Converting a hubmotor to a middrivemotor

[crossbreak]

The interference that damaged this motor only occurs when the motor shaft is plunged deeper into the motor. Since nothing really pushes or pulls on the motor shaft the issue did not present until the motor was driving a bike down the road.

this is what i meant with "aligning" it axially. Sometime the language barrier sucks Maybe I should have called it "shimming". In this case a LOT of shims woulds have been needed. Do I see it wrong or was the rotor aligned axially (not only radially) in one direction by the key, which you took away from the original construction?

 

[Whiplash]

I could be wrong but I think its held axially by a circlip...

 

[mr.electric]

I think the center of the stator was extra fat and occupied the place where the axle tube is now. Upon drilling out the stator center a shoulder was cut away giving the rotor extra play.

 

[fechter]

It would be really cool if somebody made a CAD drawing of the motor based on measurements of the parts. Then in the CAD program you could measure the distance between parts and see where the clearances are needed and see how the parts fit together. It would be like having a transparent model.

Even when you have the parts in front of you, its hard to visualize how they fit exactly when you assemble the motor.

Nick, if you have a chance, post a picture of the hall sensors that shows their position relative to the stator slots. In the earlier motors, the sensors were centered in a slot. I see one picture in this thread where they are offset from the slots. I'm curious how yours are positioned.

 

[John in CR]

Concerns about these issues are why I went the other route, ie keeping the motor itself in its original form and retaining both ends of the static axle as the motor mount by using a hollow axle. I'm sure you guys with the proper metal working tools and skills can do a much more elegant hollow axle. On mine, the sun gear both held the rotor's 2nd bearing in place and prevented left right drift of the rotor via a circlip.

 

[crossbreak]

I could be wrong but I think its held axially by a circlip...

Just like my bafang. If I would have drilled out the stator carrier more than the 0.1mm i took away, I would have had the same problem as mr.electric. I just lubricated surfaces and let it slip. The way mr.electric goes now is more sophisticated than my second approach. But there is also more danger that the stator gets offset radially (since the axle does not center the carrier anymore then). Maybe one should screw and glue the stator to the hub side plate before proceeding.

 

[Whiplash]

I was under the impression he did just that with the spacer or "heat bridge" as he calls it. It looks as though he screwed through the side cover into the stator no?? That is how I was planning on going it. I think if you can do this, then drill out the stator a bit so there is no friction there, then make the spacer, you should be in business. I don't remember for sure but it seems there was a step on the shaft that both side covers rest on so the axle can't simply slide back and fourth isn't there? Obviously I know the rotor is locked in place, and I guess that might be enough either way..

 

[spinningmagnets]

I have read about a method of determining clearance by oiling two parts (so the material doesn't stick, damaging the preciseness by having to pry it off) and placing a thin wad of some type of clay/play-doh onto the section of concern. Assemble parts, disassemble, slice wad in half and measure with calipers. Similar to using plastigage to determine bearing clearance in thousandths of an inch.

When choosing an amount of clearance (length of spacer tube) I would allow for heat expansion and probably split the difference between air space on both sides of the parts of concern.

 

[Whiplash]

Yes not a bad idea but steel really does not expand much, no to mention if the shaft expands as much as the spacer does (and it should unless you use aluminum or something) all clearances should stay very similar when hot. In engines the only time you really have problems like this is with dissimilar metals where one expands more than the other.. Its also only a couple thousandths at the most anyway..

 

[mr.electric]

The best would be to dril the holes before removing the axle so it is still perfectly centered. Problem is the long axle hits the drill chuck.
I used a tread on 6 bolt disk brake adapter to locate the holes seperately on the cover then stator. Finally I used the adapter as the heat bridge/ spacer.

Pics of the hall sensors for Fechter below.

 

[fechter]

The best would be to dril the holes before removing the axle so it is still perfectly centered. Problem is the long axle hits the drill chuck.

Pics of the hall sensors for Fechter below.

Thanks for the pic. Yes those hall sensors are NOT located in the slots, but offset slightly. I assume this will result in more neutral timing and better controller compatibility.

To drill out the holes without the chuck hitting, you could use a really long drill bit (aircraft drill).

 

[mr.electric]

To drill out the holes without the chuck hitting, you could use a really long drill bit (aircraft drill).

I will pick up an aircraft bit maybe a drill press too. I have a Mac to convert next week. It will be interesting to compare.
Apparently the Mac and bmc work with castle rc controllers sensorless.

 

[bØb]

To drill out the holes without the chuck hitting, you could use a really long drill bit (aircraft drill).

I will pick up an aircraft bit maybe a drill press too. I have a Mac to convert next week. It will be interesting to compare.
Apparently the Mac and bmc work with castle rc controllers sensorless.

I think you are going to find out the MAC is a different animal
Search for the posts I have made to this thread and you will see some of the differences.

bØb

 

[mr.electric]

Yes I have a mac on my bench now. There are certainly differences. I'm thinking of trying to use the threaded holes that already exist in the stator and just drilling the the cover. It appears to be about a 3" circle. A custom heat bridge would be needed too.
The stator is such cheap pot metal that it may be good to use some type of steel insert if one planned on assembling and disassembling numerous times.
The Mac I have has a noticeable tilt to the metal retainer plate screwed into the stator. It looks like the Philips screws that hold it in place were driven in with reckless abandon. This makes me wonder if the threads underneath are still any good. I may have to drill out and rethread either way.
Whiplash,
Any ideas on how to drill a circular pattern of holes on a drill press without use of an indexed table or other fancy machine tools. I have a caliper , scribe hand tools.

