Juddering DJI Motors

[StuR]

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.

 

[StuR]

Thanks Havoc i will check the bullet connectors. It just seems a bit weird that all 6 motors are doing the same thing! I've been googling the problem till the early hours but still no joy :upset:

 

[econfly]

Thanks Havoc i will check the bullet connectors. It just seems a bit weird that all 6 motors are doing the same thing! I've been googling the problem till the early hours but still no joy :upset:

Post up a photo of the wiring. If you lengthened the power leads to the ESCs a lot and you are running 3s power, then you might have a problem with too-low voltage at the ESCs are even at the FC (or BEC). Long story short, long power leads can increase voltage fluctuations. For electronics rated at 3s minimum, and running at that minimum, you can end up with a system with high-frequency voltage fluctuations below the minimum needed to operate the system.

 

[StuR]

Hi Econfly thanks for the info. Here is a picture of my wiring although it doesn't show much because everything is sheathed.
View attachment 19204
I did lengthen the power leads to the esc by about 10 to 12 inch (250 to 300mm) and I am running a 3s 5000mah battery. What do you think I should try?

 

[econfly]

Hi Econfly thanks for the info. Here is a picture of my wiring although it doesn't show much because everything is sheathed.
View attachment 23559
I did lengthen the power leads to the esc by about 10 to 12 inch (250 to 300mm) and I am running a 3s 5000mah battery. What do you think I should try?

Do you have a 4s power source? If so, give that a try. I'm just guessing about the problem, but given your description of all motors being affected I have to think there is systemic issue, which I'm guessing to be due to voltage dropping below spec somewhere. My thinking on trying 4s power is that any voltage dips will still be there, but they will be 3.6 volts or so higher at 4s and therefore probably not so low as to cause the problem you are seeing. Just a guess.

You are generally better off extending the motor wires and keeping the ESC power wires as short as possible (details here). Now that may not solve your problem (because we don't know what the problem is yet), but this is a much better approach even if longer power wires are not the problem. If it were my rig I would re-wire it, putting the ESCs as close to the distribution board as reasonably possible, and extending the motor wires (more work, I know). That is a good thing regardless. If it fixes the problem, all the better.

 

[Treg]

You are generally better off extending the motor wires and keeping the ESC power wires as short as possible (details here). Now that may not solve your problem (because we don't know what the problem is yet), but this is a much better approach even if longer power wires are not the problem. If it were my rig I would re-wire it, putting the ESCs as close to the distribution board as reasonably possible, and extending the motor wires (more work, I know). That is a good thing regardless. If it fixes the problem, all the better.

I agree about the wire length, it should be added to the motors not the ESC.

 

[StuR]

Thanks Econfly. I don't have a 4s but i will borrow one. I'm just working through / eliminating various possible factors before I re-wire!! What your saying makes total sense though. Thanks again. I will let you know how i get on. One positive is the airframe a great bit of kit for the price.

 

[StuR]

Well I've taken out the extensions i put into the ESC wires for one of the ESC`'s and tried it. No change the motor ran the same as all the others (juddering round). So should i investigate the PBD or will i need to remove the extensions for all the ESC's to run a proper test?

 

[econfly]

Well I've taken out the extensions i put into the ESC wires for one of the ESC`'s and tried it. No change the motor ran the same as all the others (juddering round). So should i investigate the PBD or will i need to remove the extensions for all the ESC's to run a proper test?

Maybe try it with the other motors disconnected. Another possibility is a short somewhere. Any chance the motor mount screws on the new build were long enough to reach into the motors and contact the windings or grounded metal?

 

[Hexacrafter]

I have seen this before......
I agree with econ... check that the motor mounting screws are not too long.
Disconnect the motors (without props) and spool up in hand,,,, if no problem use shorter screws....

 

[StuR]

I've removed the motor including motor mounting screws (it turns ok in hand), reduced the ESC power lead & signal line to original length. Then connected the motor & ESC direct to the RX, VU & battery. But the motor still judders round.. AAARRRGGGG!! Only thing i can think of is its the ESC. But i can't understand how lengthening the ESC power leads (by 320mm) and signal line could of effected the ESC?? Anyone any thoughts or suggestions??
Cheers
Stu.

 

[econfly]

I've removed the motor including motor mounting screws (it turns ok in hand), reduced the ESC power lead & signal line to original length. Then connected the motor & ESC direct to the RX, VU & battery. But the motor still judders round.. AAARRRGGGG!! Only thing i can think of is its the ESC. But i can't understand how lengthening the ESC power leads (by 320mm) and signal line could of effected the ESC?? Anyone any thoughts or suggestions??
Cheers
Stu.

I think all you can do at this point is work the problem back until it goes away.

 

[StuR]

Hi Folks. Well I finally sussed out what the problem was.... . . motor screws were a fraction too long and they damages the motors. Talk about feeling a D!(£HEAD. This is not my first build, which makes a stupid mistake sting all the more!! Thanks for all the help and suggestions though. The banging you may have heard was my head on the table, the screams are my wallet.