Brushless motor losing power

[Edward Po]

Hi all:

 

I have been experiencing gradual power loss in couple of my electric powered planes. I used to able to fly half throttle throughout the entire flight using only full throttle for aerobatic. Lately, I found that I need to fly at almost full throttle just to ensure that my plane does not stall during flight, this happened even when I am using new fully charged batteries. Brushless motors are Turngiy and Racer and has about 70 flights on these planes. 

 

Can anyone advise me the cause of my problem.

 

Thank you in advance.

Edited January 7, 2023 by Edward Po

[GrumpyGnome]

70 flights is nothing for a brushless motor..... afaik, the only thing in the motor that could affect performance is the bearings.  A drop of oil needed perhaps?  Or maybe a loose magnet. Seems a coincidence for multiple motors to be affected though.

 

Are you using your batteries 'cold'? Performance is often noticeably worse in the cold.

Edited January 7, 2023 by GrumpyGnome

[Paul De Tourtoulon]

Sounds like battery problems as above cold or  like us just  getting old.

[Denis Watkins]

Agree with both the above posts,

But just check your Tx Monitor

That your throttle stick is registering full movement from top to bottom.

An interested party at the field picked up my radio and was click clacking the buttons.

Later I discovered I had about half stick throttle.

[Frank Skilbeck]

A bit left field, but check your charger lithium setting hasn't been inadvertently changed from Lipo to Life, friend had done this on his charger and as a result his lipos weren't being fully charged. 

 

But the last time I had an electric setup lose power was a loose magnet rubbing on the static section.

[SIMON CRAGG]

A bit of a long shot, but have you re set your ESC to default recently (possibly by mistake).

 

You could have inadvertently changed the timing, which can make a significant difference to the power output!.

 

You have possibly done this already, but "Balance charging" your lipos might reveal any cells that are down.

 

Good luck and please let us all know what the issue was. 

[PeterF]

A member of our club had an issue like this and I diagnosed it when I found that I could pull the prop forward by 10-12mm. The motor was held together by a collet with grub screws not a circlip and the collet had moved down the shaft. When full power was applied the prop thrust pulled the motor can forward so that the magnets and coils were only half overlapping hence half power. When power was off the magnets pulled the motor back to the normal position quite strongly so nothing seemed wrong, you need to give the prop a good tug (with the battery disconnected) to see if the is the problem.

[Paul De Tourtoulon]

3 hours ago, Denis Watkins said:

Agree with both the above posts,

But just check your Tx Monitor

That your throttle stick is registering full movement from top to bottom.

An interested party at the field picked up my radio and was click clacking the buttons.

Later I discovered I had about half stick throttle.

Anyone touching my radio let alone clicking the switches is liable for either running his fingers through a prop or if it's my turbine his hand up the exhaust, NEVER touch someone else's radios without their permission and with them present !!!

[Geoff S]

It's odd that you have a similar problem on 2 motors at the same time.  I would look for a common feature which, in this case, is the batteries or the transmitter.  Check your charge routine to be sure the batteries are full charged and your transmitter settings to be sure full throttle on the stick is full throttle on the output.  A useful tool in the investigation is your wattmeter - are the motors drawing the current you'd expect?

[Paul De Tourtoulon]

1 hour ago, Geoff S said:

 A useful tool in the investigation is your wattmeter - are the motors drawing the current you'd expect?

Yes an excellent tool, you will be surprised at the real figures that your motors actually draw, mine a few at least 25% less than stated and some more than 35% !

[MattyB]

First port of call here has to be checking cell voltages and IR, both on and off load, as the batteries are by far the most likely element of the powertrain to be causing these symptoms. Run the peak power test 3 or 4 times with (say) 30-45 seconds of mid throttle running in between so you can see how the pack behaves at different levels of discharge.

[MattyB]

1 hour ago, Paul De Tourtoulon said:

Yes an excellent tool, you will be surprised at the real figures that your motors actually draw, mine a few at least 25% less than stated and some more than 35% !

What the powertrain draws is a function of the motor Kv, input voltage and load (I.e the prop or fan) chosen. The “max wattage rating” given by some motor manufacturers is a) frequently highly inaccurate and b) not really a useful metric anyway. It’s far better to size your motor using a combination of the max current you are likely to pull and the 3W/g rule of thumb (for prop models only - EDFs can safely achieve much higher W/g ratings because of the enhanced cooling available).

 

Edited January 7, 2023 by MattyB

[Lima Hotel Foxtrot]

9 hours ago, Denis Watkins said:

 

An interested party at the field picked up my radio and was click clacking the buttons.

Later I discovered I had about half stick throttle.

UNBELIEVABLY bad form!

[Andy48]

My guess is that if it is happening with 2 setups, then it is cold batteries. Using cold batteries in winter will make a significant difference to the power output.

[Edward Po]

20 hours ago, GrumpyGnome said:

70 flights is nothing for a brushless motor..... afaik, the only thing in the motor that could affect performance is the bearings.  A drop of oil needed perhaps?  Or maybe a loose magnet. Seems a coincidence for multiple motors to be affected though.

