Motor wouldn’t start if a prop was fitted - think I fixed it with timing?

[Lipo Man]

Here’s an odd one. I’m building a (very impressively designed) Warbird Replicas FW190. I’ve fitted an 800kv 4250 motor and a 60A BLHeli ESC. The motor ran up perfectly on the bench with no prop attached (safety first!). However, when I fitted a prop the motor would simply judder making a pretty horrible noise and wouldn’t spin. Take off the prop - works fine again!

I know nothing about exactly how ESCs work, but had a hunch that it might be a timing issue. So I went into the ESC settings and switched timing to “Low” (there seem to be five settings and I’m now on the lowest one). And voila - it works fine! Very bemused but all seems ok so I guess I’ll try to fly it!

Sharing in case anyone else has a similar issue. 

[Paul De Tourtoulon]

If it doesn't turn at all, then it's probably a bad/dry solder contact from the Esc to the motor.

[Lipo Man]

52 minutes ago, Paul De Tourtoulon said:

If it doesn't turn at all, then it's probably a bad/dry solder contact from the Esc to the motor.

It now seems to work fine just by changing the timing. I’ll check the joints in any case, but it doesn’t seem to be the problem this time. 

[Bob Burton]

What happens if you change the timing back to its original setting ?

[Denis Watkins]

Count the magnets in the motor

Here from RCgroups

For a brushless motor, the number of poles (magnets) determines the optimum timing. Less timing advance is more efficient and higher timing advance is more powerful but uses more juice, within the range that a particular motor can use.

 

E-flite Pro ESC timing recommendations:

Low Timing Advance
Timing Degrees – 5 & 10
Motor Poles – 2 to 4
Expected Performance – Good balance of power and efficiency
Motor Poles – 6 or more
Expected Performance – Best efficiency and run time (lowest power)

Standard Timing Advance
Timing Degrees – 15 & 20
Motor Poles – 6 to 12
Expected Performance – Good balance of power and efficiency
Motor Poles – 14 or more
Expected Performance – Best efficiency and run time (lowest power)

High Timing Advance
Timing Degrees – 25
Motor Poles – 12
Expected Performance – Highest power, less efficiency
Motor Poles – 14 or more
Expected Performance – Good balance of power and efficiency

[Geoff S]

I would be more inclined to suspect poor connections somewhere that only became a factor as you manipulated the wires during the installation.  After all, the motor wouldn't 'know' there was a prop fitted before it started to turn and there would be minimal load at just a few rpm.  I feel the timing is a red herring.

[Phil Green]

I'd suggest it's the combination of a low-KV motor and a Heli ESC that expects a high KV so as standard the timing will be way off.

Pete is your Lecky Heli man, he'll know for sure 😊