 

[Whiplash]

That's a rough one. You could use an angle finder and do a hole every so many degrees like every 60* drill a hole and use a compass to get the circle distance then center punch each hole. I have a lathe/mill so I'm hopefully going to come up with something easy and quick. We'll see how I do! I'm going to tear the motor down tomorrow hopefully.

 

[crossbreak]

The stator is such cheap pot metal that it may be good to use some type of steel insert if one planned on assembling and disassembling numerous times.

Once you screwed the stator carrier to the sideplate with the heatbridge/space you should glue it together with heatsink glue (additional to the screws) before drilling out the center hole of the stator. If you ever seperate stator and sideplate after this, it's not likely you get it centered again.

Sadly you wont be able to get hands on the hallsensors after this.

The most sophisticated method would be to insert a needle bearing to the drilled out center hole. This way the carrier would be centered perfectly.

Edit: If I got it right, this would only make sence on a bafang, since the MAC already has such a bearing.

 

[Whiplash]

Now that idea I like! I wonder how the shaft not being hardened would handle this? I bet you can get bearings pretty cheap! Any takers on the bearing search? Lol!

 

[crossbreak]

Okay, I just recognized again one axle bearing is inserted directly into the stator carrier rather than the sideplate?? Then there is no need for a needle bearing here. It's time i get hands on a MAC :?

Someone here who would sell me one with burned phase wires, for a price a student is able to pay?

 

[bØb]

mr.electric wrote:
Yes I have a mac on my bench now. There are certainly differences. I'm thinking of trying to use the threaded holes that already exist in the stator and just drilling the the cover. It appears to be about a 3" circle. A custom heat bridge would be needed too.
The stator is such cheap pot metal that it may be good to use some type of steel insert if one planned on assembling and disassembling numerous times.
The Mac I have has a noticeable tilt to the metal retainer plate screwed into the stator. It looks like the Philips screws that hold it in place were driven in with reckless abandon. This makes me wonder if the threads underneath are still any good. I may have to drill out and rethread either way.
Whiplash,
Any ideas on how to drill a circular pattern of holes on a drill press without use of an indexed table or other fancy machine tools. I have a caliper , scribe hand tools.

WOW, I'm blown away by that. I bought my MAC about a month ago and ran it off and on for about an hour. I then disassembled it and was impressed by the design and workmanship in it. At my age and with all the things I have seen, I'm not easily impressed. My only possible negative comment would only be with the wiring up of the cable. It worked and was not in danger of failure, just could have been done a little neater. The wiring has to be cut loose for modifications to be done anyway. It looks as though my stator holder was probably CNC machined from solid rod. The little cover that keys the stator holder to the shaft is cast, but machined on all the fitting surfaces. It fits real close and when lined up, it just pops in place.

Do you have any pictures of your disassembly?

I used the little cover that keyed the stator holder to the shaft for a drill guide. I put the axle thought the bearing on the freewheel side cover. Turned the little cover over so the flat side would go to the flat inside of the freewheel side cover and slid it on the axle. Put two metal blocks between the cover and the drill press table, one on either side of the freewheel hub, to keep the freewheel hub of the table and put the excess axle through the center hole in drill press table. Rotated the little cover around to get the bolt pattern orientation I wanted and held everything together by hand and drilled the first hole. I pretty sure the holes are 11/64". Immediately after drilling the first hole, put the shank of another 11/64" drill bit through the first hole to key the cover in place. Then I drilled the other five holes. I used the same method to drill the heat bridge after I made it and the heat sink also. You can screw all the bolts in with your fingers and after assembly with a 12 tooth sprocket on the brake side, I can rotate the entire assembly it the direction of rotation with one finger. The shaft is held axially by the brake side bearing only. The shaft is free to move axially through the freewheel side bearing. The entire motor assembly is held only by the freewheel side cover. Any expansion differential is taken up by the axial alignment of the sun gear and the planet gears.

bØb

 

[crossbreak]

...I wonder how the shaft not being hardened would handle this?...

This bearing hardly take any loads if assembled right. There is no need for a hardened shaft. The rollers are hardened, they would flatten the surface after time. But as said this would only make sense in a bafang

 

[Whiplash]

Found one for $4!!

http://www.reidsupply.com/sku/IKO-TLA1712Z/

 

[Whiplash]

I just noticed this one is 12mm long so it might serve two purposes!

 

[bØb]

Okay, I just recognized again one axle bearing is inserted directly into the stator carrier rather than the sideplate?? Then there is no need for a needle bearing here. It's time i get hands on a MAC :?

That big bearing in the stator holder of a MAC is NOT an axle bearing. That hollow shaft that is in the bearing I.D. is part of the sun gear/rotor. None of that ever touches the shaft/axle. I have posted several times telling all: If you connected the wires up and supported the motor by the stator, you could run it in your hand. The rotor and the stator are held apart by that big bearing.

bØb

 

[crossbreak]

Thx for clearing this. But then there is no obvious reason to keep it 100% centered. The airgap is kept already 100% centered by that big bearing. The planetary gearset is ok if 99% centered.

 

[Whiplash]

Oh OK I need yo get mine apart, its just too hard to visualize with only pics...