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Old 2020.06.27, 05:10 PM   #1
TyrellMadeMe
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Join Date: May 2020
Location: Washington, DC and Driggs, ID
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Help! Kyosho 4100kv motor failed...or something else?

Hello!

I just set up and started driving a MR03 EVO N-MM2 chassis with the Kyosho 4100kv brushless motor. After an aggregate of 55 minutes lapping my (shortened) Mini-96 track in 50 lap stints, the car will not move - forwards or backwards.

How can I tell if the failure is with the motor, the ESC, or something else?

Symptoms:
1) When I take off the rear axle/diff, turn the car on, and pull the trigger on the radio (forward or reverse), the pinion rotates about 1/4 to 1/2 of a turn then stops. There is a faint “electronic” humming/clicking sound coming from the motor for as long as I keep the trigger pulled.
2) When I try to pull the trigger again, the motor still makes the humming/clicking sound, but the pinion won’t move again until I power cycle the car.
3) The steering servo works normally when I turn the radio’s wheel.
4) The car stopped running right after I hit a wall. It bounced/rolled backwards and I hit the throttle, and nothing happened. (I do hit the wall a lot!)
5) I put new batteries in the car, and that did not fix the problem.

Yesterday, I ran the car with the box stock setup, Kyosho 6t pinion. Today, I switched to a PNR pro match 8t (and switched to the MM2’s “B” motor spacers). To change the motor spacer, I did need to unplug the motor’s leads from the ESC leads and remove the motor from the case. Per the chassis manual, I removed the pinion from the “naked” motor (with the supplied tool) and the put the pro match 8t onto the motor by pressing the motor sprindle straight down into the pinion on in a table tap.

Any advice would be much appreciated. Thank you!
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Old 2020.06.27, 08:11 PM   #2
SuperFly
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If I had to guess, I'd go with 1 of the 3 motor wires being loose. I've never taken apart a Kyosho brushless, so I'm not sure if you can fix a loose connection in the can. Did you plug a couple of the wires back incorrectly?

My limited understanding of the 3 poles of a brushless motor is kind of like people doing the wave; if you have just two people, you're just going back and forth, but with a third, you can have a cycle and a direction of rotation.

Blowing FETs isn't something I hear about with brushless cars. But I have found (sensorless) brushless motors to be sensitive to starting from a dead stop because of weak batteries or tight gear mesh. That little bit of rotation makes me think it's just missing the 3rd component to spin.
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Last edited by SuperFly; 2020.06.27 at 08:14 PM.
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Old 2020.06.27, 10:06 PM   #3
TyrellMadeMe
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Great tip! Thank you! I should have checked the wiring connections more throughly. I just went down to the basement and everything looked good, all three connectors are seated properly, but when I started manipulating the wiring, the yellow wire from the ESC fell right off in my hands. So, SuperFly was correct, one of the three connections had failed! I guess that wall hit was the final straw.

It looks like the wire sheared off right at the solder joint. No excess wire exposed past the insulation, and a blob of solder on the board’s middle terminal. My soldering skills are limited, but I can probably fix this without making a total mess.

However, is this the sort of thing that Kyosho would consider for a warranty repair, or is it “normal wear and tear”? I’m within their 90 day warranty (bought the chassis on June 11). If this is “normal”, I’d be disappointed to learn the EVO chassis is so fragile. (I’ve run my brushed MR03 into the wall WAY more times, and it’s still going.) I sent an email to Kyosho America earlier today explaining the problem...before SuperFly’s diagnosis. If they offer to do a repair, is it worth it or do they have a super-long turnaround time?

Thanks again for the help!
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