorted turn/s which oppose the magnet field generated by the applied waveform from the speed controller. Where the maximum power available is limited, (overcurrent protection), the loss of power due to the eddy currents generated in the shorted turns can produce heating and or other effects.

Most sensorless motor speed speed controllers use back EMF and inductance effects to determine the required waveform to be generated. Where the FEEDBACK mechanism, (back EMF and inductance) is effected the resultant effect upon the operation of the motor can range from complete failure to operate, through stuttering, to slow rotation, (effectively reduced Kv), rotational speed plateau, and even engine fire.

The reference to shorted turn is used to generalise a series of different types of winding short and leakage conditions for simplicity. The types of shorts can be a single turn in a single pole through to phase to phase shorts and or leakage. The reference to a winding is to included all poles of the motor connected to a single phase from the motor speed controller.

Simple fault finding would tell where the fault lays. If you substitute the ESC or Battery and it makes not difference then they are eliminated as a cause. If swapping out the motor fixes the problem then the motor is definitely the issue.

If the motor is complete, (no missing parts including magnets) and it rotates freely under hand turning then there is only two remaining items to suspect. Either the windings have a fault or the magnets have either gained or lost magnetism. As for the appearance of the windings you are only able to examine a small percentage of the motor windings and most motor winding to winding problems occur where heat is at its highest and cooling air reach is least and this is in the middle section of the coli/s. Without resorting to some serious test equipment capable of measuring inductance and reluctance the generator test is the cheapest and most accurate method of measuring the efficiency, (relative - comparing the other windings), of the three windings in a permanent magnet 3 phase brushless motor.

Where an ESC, (sensorless motor speed controller), has a current limiting or similar protection mechanism the only real method of protection apart from load disconnection is to reduce output current to avoid damage including from overheating. The reduction in current can take the form of even a reduction in throttle output, (and hence motor speed), in some Speed controllers in a similar manner to the "Soft" voltage cutoff on some motor speed controllers.

Just as I was taught!

Have fun!
 
#13
checked with my friend, the beef went haywire after having a serious impact with the ground. he was flying the ft storch, 10*4.7 prop, 3s 2200 mAh lipo. he was flying at a low altitude, was trying some moves, lost control and the plane hit the ground nose first. it was a tarmack, not a soft ground. the additional prop adapter that comes with the beef bent slightly so it must've been a hard impact. the motor started giving problems right after this incident. visually the motor seemed fine at that time and wasn't hot hot. my guess, winding issue. I still need to check it with an ohm meter, have national holidays here, will do so in the coming week.
 
#14
so the other day i decided to finally change the winding of the beef. but before doing so i gave one solid wiggle to the bullet connectors. Surprisingly one of them came off, i soldered it back and now the motor is as good as new.
could this issue be faced cause of a bad joint or a breakage in wire?
 

Hai-Lee

Old and Bold RC PILOT
#15
Each motor wire is actually a number of wires, (windings), joined together. I might have been that one of the wires, (windings), had become detached in the rear of the connector and so caused the strange behavior. Your wriggling of the connector may have caused the remaining wires, (windings), connected to the connector to detach and so mystery solved.

Good find!

Have fun!