Anyone who has experience with smaller motors knows that if they are in a toothpick and you fly a slightly sharper freestyle with them, it doesn't last long, or until the first small hit. The 2 mm shaft bends very easily. In total, I already have 6 motor bells with a bent shaft, otherwise the motors are basically fine.
I pushed the shafts out of the motor bells and they are visibly bent, pushing the shafts out was not a problem if you have a jig.

Can it be straightened? I personally doubt it. Maybe someone knows how to do it.
Don't know if the shafts can be bought? I've searched and can't find anything for these motors, specifically the GEPRC GR1404 motors.

It's a shame to throw motors in the trash when you just need to replace the shaft with the bearings and they're like new.

Thanks for the enlightenment.
M. B.

You can give this a shot: (should work the same even if you’ve removed the shaft from the bell)

Being a hobby machinist I can tell you taking the bend out of small diameter shafts is fairly difficult.

My suggestion is to buy 2 mm dovel pins since they are ground from factory to relatively tight tolerance.Careful with the steel grade as you will need to tread the dovel pin on one end, cut it to length and file a chamfer down n the edges.

Frankly speaking this is too much work and time consuming for a person who even owns a lathe.

you might get them working, but a bend shaft means its overall an overused motor. motors with bended shaft wont perform the sameway, i couldnt get one shaft that straight.

i would suggest to fly or build different, maybe a more tanky build with good armguards or triblade befor biblades for durability of motor in crashes. or shrinking the weight to get less force in crashes.

maybe geprc will provide some motorshafts for free, if you ask for it ;-)

I asked them already, they provide new motors only. Geprc will not send the motor shaft only.

what allupweight do you get on your build?

227g including Gaoneng 4s900mAh HV, without naked GoPro ...

To make this completely clear. I built a Smart 35 HD from components and modified it a bit, made it lighter somewhere, added a bit of TPU somewhere, put a single reasonable HQ T3.5x2x3 (newly also HQ T3.5x2.5x3) propeller. With the other propellers, it was not possible to tune the quad the way I wanted, and I tried almost all propellers. You can't reasonably get rid of propwash with other propellers and the spool up wasn't what I wanted either. E.g. the original Avan propellers are more durable, but they will never fly really well. The biggest progress was the Blujay ESC firmware with RPM filtering and BF4.3 with significantly suppressed filters, this together made it possible to turn the original fairly well-flying quad into an excellent quad (a master mult. is at 1.9 and motors are only slightly warm).

Now the Smart35 HD flies really well and I don't want to change anything about it, it really took me a long time to get it right.

I have this quad so that I can fly it basically anywhere, where I don't have to go outside civilization with the great-flying APEX 5. Time is short, so I fly the Smart more often, and the more often it is flown, the more often it crashes... The problem is not that the arms wouldn't protect the motor, they do, but the 2mm shafts bend even through the prop hitting something with the motor disarmed, it's just soft... 5mm shafts on a 5 inch quad will last considerably more.

(05-Sep-2022, 10:43 PM)kafie1980 Wrote: Being a hobby machinist I can tell you taking the bend out of small diameter shafts is fairly difficult.

My suggestion is to buy 2 mm dovel pins since they are ground from factory to relatively tight tolerance.Careful with the steel grade as you will need to tread the dovel pin on one end, cut it to length and file a chamfer down n the edges.

Frankly speaking this is too much work and time consuming for a person who even owns a lathe.

The shaft is not in the shape of a simple cylinder. On the propeller side, the diameter is only 1.5 mm (T style mount) and towards the engine, before the diameter increases to 2 mm, there is a flange that defines the depth of insertion of the shaft into the motor bell. Further, the shaft is grooved so that it does not rotate in the bell. I have a lathe, but this cannot be produced on a lathe at home in an acceptable amount of time.

Tomorrow I will try to straighten one shaft and then air test it to see if there will be vibrations. I tried to bend the shaft using a simple fixture in the chuck. It was very easy, just by hand, it's just soft.

my suggestion would be, for that small and not hubgry motors, go for a 450mah 4s battery as a try.
as you told you wont change anything, you might not be able to improve it to get less bended shafts.

maybe other 1404 are more durable? the xnova maybe?

Total layperson here..... I just got a pair of vicegrips and bent them back into place with my eyes as the only reference to how straight they were again. Ghetto AF but they worked and prolly caused the filters on the FC to work a bit. Mind you this was for whoop motors with a 1mm shaft.