 

Are you using your batteries 'cold'? Performance is often noticeably worse in the cold.

Dear all:

 

Thank you all gentlemen for your feedback, The reply to all the above comments and advice are as follows:

1) I live in SIngapore which is a tropical country, the average temperature ranges from 24 to 32 degree C, so there should be no problem with  cold batteries. In fact, I am more concern with batteries heating up in the car interior. 

2) I have used both new and old batteries and it these batteries are always fully charged via balance charge cycle just before flying

3) The older batteries has about 75 charge cycle, while the newest one has less than 35 charge cycle.

3) Batteries condition are closely monitored, I record all parameter of individual batteries and cells before and after each flight. So far the capacity of individual batteries has never fell below 11.3V (3S 3,200maH) after each flight. 

4) Transmitter (Futaba 10J) has never been handled by another party.

 

I guess the best and only way to find out whether if is battery or motor fault is to purchase one new battery and one piece brushless motor and try it out on one of the plane!

[Edward Po]

21 hours ago, Frank Skilbeck said:

A bit left field, but check your charger lithium setting hasn't been inadvertently changed from Lipo to Life, friend had done this on his charger and as a result his lipos weren't being fully charged. 

 

But the last time I had an electric setup lose power was a loose magnet rubbing on the static section.

Thanks, I always check before every charge cycle, in fact the build in voice recording always remind us to the check the type of battery being charged

[Edward Po]

20 hours ago, PeterF said:

A member of our club had an issue like this and I diagnosed it when I found that I could pull the prop forward by 10-12mm. The motor was held together by a collet with grub screws not a circlip and the collet had moved down the shaft. When full power was applied the prop thrust pulled the motor can forward so that the magnets and coils were only half overlapping hence half power. When power was off the magnets pulled the motor back to the normal position quite strongly so nothing seemed wrong, you need to give the prop a good tug (with the battery disconnected) to see if the is the problem.

Wow, 10 to 12mm movement is a lot especially on small motor!

[Edward Po]

18 hours ago, Geoff S said:

It's odd that you have a similar problem on 2 motors at the same time.  I would look for a common feature which, in this case, is the batteries or the transmitter.  Check your charge routine to be sure the batteries are full charged and your transmitter settings to be sure full throttle on the stick is full throttle on the output.  A useful tool in the investigation is your wattmeter - are the motors drawing the current you'd expect?

I don't own a watt meter, I guess it is time for me to purchase one!

[GrumpyGnome]

Ah, unlikely to be the cold then!

 

A Wattmeter will be able to tell you if the batteries 'sag' under load (large voltage drop), but as you don't know what the motors used to draw, you'll probably learn little else.

 

I think we're shooting in the dark a little tbh.  As it's multiple planes having this issue, with multiple packs, it's LIKELY to be something that's common, hence the suggestions re tx and charger. Let's consider this piece by piece....

 

a) Transmitter; If someone has been tampering, I'd expect either all planes to be affected, or just the one that was selected at the time.... are just these two models affected? Have you changed anything? If so, change it back and see if that helps.

b) Charger; if this has issues, it's likely to affect all battery packs, and all planes.  In your first post, you talk of 'new fully charged batteries' - do these planes have the same issue with older, fully charged packs?  If all packs, in all planes, have issues, then it's likely to be the charger. 

c) Batteries; if these planes perform ok on older packs, then it sounds like your new batteries are at fault.

d) ESC; have you changed anything to do with the esc's on the affected planes? If so, can you change it back and see if that helps? It seems unlikely for two escs to suddenly show the same behaviour, but can you try a different esc to see if that helps?

e) Connections; it may sound daft, but check all your connection between battery, esc and motors.

f) Propeller; I assume these are in good condition?

g) Motor; this is all that's left now.  Brushless motors are simple things, and any drop in performance is almost certainly a mechanical issue (bearings, magnets, shaft, friction, windings).  Whilst it's unusual for 2 motors to show the same problem (or two escs for that matter) , it could just be a Lemony Snickett moment! Carefully inspect the installation - all firmly fixed? Any movement in any direction other than rotating the propeller? Turn it slowly by hand, and listen for any grinding/rubbing noises; feel for any grabbing, or unusual movement.  Finally, if all seems OK, remove a motor, and inspect the windings and magnets for any issues, like rust or excessive dust.

 

Hopefully, this will help track down the issue.   

[Frank Skilbeck]

One other thing you can do, is use you cell checker to check the cell voltages under load. Club mate had a couple of fairly new batteries fail and the cell checker showed the voltage on one cell collapsing under load, on two separate batteries.

[Andy Stephenson]

Frank,

 

This exactly how I did it for a club mate on the field. We plugged a cell checker into the balance connector and ran the motor up. This clearly showed one cell's voltage collapsing under load. The voltages looked OK otherwise, so this was the only way it showed up that it was the battery at fault.

[kc]

Everything has been mentioned so far except throttle trim.......worth checking whether that has been altered.