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FT 20A ESC/Motor Power Pack A Pulsing Issue

#1
I installed a new Power Pack A into the FT Tiny Trainer that I built from scratch in January. On my maiden flight I successfully flew without crashing six times, then on my seventh flight a turkey buzzard attacked my plane, sending it crashing to ground. Most of the damage was sustained by the swappable power module. I rebuilt the power module and the nose of the plane. After making the cosmetic repairs, I started by re-binding my NX8 Spektrum transmitter to a Spektrum AR410 receiver, and then calibrated the ESC next. Without the prop, I pushed the throttle stick from 0 to 100% and motor powered up smoothly. Then I install the prop and pushed the throttle stick from 0 to 100% and the motor started pulsing. My 3S battery is fully charged, but my ESC acts like it is sensing a low voltage condition. I changed batteries and the response is the same. If I remove the prop the motor spins up nicely. I don't have a second motor to test my ESC, so I am seeking advice on what to do next?
 
#2
Sounds like in the vulture attack one or more of you motor to esc wires was severed or broken. I’ve had this issue and it always links to a faulty wire, inspect all your wires and connections between the esc and motor. Those wires are very fragile and break off if bent too sharply out too many times.
 
#3
I have checked all the wires and can't see any visible breaks or disconnects. I can run motor at 100% without the prop and the motor does not pulse, even when I wiggle the wires to check for broken wires or loose connections that I can't see. The pulsing occurs only when the prop is on the motor.
 

Musdang

Not Quite Legendary
#4
Did you make sure the screws are not touching the windings of the motor? If you use the longer screws you can ruin your motor and esc. I’ve done this twice and both times it was a similar problem to yours. You can check if it’s damaged by taking two of the wires and if there’s no resistance, it’s likely you have a problem. Do that with every combination.
 

quorneng

Master member
#5
Probably the only way to demonstrate there is a problem is to buy an identical motor but do be careful with its screws!
If that runs without the pulsing then you know it is the old motor. If the new motor also pulses then you know it is something else possibly the ESC but you do now have a spare motor.
Without some very sophisticated test gear direct substitution is the only practical option. Even with the test gear it will not fix the problem only tells you where it is!
 
#6
There were three size screws that came with the motor, short, medium, and long. When the plane crashed the motor popped off the firewall because the small screws barely held the motor in place. When I remounted the motor, I tried using the small screws, but they would not thread because the first thread was stripped from the crash. I was able to use medium size screws to mount the motor, but I could see if the screws were touching the windings. May they were touching and this is my problem. I feel if the small size screws were a tad longer, they would have held the motor to the firewall and prevented it from breaking loose. It sounds like I need to order another motor and ESC based on your assessments. I really appreciate you feedback.
 

Musdang

Not Quite Legendary
#7
There were three size screws that came with the motor, short, medium, and long. When the plane crashed the motor popped off the firewall because the small screws barely held the motor in place. When I remounted the motor, I tried using the small screws, but they would not thread because the first thread was stripped from the crash. I was able to use medium size screws to mount the motor, but I could see if the screws were touching the windings. May they were touching and this is my problem. I feel if the small size screws were a tad longer, they would have held the motor to the firewall and prevented it from breaking loose. It sounds like I need to order another motor and ESC based on your assessments. I really appreciate you feedback.
Do you have another motor? The esc was fine for me both times. It may just be the motor.
 
#8
I have checked all the wires and can't see any visible breaks or disconnects. I can run motor at 100% without the prop and the motor does not pulse, even when I wiggle the wires to check for broken wires or loose connections that I can't see. The pulsing occurs only when the prop is on the motor.
Running without the prop was the same for me, but it was a very obvious break at one of the solder joints. With the prop on it requires more oomph to get the motor spinning and it might not be able to get over the ‘ bump’ to get started with the added resistance in the wires.
 
#11
Just bought a Tiny Trainer from Flitetest, electronics-hardware package included. Same problem that Rockyflyier describes above, except that it's never even been off the work bench. Brand new flite battery fresh off the charger, RX-TX bound. Try to power up the throttle stick & the motor will run up to about 1/3rd throttle. Beyond that, it starts pulsing on-off on about a half-second frequency, or simply quits. Sometimes, it just won't spin the motor at all. All brand new stuff from Flitetest right out of the box, assembled strictly according to the (rather limited) instructions. So now I'm removing & resoldering the ESC-to-motor connectors, looking for pinched wires at the firewall, & wondering if the ESC or motor or both are just defective. I do not have a spare motor or ESC lying around for testing; didn't think that should be necessary. Once I make yet another trip to a local hobby shop (aileron servo adjustable linkages were missing) for new banana connectors & resolder, I'll try to recalibrate the ESC, but this would be the first ESC I've ever had that was wacky from the start.
 

luvmy40

Elite member
#12
Just bought a Tiny Trainer from Flitetest, electronics-hardware package included. Same problem that Rockyflyier describes above, except that it's never even been off the work bench. Brand new flite battery fresh off the charger, RX-TX bound. Try to power up the throttle stick & the motor will run up to about 1/3rd throttle. Beyond that, it starts pulsing on-off on about a half-second frequency, or simply quits. Sometimes, it just won't spin the motor at all. All brand new stuff from Flitetest right out of the box, assembled strictly according to the (rather limited) instructions. So now I'm removing & resoldering the ESC-to-motor connectors, looking for pinched wires at the firewall, & wondering if the ESC or motor or both are just defective. I do not have a spare motor or ESC lying around for testing; didn't think that should be necessary. Once I make yet another trip to a local hobby shop (aileron servo adjustable linkages were missing) for new banana connectors & resolder, I'll try to recalibrate the ESC, but this would be the first ESC I've ever had that was wacky from the start.
If you bought a poawer pack from flite test, there should not have been any soldering necessary.

Did you calibrate the ESC?
 

quorneng

Master member
#14
The thing to remember is that the ESC has to "monitor" when to send the next pulse to next coil. To do this is "reads" the tiny voltage generated by the unpowered coil as it passes the magnet. It does this at least 100 times a second.
Whilst this may be OK when the motor is off load as the amps are low but any extra resistance from a poor joint or even a tiny short circuit will confuse the ESC so it will drop back to trying to start the motor with a a single big pulse. If the ESC is still unable to 'read' what to do next it simply resorts to sending another big pulse. In this condition the motor just oscillates.
Be aware the short start pulses are big so if you leave the motor oscillating for more than a few seconds either the ESC will be damaged or the motor will overheat.
The ESC to motor connections connections have to really good.
 
#15
If you bought a poawer pack from flite test, there should not have been any soldering necessary.

Did you calibrate the ESC?
Yes, actually calibrated it three times, just to be sure. Soldering was done because 2 of the motor leads felt really wobbly at their plug ends, as if perhaps very little of the wire was soldered under the heat shrink. The thing now runs better but only up to about 2/3 throttle then starts cutting in/out again (pulsing). I'm stumped.