Magic Pie III 48V installation trouble

[Andrew Rogers]

Hi,

I've just purchased a Magic Pie 3 kit, 48 V 10ah battery, rear hub motor and installed. Installation seemed to go smoothly but the motor stopped on the second short test run, power cut out.

I found that the main power cable to the motor had wrapped around the axel as per the photo (unfortunately blurry but still shows what happened, I had partially removed the wheel when the photo was taken).

Upon opening you can see that the cable has pulled against the side of the housing broken the insulation on the positive wire and appears to have created a short.

Two questions:

a) How did this happen and how do I stop a repeat? The motor is connected to a brand new frame, there's evidence to suggest that the axel has been able to spin within the dropouts, no damage to the axel, no damage to the dropouts (per photos), it's physically impossible for the axel to have spun within the dropouts give the width of the axel across the threaded section.

The only thing I can think of is that the axel has spun relative to the hub.

b) I can re-solder the wire to remove the damaged section, is there anything I need to be aware of in doing this? any risks with re-soldering?


Any help would be greatly appreciated.


Regards,


Andrew Rogers

[Bikemad]

Hi Andrew andto the forum.

After looking at your photos, it would appear that the stator assembly has somehow spun on the axle.

I you look at the attached picture below, you should be able to just see the drive key which should securely locate the stator assembly onto the axle.  I can only see three possible reasons that could cause the problem you have:

• The key has been dislodged and fallen out during the initial assembly process when the axle was pressed into the stator.
• The key has sheared, allowing the stator to spin.
• The aluminium stator casting has come detached from the steel insert, allowing it to spin.

I think out these three options, the first is the most likely. Take a good look at the key-way slot and see if there is a rectangular key inside, which should look similar to the one shown in this diagram but with rounded ends:


Which probably looks more like this:


If the key is missing, the axle will need to be pressed out and a new key fitted and the axle pressed back in again before the hub can be used.

It's impossible to tell just by looking whether the controller has been damaged by the shorted wires, but there is certainly a fair bit of black from the arcing produced by the short circuited power cables.

If you purchased this wheel from a local dealer, you will need to contact them and explain what has happened.
If you purchased direct from GM in China, I suggest you contact David at GM directly (wyh@goldenmotor.com).
It would be a good idea to attach the pictures, or at least include a link to this post (http://goldenmotor.com/SMF/index.php?topic=4249.0) so they can hopefully see the pictures (and my comments) here.

Please let us know what you find after you have taken a closer look.

Alan
 
P.S. I strongly advise using torque arms with an aluminium frame.
 

[Andrew Rogers]

Alan,

Thank you so much for the very comprehensive and speedy reply.

I didn't know whether the axel was secured via a spline or a key but you've clarified this. From your comments I suspect that the key was not placed during manufacturing.

Attached are two more detailed photographs. The second shows a piece of wire that I'm able to insert into the key slot... I can get this in to a depth of 1inch/2.5cm before it stops. This seems to suggest that the key is missing. There was no sign of damage (beyond the shorted wires/black) when I first opened it, no broken bits of metal, bits of key etc.

I'm wondering whether by looking at the relative position of the rebate on the axel compared to the whole in the hub that the wires from on my wheel vs a good working MPIII would confirm if the axel has moved relative to the hub? (unless of course it's completed exactly one rotation)

I purchased the unit directly from China (shipped to Australia) so will get in touch with David now.

I've now secured a torque arm, the frame is Chromoly but the dropouts don't seem to be particularly heavy gauge so I'm sure it's worth the extra protection.

Included below also are some photos of a battery mount I fabricated. It gets the battery forward and lowers the centre of gravity. I've not been able to test ride but it feels like it will make a significant difference to handling. You can now pick the bike up immediately in front of the seat tube and it's balanced front to rear. It's a relatively large frame (22").

I'm slightly nervous that I met get problems with water getting in around the key hole. Would be interested in any other feedback on the design.


Thanks again for the assistance.


Andrew

[Morgen 3Eman]

It looks like you have rotate 180 from my MP3.

ttfn
Dennis

[Morgen 3Eman]

And with the low torque this thing generates, your key has to be missing. 

TTFN,
Dennis

[Morgen 3Eman]

And maybe I should check to see if my key is in there....

TTFN,
Dennis

[Bikemad]

It looks like you have rotate 180 from my MP3.

Dennis, you didn't look closely enough, did you?

