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Motor stutters near full throttle

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Richard Hayward 612/03/2020 10:06:58
41 forum posts

Hope you guys can help me again. I've recently bought the new VQ Spitfire. From the UK importers (Macgregor) I also bought the recommended motor / ESC combination (720KV, 860w motor and an 80A ESC). Transmitter is Futaba 10J (which I am using quite happily with an Acrowot and Phase 5e). Battery is a fully charged 5s. Prop APC 13x8E.

I set up the Tx throttle range as per instructions. Motor powered up OK, but passing around three quarters throttle, it started juddering and rpm tailed off. Amps at this point around 25 - dropped as the stuttering started.

Returned both items for refund. New ones exactly the same! Tried changing the timing from Med to Low and High. No significant change. Returned both for a refund and bought another similar combo from different supplier (different badge, but pretty sure same manufacturer). Same result!!

So, I'm thinking it can only be a Tx problem? I'm at a loss - any suggestions gratefully received!!

Bob Cotsford12/03/2020 10:17:12
8382 forum posts
463 photos

What voltage is the battery pack showing when it starts stuttering? Are any of the connectors getting hot?

Richard Hayward 612/03/2020 10:37:27
41 forum posts

Thanks Bob. Out at the mo. Will try when home and also a different battery

Colin Carpenter12/03/2020 10:52:37
635 forum posts
35 photos

Don't the car boys call that cogging ? I've had it on two planes ! Both times it was dodgy motor/esc connectors . Took a lot of investigation on bench but eventually plug lead parted ! Saw it on a club mates plane and he got it down and leads parted with just a gentle tug ! You can bring down the top end of the throttle curve as well if testing doesn't show up soldering . Did this by 8% on new bipe till got it on bench. Hope this helps ! Colin

Richard Hayward 612/03/2020 10:55:17
41 forum posts

Thanks Colin. Something else to try when I’m allowed home after shopping!

Engine Doctor12/03/2020 11:04:27
2466 forum posts
39 photos

I have had this problem on one of my planes. It sometimes wouldn't restart after closing the throttle but would just oscillate . Problem on that model was poor quality / connection on the bulit conectors on the motor leads. Another model with similar problem was a broken lead in motor.

Richard Hayward 612/03/2020 11:13:26
41 forum posts

Thanks ED. It does seem to be pointing to the motor connections, but does seem odd that same prob on three motors from different sources. Still out shopping, so will continue later.......

J D 812/03/2020 11:27:18
1439 forum posts
84 photos

Another who had the same problem and it did turn out to be poor connection on a motor wire.

Denis Watkins12/03/2020 11:36:49
4322 forum posts
104 photos
Posted by Richard Hayward 6 on 12/03/2020 11:13:26:

Thanks ED. It does seem to be pointing to the motor connections, but does seem odd that same prob on three motors from different sources. Still out shopping, so will continue later.......

Timing Maybe?

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.

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

Peter Miller12/03/2020 11:38:05
10946 forum posts
1272 photos
10 articles

Just a thought.

George at 4-Max always tells me to cut off the soldered ends of the wires and use lead solder to make the joint or solder on the plugs and bullet connectors.

Non lead solder is rubbish for home soldering.

SIMON CRAGG12/03/2020 11:51:14
556 forum posts
5 photos

Several of us in the club had the same problem with the Durafly Vampire.

After changing fan units / esc's etc. it turned out to be one of the bullet connectors to the motor.

Several fan units had the same fault.

It was fine at low to medium rpm, but at high rpm the vibration caused one of the connectors to make and break quickly.

Hope that helps.

Colin Carpenter12/03/2020 12:08:05
635 forum posts
35 photos

Having re-read OP it seems really strange that 3 combos have same problems ???? I take it the tx works normally on other planes ?? Set up another model memory ?? Colin

J D 812/03/2020 12:12:50
1439 forum posts
84 photos

Richard may be on to something with the battery, would a poor connection here result in the same problem?


Richard Hayward 612/03/2020 12:48:52
41 forum posts

Thanks for all your interest. I’m in the process of charging a different battery. The existing one works fine with a Quantum motor in my Acrowot using the Futaba radio. Will try out all your ideas later today.

Richard Hayward 612/03/2020 14:34:18
41 forum posts

Tried a 4s battery - same result. Have changed the timing from Med to Low and High - same result. Connectors don't feel hot, but there is a lot of propwash. Have emailed Steve Webb (who I bought the setup from) to see if has any ideas. Meanwhile, keep coming up with suggestions please!

Colin Carpenter12/03/2020 15:01:51
635 forum posts
35 photos

Struggling now !😥😥 Reset throttle end points / curve !! Try different Rx ? One that's ok in different plane !! Colin

Richard Hayward 612/03/2020 15:08:05
41 forum posts

Thanks Colin. Will go and have a play.........

extra slim12/03/2020 15:47:11
480 forum posts
48 photos

Had this a good few times, from my experience, it is either 1. Timing or 2. Re-solder connectors on both ESC to motor and motor to ESC.. do one at a time if you want to find out which one it was... if these fail, it tends to be wire in the motor windings.. but rare for me.

Richard Hayward 612/03/2020 16:03:46
41 forum posts

Thanks Extra Slim. I'm very tempted to solder new connectors on motor and ESC - just want to check that it won't bu@@er the warranty if it doesn't work.

Colin Carpenter12/03/2020 16:32:12
635 forum posts
35 photos

Richard. It's highly improbable that 3 combos have the same fault from new especially if pre soldered ! Can you not put a working motor /esc into the mix to prove tx and Rx and lipos are ok ??? Scratching my hair out now !!😀😀😀😀 Colin

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