(06-Sep-2022, 12:36 PM)MomoBrut Wrote: The shaft is not in the shape of a simple cylinder. On the propeller side, the diameter is only 1.5 mm (T style mount) and towards the engine, before the diameter increases to 2 mm, there is a flange that defines the depth of insertion of the shaft into the motor bell. Further, the shaft is grooved so that it does not rotate in the bell. I have a lathe, but this cannot be produced on a lathe at home in an acceptable amount of time.

Tomorrow I will try to straighten one shaft and then air test it to see if there will be vibrations. I tried to bend the shaft using a simple fixture in the chuck. It was very easy, just by hand, it's just soft.

I kinda agree that manually machining and matching tolerances is time consuming.  

If you have the right tooling it can all be done. You can literally do it on a watchmakers lathe. Grooved as in a keyway or just knurled? Should still be doable.

But again what's that motor worth to you and if you do this kind of repair work often. For me to spend 30 mins on the lathe to save a $20 motor might start to make sense if I have plenty of free time on my hands. 

I have a concern that the shaft dimensions may not even be universal and will differ across manufacturers or even models/versions.

If you want to just remove the bend in the old shafts and assuming you have a test indicator, some collets for smaller diameters, and a 4 jaw independent lathe chuck there can be a way to do it. Mount the shaft in a collet and revolve the shaft with the test indicator which will indicate the high/low spots, mark the high spots and clamp the motor shaft in an independent 4 jaw applying more pressure to the jaw on the high side. One issue here is that most 4 jaw chucks for larger lathes might not clamp something in such small diameters. If you had a 6 jaw lathe chuck then you can get the shaft even more accurate.

Sorry for the side track but just sharing options for someone that has the right gear.

I wrote to Geprc again. The answer is not and will not be from someone who is technically proficient, it is simply a sales person who can only answer simple questions and is not there to solve anything other than processing orders, that is my feeling. And I have a feeling he doesn't even know what a shaft is. Very common with these types of companies. Do any of you have any idea who makes the motors for Geprc, I have a feeling they don't make them themselves. If they really made them, it wouldn't be a problem for them to send it. They simply have ready-made motors, nor do they have separate motor bells.

maybe single shafts would cost the same if the send a full set motors. i would ask for a full replacement...
"im not happy, if no shafts available, i would line to get a full replacement" that would be what a sales person could do for you ;-) ask for it

(07-Sep-2022, 03:35 AM)kafie1980 Wrote: I kinda agree that manually machining and matching tolerances is time consuming.  

If you have the right tooling it can all be done. You can literally do it on a watchmakers lathe. Grooved as in a keyway or just knurled? Should still be doable.

But again what's that motor worth to you and if you do this kind of repair work often. For me to spend 30 mins on the lathe to save a $20 motor might start to make sense if I have plenty of free time on my hands. 

I have a concern that the shaft dimensions may not even be universal and will differ across manufacturers or even models/versions.

If you want to just remove the bend in the old shafts and assuming you have a test indicator, some collets for smaller diameters, and a 4 jaw independent lathe chuck there can be a way to do it. Mount the shaft in a collet and revolve the shaft with the test indicator which will indicate the high/low spots, mark the high spots and clamp the motor shaft in an independent 4 jaw applying more pressure to the jaw on the high side. One issue here is that most 4 jaw chucks for larger lathes might not clamp something in such small diameters. If you had a 6 jaw lathe chuck then you can get the shaft even more accurate.

Sorry for the side track but just sharing options for someone that has the right gear.

I've started trying to straighten the shafts and I have a problem with the lathe collet, it's too big, I have to sort it out and it won't be right away. It is almost impossible to straighten the shaft directly, the rotation deviation is really at the limit of measurability. And as you wrote, there is a problem with the deviation of the attachment in the larger collet itself. The shaft needs to be straightened with a motor bell, and a disk with a larger diameter is best mounted on it, which will show the deviation more clearly. And then straighten the shaft through it with a greater and more precise moment.

Update...
I tried 3 more collets of different sizes that I was able to get quickly. I've tried 5 collets in total, it's basically impossible to hold a 2mm shaft consistently in them. It is simply impossible. I tried to mount a completely new and completely straight bell motor in them. I estimate that out of 5 mounting attempts, it is possible to mount it 2 times in such a way that it is exactly centered. So there is absolutely no way to go here, and buying a new collet with more jaws that will comply is simply not worth it. And not even the time I spent with it...
Probably the only way is to test the motor bell on its stator with original bearings and mark the place of deviation, then put the motor bell in a collet, align and test again on the stator. In other words, a pain in the ass.

Why the hell don't they sell the shafts separately? The replacement takes a few minutes for a slightly experienced person and the problem is solved.