Andrew's axle is obviously a newer version which no longer has the milled slot for the wire. Instead, it simply has a nicely radiused section which appears to have been incorporated into the new casting to allow clearance for the cable eliminating the milling operation which was responsible those nasty sharp edges that Dennis and I had already mentioned.

The strange thing is that the key-way still appears to be in the correct position, approximately 90? clockwise from the relieved area.

Andrew, I have been thinking about your test where the wire enters approximately 1" and realised this could still be the case, even if a key is fitted.
If you look at the picture attached below showing the opposite end of the axle, you can clearly see a gap above the key which looks big enough for your piece of wire to slide into very easily .

I think we need to find another way to prove whether or not the key is actually fitted.

If it were mine, I would remove one of the side covers and mount the axle in a vice using soft jaws or scrap pieces of aluminium etc. to protect the axle. I would then use a marker pen to draw a line across the stator casting, over the steel insert containing the key-way and onto the axle, before trying to turn the stator by hand to see if anything moves where it shouldn't.

Alan
 

[Morgen 3Eman]

Hi Alan,

I'll admit I did not study the photos terribly closely.

Here is what I did notice.  My photo is taken from the right side, with the phase wires going up.  The cable relief slot in the axle is on the  right side.

His photo is taken from the left side, with the phase wires going up.  The cable relief slot is on the left side, as if the axle has been rotated 180 from my photo. 

Maybe they don't actually have any machining specs?

I'll take a closer look.   

TTFN,
Dennis

[Andrew Rogers]

Alan,

Thanks for the advice again, I've done as suggested only using the bike frame to fix the axel to and there is clearly no key fixing the axel to the stator casting. See photos below with line marked and stator rotated through three different positions.

I'd emailed David but no response yet, will ping him again today with the additional information.

Thanks again for you help - really appreciated.

Regards,

Andrew Rogers

[Bikemad]

there is clearly no key fixing the axel to the stator casting.

Andrew, I'm going to disagree with you regarding the key, because I think the key is fitted and is still locating the steel insert correctly onto the axle, but the aluminium stator casting appears to be slipping on the outside of the steel insert.

I can only see three possible reasons that could cause the problem you have:

• The key has been dislodged and fallen out during the initial assembly process when the axle was pressed into the stator.
• The key has sheared, allowing the stator to spin.
• The aluminium stator casting has come detached from the steel insert, allowing it to spin.

I had a good look at your pictures and the key-way does not seem to be moving with the stator. I think this would have been easier for us to see if you had marked all the way across the joint as I originally suggested: 

I would remove one of the side covers and mount the axle in a vice using soft jaws or scrap pieces of aluminium etc. to protect the axle. I would then use a marker pen to draw a line across the stator casting, over the steel insert containing the key-way and onto the axle, before trying to turn the stator by hand to see if anything moves where it shouldn't.

The steel insert is most likely secured into the centre or the stator during the casting process as the molten aluminium flows around it and fills up the mould, if this is the case you're going to need a complete new stator assembly, or preferably a replacement hub.

If you can repeat the experiment again, but this time with the pen mark right across the joint between the steel insert and the stator (as indicated below) and take some more photos showing before and after, and it will hopefully show the movement between the stator and the insert much more clearly.



Alan
 

[Morgen 3Eman]

Good eye, Alan.

The stator is clearly rotating about the steel collar and axle.  Scarey.

TTFN,
Dennis

[Andrew Rogers]

Alan,

Apologies - I missed that - and you were correct. See photos.

Andrew

[Bikemad]

The stator is clearly rotating about the steel collar and axle.  Scary.

And here's the result of combining the two pictures:


A single image that clearly shows exactly where the movement is taking place, I think this will be clear in any language.

Alan
 

[Morgen 3Eman]

Nice work on the photo!  We all can easily see what is happening. 

TTFN,
Dennis

[Andrew Rogers]

Just a final note on this - Golden Motor have since shipped a replacement stator/axel/controller/wiring loom assembly, I've fitted and the bike is working fantastically.

A huge thanks to Alan for your assistance.

Secondly, I have to say I had some trepidation about ordering directly from China and read mixed reports about Golden Motor's customer service. In this experience I couldn't fault it, replies were reasonably responsive. No resistance to replacing the faulty parts, importantly they didn't require that I return the failed components which is a major hassle usually. The replacement items shipped from China in 4 days (faster than inter capital city freight in AU). I called them at one stage and was able to speak to people in english that communicated well and solved my problems. Impressed.

Andrew