Standard Repaired damaged gimbal and legs, gimbal still not fully initializing, and can’t link RC to aircraft

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This is my first DJI drone; I bought a used P3S off FB Marketplace, knowing I’d need to do some repairs, but figured I’d still come in under the cost of buying one in flight-ready condition. Well, it’s getting close to that cost.

Previous owner admitted to pulling a stupid — according to his story, he cut the engines mid-flight, figuring he could reengage before impact. (He was incorrect.) Damaged the gimbal, broke one of the landing gear, camera seems intact.

I’ve replaced the yaw and pitch motors, the gimbal arms, the ribbon cable (with a generic — I know, I know), and the main gimbal board (fully tested before shipment; shop sent testing video). (Also, repaired the landing gear, but antennas and compass board look fine.) On power-up,
• gimbal pitch and roll appear to stabilize
• yaw remains full left
• some motor controller sounds like it’s intermittently chirping
• RC can’t connect to aircraft; sync button on the aircraft is solid red and doesn’t feel/sound like it’s moving/clicking.

What’s next? Ribbon cable again? Something wrong with the yaw motor? Something wrong with the sync button or the board it’s on?

Video of power-up sequence and screenshot of disconnected DJI GO app.
 

Oso

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What’s next? Ribbon cable again? Something wrong with the yaw motor? Something wrong with the sync button or the board it’s on?
Welcome to the forum.

I think that most of us here will say to use only an OEM ribbon cable, so you'll probably end up changing out your generic. First try other things before spending more.

I'm not at all an expert, but it seems like whenever there is a question about the camera facing left or right one of the culprits is the yaw motor shaft magnet washer being out of alignment.
From what I understand its very fragile and can break easily during the alignment process. Check here or try searching for related terms or hopefully a more experienced member will chime in.

It has proven too common over the years for the P3S link switch to completely detach from the main board during a crash. Sometimes people can hear it rattling around inside the shell. You'll need to open the shell to see if the switch remains or is damaged.

People have dealt with a missing link switch in various ways. If they find the switch, resoldering. If not, rigging it with wires or putting the AC in link mode with a screwdriver since linking is not often needed again after achieving it once. You can search the forum for more info such as here or here for example.

Others have ordered a new switch. The part linked below is what people have commented here has worked. It seems that when they are in stock, they often come in lots of 10. If out of stock, you should be able to find it somewhere online. You also may be able to find someone here on the forum who has an extra one...or nine.

(d) 10 Pcs CESS Tact Push Button Micro Mini Touch Switch Momentary 3.2x4.2x2.5mm SMT SMD: Amazon.com: Industrial & Scientific
 
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Welcome to the forum.

I think that most of us here will say to use only an OEM ribbon cable, so you'll probably end up changing out your generic. First try other things before spending more.

I'm not at all an expert, but it seems like whenever there is a question about the camera facing left or right one of the culprits is the yaw motor shaft magnet washer being out of alignment.
From what I understand its very fragile and can break easily during the alignment process. Check here or try searching for related terms or hopefully a more experienced member will chime in.

It has proven too common over the years for the P3S link switch to completely detach from the main board during a crash. Sometimes people can hear it rattling around inside the shell. You'll need to open the shell to see if the switch remains or is damaged.

People have dealt with a missing link switch in various ways. If they find the switch, resoldering. If not, rigging it with wires or putting the AC in link mode with a screwdriver since linking is not often needed again after achieving it once. You can search the forum for more info such as here or here for example.

Others have ordered a new switch. The part linked below is what people have commented here has worked. It seems that when they are in stock, they often come in lots of 10. If out of stock, you should be able to find it somewhere online. You also may be able to find someone here on the forum who has an extra one...or nine.

(d) 10 Pcs CESS Tact Push Button Micro Mini Touch Switch Momentary 3.2x4.2x2.5mm SMT SMD: Amazon.com: Industrial & Scientific
Thanks for the tips! Before I go to the trouble of adjusting the magnet on the yaw shaft — I found a video involving acetone and a small torch to gently break the magnet free of its adhesive — I adjusted the arm on the shaft, by just about 90°, and the gimbal seems to stabilize pretty close to level and centered! (That has the set screw fully on the round part of the shaft, so it’s not a good permanent fix, but it’s a good proof of concept! Now, if only I could mount the motor rotated 90°…)

As for the switch, yeah, it’s just gone — see attached. I’ll probably just short it with a screwdriver for an initial link, for now.
 

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Welcome to the forum.

I think that most of us here will say to use only an OEM ribbon cable, so you'll probably end up changing out your generic. First try other things before spending more.

I'm not at all an expert, but it seems like whenever there is a question about the camera facing left or right one of the culprits is the yaw motor shaft magnet washer being out of alignment.
From what I understand its very fragile and can break easily during the alignment process. Check here or try searching for related terms or hopefully a more experienced member will chime in.

It has proven too common over the years for the P3S link switch to completely detach from the main board during a crash. Sometimes people can hear it rattling around inside the shell. You'll need to open the shell to see if the switch remains or is damaged.

People have dealt with a missing link switch in various ways. If they find the switch, resoldering. If not, rigging it with wires or putting the AC in link mode with a screwdriver since linking is not often needed again after achieving it once. You can search the forum for more info such as here or here for example.

Others have ordered a new switch. The part linked below is what people have commented here has worked. It seems that when they are in stock, they often come in lots of 10. If out of stock, you should be able to find it somewhere online. You also may be able to find someone here on the forum who has an extra one...or nine.

(d) 10 Pcs CESS Tact Push Button Micro Mini Touch Switch Momentary 3.2x4.2x2.5mm SMT SMD: Amazon.com: Industrial & Scientific
Improvement! I successfully synced RC to aircraft, so now I’ve progressed to “attempt to calibrate compass, where it complains about Strong Magnetic Interference“, and probably IMU calibration as well.
 
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So! After another FW update or two, I successfully calibrated the compass, and the IMU, and took a successful flight!

Only remaining issues are a) no gimbal pitch control or stability — it just pitches to whatever position gravity and momentum dictate, not held steady by the automatic controls, nor controllable from the RC, with no corresponding errors — and b) gimbal roll drifts a bit.

I haven’t replaced the pitch motor or board yet, nor the roll board, but pitch is the bigger issue. Is there any way to test board vs motor, or could it be the flex ribbon cable?
 
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It no longer seems relevant to this thread, but I have found many problems with mylar ribbon replacements in printers are due to inadequate thickness, and can be fixed by adding tape to the non contact side.
(this obviously will not work on double sided ribbons)
 

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