Juddering DJI Motors

[StuR]

Firstly apologies if this is in the wrong section. Because i';m unsure of the cause of the problem i was not sure which section to post this in.
I recently decided to strip the electronics from my F550 Y6 & mount everything on a Fortis Titan Y6. The build went well apart from.. I';ve just tested on the bench (without props!) and ALL the motors judder. I';m using the standard DJI 920 KV motors & 30A OPTO esc';s. To complete my build I had to use a simple power distribution board (fusuno) & lengthen the power leads and leads that plug into the FC. I did this by using the exact same type & length of wire & soldered joints adding heat shrink covers. I';m sure i didn';t cross wires because everything is colour coded.
I';m guessing that lengthening the wires has knackered my esc';s and/or motors in some way.
Has anyone got any suggestions as to what the problem might be?
Many thanks
Stu.

[DarkButterfly]

Hi and welcome,

Sounds like you have a lack of power somewhere, best thing to do is unplug each ESC and motor, then reconnect them one at a time, plug it into your Rx on its own without the FC, then test to see if it still judders, do this for each motor and ESC, then reconnect to the FC and test, it may be that they need calibrating.

[Cloudbuster]

I agree lack of urggs mate !!! Motors not getting enough current by the sounds of it ... Whats the rating on the new disi board most of the cheap chinese ones are whoffally incapable of processing the current needed for six mtrs..

Regards rob

[StuR]

Thanks DarkButterfly & Cloudbuster I will try connecting direct to Rx one at a time. I will let you know how i get on. The PDB is a cheap board, its a Fusuno from FastLad rated at 200A max. I didn';t think DJI OPTO Esc';s could be calibrated?
Cheers.

[Friskle]

No, you cant calibrate DJI OPTO ESCs, they have no throttle range settings to calibrate, if it was all working previously, then it could well be a dry solder joint, lengthening the wires shouldnt affect power so long as you have used similar rated wire, a good test for that , is are the wires getting hot, another possible thing, is any slight break in a motor wire, or any of the main esc wires, or the board, has is faulty.

As above, i would check each motor and ESC separately, without the board, and see if they run individually.

[StuR]

OK. I eliminated the FC & PDB & brought the ESC power leads back to their original length. I conected the ESC & motor directly to the Rx and tested but the motor still just judders round. AAARRRHHHHH 
The only thing I can think of is the ESC. Its a DJI OPTO 30A. For some reason lengthening the power leads and ESC signal line has effected the ESC';s ? Anyone any thoughts?
Cheers
Stu.

[Chami82923]

Are they juddering just at idle speed, when you increase the throttle above 20% do you get the same juddering?  If it';s just at low speed you may simply need to increase the idle speed.

Callum

[John A]

Just a few thoughts......

Do the motors run smoothly at say, 50% throttle? If they do, it could be just at start-up so the thought is do the motors require the props which could be acting as a kind of flywheel. I have noted on the DJI Naza motor test it is possible to get the motor turning the wrong way without the props fitted. I believe at low throttle the length of your leads would have little if any effect on the motor/ECS as the current will be relatively low, and indeed, if you have matched or exceeded the original ESC/motor wire gauge I would not expect a problem.

Final thoughts, are you experiencing noise on the ESC signal wires? If you keep the power wires ( battery and motor leads ) as far away from the signal lines as you can, does this help? Is the signal ground good? (electrical noise can also travel up a ground line unless it is well bonded to the main ground)

[StuR]

Thanks for the responses chaps. Im still working back to try & eliminate things one at a time. Im getting the motor judder regardless of where the throttle stick is at.
Cheers.

[StuR]

Hi Chaps. Well I got to the bottom of what the problem was... ..  motor mount screws were a fraction too long and D!C£HEAD here didn';t notice, cranked them up & ruined ';SIX'; motors. Talk about feeling stupid. This is not my first build & I sized the bolts up, thinking... "um they look fine" ARRGGGHHHH oh well I least its problem solved just an expensive balls up.
Thanks for all the help.