• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Brushless motor stalling?

Mera'din

Junior Member
#1
So I just finished maidening my fd3d and it flew great, with one big problem. I couldn't go full throttle. When I did the motor made a weird screeching sound until I backed it down in throttle.

I am using a plush 40 amp esc and a turnigy ntm prop drive 28-25, 1200kv and a 10-4.7 slowfly prop.
 

Mera'din

Junior Member
#4
3 cell, I was on the lowest timing setting. i bumped it up to the middle and the high, still misbehaves. For giggles, I put a 2 cell in and was able to go full throttle.

Spec wise it says it can pull 3s, my guess it is pulling too many amps and the 10x5 is the culprit. Looking at the amp rating it shows a max of 18 amps. I will test again but I am pretty sure it is doing more than that in the plane.
 

xuzme720

Dedicated foam bender
Mentor
#5
Are you checking actual amp draw? Sometimes you end up pulling more (or less) amps than you might think for many different reasons...Props are usually the main culprit though.
 

xuzme720

Dedicated foam bender
Mentor
#7
yup, same meter here. Seems like something else is amiss...unless you haven't checked yet. Anyway let us know, my gut thinks it's the prop...but gut's a dumb@##
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#8
Mera'din,

It's not your motor stalling. It's your Prop.

At full speed your motor is turning somewhere between 13320 and 15520 RPM. Nicer props will spec a maximum speed in terms of 40,000-200,000 RPM/in of prop, which would range from 4-20k RPM for your selected prop diameter. The actual spec is dependent on how the prop is built (shape, material, thickness), but typically the slower the prop the lower the number.

Don't know about the spec of yours, but the signs are there: tone in the motor changes to a warble, thrust drops dramatically.

Demo: (he's showing off reliability of prop savers, but runs a SF into a stall about 1:05)


Couple of options:

  • If you have enough thrust before it dies off, you can dial the throw back in your radio, so you never give too much throttle. Make this setting on a freshly charged battery, since WOT RPM drops with charge.
  • If you have a prop balancer, you could *carefully* trim a half inch or more from the prop and rebalance. just make sure your cuts are clean and sanded prior to balancing -- don't want it throwing off a dirty edge.
  • Pick another prop: You can raise the diameter, while picking a faster pitch, should give you the amp draw+thrust increase. A nicer brand with a better prop design may or may not take the extra RPMs -- most of this is fighting the physics.

You've gotten just about all you can out of that poor prop, just before it stalls. If that's not enough, time to move to a new prop.
 

Mera'din

Junior Member
#10
Not sure on the prop stalling issue. It makes a horrendous electronic screeching noise and does it with every 10x4.7 prop I tested, Slowfly and APC style.

I am going to check the amp draw as it seems to be more a electronic sound. I couldn't see the video you posted so I am not sure if the sound you are talking about is the same I am. I will see if I can take a video and post it.
 

Tritium

Amateur Extra Class K5TWM
#11
I have purchased motors before that had metal chips in the rotor magnets that gave a similar issue. Also whether new or old many Chinese bearings are total JUNK and that could also be the issue.

As to what others have said. Try an 8" prop and see what happens. They are cheap!

Thurmond
 
#12
It really seems like an over speed, or over voltage issue. Another thing to check is the motor to ESC connections. If there is a poor connection and it momentarily loses contact during flight it can make crazy sounds. I recently had a similar issue where a bullet connector had corroded on the motor harness. It worked OK, until high throttle then it screeched terribly.
 
#15
Worn bearings, loose shaft, bent shaft, missing/damaged magnet, 'bell' shifting position under thrust, ESC timing, swamp gas reflecting off Venus..
 

Tritium

Amateur Extra Class K5TWM
#16
Does the vibration exist if you try it without the prop? The NTM may have missed its "Hand Quality Check" and received a "pencil whipping" on the test paperwork.

Thurmond
 

xuzme720

Dedicated foam bender
Mentor
#17
Sounds like bearings/bushings to me, but sometimes audio can be distorted at those levels.

A test run without the prop would probably tell you more.
 

willsonman

Builder Extraordinare
Mentor
#18
I agree with others. This seems like a mechanical issue. Bearings it sounds like. Try oiling them if you can. Also, check your wires. If you have any risk of the contacts touching or if you have a slightly burned wire. In my polaris I had a wire start to go and it caused this. Replaced the one wire and it was all good.
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#19
Could be a bad solder point on one of the wires. Could be a balance issue. On my tricopter one of the motors/props was out of balance, but it didn't show up until I applied nearly full throttle, then it would shut down.