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Help! Ft Gremlin Motor Issue

#1
I built an Ft gremlin over the fall and have been flying it for the past couple of months. This week, the front right motor has been malfunctioning. When I arm the quad, all of the motors arm normally, but when I give it throttle to take off the front right motor(motor 2) stays at the same rpm as it does when it is just armed. I have crashed it a couple of times, but it continued to fly normally. I checked all of the solder connections and all of the wires are connected. I went into Betalight, to the motors tab and individually tested motor two(the motor that was giving me issues). At full throttle, it was still just at the "armed" rpm. What steps should I take to fix this problem?
 

PsyBorg

Wake up! Time to fly!
#2
I would replace the signal wire for that esc. They are fine wires and easily broken inside the casing if a stick or something manages to get up in there and stretch the wire on hard impacts.

If that didnt help connect the signal wire to one of the 3 other functioning connections and see if the motor will spin properly.

If that doesnt help try reflashing the esc's

Finally if all else fails remap that motor to another port.
 
#4
When I armed my quad the motor would spin at a slightly lower rpm then the other motors. I tried replacing the signal wire like PsyBorg recommended. I also updated the esc firmware. For me, that didn’t work so I ordered a new motor and esc. I replaced the esc and it worked fine. When you say delayed spin do you mean that the motors arm at different times, or do they spin at a different rpm when armed?
 
#5
When I armed my quad the motor would spin at a slightly lower rpm then the other motors. I tried replacing the signal wire like PsyBorg recommended. I also updated the esc firmware. For me, that didn’t work so I ordered a new motor and esc. I replaced the esc and it worked fine. When you say delayed spin do you mean that the motors arm at different times, or do they spin at a different rpm when armed?
So, In betaflight when I am on the motor tab motor 1 and motor 2 don't start spinning until those values I posted above. So I guess that means they don't arm until that value. When I arm the quad, Motors 3 and 4 spin fine and nothing from 1 and 2 until I get above half throttle, then 1 and 2 will began spinning. I hope this makes my issue more clear. I'm assuming I will have to replace the ESC or the Motor, just hoping to narrow it down!
 
#6
One thing that I did to make sure that it was either the motor or the esc was to check my connections using a multimeter. I did not do this with my quad, but I suppose you could put the motor and esc from motor 3 or 4 on the motor ports for 1 or 2. If it works normally, then put the motor from either motor 1 or 2 on the esc from motor 3 or 4 . If that works normally then it is most likely an faulty esc, but if it doesn’t work, then it is most likely a problem with the motor. By doing this you would be troubleshooting for the flight controller, the esc, and the motor in 2 steps instead of 3.
 

ElectriSean

Eternal Student
Mentor
#7
I think it's more likely that the motors would suffer damage in the crash, but the only way to know for sure is to swap stuff around. Try hooking one of the motors that is misbehaving to an ESC that you know is working.
 

PsyBorg

Wake up! Time to fly!
#8
Ok from what I see.. motors and escs seem fine. If the esc was bad the motor would not spin. If the motor was damaged from a crash you would get start and stop action.

The fact they start at different rpm says to me the esc's lost track of calibration.

I would go into blheli and see what min throttle and max throttles are at. While you are in there it probably would not hurt to reflash them.

I am not sure if you are using dshot or not but I suggest you go with multishot and flash 16.5 on the esc's. That protocol is faster then dshot 300 which is max usable for the femto controller.
 
#9
3 HOURS LATER...
Okay, I was using ONESHOT125, I Tried the following.
MULTISHOT: Motor 1=1563, Motor 2=1692, Motor 3 and 4 Normal operation.
DSHOT150: Motors 1-3 normal operation, Motor 4: doesn't spin at all
DSHOT300: Motors 1-3 normal operation, Motor 4: doesn't spin at all
Sorry I'm not sure how to flash 16.5 to the esc's.
I continued troubleshooting anything I could think of, so I decided to re-watch the original setup from the FT build video by TJ. I followed all the steps and as soon as I got to the part where he calibrated the ESCs, I knew that was probably the issue. I performed the steps and BOOM! everything is working perfect now!

Thank you RHengelsberg, ElectriSean and PsyBorg for all your suggestions! it got me off my backside to get this thing fixed!

Now for the test flight!

One last question, is there a post for proven, optimal settings and tuning for the stock gremlin?
Thanks again!
Turbo!
 

PsyBorg

Wake up! Time to fly!
#10
Gratz on slogging thru and gettin in the air.

The femto has a strange thing about dshot. May be a factory flash thing. Some femtos will not run dshot without mapping motor 3 or 4. Some wont do multishot. This is why I asked what you tried.

As far as a cookie cutter set up there is no such thing. Each build will have different "quirks".

The good thing is beta flight is pretty forgiving and will get you in the air on stock pids. It wont be the best tune but you can learn and work that all out easy enough with some research and questions.

For the gremlin as far as rates and starting advise I can help you out with some smoother settings provided you have properly set up channel centers and end points.

These things "can" fly on 3s but I seriously suggest you learn 2s and tuning before trying as you can fry escs and motors in a matter if seconds on stock pids.

Roll & Pitch rc rate 0.44
Yaw rc rate 1.90
Roll super rate 0.90
Pitch super rate 0.89
Yaw super rate 0.54

NO EXPO ON ANYTHING.

This is for assisted mode using horizon. NEVER use angle mode.
This will give you smooth transitions in and out of hover so you are not fighting the computer for indoor "tinywhoop" ish feel.

Horizon strength 20 transition 20
Angle limit 10. Sensitivity 25.

If you try tuning start with P gains and do 5 point changes at a time on one channel at a time and see if its better or worse. Try each change no more then 15 -20 seconds before landing and feeling motor temps.
 
#11
You’re welcome and congratulations! I fly my gremlin in acro mode, and am going to be racing it in a very tight course. Does anyone know how to tune it so that it feels locked in, but not overly sensitive?
 
#12
Gratz on slogging thru and gettin in the air.

The femto has a strange thing about dshot. May be a factory flash thing. Some femtos will not run dshot without mapping motor 3 or 4. Some wont do multishot. This is why I asked what you tried.

As far as a cookie cutter set up there is no such thing. Each build will have different "quirks".

The good thing is beta flight is pretty forgiving and will get you in the air on stock pids. It wont be the best tune but you can learn and work that all out easy enough with some research and questions.

For the gremlin as far as rates and starting advise I can help you out with some smoother settings provided you have properly set up channel centers and end points.

These things "can" fly on 3s but I seriously suggest you learn 2s and tuning before trying as you can fry escs and motors in a matter if seconds on stock pids.

Roll & Pitch rc rate 0.44
Yaw rc rate 1.90
Roll super rate 0.90
Pitch super rate 0.89
Yaw super rate 0.54

NO EXPO ON ANYTHING.

This is for assisted mode using horizon. NEVER use angle mode.
This will give you smooth transitions in and out of hover so you are not fighting the computer for indoor "tinywhoop" ish feel.

Horizon strength 20 transition 20
Angle limit 10. Sensitivity 25.

If you try tuning start with P gains and do 5 point changes at a time on one channel at a time and see if its better or worse. Try each change no more then 15 -20 seconds before landing and feeling motor temps.
Thanks man! I'll give this a shot! I just flew a battery to test everything out on stock settings and it was flying great! Unfortunately its starting to rain so, hopefully I can find a window to fly and try out these settings!